That’s not junk!!!

... it's ART!

… it’s ART!

A few days ago I found a DYMO LabelWriter 400 Turbo had been tossed into a cardboard box with used toner cartridges and broken printer parts.1 After making sure this really was a box of lost things, I swiped the label printer along with its power cord.

Tiny little printers such as this kind of label writer never use inkjet cartridges or require laser cartridges.  They print using heat – like receipt printers.  The catch, since they can’t get you with inkjet/toner cartridges, is that the labels are stickers with specially treated heat sensitive non-sticky sides.

Ideally, I would love to feed this little printer some cheap receipt paper and run it as a small, cheap, USB tethered printer.  I already have an Adafruit IoT printer, which I love dearly – but it would be awesome to have one that my daughter could use.  Apparently this has already been done more than once.

After loading up the newest drivers for the printer and trying out the newest software for it, I couldn’t get my laptop running Win 7 to recognize the printer.  I’m looking forward to tinkering with this.  :)

  1. Photo courtesy of Tinkerbots []

DrawBot Pen Holder Post Mortem

Yoda, standing tall

Yoda, standing tall

Two days ago I designed a new type of pen holder for my drawing robot based upon what I had learned from examining the pen holders other people have designed and used.

Here’s what worked and what didn’t:

  1. WORKED:  The fit.  I’m really happy with how the pen holder went together.  It’s always very satisfying to print a part you just designed and have it “just fit.”  With the zip tie holding the micro servo in place, neither the micro servo tab nor the zip tie protrude beyond the flat surface of the pen holder.  The groves for the rubber band to hold the pen in place work very well.  The pen doesn’t move side-to-side, get pushed back into the holder, and it is very easy to reposition the pen or change pens entirely.  While it’s not as elegant as, say, a metal spring, it works very well and doesn’t require a bunch of moving parts.
  2. WORKED:  The amount and placement weight.  I hot glued a AA battery to either side of the pen holder, as close to the center as I could manage around the hole for the pen.  This weight seemed to work perfectly.  There was enough weight that the cords hung in straight lines, but not so much that it seemed to cause a strain on the motors.  The placement of the weights seemed to work well as there was no noticeable pendulum swinging of the pen holder, despite me running the robot at about three times it’s usual top motor speed and about twice it’s normal acceleration.1
  3. WORKED:  The multiple points of cord attachment.  Having a row of holes for connecting the cords at different points along the top central edge of the pen holder worked out great.  To test the balance all I did was stick a small paperclip through a hole.  If the holder balanced with the flat edge upright and vertical, that’s the point I needed.  It was easy to find the balance point and easy to connect the cords.
  4. WORKED:  The single point of cord attachment.  When I was using a crappy cardboard pen holder with cord attachment points very far apart, the entire pen holder would tip to one side or another when it got close to that side.  This caused a bubble-like distortion effect towards the edges of the drawing.  While this could be a cool effect to intentionally inflict on a drawing, it’s not what I was going for with that crappy cardboard design.  Having the two cords meet at exactly the same point worked out incredibly well.  Even when the robot was drawing the top left corner of Yoda’s lightsaber, the pen holder was always perfectly vertical.
  5. WORKED:  Shape of pen holder flat side.  The pen holder I’ve designed is roughly teardrop shaped, with a flat top.  My thought with giving it a “flat top” was that it wouldn’t potentially develop a central raised point (between the circular top edge of the pen holder and the device I was using for the pen lift) when I was doing a pen lift.  I figured that if I was using a “flat top” it was possible for the pen holder to be balanced on the edge of the flat top and the point of the servo arm – essentially turning my full contact pen holder into a three point contact pen holder with the servo arm as one of the points.
  6. DIDN’T WORK:  Motor skipping?  There is a large section in the middle of the drawing of Yoda, pictured above, that looks like it was shifted downwards slightly.  This could have been because I was fussing a little with the robot while it was working.  It could also have been because I was running the robot pretty fast (motor speed of 1600 when the normal is 600), because I had increased the acceleration (400 instead of the default 800), because I had the pots turned down too low (maybe, but the current settings have worked reasonably well for other drawings), because the pen holder was too heavy and causing too much strain on the motor (very unlikely since this holder is lighter than the cardboard abomination I was using) or some combination thereof.  My guess is that I probably need to increase the pots when I increase the speed.  It’s really unlikely that the pen holder itself was to blame for these missteps.2
  7. DIDN’T WORK:  The pen lift.  I haven’t drawn anything with a pen lift yet – but I did test the pen lift last night after Yoda was done.  I noticed a few minor problems with the pen lift – but nothing to indicate I was on a completely wrong track.
    1. The first problem is that I glued the two batteries slightly too close to the clearance area for the micro servo arm.  This is why the next version will include a holder for the AA batteries – to ensure they don’t get in the way.
    2. Second, even when fully extended the servo arm didn’t push out far enough to cause the pen tip to lift off the surface of the paper.  This could be solved by either making sure the pen tip is positioned slightly farther back, extending the servo arm, or creating a servo arm powered cam, similar to Dan Royer’s Makeangelo (check out the video at about 4:35 for a view of the cam in action).
    3. Third, my concern is that since the micro servo is mounted in such a way that the servo arm sweeps from right to left, it could cause a similar sweeping motion to be applied to the pen tip – assuming I work out the pen tip depth issues.  It’s possible that sweeping the arm upwards or downwards might minimize this effect.  I just have no idea whether this is a valid concern or not – the servo arm might move so quickly that it’s not a real concern.
    4. Also, while not an actual issue, the servo motor cable applies a bit of weight to the pen holder.  This will require me to reposition the cord attachment points – and may require me to add extra weights to the pen holder itself.

Once I change the pen position and maybe use a larger servo arm, I’ll try a vector drawing which requires pen lifts and re-evaluate this design.  Overall, this design has basically worked beautifully.  I’m looking forward to experimenting with some new variations on the design to see if I can eliminate the few remaining issues.

Posts in the DrawBot Adventure Series
  1. Wanna make a DrawBot?
  2. DrawBot Resources and Links
  3. DrawBot, the Adventure Begins
  4. DrawBots for the slow learner
  5. DrawBot - Parts Ordered!!!
  6. DrawBot - The Breakdown
  7. DrawBot - Parts Shipped!!!
  8. DrawBot - What would you draw?
  9. DrawBot - The Plan!
  10. DrawBot - The Hacks
  11. DrawBot - The Delivery?
  12. DrawBot - The Delivery, Part II
  13. DrawBot – The Assembly, Part I
  14. DrawBot – The Software, Part I (and an existential conversation)
  15. DrawBot – The Delivery, Part IV
  16. DrawBot – The Assembly, Part II
  17. DrawBot – The Assembly, Part III
  18. DrawBot – The Assembly, Part IV
  19. DrawBot – Halp!!! No - seriously, a little help?
  20. DrawBot – The Face Palm
  21. DrawBot – The Delivery, Part V
  22. DrawBot – The Silver Lining of Failure
  23. DrawBot – The Delivery, Part VI
  24. DrawBot – The Assembly, Part V
  25. DrawBot – The Assembly, Part VI
  26. DrawBot – Printed Parts
  27. DrawBot – The Assembly, Part VII
  28. DrawBot – The Operation, Part I
  29. DrawBot – The Assembly, Part VIII
  30. DrawBot – The Breakdown, Part II
  31. DrawBot – Printing!
  32. DrawBot – Printing, Part II
  33. DrawBot – Why are you crying?
  34. DrawBot – Calibration
  35. DrawBot – Pen Selection
  36. DrawBot – How to Recover from a Stalled Print!
  37. DrawBot – Drawing Success(ish)!!!
  38. DrawBot – Pen Selection, Part II
  39. DrawBot – Onwards and Upwards!
  40. DrawBot – Another Successful(ish) Drawing!, and an Update
  41. Restarting a Stalled DrawBot Drawing
  42. TSP FTW!
  43. Speedier DrawBot Drawings
  44. Two new DrawBot links! And an update!
  45. Excellent DrawBot Slides
  46. Another Drawing Robot!!!
  47. DrawBot Practice Tip: A Watched Pot
  48. The biggest inkjet printer ever
  49. Why do DrawBots draw on walls?
  50. Maze Code + Polargraph?
  51. All New Polargraph on the way!!!
  52. Ideas for improving my DrawBot
  53. DrawBot Aesthetic Re-Design Ideas
  54. The Eagle Has Landed
  55. Every Body Needs a Skull
  56. This project is not going to overengineer itself
  57. Overengineered Spools
  58. Overengineered Stepper Motor Mounts, Filament Guides
  59. Overengineered Bolt Endcaps, Case Holder
  60. Sourcing DrawBot Parts
  61. DrawBot - A Tour!
  62. DrawBot - A Preview
  63. Arduino Powered Drawing Robot Poll
  64. Building an Arduino Drawing Robot - On The Cheap
  65. DrawBot - Printed Parts Tour
  66. Unidentified Foam Object
  67. Arduino Powered Drawing Robot - Take 2 (Or 3)
  68. DrawBot, now ACTUALLY wall mounted!
  69. A Study of Drawing Robot Pen Holders and Design Considerations
  70. Drawing Robot Pen Holders, Calligraphy Pens, and Thought Experiments
  71. Ideal Qualities in a Drawing Robot Pen Holder
  72. Enough talk! Finally a pen holder!
  73. DrawBot Pen Holder Post Mortem
  74. To Maker Faire!!!
  75. Skipping! How could I forget the skipping?!
  76. Drawing Robot Penmanship
  77. PlotterBot at Maker Faire Bay Area 2013!
  78. PlotterBot.com - a new site dedicated to drawing robots
  1. I’ll pretend I was doing this for a system stress-test, but really I was impatient to get a big giant Yoda drawing []
  2. Does that count as a pun? []

Fire the DrawBot!

Last night I connected my newly designed pen holder to my finished drawing robot and attempted a relatively “quick” drawing of Yoda.  I say “quick,” because it only took about two hours.  The one lone trade-off for having an cheap and easy to build robot capable of essentially unlimited drawing sizes is that it can take a long time.  I took several photographs of my robot while it was drawing and turned them into an animated GIF, featured at the end.

Finished and mounted robot, with old pen holder

Finished and mounted robot, with old pen holder

Above is the robot itself, mounted to the wall.  I’ve made two minor changes to this setup since that photo, detailed just below.  First, I’ve placed a large sheet of sacrificial cardboard under the paper so that any pen leaks will not mar the wall.  Second, since the “home point” (exactly 130mm down from the exact midpoint between the two spots where the cord leaves the project box) is hidden by the paper when I pull it down, I needed a way to be able to center the robot without having to re-measure the home point each time.  My solution was to take a small piece of leftover plastic about the size of a pinhead and tape it to the home point on the cardboard.  Now, I can feel the home point through the sheet of paper and center the pen holder accordingly.

Home point for centering the pen holder

Home point for centering the pen holder

It’s a little difficult to make out in the photo above, but you can see the two big arrows pointing to the home point and a slight bulge in the tape caused by the small plastic speck.

Brand new pen holder, assembled

Brand new pen holder, assembled

This picture shows the pen holder fully assembled.  I operated it the first time without the benefit of a servo motor cable.  I wanted to see if the pen holder would work well.  Once the drawing was about 2/3 done and I was pretty happy with the pen holder’s operation, I soldered up a cable to connect the servo lift port to the servo motor.

Drawing robot in action

Drawing robot in action

The above animated GIF is comprised of eight separate photos from my digital camera on a tripod, combined in GIMP.  I’ve never to make an animated GIF from a series of photos, but it very quick and painless.  Since video takes up a lot of space and battery power, I figured a series of photos would be the easiest way to create a “time lapse” of the robot’s operation.  You don’t get the low drone and hum of the motors, but you can see how it operates.  Now that I’ve done one, I’m looking forward to making more of these.

Yoda, standing tall

Yoda, standing tall

And here is Yoda!  As you can see from the ruler next to him, he’s about 35 inches tall from the tip of the lightsaber to his feet.  There’s a “band” of the drawing that appears to be shifted downwards slightly, causing a little overlap at the bottom of that region and a slight gap above.  This is probably due to me fiddling with the robot, but it could also be due to the motors slipping or skipping slightly during operation.  If it was due to me fiddling with the robot, then the fix is simple – I just need to be more patient.  If it was due to the motors skipping steps, then turning up the pots just a little would probably fix that.  Given that this is the very first drawing from my very first draft of a new pen holder, I’m really happy with the result.

Enough talk! Finally a pen holder!

Doesn't look like much, does it?

Doesn’t look like much, does it?

I admit it, I’m prone to verbosity.   I wrote 2200 words just discussing the kinds of pen holders other people have used and another 2300 words talking about what I consider to be ideal qualities in a pen holder.1 In some ways, the pen holder is possibly the least important part of the entire robot.  When you can use something like a binder clip or cardboard, hot glue, and dead batteries to create really amazing drawings, it’s almost a waste to spend any time thinking about what makes an idea way to hold a pen.  However, since I’ve got the rest of the robot looking and working just like I always wanted, I’ve latched onto this last part as something I would like to optimize.

Above is an OpenSCAD rendering of a pen holder I’m getting ready to try out.  As I type these words, my Replicator is a little over 50% done printing the pen holder.  Before my three most recent posts discussing pen holders I had been working on an overly complicated, multi-part, pen holder.  It consisted of several pieces that would be printed simultaneously, several spots for captive nuts – the features went on and on.  Don’t get me wrong – a pen holder like that might be genuinely great – but I’m not sure that level of complexity is necessary or in any way worth the design time.

The design pictured above meets several of my criteria for an ideal pen holder.  For your consideration, I submit the following features, design choices, and design elements:

  • Just one very lightweight part.  This printed part would require only a rubber band to keep the pen in place and, if you’re using a micro servo, a single zip tie to keep that in place.  At the moment the design doesn’t include a space for weights.  Once the part is done printing, I’m going to put it together with the micro servo and pen and see how it hangs.  If it looks okay, I’ll hot glue some batteries to it in various spots.  If that works well, I’ve already got a variation on this design which includes some printed tabs for adding dead batteries for weight.  The part itself uses very little plastic and prints fairly quickly.  
  • “Full contact” stabilizer.  In a prior post I discussed the several types of pen holders and how they can have a single point of contact with the drawing surface, three points of contact, or “full contact.”  While the Polargraph style pen holders use a blank CD (120mm in diameter), the above just uses a mostly round shape 80mm across.  I don’t know if this is wide enough or not, but this is a first draft.
  • Pen held at angle.  Felt pens and markers don’t really require they be held at an angle, but I can’t imagine it would hurt.  Well, I suppose they could have too much ink come through – but I could just run the robot a little faster.  There’s no science behind my choice of the pen tilt at a 15 degree angle, it just seemed like a reasonable number.  Since it’s a parameter in the OpenSCAD file, I can easily go back and change it if this is just a terrible choice.
  • Cord attachment points #3, the “Single cord convergence point, not at the pen tip.”  This pen holder is designed to allow the cords to essentially meet at one specific point – namely one of the tiny holes in a row along the top edge of the pen holder.  These are most visible in the top left of the above picture.
  • Centering point viewer.  Since the cord convergence point is centered on one of those tiny holes, the user of this pen holder can look through a tiny hole the the flat surface of the pen holder to make sure the pen holder is properly centered and homed.
  • Multiple points of cord attachment.  Depending upon pen type, pen weight, and pen holder weight and distribution I could imagine there might be different optimal points of cord attachment.  The top edge of the pen holder has a series of holes through which the cord could be fed.  The way to attach the cords would be to create a small loop in the end of the cord, feed it through one of the holes and then hook it onto the protuberance at the end of the row of holes. (You might have to look at the top left picture a bit to notice this bit). The other cord would be fed through the same hole – just on the other side and hook onto the same protuberance.  This setup was inspired by Dan Royer’s multiple point of attachment set up and the AS220 labs “clip stabilizer.”
  • Pen held securely in place and depth.  A rubber band should do the job of keeping the pen in place nicely.  I added a groove to the top edge of the holder where the rubber band can rest.  I can’t imagine needing a cord attachment point as far back as the groove near the pen holding cylinder, so I fully expect the last four or five holes can be eliminated, which means I can use the groove around the pen holding cylinder as it was originally designed – to serve as the resting point for the rubber band.
  • Multiple pen diameters/pen lengths.  Although this holder was designed for a pen with a maximum radius of 20mm, it could probably accommodate up to 25-30mm.  All but one of the pens in my house would fall in the sub-20mm-diameter category.  The reason for having the rubber band point so far back along the pen is that most pens are tapered towards the marker tip, which means you can’t really hold the pen any closer than 20-30mm back from the tip.  The holder is designed to hold the pen 30mm back from the pen tip, which is enough to accommodate all but the absolute largest marker.
  • Holder for micro servo.  The holder was specifically designed for my micro servo.  Once the micro servo is inserted (in the orientation shown by the shadowy looking micro servo in the images above) one of the tabs for the micro servo sits completely flush with the flat side of the pen holder.  There are holes on either side of the micro servo through which a zip tie can be fed.  There’s even just enough clearance so that the zip tie itself doesn’t protrude past the flat surface of the pen holder.
  • Clearance for the widest servo arm.  I know many others have designed much better mechanisms for having a micro servo perform a drawing robot pen lift.  Since this is literally my very first attempt to incorporate a micro servo into one of my drawing robot projects, I figured I would just use a bare-bones approach and have the servo’s arm directly push the pen holder off the drawing surface.  I’m positive there are more optimal ways to do this but again, this is a first draft.

I’ve uploaded the files to Thingiverse, to be followed by my janky OpenSCAD file.  It started off totally parametric and then as I got close to finishing it, I just started entering in numbers that would make it work.  I’ll go back and improve it, but for now I’ll share what I’ve got.

Posts in the DrawBot Adventure Series
  1. Wanna make a DrawBot?
  2. DrawBot Resources and Links
  3. DrawBot, the Adventure Begins
  4. DrawBots for the slow learner
  5. DrawBot - Parts Ordered!!!
  6. DrawBot - The Breakdown
  7. DrawBot - Parts Shipped!!!
  8. DrawBot - What would you draw?
  9. DrawBot - The Plan!
  10. DrawBot - The Hacks
  11. DrawBot - The Delivery?
  12. DrawBot - The Delivery, Part II
  13. DrawBot – The Assembly, Part I
  14. DrawBot – The Software, Part I (and an existential conversation)
  15. DrawBot – The Delivery, Part IV
  16. DrawBot – The Assembly, Part II
  17. DrawBot – The Assembly, Part III
  18. DrawBot – The Assembly, Part IV
  19. DrawBot – Halp!!! No - seriously, a little help?
  20. DrawBot – The Face Palm
  21. DrawBot – The Delivery, Part V
  22. DrawBot – The Silver Lining of Failure
  23. DrawBot – The Delivery, Part VI
  24. DrawBot – The Assembly, Part V
  25. DrawBot – The Assembly, Part VI
  26. DrawBot – Printed Parts
  27. DrawBot – The Assembly, Part VII
  28. DrawBot – The Operation, Part I
  29. DrawBot – The Assembly, Part VIII
  30. DrawBot – The Breakdown, Part II
  31. DrawBot – Printing!
  32. DrawBot – Printing, Part II
  33. DrawBot – Why are you crying?
  34. DrawBot – Calibration
  35. DrawBot – Pen Selection
  36. DrawBot – How to Recover from a Stalled Print!
  37. DrawBot – Drawing Success(ish)!!!
  38. DrawBot – Pen Selection, Part II
  39. DrawBot – Onwards and Upwards!
  40. DrawBot – Another Successful(ish) Drawing!, and an Update
  41. Restarting a Stalled DrawBot Drawing
  42. TSP FTW!
  43. Speedier DrawBot Drawings
  44. Two new DrawBot links! And an update!
  45. Excellent DrawBot Slides
  46. Another Drawing Robot!!!
  47. DrawBot Practice Tip: A Watched Pot
  48. The biggest inkjet printer ever
  49. Why do DrawBots draw on walls?
  50. Maze Code + Polargraph?
  51. All New Polargraph on the way!!!
  52. Ideas for improving my DrawBot
  53. DrawBot Aesthetic Re-Design Ideas
  54. The Eagle Has Landed
  55. Every Body Needs a Skull
  56. This project is not going to overengineer itself
  57. Overengineered Spools
  58. Overengineered Stepper Motor Mounts, Filament Guides
  59. Overengineered Bolt Endcaps, Case Holder
  60. Sourcing DrawBot Parts
  61. DrawBot - A Tour!
  62. DrawBot - A Preview
  63. Arduino Powered Drawing Robot Poll
  64. Building an Arduino Drawing Robot - On The Cheap
  65. DrawBot - Printed Parts Tour
  66. Unidentified Foam Object
  67. Arduino Powered Drawing Robot - Take 2 (Or 3)
  68. DrawBot, now ACTUALLY wall mounted!
  69. A Study of Drawing Robot Pen Holders and Design Considerations
  70. Drawing Robot Pen Holders, Calligraphy Pens, and Thought Experiments
  71. Ideal Qualities in a Drawing Robot Pen Holder
  72. Enough talk! Finally a pen holder!
  73. DrawBot Pen Holder Post Mortem
  74. To Maker Faire!!!
  75. Skipping! How could I forget the skipping?!
  76. Drawing Robot Penmanship
  77. PlotterBot at Maker Faire Bay Area 2013!
  78. PlotterBot.com - a new site dedicated to drawing robots
  1. I haven’t even started blathering on about different kinds of pens! []

Ideal Qualities in a Drawing Robot Pen Holder

Even something as cool as this...

Even something as cool as this…

In my last post I tried to list off as many uniquely designed drawing robot pen holders as I could find.  The reason for documenting them as I did, and pointing out certain design choices, was to help me identify ideal qualities in a drawing robot pen holder.  Before I dive too far down this rabbit hole, I should mention that Stuart Childs has an excellent post on his site discussing the particular challenges faced by those who seek to design a pen holder.

Before we can talk about how what makes a good pen holder, we have to agree on some of the terminology:

  1. Pen holder.  This is just the device that holds the pen and hangs down against the paper for drawing.  While it is sometimes called a “gondola,” I’ll refer to it as “pen holder” in this post.
  2. Cord.  Different drawing robots use different methods for controlling the gondola.  Some use monofilament fishing line (as is my preference), others use toothed belts, some use beaded cords.  For ease of reference, I’m just going to use the word “cord” to refer to whatever method might be used to connect your pen holder to the motor spools/sprockets.
  3. Hanging triangle.  When you draw an imaginary line between the two stepper motors, the cords from each motor meet at a point on the pen holder, forming a triangle pointing downwards.1
  4. Cord convergence point.  The “cord convergence point” is the, sometimes imaginary, point where the two pieces of cord meet to form the tip of the hanging triangle.  Many times the cords don’t actually physically meet.  In those cases, the “cord convergence point” would be the point where the two cords would meet if both cords were perfectly straight lines that continued through their point of attachment to the pen holder.
  5. Up / Down / Left / Right.  These directions will assume your robot is mounted to a wall/large sheet of plywood and you are facing the wall.  ((This could cause a mention of a “pen up” to be confusing, so I’ll try to avoid this phrase))
  6. Forward / Back.  Again, assuming you are facing a wall on which the robot is mounted, forward here would mean going towards the wall and back would mean moving away from the wall.

Without further ado, a list of ideal qualities in a drawing robot pen holder.  While not in any particular order, I’m listing them by number for ease of reference later.

  1. Secure pen holder.  The pen holder must, as you might imagine from it’s title, hold the pen used for drawing.  If it doesn’t hold the pen securely, you’ll get squiggly lines when you don’t want them and really squiggly lines when you only want somewhat squiggly lines.  It is important to note that a pen should be held securely so that it doesn’t move around left/right/up/down or back and forth.  Even if a pen is held securely with respect to left/right/up/down, it could still accidentally be pushed back (or, I suppose get pulled forward?) causing the pen to not touch the drawing surface (or always touch the drawing surface) despite pen lifts.
  2. Adjustable pen holder diameter.  An ideal pen holder should be able to hold a big fat marker or a teeny tiny marker.
  3. Adjustable pen position.   I’ve noticed that some pens are a lot narrower near the pen’s tip.  Thus, some pens will need the pen tip to be closer or farther from the wall, depending upon it’s own characteristics.
  4. Adjustable tilt to pen.  Although markers can pretty much draw at any angle, other pens (such as ball point or gel ink) just won’t work when they’re nearly horizontal.
  5. Incorporate a micro servo.  Single line drawings are really awesome – but with the addition of a micro servo for pen lifts, the robot becomes infinitely more versatile.
  6. “Depth” of pen holder.  Just to choose a term, this would be the distance the pen holder sticks out from the wall.  To strain the metaphor, the “shallower” the pen holder the less it can tilt or tip front/back or up/down.  Conversely, the “deeper” the pen holder, the more it could tilt or tip as it moves.
  7. Distance of center of gravity from wall.  This is an interesting one.  When I started building my robot, I thought the best thing to do was to have the wires leave the project box as close to the wall as possible – so that they would “encourage” the pen holder to hang closely to the wall.  Then I realized that it was actually equally important to achieve a balance of the pen holder.  With most of the considerations here, I can pretty much determine whether it is better to choose a configuration one way or the other.  Unfortunately, with this issue, I can’t decide whether it is better to have the pen holder’s center of gravity close or far from the wall.  Of course, not knowing won’t stop me from pontificating, eh?
    1. First, let’s agree there’s no apparent benefit to having a pen holder designed so that it is “deep” and balanced such that the center of gravity is farther from the wall.
    2. Second, the only apparent benefit I can think of to have a “shallow” pen holder is that it might reduce tipping/tilting somewhat.
  8. Adjustable line attachment points.  As the weight of the pen holder changes, so would it’s center of gravity.  Thus, the attachment points should also change.
  9. Adjustable weight.  Weight is one of the more finicky variables.  If the pen holder is too heavy, the motors will have a harder time, require more power, and be noisier.  If the pen holder is too light, there may not be enough pressure against the drawing surface, the cords may not be held taut (and thus will not behave as the program expects them to), it won’t be as responsive to the tugging of the two cords, and will tend to tip up or down or bind against the wall.
  10. Balanced pen holder.  An ideal pen holder should be balanced so that it doesn’t want to tilt left/right, up/down, or forward/back.
    1. In this video from Darcy Whyte’s site you can see how a pen holder that appears to not be balanced well tends to tilt or tip in response to a change in direction – essentially pivoting around the pen’s tip.  When this happens the pen either doesn’t move as much as the program expects causing certain features to be too short or the lines and curves drawn will appear to have a “stuttering” quality caused by the pen not moving with the cord because the pen tip is binding against the wall and then releasing suddenly and going too far.
    2. I used to think it would be more advantageous to have slightly more weight on the forward side of the pen holder – now I’m not so sure.  What I used to think was that by having the front end of the pen holder heavier, it would somehow exert more force on the wall.  However, there really isn’t any logical reason this should be the case.  Or, until I put a force sensor on the wall and test it, I don’t think I can claim this to be the case.  Watching videos of drawing robots and my own drawing robot in action, I now think that a very light touch on the wall might be more ideal.  Let’s assume any decent pen, especially markers, aren’t going to require a lot of force to leave a mark.  The more force with which the pen is pressed against the wall, the more likely the pen tip is to bind against the wall and draw stuttering lines or lines that are too-short.  Meanwhile, a very well balanced pen holder that is lightly pressing against the paper should not bind at all, resulting in more accurate lines.
  11. Points of contact.  There are any number of different designs for pen holders.  Some of them only touch the drawing surface with the pen tip (like the Der Kritzler, AS220 Labs and GarabatoBot), while others tend to have three points of contact (such as Makeangelo 1 & 2), and some basically have a large wide flat surface which meets the drawing surface (Polargraph, Mr. Drew, and DRBO).  My original mis-use of John Abella’s pen holder design actually had two points of contact – the pen tip and then the sack of batteries that hung from the holder.  A few comments about these different styles:
    1. One point of contact.  This single point of contact will always be either the pen tip or device used to create a pen lift.  Either way, the resulting pen holder can easily tilt left/right, back/forward, up/down, or any combination no matter how well balanced.  If you’re going with a single point of contact design anyhow, I suspect a well balanced and “deep” pen holder might work best.  Here, by deep, I mean a pen holder that sticks out from the wall.  My suspicion is that dialing in the pen’s balance, you might be able to achieve a favorable angle of pen-to-paper.  Having a “deeper” pen holder would allow more room for the robot operator to adjust the cord attachment points.
    2. Two points of contact.  This is just a bad idea – just don’t do it.  The way I implemented this involved a weight hanging below the pen tip.  When the pen moved too fast, the weight would swing causing a pendulum like wobble in the drawing.
    3. Three points of contact.  This seems, intuitively and by observation of Dan Royer’s videos, to be a stable pen holder design choice.  The two extra points of contact (in the case of Dan’s Makelangelo below and to either side of the pen tip) prevent the pen holder from tilting back/forth, left/right, or even up/down.  A three point of contact pen holder could still have a sway left/right problem, but that’s so bad if it means you’re eliminating all that tilting.
    4. Full contact.  This setup, like the three point contact, eliminates any form of tipping and is possibly less susceptible to left/right swaying.  Unlike the single point of contact setup, I think this kind of pen holder might benefit from being shorter (as in doesn’t stick that far out from the wall)

      ...can be drawn by something as ugly as this

      …can be drawn by something as ugly as this

  12. Cord attachment points.  There appear to be about several different ways of approaching cord attachment to the pen holder.
    1. The cord convergence point is exactly at the pen tip.  This kind of setup requires nice big bearings or metal tubes that allow the cord attachment points to rotate around the pen tip.  As the angle where the two cords meet changes, the two cord attachment points rotate to accommodate.  Getting the cord convergence point to be centered on the pen tip is much more complicated to design and expensive to build.  Look to the Polargraph and Ragnar drawing machine for examples of this type of design.  This is particular design choice does not introduce any distortion.
    2. Off-center but close together.   This is a very simple and extremely common method of cord attachment.  Each cord is connected to the pen holder a little to the left and a little to the right of center with the pen usually a little below that.  As long as the two cord convergence points aren’t really far apart, this method will introduce very little distortion.  Additionally, by having the two cord attachment points separate, this kind of pen holder enjoys a little extra stability.
    3. Single cord convergence point, not at the pen tip.  I have not been able to find any pen holders that use this method of cord attachment.  It would basically involve using a single point of cord attachment, either by simply tying the two cords to the same point or by using two pivoting arms as with the Polargraph or Ragnar drawing machine.  Rather than the pen tip being at the same point as the cord convergence, the pen tip would be at some point a constant distance and position from the cord convergence point.  I think the reasons this type of holder isn’t seen is that it is so easy to build an “off-center but close together” style pen holder, any distortion with the “close together” method is extremely small, and having the cord attachment points separate provides the added benefit of a little extra stability against tilting.  However, as long as stabilizers (three point of contact or full contact) are used, there shouldn’t be any reason not to employ a single cord convergence point.
    4. Devil-may-care.  The big Deathstar at the top of the post was drawn by the ridiculously crude pen holder pictured above.  Even with the cord attachment points being 120mm apart, the results are really great.2 Building a pen holder with this design choice will introduce some distortion.  It’s unlikely someone is going to be as foolish as I was to build a pen holder with cord attachment points as wide as 120mm.  However, even in such an extreme case, the distortion was shockingly small.
  13. Location of weights.  While I haven’t done any tests on this, I’m fairly certain that having the weight of the pen holder as tightly packed around the cord attachment point as possible is most advantageous.  The last thing you want is for an off-center weight to cause the pen holder to sway during a direction change.

Enough talk!  I think it’s time I start actually designing a pen holder!

Posts in the DrawBot Adventure Series
  1. Wanna make a DrawBot?
  2. DrawBot Resources and Links
  3. DrawBot, the Adventure Begins
  4. DrawBots for the slow learner
  5. DrawBot - Parts Ordered!!!
  6. DrawBot - The Breakdown
  7. DrawBot - Parts Shipped!!!
  8. DrawBot - What would you draw?
  9. DrawBot - The Plan!
  10. DrawBot - The Hacks
  11. DrawBot - The Delivery?
  12. DrawBot - The Delivery, Part II
  13. DrawBot – The Assembly, Part I
  14. DrawBot – The Software, Part I (and an existential conversation)
  15. DrawBot – The Delivery, Part IV
  16. DrawBot – The Assembly, Part II
  17. DrawBot – The Assembly, Part III
  18. DrawBot – The Assembly, Part IV
  19. DrawBot – Halp!!! No - seriously, a little help?
  20. DrawBot – The Face Palm
  21. DrawBot – The Delivery, Part V
  22. DrawBot – The Silver Lining of Failure
  23. DrawBot – The Delivery, Part VI
  24. DrawBot – The Assembly, Part V
  25. DrawBot – The Assembly, Part VI
  26. DrawBot – Printed Parts
  27. DrawBot – The Assembly, Part VII
  28. DrawBot – The Operation, Part I
  29. DrawBot – The Assembly, Part VIII
  30. DrawBot – The Breakdown, Part II
  31. DrawBot – Printing!
  32. DrawBot – Printing, Part II
  33. DrawBot – Why are you crying?
  34. DrawBot – Calibration
  35. DrawBot – Pen Selection
  36. DrawBot – How to Recover from a Stalled Print!
  37. DrawBot – Drawing Success(ish)!!!
  38. DrawBot – Pen Selection, Part II
  39. DrawBot – Onwards and Upwards!
  40. DrawBot – Another Successful(ish) Drawing!, and an Update
  41. Restarting a Stalled DrawBot Drawing
  42. TSP FTW!
  43. Speedier DrawBot Drawings
  44. Two new DrawBot links! And an update!
  45. Excellent DrawBot Slides
  46. Another Drawing Robot!!!
  47. DrawBot Practice Tip: A Watched Pot
  48. The biggest inkjet printer ever
  49. Why do DrawBots draw on walls?
  50. Maze Code + Polargraph?
  51. All New Polargraph on the way!!!
  52. Ideas for improving my DrawBot
  53. DrawBot Aesthetic Re-Design Ideas
  54. The Eagle Has Landed
  55. Every Body Needs a Skull
  56. This project is not going to overengineer itself
  57. Overengineered Spools
  58. Overengineered Stepper Motor Mounts, Filament Guides
  59. Overengineered Bolt Endcaps, Case Holder
  60. Sourcing DrawBot Parts
  61. DrawBot - A Tour!
  62. DrawBot - A Preview
  63. Arduino Powered Drawing Robot Poll
  64. Building an Arduino Drawing Robot - On The Cheap
  65. DrawBot - Printed Parts Tour
  66. Unidentified Foam Object
  67. Arduino Powered Drawing Robot - Take 2 (Or 3)
  68. DrawBot, now ACTUALLY wall mounted!
  69. A Study of Drawing Robot Pen Holders and Design Considerations
  70. Drawing Robot Pen Holders, Calligraphy Pens, and Thought Experiments
  71. Ideal Qualities in a Drawing Robot Pen Holder
  72. Enough talk! Finally a pen holder!
  73. DrawBot Pen Holder Post Mortem
  74. To Maker Faire!!!
  75. Skipping! How could I forget the skipping?!
  76. Drawing Robot Penmanship
  77. PlotterBot at Maker Faire Bay Area 2013!
  78. PlotterBot.com - a new site dedicated to drawing robots
  1. This is a term I only learned today from the context of Sandy’s comment in an earlier post.  This term is just so perfect and useful in describing drawing robot set-ups, I just have to include it here. []
  2. Unfortunately, the Sharpie started to run out of ink about 2/3 through the picture, which does detract from the drawing somewhat. []

Drawing Robot Pen Holders, Calligraphy Pens, and Thought Experiments

Just hanging out

Just hanging out

In discussing Sandy Noble’s Polargraph pen holder I mentioned how his design is optimized so that the point where the two cords meet is always the same as where the pen tip meets the paper.1 In the comments, he explained his rational, “So the pen tip is always at the tip of the hanging triangle, and there’s no distortion that way.”  My response was that “…if the pen holder has a single ‘hanging triangle’ point in it with the pen tip a constant distance from that ‘hanging triangle point,’ the drawings should appear identical to those created at the ‘hanging triangle point’ – just offset by the constant distance.”

This morning Sandy updated his site with a post explaining, using several diagrams, the basis for his prior theory and how he came to agree with my point. (Not that he’s changing his pen holders…  ;)  )

Without as much fancy-schmancy maths and geometry, I figured I would explain the thought experiment I used to conclude that a pen tip that is always a constant distance and position from the “hanging triangle point” will always produce an accurate distortion-free drawing.  To help illustrate these thought experiments, I’ve enlisted the help of Yoda.  “Hi Yoda!”

Fig 1:  Yoda, being drawn by a drawing robot

Fig 1: Yoda, being drawn by a drawing robot

In the picture above, Yoda is being drawn by a drawing robot.

Fig 2: Yoda drawing, annotated

Fig 2: Yoda drawing, annotated

Above, I’ve labeled the important parts of the drawing.  On the top left “Motor A,” on the top right “Motor B,” which are attached by cords to the pen holder indicated by the dark blue line.  Here, I’ve shown Yoda as he would be drawn by a drawing robot, where the robot then draws two more points.

Let’s say, because we’re feeling whimsical today, we want to add a second pen to our pen holder.  We’ll use a red pen and affix it below the blue pen in such a way that the red pen will always be directly below the blue pen by the same distance.

Fig 3:  Another pen

Fig 3: Another pen

For the moment let’s pretend the red pen is capped so it won’t leave a mark.  Now we’ll try to predict the position of the red pen at different points along the original drawing.

Fig 4: Where's the red pen?

Fig 4: Where’s the red pen?

It turns out this task is pretty easy.  The red pen, at any given point during the Yoda drawing, will always be directly below the blue pen by the same exact distance between the two pens.  Okay, now let’s draw Yoda again – this time with the red cap off.

Fig 5: Double vision

Fig 5: Double vision

We get two Yodas!  How awesome is that!  The reason I mentioned calligraphy pens in the title of this post is because it shows another way to think about this process.  When we write with a calligraphy pen we don’t have one end of the pen wildly distorted – in theory the two points on the calligraphy pen are always a constant distance from one another and moving together (as long as we don’t rotate the pen when we write).  You could imagine instead of a blue and red pen above, we’ve put a single calligraphy pen that’s as wide as the black line representing the distance between the two pens above.  The resulting drawing would look like a Yoda – that had been smudged downwards by the same distance.

Let’s now draw Yoda again, but capping the blue pen and still tracking where the blue pen would be.

Fig 6: Not using the blue pen

Fig 6: Not using the blue pen

We should end up with a result very similar to Fig 4.  It’s the same Yoda, only red and shifted down from the original blue Yoda by the distance between the two pens.

Let’s draw Yoda again – this time we’ve still got a pen holder which has the cord from Motor A meet Motor B at exactly one point.  As Sandy points out, this is really easy to do when you aren’t worrying about making that exact point be the same precise point as the pen tip.  Directly below point where the two cords meet on the pen holder, we’ll put the red pen.  From a functional standpoint, this setup is identical scenario to Fig 6.

Fig 7: Drawing just one red Yoda

Fig 7: Drawing just one red Yoda

Now we have a red Yoda, shifted down on the paper by the distance between the point where the two cords meet and where the red pen touches the paper.  It’s important to note that there’s no special magic to having the red pen directly below the point where the cords converge.  This pen tip just needs to be a constant distance and position from the cord convergence point at any given time.  While it might be more difficult to build a pen holder that holds the pen far off to one side, there’s no reason this wouldn’t work.

Fig 8: Yoda, now in green

Fig 8: Yoda, now in green

The lessons I take from this thought experiment are:

  1. As long as the pen is a constant distance and constant position from the point where the two cords meet, your drawing will not appear distorted – just shifted by the same constant distance and position.
  2. When calibrating the robot, the operator would need to calibrate the pen holder position by the cords convergence point – not the pen point.  This means that the preview in your software won’t match exactly the position of your drawing on the paper.  
  3. While not part of the thought experiment per se, I think we can all agree that the more weight that is not centered on the cord convergence point, the more likely the pen holder is to sway.
  4. I’m willing to defer to Sandy’s experience that pen holders that do not have the cord convergence point the same as the pen tip are, “Easier to design, easier to build, and cheaper, far, far cheaper.”

Thanks Yoda!

P.S.  Just in case you’re wondering – the reason that SVG of Yoda above is so large is because it includes the full TSP version of Yoda I’m getting ready to draw.  :)

Posts in the DrawBot Adventure Series
  1. Wanna make a DrawBot?
  2. DrawBot Resources and Links
  3. DrawBot, the Adventure Begins
  4. DrawBots for the slow learner
  5. DrawBot - Parts Ordered!!!
  6. DrawBot - The Breakdown
  7. DrawBot - Parts Shipped!!!
  8. DrawBot - What would you draw?
  9. DrawBot - The Plan!
  10. DrawBot - The Hacks
  11. DrawBot - The Delivery?
  12. DrawBot - The Delivery, Part II
  13. DrawBot – The Assembly, Part I
  14. DrawBot – The Software, Part I (and an existential conversation)
  15. DrawBot – The Delivery, Part IV
  16. DrawBot – The Assembly, Part II
  17. DrawBot – The Assembly, Part III
  18. DrawBot – The Assembly, Part IV
  19. DrawBot – Halp!!! No - seriously, a little help?
  20. DrawBot – The Face Palm
  21. DrawBot – The Delivery, Part V
  22. DrawBot – The Silver Lining of Failure
  23. DrawBot – The Delivery, Part VI
  24. DrawBot – The Assembly, Part V
  25. DrawBot – The Assembly, Part VI
  26. DrawBot – Printed Parts
  27. DrawBot – The Assembly, Part VII
  28. DrawBot – The Operation, Part I
  29. DrawBot – The Assembly, Part VIII
  30. DrawBot – The Breakdown, Part II
  31. DrawBot – Printing!
  32. DrawBot – Printing, Part II
  33. DrawBot – Why are you crying?
  34. DrawBot – Calibration
  35. DrawBot – Pen Selection
  36. DrawBot – How to Recover from a Stalled Print!
  37. DrawBot – Drawing Success(ish)!!!
  38. DrawBot – Pen Selection, Part II
  39. DrawBot – Onwards and Upwards!
  40. DrawBot – Another Successful(ish) Drawing!, and an Update
  41. Restarting a Stalled DrawBot Drawing
  42. TSP FTW!
  43. Speedier DrawBot Drawings
  44. Two new DrawBot links! And an update!
  45. Excellent DrawBot Slides
  46. Another Drawing Robot!!!
  47. DrawBot Practice Tip: A Watched Pot
  48. The biggest inkjet printer ever
  49. Why do DrawBots draw on walls?
  50. Maze Code + Polargraph?
  51. All New Polargraph on the way!!!
  52. Ideas for improving my DrawBot
  53. DrawBot Aesthetic Re-Design Ideas
  54. The Eagle Has Landed
  55. Every Body Needs a Skull
  56. This project is not going to overengineer itself
  57. Overengineered Spools
  58. Overengineered Stepper Motor Mounts, Filament Guides
  59. Overengineered Bolt Endcaps, Case Holder
  60. Sourcing DrawBot Parts
  61. DrawBot - A Tour!
  62. DrawBot - A Preview
  63. Arduino Powered Drawing Robot Poll
  64. Building an Arduino Drawing Robot - On The Cheap
  65. DrawBot - Printed Parts Tour
  66. Unidentified Foam Object
  67. Arduino Powered Drawing Robot - Take 2 (Or 3)
  68. DrawBot, now ACTUALLY wall mounted!
  69. A Study of Drawing Robot Pen Holders and Design Considerations
  70. Drawing Robot Pen Holders, Calligraphy Pens, and Thought Experiments
  71. Ideal Qualities in a Drawing Robot Pen Holder
  72. Enough talk! Finally a pen holder!
  73. DrawBot Pen Holder Post Mortem
  74. To Maker Faire!!!
  75. Skipping! How could I forget the skipping?!
  76. Drawing Robot Penmanship
  77. PlotterBot at Maker Faire Bay Area 2013!
  78. PlotterBot.com - a new site dedicated to drawing robots
  1. Photo courtesy of Kristina Alexanderson []

I swear I’m not jealous!

Green eyed monster

Green eyed monster

Before Maker Faire announced the official call for Makers, I had already downloaded and printed out the “call for Makers” information from the most recent Maker Faire and handwritten all of my responses in the form – just so I would be ready to submit my application to be a Maker this year. ((Photo courtesy of @Doug88888)) I ended up submitting my application within just a few hours of the call going out.

After I had submitted my application, my daughter wanted to submit her own application.  Of course I was happy to help her, so I helped her prepare an application and submitted it on her behalf a little after 11pm on March 14, 2013, just under the wire.

Today Maker Faire sent her an acceptance!  My daughter is going to be exhibiting at Maker Faire Bay Area 2013!

.

..

I just hope my acceptance letter comes soon.  :/  Senior year all over again…

A Study of Drawing Robot Pen Holders and Design Considerations

MakerBlock's Cardboard Gondola, Annotated

MakerBlock’s Cardboard Gondola, Annotated

The pen holder for a drawing robot is one of the most deceptively simple aspects of the entire machine.  Stripped down to the most basic elements, the pen holder is nothing more than a small device used to connect to both cords from each motor to the pen.  However, there are a number of extremely important, and subtle, design considerations that are not immediately evident.

Since Hektor’s debut in 2002, and arguably as far back as SIGGRAPH in 1988, people have been working on vertical pen plotters.  In that time

I guess I should start this post with a discussion of the different gondolas out there.

In no particular order they are:

  1. Binder clip.  One version of the AS220 DrawBot used a simple binder clip holding a pen as the gondola/pen holder.  It doesn’t get a whole lot simpler than that.  It appears from the video associated with this post that the pen is held on a somewhat rigid rail.  Similarly, Dustyn Roberts’ SADBot also used a big huge clip as a pen holder/weight and James Provost’s InternBot used a few binder clips.  However, the most hacked together system is easily Josh Myer’s Muralizer which consisted of a lump of Play-Doh enveloping the pen.
    AS220 Labs Pen Holder

    AS220 Labs Pen Holder

    SADBot Pen Holder

    SADBot Pen Holder

    Muralizer Pen Holder - Powered by Play-Doh

    Muralizer Pen Holder – Powered by Play-Doh

  2. Clip Stabilizer plus Binder Clip.  The “production version” of the AS220 DrawBot included lasercut spool parts, motor mounts, and a “clip stabilizer.”  The setup described in the assembly instructions appears to indicate that the pen can be held reasonably steady using this design.  However, having spoken to Shawn Wallace about these designs, he advised that this is really a non-optimal setup that has a lot of wiggle to it.
    AS220 Labs Clip Stabilizer Design

    AS220 Labs Clip Stabilizer Design

    AS220 Labs Clip Stabilizer plus Binder Clip

    AS220 Labs Clip Stabilizer plus Binder Clip

  3. Der Kritzler by Alex Weber.  This “gondola” made use of several lasercut parts creating a long wooden “cage” which held the pen in place along with a servo activated pen lift.  I can’t quite tell how the “pen lift” operates, whether it retracts the pen itself or whether it pushes something in front of the pen’s tip preventing the pen from leaving a mark.  Either way, this drawing robot pen holder has a feature that I never really appreciated until now – the wooden cage is suspended by two wooden “wings” which keep the point of attachment to the toothed belt at it’s midpoint.  I’ll discuss this feature more later.

    Der Kritzler Pen Holder

    Der Kritzler Pen Holder

  4. My first gondola was one of my own design and it was a miserable failure.  The central ring was too large to accommodate the marker pens I was using.  Also, it wasn’t heavy enough to make the monofilament hang in a straight line.

    Crappy Gondola

    Crappy Gondola

  5. Sandy Noble’s Polargraph.  Sandy has probably logged more hours with his drawing robots than just about anyone else.  So, when he uses a particular setup for his pen holder, there’s got to be something to it.  The interesting features of his gondola are that the weight is concentrated around the pen tube by use of several large bearings and, as with several other designs here, the cords to the pulleys are centered over the holder’s center of gravity.  After I published this post, I found a printable Polargraph-style pen holder by Lanthan on Thingiverse.

    Sandy Noble's Polargraph Gondola

    Sandy Noble’s Polargraph Gondola

  6. John Abela’s Gondola.  I used John’s designs with my first drawbot, but without the blank CD.  For the first time today I noticed that all of John’s pictures show the printed gondola glued to a blank CD for stability.1 When I used his design I just tied the top of the printed gondola to the monofilament line and added a ziplock baggie with dead batteries for weight.  The result was a reasonably decent gondola that was pretty finicky.  If the robot started drawing too close to one side or the other, the holder tended to twist and the pen made little to no contact with the paper.  I can see why the blank CD was such a good idea.

    John Abella's Polargraph Gondola

    John Abella’s Polargraph Gondola

  7. Dealywhopper’s Dr. Scratchy Polargraph Gondola.  Similar to John Abella’s Polargraph derivative is Dealywhopper’s Mr. Scratchy setup.  It’s an amusing mixture of high tech 3D printed parts and hot glue hackery.  There’s just something about its simplicity that really tickles me.  Print the part, add some glue, slide the binder clip into the groove, glue the holder, some pennies for weight, and a micro servo to an old CD and you’re done.  The interesting thing about this one is that the majority of the weight is off-center towards the drawing surface.

    Dealywhopper's Dr. Scratchy Polargraph Gondola

    Dealywhopper’s Dr. Scratchy Polargraph Gondola

  8. Dan Royer’s Makelangelo.  In the spirit of open source Dan Royer has been working on and blogging about his Makeangelo and Makelangelo 2 robots.  Dan’s Makeangelo is, like my first Polargraph derivative ‘bot, based on an Arduino Due and Adafruit Motor Shield.  If you check out his Youtube channel, there’s about two dozen uploads documenting Dan’s experiments with different pen holder configurations.  The version he’s shipping with his latest kit, which you can see below (the image is also a link to the video), uses three lasercut pieces to hold a pen and allow for an interesting pen lift.  Although you can’t see it in the image below, there is a third lasercut piece which appears to slide forward and backwards with the micro servo.  In the forward position it would push the pen holder top off the wall.  The holder includes two rows of holes along the top for attaching the motor strings above the holder’s center of gravity.

    Makeangelo 2 New Pen Holder

    Makeangelo 2 New Pen Holder

  9. Drawing Machine by Ragnar.  This drawing robot by Ragnar, a co-founder of Havtek, is exceptional for its incredibly high quality drawings and bespoke pen holder.  Ragnar provides a detailed description of his setup in two posts.  This may be the single most beautiful pen holder of the bunch.  With heavy brass pieces, there appears to be no further need for any additional weights.  As you’ll notice from his other photographs, the two brass arms are in the centered along the body of the pen holder.  This pen holder looks like each of the parts came off of an assembly line just destined to be part of an awesome drawing robot.

    Ragnar's Drawing Machine Pen Holder

    Ragnar’s Drawing Machine Pen Holder

  10. GarabatoBot (aka DoodleBot) by Made by Miguel Ángel de Frutos.  This is one of the most interesting drawing robot pen holders ever made – if for no other reason than it integrates almost all of the critical components into the pen holder itself.  As I recall, several other projects had tried to use integrated motors but found that the resulting pen holder/robot combination was too heavy to lift itself.  Miguel’s design is well documented on his site and the printable parts are shared on Thingiverse.

    GarabatoBOT robot by  Miguel Ángel de Frutos

    GarabatoBOT robot by Miguel Ángel de Frutos

  11. Harvey Moon’s Drawing Machine.  What makes Harvey Moon’s drawing robot pen holder particularly interesting is his choice to have the pen actually move up and down.  The pen holder incorporates a second non-drawing point and a rack-and-pinion system to advance and retract the pen.  I have to admit, I really like the aesthetic quality of having a no-foolin’ pen lift.

    Harvey Moon's Drawing Machine Pen Holder

    Harvey Moon’s Drawing Machine Pen Holder

  12. Darcy Whyte’s Mr. Drew.  Darcy Whyte aka Mambohead has been blogging about his own Polargraph variant2 for quite some time and worked through several different pen holders, including one designed specifically for a smaller drawing robot.  His designs use layered clear lasercut acrylic to build up a gondola which incorporates a springy clamp for holding the pen in place.  This video gives a really good tour of Darcy’s pen holder and explains several of the more important features.
    1. There are two pieces of threaded rod on either side of the pen holder.  By stacking pieces of acrylic you can adjust the position where the wire connects to the gondola.
    2. There is a pen clamp using a rubber band, as indicated above.  The best part about this clamp is that he uses varying pieces just below the pen to adjust the tilt on the pen, in case it requires a slight angle to draw on a more vertical surface.
    3. There is a third piece of threaded rod at the bottom of the gondola where additional weights can be attached.
    4. The clear acrylic and strategically placed holes in the top of the pen clamp allow the operator to see where the pen contacts the paper.

      Darcy Whyte's Mr. Drew Pen Holder

      Darcy Whyte’s Mr. Drew Pen Holder

  13. Stuart Childs DRBO.  Stuart Childs sells a lasercut Polargraph-compatible robot kit.  Once assembled it is a stand-alone drawing robot.  The most interesting difference between Stuart’s robot and Sandy’s setup is the construction of the pen holder.  I’ve included a picture of the front and back of the pen holder below to give you an idea of what it looks like.  Per Stuart’s comment below, his own gondola was inspired by Darcy’s Mr. Drew.3 For a better idea of how it is assembled and how it operates, you should definitely check out Stuart’s excellent step-by-step assembly photographs.  This pen holder has a small circular lasercut piece which attaches to the business end of a micro servo, to push ahead of the pen’s tip – allowing for “pen lifts.”  There are two features in particular that I really like.
    1. First, I like how the “arms” which connect to the motor cords can swivel.  This is a very clever way around several potential problems.  When tying the two cords to points on the pen holder, there are issues with placing them too far or to close together.  Too far apart makes the pen holder extra stable, but the image drawn are distorted.  Too close together minimizes distortion, but the pen holder can start to swing like a pendulum, causing wibbly wobbly lines.  Additionally, if the cords from the motors have too much “twist” in them, the entire pen holder can actually be turned sideways and will stop drawing entirely.  (I suspect just about any Polargraph-style pen holder which uses a large wide flat surface would be sufficient to combat the cord twisting/torquing problem.)  Looking back to the AS220 Labs pen holder, you can see that it appears to use two rigid rails instead of string.  The arms in Stuart’s robot essentially allow the cords from the motors to act as if they’re very close together – but probably wouldn’t allow much in the way of pendulum action.
    2. Second, I appreciate his spring-loaded pen holder.  This feature would allow his robot to accommodate a variety of pens or drawing implements.  While a rubber band would obviously work as a quick hack, a true metal string would stand up to repeated use.

    Stuart Childs’ DRBO Pen Holder

    Stuart Childs’ DRBO Pen Holder

  14. DrawBot Quick Change Pen Holder by UechiMike.  Thingiverse user UechiMike designed his own pen holder which he identified as a derivative of Dan Royer’s Makeangelo.  You’ll notice that UechiMike’s pen holder, like the DRBO immediately above, uses a rubber band in place of a spring as a way to accommodate a variety of pen sizes.  UechiMike’s pen holder has holes on either side for routing the monofilament wire which, it looks like, are tied around.  I have to wonder if the holder has any problem with torquing.  You’ve got to love the recycling of dead AA batteries here.  The only “gripe” with the design is that there isn’t any room for a  micro servo to for pen lifts.

    DrawBot Quick Change Pen Holder by UechiMike

    DrawBot Quick Change Pen Holder by UechiMike

  15. Screwless Sharpie Holding Gondola by Bluemetal.  Simple and sweet, this design doesn’t seem to have any weights or moving parts.  Just a bit of printed plastic and a push-fit hole designed for Sharpies.

    Screwless Sharpie Holding Gondola by Bluemetal

    Screwless Sharpie Holding Gondola by Bluemetal

  16. MakerBlock’s Cardboard Gondola.  Okay, now the most intricate, well designed, and durable feat of engineering ever to meet a marker.  My very own cardboard gondola.  As you can see, I slapped four AA batteries and a pen to a jagged piece of cardboard.  While it worked for several drawings4 it’s clearly nonoptimal.  The cord attachment points are wide enough to cause distortion and not well balanced enough to prevent swinging.  The only reason I slapped this together was that I was anxious to put my drawing robot to work.

    MakerBlock's Cardboard Gondola, Annotated

    MakerBlock’s Cardboard Gondola, Annotated

Frankly, my crappy gondola is a testament to the how forgiving DrawBot setups are.  Even though I’ve been admiring drawing robot setups for probably a year and a half now, I’ve really only started to understand some of the design decisions.  I’ll go ahead and publish this post5 and get to work on the next one laying out what I’ve learned from the different pen holders featured above.

Posts in the DrawBot Adventure Series
  1. Wanna make a DrawBot?
  2. DrawBot Resources and Links
  3. DrawBot, the Adventure Begins
  4. DrawBots for the slow learner
  5. DrawBot - Parts Ordered!!!
  6. DrawBot - The Breakdown
  7. DrawBot - Parts Shipped!!!
  8. DrawBot - What would you draw?
  9. DrawBot - The Plan!
  10. DrawBot - The Hacks
  11. DrawBot - The Delivery?
  12. DrawBot - The Delivery, Part II
  13. DrawBot – The Assembly, Part I
  14. DrawBot – The Software, Part I (and an existential conversation)
  15. DrawBot – The Delivery, Part IV
  16. DrawBot – The Assembly, Part II
  17. DrawBot – The Assembly, Part III
  18. DrawBot – The Assembly, Part IV
  19. DrawBot – Halp!!! No - seriously, a little help?
  20. DrawBot – The Face Palm
  21. DrawBot – The Delivery, Part V
  22. DrawBot – The Silver Lining of Failure
  23. DrawBot – The Delivery, Part VI
  24. DrawBot – The Assembly, Part V
  25. DrawBot – The Assembly, Part VI
  26. DrawBot – Printed Parts
  27. DrawBot – The Assembly, Part VII
  28. DrawBot – The Operation, Part I
  29. DrawBot – The Assembly, Part VIII
  30. DrawBot – The Breakdown, Part II
  31. DrawBot – Printing!
  32. DrawBot – Printing, Part II
  33. DrawBot – Why are you crying?
  34. DrawBot – Calibration
  35. DrawBot – Pen Selection
  36. DrawBot – How to Recover from a Stalled Print!
  37. DrawBot – Drawing Success(ish)!!!
  38. DrawBot – Pen Selection, Part II
  39. DrawBot – Onwards and Upwards!
  40. DrawBot – Another Successful(ish) Drawing!, and an Update
  41. Restarting a Stalled DrawBot Drawing
  42. TSP FTW!
  43. Speedier DrawBot Drawings
  44. Two new DrawBot links! And an update!
  45. Excellent DrawBot Slides
  46. Another Drawing Robot!!!
  47. DrawBot Practice Tip: A Watched Pot
  48. The biggest inkjet printer ever
  49. Why do DrawBots draw on walls?
  50. Maze Code + Polargraph?
  51. All New Polargraph on the way!!!
  52. Ideas for improving my DrawBot
  53. DrawBot Aesthetic Re-Design Ideas
  54. The Eagle Has Landed
  55. Every Body Needs a Skull
  56. This project is not going to overengineer itself
  57. Overengineered Spools
  58. Overengineered Stepper Motor Mounts, Filament Guides
  59. Overengineered Bolt Endcaps, Case Holder
  60. Sourcing DrawBot Parts
  61. DrawBot - A Tour!
  62. DrawBot - A Preview
  63. Arduino Powered Drawing Robot Poll
  64. Building an Arduino Drawing Robot - On The Cheap
  65. DrawBot - Printed Parts Tour
  66. Unidentified Foam Object
  67. Arduino Powered Drawing Robot - Take 2 (Or 3)
  68. DrawBot, now ACTUALLY wall mounted!
  69. A Study of Drawing Robot Pen Holders and Design Considerations
  70. Drawing Robot Pen Holders, Calligraphy Pens, and Thought Experiments
  71. Ideal Qualities in a Drawing Robot Pen Holder
  72. Enough talk! Finally a pen holder!
  73. DrawBot Pen Holder Post Mortem
  74. To Maker Faire!!!
  75. Skipping! How could I forget the skipping?!
  76. Drawing Robot Penmanship
  77. PlotterBot at Maker Faire Bay Area 2013!
  78. PlotterBot.com - a new site dedicated to drawing robots
  1. Face palm []
  2. How awesome is it that Darcy worked with Sandy on pen holder designs?! []
  3. TeamTeamUSA created his own variation on Stuart’s pen holder and made the plans freely available on Ponoko []
  4. Four Deathstars and a Firefly class starship []
  5. I’ve been sitting on it now for a few days []

Dogs and cats living together!

Real wrath of God type stuff

Real wrath of God type stuff

I’m basically through with CD’s.  I don’t even want the ones I have.  I would much rather just have the MP3’s since they’re just so much easier to organize and play.  This has been the case for a while now – the last time I bought a physical CD was four years ago.  The CD before that was eight years ago.

I was looking at buying an album off of Amazon the other day only to discover it was $3 cheaper for me to buy the physical CD, which comes with an MP3 “autorip” copy in my Amazon account, than to just buy the MP3 album in the first place.  Three dollars isn’t enough to make a tremendous difference in my lifestyle, but at the same time, that’s 1/3 the cost of the CD + MP3 album.  I can’t imagine why I would want to pay $3 more for the MP3 album when I could save $3, get the CD and MP3 album, and give or throw away the CD.

Interestingly, now that the United States Supreme Court has upheld the “First Sale Doctrine,” at least in relation to international textbook sales, I wonder if I’m perfectly justified in buying the CD+MP3 for $9 and selling off the CD for a modest amount.  (Are there still used CD buying places?!?)  After all, it’s not as if I’m making unauthorized digital copies, I’m just selling the physical CD and keeping the digital copies I purchased… right?

Random Gripes of The Day

Feeling stuffed?

Feeling stuffed?

I was annoyed by two things today and I have decided to share them with you. ((Photo courtesy of Göran Arvidson)) It’s more about the sharing than actually imparting information, but these are two things I feel kinda strongly about.  The day is young yet, so I reserve the right to add more things to this list.  :)

  1. I was going through my PayPal transactions for the last year and I discovered that providing a full and immediate refund costs me $0.30.  That’s pretty lame.  When they perform the refund, they get their money back.  All they’re out is a few zeros and ones.  And, frankly, it’s enough that I think my next few projects will be Stripe based rather than PayPal based.  PayPal’s API is a pain, I’m convinced requiring PayPal over a credit card (via Stripe) for transaction probably costs me conversions ((Oh, I could go on and on about PayPal versus Stripe and the posts about the relative benefits and conversions)) , and their policies are worse
  2. Online forms that require multiple steps across multiple submission pages.  The first thing this kind of UI tells me is that the people who wrote the page wanted something done quickly and easily (for them) and didn’t spend a lot of time thinking about usability.  Because I have a tendency to overthink things, I sometimes go back and revise an earlier step depending upon what I see in a later step.  When I see an online form that requires multiple steps I will typically feed it bogus information first so I can see the rest of the steps.

Um.  That’s all I’ve got to grumble about today.

Actually, in hindsight, if those are my biggest problems of the day, I’m doing pretty well!