The best apps for your crappy burner phone

Crappy phone, great apps

Crappy phone, great apps

I recently purchased a cheap pay-as-you-go Android smartphone with no intention to ever use the phone feature.  After removing several non-essential apps from the phone, I installed the following useful (and free!) apps:

  • UTILITY
    • Plane Mode Tweaker by Chislon Chow
      • This app allows you to let your WiFi through the phone’s “Airplane Mode.”  All cell phones, even those that have never been registered with any phone carrier, will periodically communicate with nearby cell towers.  Using this app, I can turn off that ability – while still leaving the WiFi untouched.  By turning off just the cell radio in the phone, I was able to extend the battery life significantly.
    • Tina Time-Lapse by B.nana Technology
      • This is a really great free app with lots of settings.  If you buy the paid app, it seems to have more settings and abilities.
    • Voice Recorder by Mamoru Tokashiki
      • I’ve been using this useful app for years to make notes to myself.  ((And once to record the sounds of a tiger.))1
    •  VNC Viewer by RealVNCLimited
      • Control any other computer running a VNC server.
    • GPS Navigation
  • ENTERTAINMENT
    • Chess Time – Muliplayer Chess by Haptic Apps LLC
      • Great app if you enjoy the occasional chess game.  I use it to play against friends2 all the time.
    • IMDB Movies & TV
      • Sometimes you just have to know the name of the actress who’s playing the barrista.
    • Shazam
      • Sometimes you just have to know the name of a song playing in a movie or TV show.
    •  Netflix
      • It is downright ridiculous to me that I can buy a $20 appliance for watching movies over a wireless connection.

Also, once you install apps on the phone, you’ll want to go to the app manager and move them to “internal memory.”  Although it sounds the phone is asking you if you want to move all the apps to the very limited 1GB of the phone’s internal memory, what you’re really doing is moving the apps to the “internal memory” of the 4GB microSD card.

  1. True story. []
  2. And enemies []

Why You Should Buy a Crappy Burner Phone

LG Dynamic Optimus (LG 38c)

LG Dynamic Optimus (LG 38c)

I recently purchased a cheap “pay-as-you-go” Android smartphone after reading about it on Slashdot.  The phone in question is an “LG 38c” being sold under the name, “LG Optimus Dynamic” with triple “Tracphone” minutes which you can pick up from Amazon for $19.99.

Before you rush out and get one, the processor is underpowered, the screen is small, it only comes with a 4GB microSD card and very limited internal memory, the viewing angle is relatively narrow, the touchscreen is a flexible plastic rather than sturdy glass, and runs an older version of the Android operating system that can’t handle many apps.12

That said, you would be hard pressed to be able to build or buy a device for $20 that is as capable as this little phone.  The phone can use WiFi, can run the Netflix movie viewing app, be used as a web browser, alarm clock, MP3 player, digital camera, digital video recorder, GPS navigator, send and receive email (over WiFi), and run many useful apps available from the Google Play store.  Also, you may not be aware of this or not, but every single cell phone out there – even those without any cell phone plan – is capable of dialing 9-1-1.  ((Obviously, this phone can be as cheap as it is because the phone company is subsidizing the cost, hoping you make it up by buying phone minutes.  Although I’m basically breaking this business model on a small scale, I just don’t seem to feel that guilty about it.))

  1. One amusing downside to buying a crappy burner phone is that your wife will look at you like you’re crazy.  She’s not going to think you’re a super spy or a drug dealer or anything cool like that. []
  2. Right, Honey?! []

XY-Plotter Robot Kit v2.0 Unboxing

The crew over at Makeblock.cc were kind enough to send an XY-Plotter Robot Kit v2.0 my way for a review.  I’ll be assembling the the robot and posting pictures of the process soon, but for now I wanted to do an unboxing preview for you.

The Box

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The first step to any unboxing review must, necessarily, start with the box in which the product arrives.  The box arrived safe and sound from China and was well packaged for transport.  Most parts were wrapped in plastic, the electronics were in anti-static bags, and the boxes were nestled in thick foam padding.  The blue anodized aluminum beams were mostly not wrapped in anything.  There were no noticeable scratches on any of them.  I did find a few blue anodized aluminum burrs from the parts in the box.  Keep an eye out for them if you’re opening the package on carpet, as I did.

The Electronics

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Above are the pictures of electronics.  As mentioned earlier, each board arrived in its own little anti-static baggie.  The card with the QR code to the instructions and rubber feet were a nice touch.  At this point you’ll notice that the connector ports on all of the boards have colored coded stickers to assist with assembly.  Clockwise starting at the top left corner, the box includes the card with the QR code to the instructions, three Me RJ25 Adapters, two Me Steper Driver v1.0 boards, an Me Baseboard, and four sticky-backed rubber feet.

The Tools

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Clockwise starting at the top left corner, the box includes RJ25 cables, a USB micro cable, three timing belts, three micro switch buttons, three lasercut acrylic “LS” brackets for the micro switches, 11 tiny screws, one lasercut acrylic “servo bracket,” another RJ25 cable, a small Philips screwdriver, a 2.5mm hex screwdriver, a 7mm wrench, two 1.5mm hex wrenches, a Micro Servo, a lasercut acrylic “Baseboard,” and one Beam 0808 72/80 aluminum beam.

The Hardware

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There are a lot of hardware parts in the main cardboard box:

  1. Shafts
    1. 2x D shafts, 4 x 56mm
    2. 1x linear motion shaft, D4 x 80mm
    3. 1x threaded shaft, 4 x 39mm
  2. Flexible coupling, 4 x 4mm
  3. 6x timing pulleys 18T
  4. 8x flange bearing, 4 x 8 x 3mm
  5. 43x M4 nuts
  6. 25x plastic ring, 4 x 7 x 2mm
  7. 6x cutable linkage 3, anodized blue aluminum
  8. 6x linear motion slide unit, 8mm
  9. Beams
    1. 4x Beam 0824 48
    2. 1x Beam 0824 80
    3. 4x Beam 0824 96
    4. 2x Beam 0824 112
  10. 2x 42BYG Stepper Motor Bracket
  11. 2x bracket, 3 x 3
  12. 4x plate, 3 x 6
  13. 5x bracket, U1
  14. 3x belt connector
  15. 1x Beam 0828 16
  16. 1x 42BYG Stepper Motor
  17. 12V DC power adapter
  18. 1x 42BYG Stepper Motor
  19. 31x socket cap screw, M4 x 14
  20. 28x headless set screw, M3 x 5
  21. 28x socket cap screw, M4 x 16
  22. 6x plastic rivets R4100
  23. 18x plastic rivets R4060
  24. 10x shaft collar, 4mm
  25. 18x socket cap screw, M4 x 30
  26. 12x socket cap screw, M4 x 22
  27. 30x plastic zip ties and 5x rubber bands
  28. 36x socket cap screw, M4 x 8
  29. 3x cross recessed pan head screw, M2×10 and 3x M2 nuts
  30. 10x countersunk screw, M3x8

The last picture in the set depicts all the really long pieces of the robot – the linear shafts and beams.  In order, from top to bottom, they are:

  1. 2x Beam 2424-504
  2. 2x Beam 0824 496
  3. 4x linear motion shaft, D8 x 496mm
  4.  1x linear motion shaft, D4 x 512mm
XY-Plotter Robot Kit v2.0 Review
  1. XY-Plotter Robot Kit v2.0 Unboxing

Disclaimer:  This robot kit was provided by Makeblock.cc for the purposes of unboxing and review.  They have asked that I provide my honest assessment of this kit.

Maker Faire Checklist

Maker Faire Checklist

Maker Faire Checklist

Between taking most of “Maker Faire” week off work and getting ready1 for MakerCon and Maker Faire, May was a hectic month. I remembered pretty much everything I needed for a successful2 – except “maker cards” and a metric ruler.  With a few additional tweaks, I’m sure it can be even better next year.

In case you’ve never set up a booth at Maker Faire, you get an area with several folding chairs, a few long folding tables, and a chain link fence on at least one side of you.34 To have an interesting booth, you’ll want something to put over your table and on the chain link fence.

Since my entire booth was basically a wooden box that unpacked into a robot that made decorations for my booth, set up was rather easy.

  • Attending the Fair
    • Cash5
    • A MakerBingo card
    • A list of things and people you want to see6
    • Backpack7
    • Food or snacks8
    • Phone charger9
    • Warm weather clothes – shorts, t-shirt
    • Warmer clothes, stowed in backpack, for when it gets dark and cooler10
    • Laptop, power cable11
  • Booth Setup
    • One large table covering per table12
    • One large display board to explain your project ((Like the kind for science fairs))
    • One booklet of information13
    • Caution tape14
    • Zip ties
    • Hot glue, glue sticks
    • Some kind of swag15
    • Some way to make your project interactive16
  • Booth Interior
    • Cooler, water, ice17
    • Paper bags or swag bags18
  • Feedback
    • Suggestion box, 3×5 index cards, pens19
    • Notepad for email list signup
    • LOTS of maker/business cards
    • Update the website before Maker Faire!20
  • Robot
    • Hardware21
    • 3mm hex wrench22
    • Metric ruler23
    • Paper ((One $5 roll is good enough to run a PlotterBot around the clock all entire weekend))
    • Pens and markers24
    • Blue painter’s tape and masking tape
    • Extra fishing line25
  1. Photo courtesy of Daniel Kulinski []
  2. Editor’s choice blue ribbon! []
  3. I heard an amusing anecdote from someone at Make who said they put a lot of time and energy into figuring out a good spot for all the makers.  Apparently they were a little concerned about having three drawing / art style robots next to one another!  I had a great time hanging out near PicassoBot and PancakeBot! []
  4. My daughter later pointed out there were three robots, in a row, all with a “P” in the start of their name []
  5. As a Maker, I could eat at the Maker Lounge, but the credit card machine was intermittent []
  6. This could be a whole topic in itself.  Two days is not enough to catch all the talks from just one stage.  With multiple stages, multiple demonstrations, mini-concerts all happening at the same time  []
  7. Or not.  There were several booths giving away these stringy sack kind of backpacks []
  8. Maker Faire is big and there’s a lot to see.  Although there are a lot of food options, you don’t necessarily want to drop what you’re doing just to go find food []
  9. Ideally, a portable one []
  10. Just a hoodie should be enough []
  11. These were necessary for my particular robot, but may not be for you and definitely not if you’re just attending []
  12. $15 each at KMart []
  13. Printed with clear plastic cover, spiral bound, about $7 []
  14. About $3 for a huge roll – perfect for keeping kids from rushing into your booth []
  15. Business cards, stickers, t-shirts, to any other kinds of trinkets out there []
  16. These are really the most fun kinds of exhibits/booths/projects at Maker Faire []
  17. It gets super hot and stuffy if you’re indoors, so water is key []
  18. To stow extra clothing and supplies []
  19. Pens can be donated from the hotel []
  20. Ideally, with a link to the mailing list and/or squeeze page []
  21. Bolts, washers, wingnuts []
  22. The entire robot can be assembled or disassembled with a single 3mm hex wrench []
  23. 1 meter stick or yard stick with metric markings []
  24. A whole new pack []
  25. This has never broken or tangled on me, but it’s not a bad idea to bring extra []

Printable Prosthetics: Brainstorming

An illustrative hand

An illustrative hand

My overall designs for a printable parametric hand are still far from done.  And, yet, I’ve come a long long way since jumping headfirst into the realm of open source prosthetics a little more than 30 days ago.12

Forgive the digression, dear reader, before I return you to considerations of prosthetics. After visiting the Asian Art Museum today with the family, I am feeling particularly inspired to discuss dualities.3 I find I am an often-inspired person. This is a very charitable way to describe myself by what would otherwise colloquially and clinically be considered ADHD. When I am inspired by a new topic, I tend to jump right into it – reading voraciously and trying to learn as much about it as I can. When this happens, I also tend to set aside whatever thing I was most recently working on. This means that recently I’ve done little work on drawing robots (big and small) and a multitude of other small projects that would otherwise be just amazing. However, such inspirations/distractions are not only external to a project – but can also be very much internal to a project. Consider, for instance, feature creep – the adding of ever more features to a project, usually at a faster rate than which features are resolved and refined. In order to combat this aspect of my nature, the wanting to add more and better features, I have developed a coping mechanism. To prevent myself from falling down the rabbit hole of features and improvements, I jot them down someplace – either in a blog post4 , in an email to myself, or in a notebook.5 I find that once I’ve externalized and memorialized an idea, I can continue working on a project unfettered and undistracted these other ideas.

To this end, and in the spirit of open source ideals, I will jot down some ideas while I have them:

  • How large and how small are prosthetic designs typically scaled?
    • I wanted to have a range of sizes for which my designs were optimized.  My guess would be no smaller than 85% and not much more than 160% of the size of the existing  Cyborg Beast.  Jorge Zuniga was, again, patient enough to discuss this with me.  His estimate of a range would be between about 105 – 150%.
  • What is the diameter of the Chicago Screws typically used in the creation of a Cyborg Beast?
    • From the retailer’s website, it appears the “barrel” diameter is 0.2 inches, or 5.08mm.  I’ll need to make some adjustments to holes for the Chicago Screws in the designs.
  • How important is hyperextension of these fingers?
    • The designs of the Cyborg Beast include fingers that can bend “backwards” very slightly.  Each finger joint includes a “stop” at the back of the joint.  While certainly useful, I question their necessity.  I previously designed a connection system for printable snap-fit parts ((For use in an equally noble project)) that connect very tightly and/or bend with a user specified degree of movement.  The point with me mentioning these parts is that the “stop” used at the back of each knuckle and joint in the Cyborg Beast may not be necessary at all.
  • How necessary are metal Chicago Screws to strength and durability of the hand and fingers?  
    • Before you laugh, consider this question – what is the weakest point of any given finger which uses a metal Chicago Screw when having to deal with lateral forces?  I would postulate the weakest points would be those thin plastic parts surrounding the Chicago Screws themselves.  Thus, even though the hand incorporates metal pins, I have to wonder just how much strength they are providing to the overall device.  It would be easy to conceive of a plastic prosthetic hand that was so small that there wasn’t a lot of plastic around each metal screw6.  In such a case, the weakest points would be plastic surrounding the metal parts.  Extending this conjecture, of what use are metal fasteners to a design that is primarily plastic?  The best guess I can offer is that they allow reliable and smooth operation.
  • Work on proportional fingers
    • In designing the fingers, I worked to be able to make them customizable in several different ways.  The user may specify whether the fingers have the “star grip” pads, whether the finger should be slightly shorter or longer, and scale the finger up or down – without distortion to the hardware and cord channels.
    • I need to add at least three additional options to these parametric designs.  The designs should include the option to add “mouse ears” and easily removable support structures.  Additionally, the design should also allow the user to change the diameter of the finger.  I did implement this, somewhat, in part of the design.  Without implementation throughout the entire design, these partial attempts aren’t helpful.
    • In creating the fingers shown above, I adjusted their lengths to conform to the measurements of my own hand.7 Next time, I think I would also measure finger diameters.
    • I think I should create a way to prevent finger parts from being mixed up accidentally while printing.  A possible solution is to include “mouse ears” with each finger – but embed an identifying mark in each mouse ear to label the parts.
  • Ideas on making a better parametric palm
    • The palm should be redesigned so that the fingers, at the appropriate lengths, would fit into it.  I designed the fingers quite a while since working on the palm.  I haven’t had a chance to ensure the parts would mesh well without adjustment to the scale.
    • On an entirely different note, I have an idea to redesign the entire palm.  By carefully placing deformed spheres, I was able to design a palm.  Using a similar process, I subtracted out a void for the user’s hand.  The result is a palm with an uneven thickness throughout.  Uniform thickness isn’t necessarily an interesting or useful goal.  That said, it could lead to a reduction in unnecessary plastic.  If I were to redesign the palm, I could design the internal area first8 – and then use the “Minkowski” function to create a uniformly thick shell around the internal form.  The bottom would have to be sliced off and the original internal area would need to be subtracted from it.
  • Ideas on making a more realistic hand
    • My designs so far are based primarily on the Cyborg Beast, with some minor changes.  The “Flexy-Handappears to be very organic and realistic.  It also features flexible printed connections between each finger segment.  Additionally, each finger is comprised of three segments – rather than two like the Cyborg Beast.  Interestingly, since the flexible connections between segments allows the hand to return to an “open” position, the hand only requires five tension cords – rather than five tension cords and five elastic cords.  The fingers appear to not have any “stops” behind each joint.  I have to wonder how having three segments to each finger impacts the function.  Does it allow the hand to better grip things?  Does it make the hand less sturdy?
  • Masculine/Feminine hands
    • One well-intentioned comment to my latest designs is that they are “pretty.”9 While I accept the compliment with the spirit in which it was given, it immediately made me wonder – is the hand I designed “feminine?”  Then it occurred to me that with more design effort, I could make “feminine” and “masculine” version of these hands.  I think the primary differences would be two-fold – thinner fingers and a less “hefty” palm for a more feminine version and a thicker and perhaps more “blocky” palm for a more masculine hand.
  • New developments
    • There have been a number of interesting and new developments and experiments of late.10 In no particular order, these ideas are:
  • Discussions with a 7-year-old
    • A few days ago my daughter and I were jotting down some ideas in my sketchbook.  As we did so, she saw some of the notes from the e-NABLE meeting on 3/21/2014 – including several sketches.  We discussed the problem – affordable, customized, and comfortable prosthetics.  We talked about amniotic band syndrome, how fibrous amniotic bands affect fetuses, and the different ways in which these bands can cause11 deformities to single fingers, whole hands, and a range of changes in between.  I explained how Mr. Jose Delgado Jr. had a $42,000.00 myoelectric prosthetic, the problems he has with that prosthetic, how and why he prefers his $50.00 printed replacement, and how for the price of his one prosthetic people could make 840 more prosthetics.12 She asked, “Why can’t someone use a stump to operate a hand?” I replied that this was exactly how these prosthetics worked – and I drew a few simplified sketches of the Cyborg Beast.  Her next question was, “Why can’t it move side to side?”  I said that Mr. David Ogreman had designed such a prosthetic.
  1. My first concrete step was going to an e-NABLE meeting in San Francisco on 3/21/2014. []
  2. The above picture is slightly misleading.  I haven’t confirmed that the fingers I’ve designed will properly fit into the palm that I’ve designed – or that the thumb would work at all.  Thus, the picture is partially a parlor trick and partially an indication of where I hope to take this design. []
  3. Many of the gods and goddesses in Eastern religions embody dual natures – creation/destruction, life/death, etc []
  4. In one of my several different blogs. Besides, what could be more ADHD than having 3+ blogs?!? []
  5. You may not find this as amusing as I do – but I probably have about four different sketch/notebooks. []
  6. Say, only 1mm []
  7. From pinky finger to thumb, the non-scientific measurements from knuckle to finger/thumb tip were 77mm, 102mm, 106mm, 92mm, and 72mm []
  8. Using the deformed spheres and hull trick []
  9. Thanks Erik! []
  10. I don’t even know why I’m saying “of late” when I’ve really only been involved a little over 30 days.  I guess becuase these developments are new to me? []
  11. Please forgive my lack of a more politically correct term.  If you’ve got a better or more sensitive phrase, please let me know as I will gladly adopt it []
  12. She wanted to know if he could get a refund! []

Printable Prosthetics: A Mock Hand

More progress on a fully parametric prosthetic design

More progress on a fully parametric prosthetic design

Here you can see the fingers placed appropriately with the palm. I’ve used the same “finger” designs to add a thumb.

For right now, this is just to demonstrate the progress so far.  Theoretically, the only thing left to do is crank out an appropriate gauntlet to bring the entire design together.  In reality, there’s still a fair amount of work to do.  The design for the prosthetic palms was… not elegant.  Also, I want to create a separate (but very similar) design for the thumb.1 It is possible that if I improved the finger designs, I might be able to get away without designing a separate thumb.

In the meantime, I think it looks good and would probably be functional as-is.

Onwards and upwards!

  1. I feel like the thumb should be stubbier, so I’ll go back and adjust the designs accordingly. []

Printable Parametric Prosthetics: Design Features

Parametric fingers - different lengths, same scale, with no distortion to hardware

Parametric fingers – different lengths, same scale, with no distortion to hardware

I’m not ashamed to admit it – I’m proud of these parametric designs like few of my other designs.  I’ve worked to make this design as customizable and organic as possible.  The two modules that define each finger can be customized in two important ways – they can be lengthened1 as well as scaled up or down – without any distortion or change in the size of the holes for the hardware, elastic cords, or tension cords.

Parametric fingers - with grippy bits

Parametric fingers – with grippy bits

Being able to lengthen2 the finger segments is important because it allows the user to create fingers of different lengths, as normal fingers are of different lengths, all without having to actually scale the fingers to different sizes and without causing a change in each finger’s diameter.

As I’ve discussed in earlier posts, being able to scale the parts up and down without distortion to the hardware holes is important because it allows users to use standard hardware throughout different designs.

For now, it’s back to work on the parametric palm to ensure a proper fit with these parts.

  1. Or shortened []
  2. Or shorten []

Printable Parametric Prosthetics and OpenSCAD: Parametric Optimization

Picking parametric fingers

Picking parametric fingers

This post is intended as a set of “guidelines” to creating a parametric design in OpenSCAD.

Last Sunday afternoon was spent working out a parametric design for printable prosthetic fingers.  Using the OpenSCAD function “hull” it’s relatively easy to crank out a nifty organic appearing design.  Admittedly, you have to have a working knowledge the basic union/difference/intersection function first.  However, once you do it’s really quite easy.

The feature of the design I’m most proud of is the “nail” part of the finger tip.  I designed the “nail” by using the OpenSCAD function “intersection()” on two cylinders.  The little “nubs”1 consist of a small cube, rotated so a corner is pointed straight up combined, with an identically situated cube rotated slightly.

When I’m designing something to be parametric, I usually don’t really start out designing it that way.  I first strive to create a form in OpenSCAD that resembles closely the thing I wish to design.  Then, I poke through the design code looking for those elements that are related to the design aspects I’m interested in changing based on parameters.  Once located, I replace those parts of the design code with variables that can be specified when the module is called.  I realize this is kind of a “high level” description of my design process for parametric things, but it’s still the best description.

Since last Sunday I’ve really done a lot with the design.  Some simplifying and a lot of improvements.  In the next post I’ll go over these features.  I’m really excited to show these off.  :)

  1. Meant to give the finger grip and texture []

Printable Prosthetics Fingers and OpenSCAD Design Tips

Solid finger tip for Cyborg Beast

Solid finger tip for Cyborg Beast

Above is my first attempt at designing a “solid” finger for the Cyborg Beast DIY printable prosthetic in OpenSCAD.1 The reason this is a “solid” finger is that I haven’t subtracted out any material to allow this partial finger to connect with anything else.

The problem with scaling (up or down) any design that requires fasteners and hardware is that when you do, the holes for the hardware are similarly scaled.  This leads to more post-printing work drilling holes to widen them or to find larger fasteners that won’t rattle around in too-large holes.

Thus, if the hardware consists of 3mm screws, the holes for the hardware should be 3mm no matter how much the parts are scaled up or down.  To make matters more interesting, not all holes in the model should be excepted from scaling.  The above finger tip has a plastic end that is supposed to fit into a mid-finger piece – and those parts should be scaled up or down according to the size of the overall hand.  Thus, some voids should be scaled2 and others not at all.3

I’m rather happy with how this finger has turned out so far.  It has most of what I understand to be the essential features of the Cyborg Beast fingertips, including little nubs along the finger pad to allow for gripping.  I intend to make this an option, in case a user would rather use something like Plasti-Dip to make grippy finger pads, rather than relying on printed plastic bumps.

However, converting a decent design into a parametric design requires a little more work.  The way I go about designing a parametric model is to first design one instance of the thing, in this case the finger tip.  My next step is to poke through the OpenSCAD code to locate those aspects parts that contribute to the models’ essential features – length of the finger tip, for instance.  Once I’ve found these bits, I then try to modify them so that I can insert different variables and arrive at sane variations on the model.

Wish me luck!4

  1. If this is your first time tuning in, check out the prior posts in this series using the links at the bottom of this post []
  2. Where parts meet []
  3. Such as holes for hardware []
  4. See, this is a post about finger tips and design tips!  Oh, man, I crack myself up! []

Printable Prosthetics R&D Q&A FAQ: Part The Third – The Answering

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Tuesday afternoon I had the good fortune to talk to Professor Jorge Zuniga of Creighton University regarding his insights on printable prosthetics, measurements of uneffected/effected hands, and various important design considerations.  Getting to talk to him really helped crystallize my understanding of the various measurements and the way in which the parts of the printable prosthetic1

  1. Design Ideals
    1. One of the design ideals of the Cyborg Beast prosthetic is to fashion a device that strives for symmetry with the unaffected hand.  Thus, all of the necessary measurements are taken from the unaffected extremity.  This serves two purposes.  First, it allows for the prosthetic to be similar in scale to the unaffected hand.  Secondly, the unaffected extremity tends to be, in most cases2 , slightly larger than the affected extremity.  The size difference may be due to the unaffected extremity being used more, and thus having more muscle mass, or due to the loss of muscle tone and muscle atrophy in the affected extremity.  Either way, a prosthetic designed using the measurements from the unaffected extremity should generally fit the affected extremity.  Since this particular prosthetic design uses velcro straps to fasten to the affected forearm, a prosthetic that is slightly too large can easily be adjusted to fit well by tightening the straps.
    2. Another design ideal is to create a core prosthetic design which works for the vast majority of persons.
  2. Critical Printable Components
    1. A rough sketch of the various parts of the Cyborg Beast prosthetic appear above as “Figure 2.”
    2. Palm.  This is the part that fits over the hand.
    3. Gauntlet.  This is the part that fits over the forearm, between the wrist and elbow.
    4. Four fingers, each comprised of two pieces.  The above simplified sketch only shows the fingers as a single piece.  Do not let my sophisticated drawings fool you.
    5. One thumb, comprised of two pieces.  Like the fingers, the thumb is comprised of two plastic pieces.
  3. Critical Measurements
    1. These measurements refer to the lines labeled in “Figure 1.”  All measurements relate to the unaffected extremity.
    2. F5.  This is the length of the forearm, from the interior of the elbow to the wrist.  While this could be measured along the side of the forearm, it very likely doesn’t matter.
    3. F2 (measured at 1/2 F5).  At a location along the forearm, half way long F5, the width of the forearm.
    4. H1.  This is the distance across the knuckles, from the pinky to the forefinger.
      1. When I lay my own hand flat on a table top, I perceive that an imaginary line drawn through my pinky and forefinger knuckles would end up being not exactly perpendicular to an imaginary line drawn from my elbow to my wrist.  More on this below.
      2. All of that is another way to say that I suspect H1 is not perpendicular to F5.
    5. W.  This is the width of the wrist.  Rather than being strictly measured from either side of the wrist, this measurement appears to best made using the endpoints of the H2 and H3 lines closest to the wrist.
    6. H2 and H3.  H2 is the length from the wrist to the pinky knuckle and H3 is the length from the wrist to the forefinger knuckle.
    7. All other measurements indicated might possibly be useful for refining the design, but they are primarily important for the Creighton University research study purposes.
  4. How Each Critical Measurement Informs Design
    1. F5.  Gauntlet length is not longer than 1/2 F5 and not shorter than 1/4 F5.
    2. F2.  Gauntlet forearm width is F2.
    3. W.  Gauntlet wrist width is W.  Theoretically, if the prosthetic’s palm is scaled up to accommodate the wrist width (W), the affected hand  should fit under and inside the prosthetic palm.
    4. H3 can be used to inform the relative lengths of the fingers to match the overall length of the unaffected hand.   This isn’t strictly required for a functional prosthetic.  As designed, the Cyborg Beast appears to use fingers of equal length.  However, the fingers could be scaled up or down along with the rest of the prosthetic hand.  Alternatively, and as will be discussed below, its possible that the fingers could be designed to be of different lengths.  Prosthetics for young children should contemplate fingers based upon slightly larger, 1-2cm, measurements.  The reason being that they quickly outgrow existing parts.
  5. Functional Design Considerations
    1. Thickness of parts is 3mm – 5mm, 20% fill.
    2. The wrist hinges should line up as exactly as possible with where the user’s wrist bends.  Additionally, the wrist hinge should be perpendicular to the line of the forearm/gauntlet.
    3. There should be about 1 – 2 mm of space between the hinge part on the palm and the hinge part on the gauntlet.  This allows a washer to be inserted for more fluid movement.
    4. Eliminate square corners when possible, as sharp edges can contribute to possbile injury.
  6. Cosmetic Design Considerations
    1. Using the unaffected hand for measurements also allows us to seek symmetry between the hands.
  7. Advanced Considerations
    1. Degree tilt to H1.  As mentioned above, it seems like the “H1″ line is not perfectly perpendicular to an imaginary line drawn from my elbow to my wrist.  An educated guesstimate would be that there is a 9 degree tilt to this line.  While existing Cyborg Beast designs do not include this knuckle “tilt,” including this feature in future designs may allow the prosthetic to appear and function more naturally.  However, I don’t know if there’s any real ergonomic benefit to using incorporating this knuckle tilt.
    2. Different knuckle positions for fingers.  The Cyborg Beast has a knuckle “block” that positions the attachment points for all fingers in a straight line.  The reason for this is simple – it’s a lot easier to put one long screw through the entire knuckle block to secure and strengthen all four fingers at once.  At a recent e-NABLE meeting I had the chance to inspect a 3D printed prosthetic which used different knuckle positions for each finger.  Rather than all of the knuckles in a straight line, this model featured each knuckle at a different, and more natural seeming, position.  While this can appear more natural, I’m not sure there’s an ergonomic or aesthetic benefit.
    3. Different finger lengths.  Fingers are different lengths.  The Cyborg Beast, with all fingers having the same relative knuckle positions and same finger sizes, has a more mechanical look than might otherwise be possible.  I don’t know if there’s an ergonomic benefit to using different finger lengths, but this is certainly something to explore.

Based on the above, I think I’m ready to dive back into the OpenSCAD code and work out a parametric gauntlet, fingers, and thumb.  Stay tuned!

  1. I’m basing my own designs off of his Cyborg Beast designs []
  2. Let’s just choose the large and arbitrary percentage of 95% []