Tag Archives: failed attempts

DrawBot – The Assembly, Part VIII

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Well, my newly designed motor mounts, while cool, just aren’t working.  If I were committed to using that long pine box, I could probably make a go of them.  I’ve tried several variations on this robot, and nothing has really worked so far.  Here’s what I’ve tried:

  1. In a box, mounted to the wall
    1. This just didn’t work.  The spot I found on the wall was in our robot room, behind my monstrous card catalog.  It was difficult to get to, the laptop I had it hooked up to wasn’t really talking to the robot, and I didn’t even get it fully hooked up in that location before I decided it just wasn’t going to work.
  2. In a box, under an easel
    1. In a fit of inspiration I realized that I had a painting easel, a rather nice one at that.  I took an old new canvas1 , put it on the easel, put the easel’s feet inside the long pine box, ran the monofilament line from the motor, through holes in the pine box, up behind the canvas, through an eyescrew on top of the canvas, and down over the front.  This was terrible.  It creaked, shuddered, and the pen sputtered around the front.
  3. In a box, on an easel
    1. Not ready to give up on Project Easel, I tried to put the pine box on top of the canvas and hold them together in the easel.  This really didn’t work.  Because of the location of the motors in the pine box, the canvas was either going to block the holes for the monofilament line or I’d have to run the line through the top of the box, which would have resulted in the same creaky, shuddering, sputtering problem of using the line through a hole in the box as if it were a pulley.  Either way, the entire assembly just wasn’t stable on the easel which did not want to hold it together.
  4. Bolted to a chunk of wood
    1. I actually have some spare plywood, but it’s been in the garage for a while and has a weathered look to it.  It also has a large 1.5 foot radius quarter circle cut out of it.  I figure if I’m going to keep this inside, I might as well spring for a new piece of wood.  A bit over $14 at the hardware store and I was in business.  Now that I’ve given up on my nifty motor mounts, I designed and printed a dead simple motor mount.  I could have accomplished much the same result by just drilling some holes in a piece of scrap wood. 2  I’ve also abandoned a gondola of my own design. 3
    2. The final result is essentially as follows – a 2’x4’x0.5″ piece of plywood, wrapped in butcher paper, two steppers bolted to mounts and screwed to the left and right sides at the end of the plywood.  The steppers are wired to the stepper motor in the center, and the Arduino and stepper motor controller are in an ill-fitting plastic holder which is duct taped to the front top of the plywood.  The plywood is then propped up against our built-in on which my most useless laptop is sitting, ready to run the robot.
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  1. Old because I’ve had it for about 10 years; new because it’s still in the shrink wrap.  Now, to my credit, I have actually painted on my other canvases – this is just the last one and I completely forgot about it. [↩]
  2. These will probably have been the very very last thing I’ll have ever printed with my black ABS. [↩]
  3. While cool, it just did not work well at all – I made the pen holder so large it would only hold the largest sharpie made by man, it didn’t do a good job of holding the pen against the paper, and it held the weights rather awkwardly. [↩]

How to diagnose and fix a burned out thermistor

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Unfortunately, Bender just stopped working.  As I was keeping the nozzle warm while I was working on a new model, I looked up to see a flash of fire/spark shoot out from the nozzle area, ricochet off the build platform, and disappear.  Looking at the RepG control panel I discovered that I wasn’t getting any readings from the thermistor.  Not good.

The RepG control panel showed 0.0 as the temperature, so I shut the plastruder down, not wanting the heater to burn out of control.  I restarted Bender and RepG – but I discovered that while I could control all three axes very slugishly, I could not move the extruder motor or detect temperature.  I’m guess I couldn’t have increased the temperature either, but I didn’t want to try it since I couldn’t monitor the temperature.  That about covers the symptoms.

In order to diagnose the problem I tried to isolate the various parts.  I pulled all of the wires out of the extruder board.  Then, while the wires were still out I tested the nichrome for resistance – still around 6ohms.  Then I tested the thermistor – no connectivity.  Again, not good.  I tested the  motor for continuity, and it was fine.  Since the nichrome and motor seemed fine, that left the thermistor and extruder board.  I popped a random resistor into the thermistor ports, but still couldn’t get a reading on it.  Unfortunately, after several resets of the motherboard and extruder board, I still couldn’t get the motor to move or a reading from the thermistor.  Also, I was getting an error message that the Payload was not big enough.

Rick Pollack of MakerGear suggested on the MakerBot Operators group that I reflash the extruder firmware.  After several failed attempts, I finally figured out how to flash my extruder firmware from the Arduino environment by holding down the extruder reset button.  This got rid of the payload error message as well as the avrdude errors and let me reflash the extruder.

I pulled the entire extruder apart and did a little maintenance.  I flossed the extruder pulley teeth, pulled all the stray bits of plastic out of the idler pulley wheel area, removed the old thermistor, unwrapped the nichrome (which was wound down and then doubled over itself as the original pictures in the wiki suggested) and rewrapped the nichrome (a single layer from the nozzle up the barrel following closely in the threads to make good contact everywhere) as suggested by several people in the MakerBot operators group.  I then tested the nichrome again once it had been taped down for the proper resistance, check.

Once I pulled the thermistor out of the heater assembly, I tested the thermistor at its own leads, rather than at the wires soldered to it (in case the thermistor had come apart from the wires).  Still nothing.  I plugged a random resistor into the thermistor ports and was now able to get a reading off the extruder (as well as move the extruder motor). Concluding my problem was the thermistor, I forged ahead with a plan to replace it.

Luckily, I had placed an order for some PLA and nearly every single part needed for a secondary extruder (or what would be needed to fix a broken extruder) including a new thermistor.  If you haven’t picked up backup parts, I highly recommend it.

I clipped the old thermistor off the wires, pulled out the new thermistor and taped it to a white piece of paper immediately, putting the tape across the leads just below the bead.  I then bent the leads upwards, tinned them, soldered them to the wires, taped down the wires, pulled up the original piece of tape, and then sandwiched the thermistor in tape as per the instructions.  I then plugged the heater, the motor, and the thermistor back into the extruder board – and was able to get a temperature reading, apply a little heat to the barrel, and move the extruder motor.  I also noticed that this removed the sluggishness from the 3 axes stepper motors.

With the heater, motor, and thermistor working separately I put everything back together and reassembled the plastruder, plugged it back into the board and tested it again – readings, heat, and extruder motor working.  I then popped it back into the dinos, did a test extrusion, and starting printing again.

“Rock on completely with some brand new components”