Author: Maker Block

With a little help from my friends

Thanks to the kind folks at the MakerBot Operators Group I’ve been diagnosing what’s going on with my Y axis stepper board and plastruder.

Y Axis Stepper Board

No matter what I was doing I couldn’t get the Y axis stepper board to respond to any commands.  Also, the power light on the board would light up as the MakerBot powered on – however it would immediately dim to nothing.  I swapped out every single cable, the motor, and it was always the Y axis board!  Finally, I completely pulled the board off the ‘bot, pulled every cable, and started adding the cables back one by one… and it worked!

I was concerned with why it wasn’t working, but happy it was working.  So, I bolted it back on, connected the wires… and it didn’t work any more!  What went wrong?  It was one of the opto-endstop cables.  I discovered that when I connected the front opto-endstop cable it would kill the power to the Y-axis board – or any other board!

The Y-axis three prong cable is easy to insert upside down.  And that’s what I was doing – because it fit better in that orientation.  Well, flip it upside down and rock on!

Plastruder / Extruder Temperature 0.0

Now that I could manipulate the 3 axes, I tried to use the plastruder.  I noticed that even at room temperature the thermistor was reading 0.0.  Also, the heater was smoking a little, I could smell something burning faintly, and the extruder was oozing something clear and sticky.  Not ideal.

With a lot of help from the guys at the MakerBot Operators Group I attempted to diagnose the problem.  Here’s what I tried:

  • Testing the resistance of both the nichrome and thermistor while both were still plugged into the plastruder board.  Both seemed okay – but I still could not get a reading from the thermistor.
  • One suggestion was to plug a random resistor into the thermistor ports to see whether the board and software was receiving information.  Being a complete novice and having zero spare parts around, I actually had to make a trip to the local electronics store for a single resistor. 1  Once plugged in the resistor (a quarter watt 10k) must have been resisting stuff because the board interpreted it as a temperature.  Thus, the board and software are probably fine. 2
  • Thus, I disconnected the heater wires and thermistor wires and tested them away from the board.  I really should have done this in the first place.  It would have told me that the thermistor was either burned out or no longer connected to the wires.
  • Taking the heater apart was almost painful.  The ceramic tape was a little scorched, parts of the kapton tape closest to the print head were actually burned to a blackened crisp and flaking off.  It was just not pretty.
  • The nichrome seemed to still be intact and giving the proper resistance, but the thermistor was not showing connectivity.  I was pretty bummed that I may have cooked it.  But, when I started to peel that tape away, I tried to test the resistor leads – which did show the proper resistance!  I checked the connections between the thermistor leads and the solder and discovered that one of the leads had lost its connection with the solder/wire.
  • I then tried to resolder the wire to the thermistor and then rewrap it into the kapton tape and tried its resistance again – and got a proper reading.   Then I taped it to the extruder head, to see if I could get a heat reading off of it – and I did!
  • This time, I went VERY slowly.  I tested the heater/extruder head completely apart from the printing assembly with the thermistor taped to it – I could heat and read the temperature.  I then wrapped it in tape, tried again, success again.  Then I wrapped it back in the ceramic tape, heated/read again with success.  Then I put the assembly back on the plastruder, heated/read again.
  • Now, a decision I made that I may very well regret later was to leave the nichrome wrapped as it was and not pull it all off and rewrap it.  The testing showed it was intact, it was still in its fiberglass insulation, and I had done a pretty good job of wrapping it in the first place.  In rewrapping the heater I took out as much of the burned kapton tape as I could and then wrapped it back up.
  1. I picked up a lot of other stuff while there, but this a single resistor was the actual purpose for the trip. [↩]
  2. Thanks Rick Pollack! [↩]

Pulley troubles

My MakerBot (Batch 9) uses printed pulleys.  I had attached them to my MakerBot with the bolt going down into the body with a nut underneath.  As far as I can tell, there’s only two ways to attach the printed pulleys to a ‘bot:

  1. Bolt going down into the ‘bot, nut underneath and inside, pulley with the tapered edge on the top.
  2. Bolt going up from underneath and inside the ‘bot, nut on top, pulley with the tapered edge on the bottom.
Printed pulleys, tapered end down
Printed pulleys, tapered end down

The problem with this orientation is that the pulley can slip down on the bolt.  When this happens it’s very easy for the belt to gradually ride up the tapered edge and then right off the pulley.  This ended up killing one of my test prints as the Z-stage started to descend to start the print.  Because of the way the “tapered end up” orientation of the pulley rides on the belt, I don’t think sanding away the taper would totally remove the problem.

MakerBot Build Status

The body is painted, bolted together, rods have been cleaned, XY stage installed, boards soldered and bolted on, cables run.1  I’ve affixed the opto-endstop triggers on the X and Y axes.

  • I have not installed the Z axis endstops mostly because I’m just not that keen on marring that beautiful clear acrylic sheet that is the Z stage.  I’ve created a little fitting out of balsa wood that will eventually support the opto-endstop triggers.
  • I’ve assembled the two “dinos” but not any other parts of the plastruder.
  • I need to assemble the rest of the plastruder, drop it in, and fire it up!
  1. Even if the opto-endstops are going to the wrong max/min ports for the moment. [↩]

One step forward, two steps back

As I mentioned, I had installed the Z-axis threaded rods without actually cleaning them first.  It wasn’t that bad to undo the caps, pull them out, and clean them.  In fact, it was kinda fun.

The process involves covering one end of the threaded rod with electrical tape to protect the threads and your drill, inserting that end into an electrical drill, adding 3-in-1 oil to the rod, and running the drill while holding a paper towel to the threads with a thumbnail.  It worked great and went much easier than I thought it would be.  I also used this opportunity to lower the threaded rods into the lower section of the MakerBot.  I’ll need to make sure they don’t get caught on any wires, but that will be all part of the process of zip tying all of the wires down anyhow.

Since I was going over things I had already done, I went ahead and also tightened up the Y-axis pulley.  It’s kind of a pain to adjust once the XY stage is installed, but I happen to have a very small adjustable wrench that was able to reach underneath the XY stage.

Christmas robot shopping

I went to the hardware store after work today to pick up the items on my shopping list.  Walking to their register I fell victim to their bargain basement aisle.  In the process I dropped the $3 superglue I had found and picked up four times as much for $2.  Sure, its a no-name house brand…  but as long as its reasonably sticky there shouldn’t be any problems.

I also picked up some 3-in-1 oil for the various rods.  I installed the Z-axis rods without cleaning them properly (too enthusiastic to get building).  I also bought a large flexible magnet in sheet form (the kind used for fridge magnets – only in an 8.5″ x 11″ size), work gloves, and another utility knife.

Adding the circuit boards

Once I had the opto-endstops all soldered up, I really wanted to keep going.  I made the Y-endstop cables, bolted the opto-endstops on, and bolted the motherboard and stepper motor boards to the MakerBot.  Clipped in the cables and it looks like a robot after all!  I’m going to need to organize those cables, but that will have to wait until all the other parts are in place.

An interesting side note – as I was moving the various axes someone noticed that little lights started flashing on the stepper motor boards!  Cool!  I presume moving the platform caused the motors to act like generators and pushing power to the boards, lighting up the LED’s.

Once the opto-endstops were done, I couldn’t resist bolting them on.  Once I started doing that, I wanted to make the Y-endstop cables, then the ribbon cables, and wire it all up.

If nothing else, it looks like a robot now!

Things I learned while soldering opto-endstops

The opto-endstops marked the very first parts I had to solder for this MakerBot.  Not having soldering anything more complicated than two wires together, this was an adventure and learning experience.  Here’s what I learned today:

  • The 3-pin connectors used for two of the opto-endstops (on the Y-axis stage) are in the Generation 3 MakerBot Electronics Kit (Mostly Assembled) with some of the other connector bits.  I was a little confused about this for a while.
  • It helps to lay out all the little bits in an organized fashion beforehand.
  • Keep a long thin rigid stick handy for bending delicate leads into the circuit board holes.
  • Although I read the RepRap electronics fabrication guide and found it helpful, I still felt a little lost.  I found the most effective way to solder the parts in was to:
    • Get the soldering iron good and hot
    • Put the leads through the holes
    • Bend the leads a little so that they stayed in place
    • Flipped the board over so the leads were sticking up
    • Touched the solder to where I wanted the joint
    • Gently stroked the solder with the soldering iron tip towards the joint
    • This process seemed to create a pretty good joint
  • You’re going to burn a finger at some point, accept it.1
  • This almost goes without saying, but go slowly.
  • Check and double check the orientation and placements.
  • I found it helpful to take a large sheet of aluminum foil and shape it into a tray.  This helped contain the parts I was working on and was a good way to catch the flying leads that I clipped off.
  1. I burned two. [↩]