learning the ropes

things I made at ITP and after: sketches, prototypes, and other documentation

Sunday, October 6, 2013

Troubleshooting Pololu A4988 Failure

Pololu A4988 Troubleshooting After receiving my replacement A4988 driver boards, I wanted to verify that the driver board I took out of my printer had actually failed.  After wiring up the minimum required connections, I measured the voltage at 1A, 1B, 2A, and 2B on the suspected driver board.  VMOT is 16.6V (from a spare Linksys 12V power supply)

Regardless of the voltage applied to the STEP pin,

V1B = 12.96V

V1A = 0.75V

V2B = 11.13V

V2A = 12.97V

A forum post at Pololu’s site indicates that these outputs should be stepping in response to pulses on the STEP pin.

Let’s try the new board.

V1B = alternates between 0V and 16.65V on successive pulses of the STEP pin.

V1A = alternates between 0V and 16.65V  (opposite of V1B)

V2B =  alternates between 0V and 16.65V on successive pulses of the STEP pin.

V2A = alternates between 0V and 16.65V  (opposite of V2B)

This seems to confirm that the previous stepper board that was driving the extruder motor is not functioning normally.

This does not give me further confirmation that plugging the new driver board into RAMPS is going to work normally though — and it doesn’t confirm that there hasn’t been any damage to the RAMPS board. I don’t really want to sacrifice a A4988 to figure this out.  I reviewed the RAMPS 1.4 schematic; the stepper motor outputs of the Pololu board are wired directly to the stepper motor connectors on the RAMPS board.

Maybe the Makergear IRC channel is the next stop…

posted by Michael at 10:18 pm  

Wednesday, September 18, 2013

Failure Log

I have had a Makergear version of the Prusa Mendel for just over a year now. Eventually, I may get around to posting documentation of some of the things I’ve done with it… but for now I want to document the process of troubleshooting a problem I’ve had.

The original stepper plastruder that came with the Prusa Mendel has been pretty reliable.  The most consistent problem I’ve had with it is ABS filament jamming between the direct gear drive and the idler wheel.

For a while, I’ve had my eye on replacing plastruder with the more elegant and functional Birdstruder.  The advantage: a single cam-tensioned bolt to release instead of four spring-loaded hex-headed bolts any time filament gets jammed or needs to be changed.

So, over the past few days, I’ve finished printing out the Birdstruder and replaced the standard stepper plastruder. One of the nuts disappeared during dissassembly. During the initial print run, the Mendel stopped printing.  Usually when this happens, cycling power on both external power supply and USB connection to RAMPS gets communication going again. No dice.

So — troubleshooting began.

Is it a USB communication problem?

  • Checked Windows Device Manager — board didn’t show up there.
  • Tried plugging in another Arduino Mega board. Detected without a problem.

Did something happen to the power?

  • Is Arduino attached to Prusa getting power?
  • No lights seemed to be lit anywhere on the board. Watched while plugging connection in; one power LED lit up briefly and then went out.
  • Found the nut I lost — it was sitting on the Pololu stepper driver circuit board for the extruder. Cut all power, removed nut, tried to power up again. Still not working.  Note to self: another reason to put the electronics in a case.
Removing the suspicious extruder stepper board caused the Arduino Mega lights to come back on.  When the suspicious Pololu board is inserted, the Arduino lights do not come on.  I removed the Pololu board again and tried connecting to Mendel printer via Pronterface. Success. I’m able to jog each of the axes — and heat up the build platform and extruder.

I hope the damage is isolated to the stepper board, though it is possible that the nut laying on top of the board was not really the problem — and that the Birdstruder (because the idler wheel is not turning smoothly) caused the driver to overheat. I’m not sure how I would be able to test that theory with the failed board. I could contact Pololu for assistance.

posted by Michael at 6:40 pm  

Wednesday, May 9, 2012

Todo List

Makerbot #1 (tag #4391)

  1. Purchase replacement parts:
    1. Core Tube (buy one) – http://store.makerbot.com/machined-core-tube-for-mk6-1-75-mm.html
    2. Replacement PTFE Tube (no longer carried by Makerbot) – McMaster-Carr #8547K23 – (1/4″ OD by 1/8″ ID ) order 1′ length.  Will need to be machined and beveled to the proper dimensions (to fit inside the 1/4″ ID Thermal Barrier Tube and guide 3mm ABS filament).
    3. Motors (buy two) – http://store.makerbot.com/nema-17-stepper-motor.html
    4. XY Motor Pulleys (buy two) – http://store.makerbot.com/xy-motor-pulley-for-5mm-shaft.html
  2. Print and install Heated Build Platform Strain Relief (Makerbot #2 has one of these already)
  3. Remove Automated Build Platform and replace with Heated Build Platform.   ABP does not work well for raftless printing.

Makerbot #2 (tag #6776)

General

  1. Construct a spool handler.
  2. Further calibration of printing process (such as leveling the X/Y table, further tuning Skeinforge settings)
posted by Michael Chladil at 11:43 am  

Thursday, April 26, 2012

Initial Wipe Fix

One of the tricks to getting an object printed properly is making sure that it adheres to the heated build surface.  Sometimes, it seems that this requires enabling the “raft” to prevent a thin section of a part from pulling away from the build surface.

Another trick to getting an object to adhere to the build surface is to make sure that the initial extrusion (which the gcode generated by ReplicatorG refers to as an “anchor”) does not become a blob that the extruder nozzle drags around the platform during the first few layers of a build.

From the time of its first testing, Makerbot #2 head never positioned the extruder nozzle above the silicon wiper at the beginning of a build, so it was always necessary to snag the anchor with a pencil or pliers to make sure it didn’t get pulled along by the nozzle.

The “start” section of the gcode that ReplicatorG generates contained some notes about this — and after tweaking a very short gcode file to discover the proper coordinates of the wiper, the next big challenge appeared: which file to modify.  The file which ReplicatorG notes in the comments of the gcode it generates indicated one file, but after combing through a bunch of start.gcode files, it was ultimately determined that the correct start.gcode  file was [ReplicatorG install path]\machines\thingomatic\start+HBP+Stepstruder.gcode

If ReplicatorG is installed on a different workstation, start+HBP+Stepstruder.zip should be unzipped and copied into the above file path to properly home and wipe Makerbot #2.

posted by Michael Chladil at 1:46 pm  

Tuesday, April 17, 2012

Your First Print

  1. Verify that Thing-O-Matic is powered on and connected via USB to computer.
  2. Start ReplicatorG
    1. Check Machine -> Connection to verify that the correct serial port is selected
    2. Check Machine -> Machine Type to verify that the correct machine type is selected.
      1. For Thing-O-Matic #1 this should be “Thingomatic w/ ABP and Extruder MK6″
      2. For Thing-O-Matic #2, this should be “Thingomatic w/ HBP and Stepstruder MK7″
  3. Load up a model (either from a .gcode file or from an .stl file)
  4. Make sure the part is touching the build surface
    1. Select “Move Object” on right control pane
    2. Click “Put on Platform”
  5. Click the “Build Object on Machine” button (first button on the left).  The device will home itself and then after a warm-up period (30-40 seconds), will begin printing.  You may need to wipe the initial anchor extrusion (a blob before the object’s outline is drawn) so that it doesn’t get in the way of the print.
posted by Michael Chladil at 2:47 pm  

Thursday, April 5, 2012

Makerbot Specifications / Status / Preparation

Two Makerbot Thing-O-Matics

Thing-O-Matic #1 (4391 )

  • Stepstruder Mk6+ (configured for 3mm filament)
  • Motherboard v2.5 (with Arduino 2560) – firmware v3.1
  • Automated Build Platform
  • Extruder Controller board v3.6 – firmware v3.1
  • Spindle kit (missing feed tube)
  • Calibration
  • Modifications
    • Stepper shafts ground to accommodate pulleys (probably need to replace steppers since pulleys don’t spin true)
    • Location of Z- and A-axis control boards swapped on mounting board to accommodated shipped cable lengths.
  • Issues
    • Extruder jamming – originally, unit was assembled with 3mm filament capability.  Tried to run 1.75mm filament through it before realizing this, which jammed the extruder.  After several cycles of taking apart and reassembling the extruder, I rebuilt the unit with 3mm capability and “repaired” the tip of the  PTFE tube that guides the filament through the heater.  Ultimately, we should order replacements for both of the filament tubes.

Thing-O-Matic #2 (tag 6776) — operational

  • Strepstruder Mk 7 (using 1.75mm filament)
  • Heated Build Platform
  • Motherboard v2.5 (with Arduino 2560) – firmware v3.1
  • Extruder Controller board v3.6 – firmware v3.1
  • Calibration
  • Modifications
    • Left side cutout for power supply modified to accommodate Makerbot’s change in power supply part geometry.
    • Heated Build Platform Strain Relief to prevent damage to HBP cables.
posted by Michael Chladil at 11:20 am  

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