Bringing my Huxley back to life

TL;DR: It blew up ages ago, now it's mostly fixed. If you know how to stop the motors overheating, let me know.

As an original backer of the eMaker IndieGoGo project, I got my Huxley a while ago and enjoyed it very much. I'm more interested in the things 3D printers can make than the printers themselves, so I adopted a need-to-know approach to the stack of technologies that these printers are built on. As such, when it finally failed (the Arduino chip was attacked by the blue smoke monster) I was unable to fix it quickly and it went into a cupboard for a year and half.

Fast forward to now, and my renewed masochism optimism encouraged me to repair it. I thought I would include some brief notes on my experience for people in similar situations or if people have comments on things I might have done differently.

The root cause of the Arduino (the big ATMega chip on the PCB ) failure is not know, but I believe it was something like this: the thermistor failed (the original design for this was a weak point), which caused the head to overheat and the heating resistor baked possibly shorted out. Something about this caused the Arduino to fail with a sharp crack and puff of smoke (current surge from the 19V lines to the 5V logic supply perhaps?). Hoping this was all that was at fault, I looked to replace these three elements. Things have moved on since the early days of Huxley, but there is no easy way to plot a path from the old version to the new version unless you have been paying attention as things evolved, which of course I haven't.

I bought a new Arduino (128MB instead of 64MB, which you can't seem to get anyway), a fancy ceramic heater with a metal body that just slotted into my hot end, and a glass-bead thermistor, which is far superior to the belt-and-braces version originally specified. All of these things went together (slowly) into the old rig and work well.

First time around, I never compiled the firmware or dug into that side of things much (too much like my day job), but this time I needed to. Getting a new version of the Marlin firmware from the RepRapPro GitHub worked fine, but I had to make some changes because that firmware only has options for the current Huxley models. Here are the relevant changes:

My Huxley uses nichrome wire to heat the bed (a design that has been replaced with a PCB heater with the mosfet mounted on the bed PCB ), so in pins.h I had to change HEATER_BED_PIN to 12 and FAN_PIN to -1 (I think it has been allocated to the old bed MOSFET in later versions to give a software controllable fan).

The values for DEFAULT_AXIS_STEPS_PER_UNIT needed to be changed to the 14-tooth pulley presets. I also modified the extruder rate manually as part of the calibration based on this excellent blog pos by @richrap [richrap.blogspot.co.uk]

I started using Slic3r for the STL > GCODE conversion because it seems to be what the cool kids are doing, and it looks good. I had to slow the flow rate down because the print head cools down too much with the defaults (possibly because my PLA is old and damp?). The retraction was too low I think at 1mm so I pushed it up to 3mm.

One problem I've had is that the defaults for the flow rate for infill were so high that the hot end was being overwhelmed and cooled down too much, which put tension into the filament feed and made the feeder bolt slip. I'm experimenting with feeding in more slowly.

My only remaining problem now seems to be that the X axis motor overheats halfway through printing and it's motion becomes limited, leading to filament being deposited in the wrong place. Not sure how I'm going to tackle that one so I would be interested to know if there are any relevant settings that can lighten the load on the motors.

Edited 2 time(s). Last edit at 10/26/2014 04:09PM by rupert.

Hi rupert

You probably need to adjust your motor currents - see: [reprap.org] . This shows how to do it on the Melzi, but the Sanguinololu is much the same. However, the reference voltage will depend on the stepper driver, and the various resistors that make up the circuit; if these are the original ones supplied with the kit, the reference voltage should be 0.4V - I think!

If you have an original extruder, the steps per mm should be around 920. The current firmware does have a lot of information for setting things like this up on older versions; if you look at [github.com] it says the different settings to use. For thermistor settings, see lines 107 to 117, for steps per mm, see line 359. That should get you close!

Ian
RepRapPro tech support

@droftarts Thanks for the help Ian.

I've checked the motor reference voltages and they are all more-or-less 0.4V.

I noticed that I had connected the X motor header the opposite way around to the other motors; I did this because it went backwards when it was the "right" way around during initial testing. I've reversed this now and modified the inversion flag in the firmware for the X axis. Could this have contributed to the problem?

Both the stepper driver and the motor itself get very hot, but how could I work out which one is failing? Once I know that I suppose I could try an uber-heatsink of some sort.

Since both the motor and the driver are hot at 0.4 V, either the driver, or the motor are somehow "bad". Change connectors of X and Y motors on the board and start a print that would normally heat X. Depending on what's going to be hot, you can draw some conclusions and then start deepr investigations and/or replacement.

@3Dmaker4U Switching the X and Y is a nice idea. I'll find a torture test that reliably reproduces the problem and do the old switcheroo.