Experiences building a TechZone Laser Cut Mendel

Having finally reached the end of my build (onward to calibrating it!), I thought folks might be interested in how it all went.

1) The parts showed up promptly, within a week of my order having been placed.

2) Once I opened the box, it became clear that I had just ordered a big 3D puzzle - There was no documentation inside the box - not even a web link to a starting point.

The Mechanical assembly:

1) Many of the parts were cut with lower precision than you would expect from a laser - It appears that the laser had been bumped out of perpendicular by about 5° in one axis, resulting in slanted cuts in one direction. As a result, I opted to replace the 3 drive spools with milled aluminum ones. I also had to re-drill the center holes on larger z-axis gears in order to get them to mount perpendicular to the drive shaft.

2) The mechanical assembly of the printer went fairly painlessly, except when it came to the y-axis. As documented here, I opted to use nylon spacers to separate the parts instead of attempting to use nyloc nuts to separate the parts.

3) I also ran into a documentation issue when mounting the y-axis guide rails - Apparently TechZone has upgraded their mounts to a more recent (printed) design, but since they didn't document the change in any way, I was left hunting around on the reprap wiki to determine what the part had been replaced with.

The Extruder:

1) The drive gear for the extruder suffered from the same off-axis cuts that afflicted the other drive gears.

3) It appears that the extruder body was originally designed for a hobbed bolt that was reduced from 8mm to 6mm at the point where it was hobbed. Unfortunately, the bolt that was supplied was 8mm at the hobbes, and pushed the filament too far out of line for the extruder to function.

TechZone's suggestion was to drill the filament holes in the extruder body out to 1/4 inch, which might work, but since that wouldn't have moved the hot-end as well, it still would have left a kink in the filament path. I opted to replace the extruder body with a printed one from a different supplier, and will rework TechZone's extruder some other day.

The Hot End:

1) The oak block that the hot end mounts to was cut about 1/8" too long, so that it couldn't make it through the hole in the top of the x-carriage.

2) The syringe of "Goop" that TechZone supplied had dried up and was unusable. I replaced it with Loctite 598 Black Silicone Gasket Maker.

The Electronics:

1) Mine was supplied with TechZone Generation 3 remix electronics.

2) Again, poorly organized documentation made connecting everything be a somewhat painful process. This diagram helps considerably, but is incomplete with regards to the thermocouple interface.

3) The kit came with IDC connectors, but no tool to assemble them. Google "MTA-100 T-Handle Tool" for the correct tool.

4) The MTA-100 connectors, with 2.54mm spacing simply do not fit the endstop connectors, which have 2mm spacing.

5) I can't say I like the current adjustment pots on the stepper boards - they're almost unreadably tiny, and lack end stops, making it difficult to tell what you're doing when you adjust them.

6) The cable which was supplied for connecting the hot end to the extruder board was at least 6" too short to be useful, and had to be replaced.

7) Once I had everything connected, I found that the code which reads the hot-end temperature is very susceptible to interference, and will overheat the tip if there is interference on the OneWire data line. If you end up replacing the temperature control cable with standard Cat-5 Cable, you will end up with one of the heater wires making a twisted pair with the OneWire data line. Make sure that you connect that heater wire to ground, rather than +voltage.

8) On the subject of OneWire, the firmware for reading the thermocouple requires at least 40ms to read the data line, and has interrupts blocked for most of that time. This seems like a bad idea when interrupts are being used to control the extruder.

The Firmware:

1) Communication between the mainboard and the extruder board are being run at 1,000,000 baud - which is not reliable over unshielded wire. This leads to RepSnapper reporting 0 as the hot-tip temperature, on occasion. I'm guessing that it was hacked up to that speed before the extruder motor controls were moved to separate step/direction pins, and was never backed down to a reasonable value.

2) Recent changes to Skeinforge will require you to recompile the mainboard firmware, in order to re-calibrate the extruder (Skeinforge now defines one mm of extruder movement as one mm of incoming filament, rather than as one mm of extruded plastic).

3) Getting a copy of the firmware proved to be more difficult than necessary, because if you don't know where to look, you won't find it (It's here - close to the bottom of the page).

4) The firmware has not been updated recently, and is badly out of sync with the official firmware. Unfortunately, the most recent incarnation of the official firmware doesn't appear to compile properly for Generation 3 hardware.

Final thoughts:

1) Better Documentation Please!!!

2) I don't like the generation 3 extruder board - it was originally designed to run a DC motor, and uses a software hack to run the stepper motor. As a result, the motor is run badly (You can hear how badly it is being run in comparison to the other 3 axis - it works, but it sounds awful). The "Monolithic" kit sounds like an improvement, but leaves you repairing or replacing a $165 board whenever you damage it.

3) I don't like the thermocouple interface - it's a cool idea, but since it takes 40ms to read it, it's going to impact timing on the extruder motor. Switching to the "Monolithic" electronics could help here, but your firmware still ends up spending the bulk of its time waiting on the thermocouple, rather than actually running your print. Everyone I've talked to has said that their prints improved when they switched to using a thermistor.

4) Contacting TechZone seems like an exercise in frustration, particularly when you run into a problem on a Friday evening, and know you won't get any kind of answer until Monday or Tuesday at the earliest - I understand that they're not a 24/7 business, but given that their customers are hobbyists, they could spend a couple of hours on the weekend answering emails.

My experiences with tech zone gen3 remix:

Firmware: I run the official fived version "reprap 64bit-mendel-20100719", and it works fine as long as you turn off acceleration, but it is quite dated. You might be interested in teacup which seems to be the best (and only?) newer firmware that works with gen3 and seperate extruder controller.

Final thoughts 2)
You really want to add a separate stepper controller to drive the extruder motor, as the DC hack is just that, a hack. You can either buy another controller from techzone, or add a pololu or stepstick and attach it to a stripboard or a breadboard (which I prefer).

Final thoughts 3)
Perhaps it won't be as much of a problem if you add a dedicated stepper controller to the extruder? If not, just use a thermistor, I've had no problems with mine.

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-Nudel
Blog with RepRap Comic

A bit of follow-up on the extruder:

Reworking the extruder required me to move pretty much every hole in the bottom plate, by drilling them out to 1/4 inch, plugging with dowel, and then redrilling 1/16 away from the original hole. I also had to add a 3/32 inch "lift" to the extruder, in order to keep the large drive gear from grinding against the x-carriage.

It extrudes, but now I have to recompile the firmware in order to up the E0_STEPS_PER_MM.

[edit] A bit more follow up - apparently I still have enough noise on the hot tip cable to keep it from reading the temperature reliably, which messes up its temperature control to the point that it keeps letting things cool down to the point of jamming the extruder. I suspect that the only good solution is going to be to switch to a thermistor.

Edited 1 time(s). Last edit at 06/18/2011 12:21AM by raldrich.

raldrich Wrote:
-------------------------------------------------------
> A bit more follow up - apparently I still have
> enough noise on the hot tip cable to keep it from
> reading the temperature reliably, which messes up
> its temperature control to the point that it keeps
> letting things cool down to the point of jamming
> the extruder. I suspect that the only good
> solution is going to be to switch to a thermistor.


I seem to be having the same issue. Some times the nozzle won't even begin to warmup. Reprap host just displays 2000C for extruder temp. Other times it bounces between a legit temperature and 2000C.

I am so annoyed by all the things that simply don't work. I am going to try to isolate and shield the data line to the A/D but I am guessing that I will have whole new electronics by the time I finally get the temperature sensing working correctly.

I wonder if your thermocouple might be shorting to the tip. Although I've had issues with the speed and reliability of Gen 3 Remix with the Thermocouple AD combination, it has always read accurately for me.

Edited 1 time(s). Last edit at 06/20/2011 10:27PM by brnrd.

Odemia Wrote:
> I seem to be having the same issue. Some times
> the nozzle won't even begin to warmup. Reprap
> host just displays 2000C for extruder temp. Other
> times it bounces between a legit temperature and
> 2000C.
>
> I am so annoyed by all the things that simply
> don't work. I am going to try to isolate and
> shield the data line to the A/D but I am guessing
> that I will have whole new electronics by the time
> I finally get the temperature sensing working
> correctly.

I finally decided to give the techzone thermocouple its highest likelyhood of working, and reworked the cable. I'm now using two separate lengths of shielded cable for it. Microphone cable for the heater, with ground connected on the shield, and power running on both inner conductors, and headphone cable for the communications - ground on the shield again - power and OneWire on the inner conductors.

The end result is that while I still see the occasional "1989" value indicating an error while reading the temperature, in general it's good enough to hold the hot end within 3 degrees of the target temperature.

Occasionally, I've also had the "2000" temperature issue that you're having. I usually find that powering everything off and reconnecting it to the computer solves that, so I'm not entirely certain what causes it. I suppose that the OneWire chip might have powered up incorrectly, since the extruder firmware seems to be running otherwise.

It appears that TechZone has also found that OneWire communications is problematic, as their new "monolithic" design puts temperature control in a separate "tip management" processor. With that design, you simply tell the tip management processor what temperature to maintain, and it takes it from there.

For myself, I'll be switching to a thermistor as soon as the RAMPS electronics I ordered show up.