Soldering robot V2

My first iteration of the soldering machine was based on Prusa MK3 chassis. It worked well enough but the wiring was very messy and I was not happy with it. It was more of an experimental platform than something useful.

For V2 I decided to use an old MendelMax 3 chassis that I had. As 3d printer that was quite outdated, but the motion platform was sturdy and reliable.

I re-used most of the carriage design from the first version. I added a GoPro fixture, so I can mound an LED light on the carriage itself instead of the side of the machine. In theory this should provide more consistent illumination for the camera.

I was also not happy with the fume exhaust design on the V1. It was using a small 40mm fan that was very noisy, the carbon activated filter piece was very small and it looked very ugly.

For the V2 I decided to put the fan and filter on top of the machine, next to the solder wire motor/extruder. It took quite a bit of experimentation to find the right hose to connect the two. I tried thin silicone hose, that was too thin and the walls would collapse during movement. I tried thicker vinyl hose but that was too rigid and would obstruct the movement of the head. Finally I settled on a corrugated PVC hose – it is flexible enough and would not collapse on it own.

The other experiment was to find what size fan I should use. I tried 60mm, 70mm and 80mm axial fans but they would not provide sufficient airflow, when the filter mount was attached. I finally settled on a 7035 centrifugal fan. I started with 120mm centrifugal fan, but that was too big and loud.

Here is a video of the fume exhaust system in action:

 

TMC2130 – setback

Well, my enthusiasm for the TMC2130 driver was premature. Faith was not kind and I discovered several design flaws after I ordered a bunch of assembled boards.

First I somehow completely missed the 5V power pin to the driver. So initially it was as dead as a door nail. I also discovered one of the config pins was not properly grounded – but that was not a big deal.

After a few bodge wires the driver sill would not respond to SPI commands. This was a rather frustrating thing and I remember having similar experience with the first PrntrBoard with 2130 drivers. Back then I had to wire a separate clock signal to each driver to get them to work.

When reading the datasheet of the 2130 chip it describes that if one connects the clock pin to the ground the chip would use an internal clock generator, but something is amiss and it does not seem to be working correctly in my version.

So back to the drawing board. I updated the PrntrBoard V2 to have a driver clock signal and now have to order new sets of PCBs.

Quite annoying. If you have a clue why the build-in clock is not working on these I would appreciate the hint.

High voltage motor driver design using TMC2130

The good old TMC2130 chip has fallen out of favor thanks to newcomers like the TMC2208/9. It is still top-shelf stuff and the preferred driver by Prusa for the Einsy Rambo as well as their MMU control board.

New chips are cheaper and cad drive more current, but the 2130 sill has one thing you can’t beat – it can handle voltages up to 46V.

Here is an example of a motor driver in the same PCIe form factor with external 3.5mm power terminal block. This allows the driver to use high voltage for example 36V or 42V to drive beefier motor.

The solder jumper on the bottom can be shorted and then the driver would take power from the carrier board.

Thermal test TMC2209 driver @1.7A RMS

I wanted to push my TMC2209 driver design to high-er current. The driver chip is relatively small and even at moderate 1.3A RMS motor current it gets very hot very fast.

Now to be fair 1.3A RMS is probably more than enough to drive most NEMA17 stepper motors. However every once in a while one can get a 1.6A motor or in my case a 1.7A motor. Now in most cases it is not required that you drive the motor with it’s maximum rated current, I just wanted to push the driver and see how it fairs under load.

Here is a picture of my very messy desk with the test setup:

I have my 1.7A NEMA17 motor on a linear rail I used for the test. Above it you can spot my Seek Compact Pro thermal camera. It is not the most accurate instrument, but does the job +/- 5 degree C.

The driver board has one 14x14x7mm heat sink on the driver chip and one 25x25x5mm heat sink on the back of the board, There is also a low RPM 5V 40mm fan blowing air horizontally across the driver boards.

First I configured the driver to use 1.6A RMS current and run a series to G1 X100;G1 X0 commands to move the axis back and forth. I used relatively slow speed, because from my experience this heats the driver the most. This test was uneventful (aka no smoke or major errors), so I proceeded to configure the driver to use 1.7A RMS current.

Here is a picture of the temperature of the board after about 15 minutes of moving the axis back & forth:

The hottest spot is around 54C. While the colors are very dramatic, this is quite cool for this type of setup.

The back side was about 45C:

In conclusion the test was very successful. In previous experiments the drivers would heat up to 70C. In this setup 54C was quite reasonable for the amount of current the driver was handling.

PrntrBoard gets upgraded to 480MHz CPU!!!

I was perusing trough the parts catalog offered by JLCPCB for their assembly service and found this awesome micro controller  STM32H750VB it is quite an upgrade over the good old F407 part. It runs newer Cortex-M7 ARM core, it has double precision FP unit and can run at sweet 480MHz. Best of all it was mostly pin compatible with the F407. I had to re-route one side of the pins, but it was fairly quick.

The only down side is that the build-in flash is a bit limited – 128KB, but I think I can work with that. I’ll order some boards with that processor once the factories in China are bully back in business.

The updated design is on my github page in the “new_cpu” branch.

LCD connector weirdness

There is no shortage of weirdness when it comes to the popular RepRap LCD connectors. The traditional connector is dual 10-pin IDC male sockets.

Alas it appears that someone made a mistake in the original schematics, so now some LCD panels have the connectors backwards. For example the FYSETC Mini 12654 Panel.

I had to create this small adapter to easily flip the direction of the wires:

Here it is i use in my PrntrBoardV2 test prototype:

Happy 2020: PrntrBoardV2 update

I’ve been busy over the holidays. Here is a summary of the recent progress with the PrntrBoard V2 3D printer controller.

I decided to give the JLCPCB SMT Assembly service a try and ordered some TMC2209 driver boards as well as some semi-assembled PrntrBoard V2 controllers. Overall I was quite happy with the results.

Here is a picture of the driver boards. I tested all of them and they worked flawlessly out of the box.

These are the semi-assembled controllers. I use semi-assembled, because only the SMT components were populated and I have to spin my soldering robot to work on the thru hole connectors.

Next I tested the sensorless homing capability of the TMC2209 drivers. After some tuning of the sensitivity parameter is works very well. You can see one linear rail axis homing with no sensors in this video:

I also decided to work on improving the mounting of the drivers to the board. The driver boards were not very stable in the PCI Express slots and I designed these little plastic holders to fix them in place.

They are bolted to the bottom of the controller PCB. The drivers are very well affixed in place.

While I was trying to get my 2004 LCD panel to work with the controller, I found that not all “standard” EXP1 and EXP2 connectors have the same orientation. At first I though that the SKR 1.3 board, just has them backwards, but I then found this article on the RepRap discussion forum. It appears that the original schematics had an error and now some boards/displays are just backwards. I quickly flipped the connector on my 2004 display and with worked, but this can be quite frustrating.

I made a small PCB that one can use to flip the polarity of the connectors. “To flip or not to flip” seems to be ongoing question.

Progress update on PrntrBoard V2

I tried to do some thermal testing on the TMC2660 drivers. First I tried running my puny motor at 2A with a 60cm 5V fan blowing at the driver. This kept the driver quite cool, which was a not interesting.

I was planning to run all 3 axis at the same time, but my heat sink was just a bit too tall and was touching the other driver :-(. I ordered slightly shorter ones, but they have to swim trough the pacific ocean first.

While I was enjoying torturing the poor motor at it’s rated limit. The thermal camera picked an unusual hot spot on the board. The reverse protection diode was cooking quite a bit. Serves me right for being lazy and not doing the reverse protection the proper way. Even with only one motor running, the diode was dissipating quite a bit of heat. I can’t imagine in what world this part is rated for 10A continuous current. Maybe it needs a small refrigerator attached.

Anyway I changed the schematics to use a proper P-channel MOSFET and a zener.

I added a small cooling pad on the PCB to help the transistor cool off. Hopefully this will not overheat with full 10A load.


I also decided to test one of the last remaining circuits on the board – the servo connectors. This proved to be quite the challenge. There was a serious contention for Timer #7 on the micro controller.

First Marlin’s temperature control was set to use Timer 7. This was not making the Servo module happy. I moved the temperature module to use Timer 8. Then I found that the SoftwareSerial code was also trying to hijack Timer 7. Moved that to Timer 12.

Finally the servo was working properly. I was able to set the position with the M280 command. I decided to quit while I was ahead.

More next week.

More LCD support for PrntrBoard V2

I was feeling elated by my success with the FYSETC mini 12864 panel and I tried my old “REPRAP Discount Graphics” panel. I thought “surely this should work as well it’s the same SPI graphics LCD after all”.

We you guessed it – work it did not. I tried software SPI, hardware SPI, nothing. Looks like I had to read the manual. Shame!!!

Here is what I found. The old “discount graphics lcd” is not quite the same chip. It uses ST7920 controller, which is a supreme oddball. It uses some very strange scheme and transfers data 4 bits at a time.

Then I remembered I had added support for hardware SPI for that chip since PrntrBoard V1. Why was it not working?

Well, it was because for some strange reason the data pins on the panel are not connected to the SPI interface on the EXP2 connector, so the u8g library has to use software SPI emulation and I didn’t add support for that.

So fixed that, now I have both hardware support and software emulation for the st7920 driver and here it is working:

Next I’m waiting on some 2004 LCD screens to arrive. These should be easier, since there is no hardware protocol involved.

~V