[WIP] 6DOF Odrive/BLDC CNC DIY build

BOM updated with my last orders (linear rods, bearings, etc...); as far as actuators go, I think it is pretty much complete (aside from some CHC/HC screws) :

https://drive.google.com/file/d/1Jem9iGReol2gM1IAn8WzwaW_47msrIWm/view?usp=sharing

I know it is quite above the 2000 euros that some people manage, but well the cost increased since and I am doing a CNC build, no plastic so obviously it is a bit more expensive. And I also know I still have the base/top platforms to build... But it is a fun / rewarding project !!

Last part of the actuator done today (turning and milling), the top cone that terminates the rods that connect to the SFU mount (and that links to the top platform). Now I am waiting for the parts for assembly (rods and bushings).

A bit of progress, got the rods today and did a quick assembly check, it starts to look like an actual actuator ! I have a few minor things to do/check before I can do a motion test and validate that I can proceed/continue with the fabrication on the 5 others. Anyway I will share soon I hope a video of this thing moving.

It is alive !!

https://youtube.com/shorts/tncyrtrseTg?feature=share

Also, quick look at the homing procedure with the optoswitch acting as the min endstop :

https://youtube.com/shorts/PBS47DqxJwU?feature=share

What's weird is that today it has been stable while yesterday with the same settings I was randomly getting the max current error on the controller.

Anyway for sure I will have at some point headaches with getting the odrive setup stable 100%; by the way, I am open for suggestions from those using Odrive as the BLDC motor controller in the actuator. I know @PeterW is using the latest firmware like I do but maybe others in the community also ? I am looking for a sample config that is known to be stable, although I am well aware each setup is unique but at least it would allow me to troubleshoot with a bit more insight.

Cheers !

What screw pitch are you using? In the picture of post #23 it looks quite small (5mm I'd guess). In the homing video it rather looks like 16 or even 20mm. How much torque does the motor provide?

It is actually a 1610 ballscrew (10mm pitch), not 5mm; regarding the motor torque, it is a 200KV motor so the torque I guess it just math based on that (unless I am wrong and you can have different torque for the same KV specs across brands).

Hi,
Congratulations for your build! Seems very strong.
I've done a similar project several years ago and got the same challenges with ODrive configuration.

I can suggest using WYBOSIMU controller which remove all the config headaches, optimize the communication speed (binary), add active security, Wifi connectivity, and more.
You can have more information on the discord.

Uuggh, math! IIRC, 200KV means 200V per 1000RPM, right? So 1000RPM is roughly 105 rad/s. That means the voltage constant is ~2Vs/rad. So the torque/current ratio also must be 2Nm/A. The Odrive can deliver 20A so it should be 40Nm. That's huge. My servo motors only have 4Nm continous and 10Nm peak torque.

But wait, 200V/kRPM means you should have a top speed of only 250RPM at 50V. That would only be 42mm/s with a 10mm pitch screw. The actuator in your video definitely runs faster. So what's wrong with my calculation?

Looking at the math myself, I end up with about 21 rad/s which gives a torque constant of 0.041 which gives about 1Nm at 20A. By the way 200KV means 200 RPM @ 1V so in my case 36V * 200 = 7200 RPM max... in my video it was taking a bit more than 1 sec for a travel of about 400mm so around 2500 RPM.

Thanks, I will take a look at your project and controller.

After some info digging and help from @PeterW regarding tuning the odrive, I managed to have the actuator moving at max speed stable without any error.

Here is a video that I think shows the difference with my previous test; notice that the pos_estimate is tracking the pos_setpoint (any shorter sinus period in FlyPT would result in loss of tracking).

https://youtube.com/shorts/GK0LNCTUEX4?feature=share

Note also that what may have been a major contributor to my previous issues were shorts in my encoder cable which were only manifesting randomly due to the whole actuator moving back and forth around the Z axis.

I also started to put the Aluminium tubing around my CNC parts; I just did the bottom one but I will likely do the long one (the one that matters most) today or tomorrow. I hope to see an improvement regarding noise level with that mounted (noise is way worse in the video than it is in reality)