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Motor Controller PCBs

A project log for Wolfie

The second version of quadrupedal robot based on custom brushless actuators

Peter WasilewskiPeter Wasilewski 11/07/2020 at 09:210 Comments

Hi!

Finally the PCBs have arrived. I guess I imagined them a bit bigger, as I was surprised by how small they really are. The outline is just 33x33mm, so I will be able to fit it behind almost any of my smaller BLDC motors. Since I last wrote I've been working on the software of the controller. For now I'm able to perform some basic operations on the motor as spinning in the non-feedback mode (voltage mode) or current feedback mode. The controller is also able to do a magnet offset calibration as well as encoder non linearity calibration and save the calibration lookup table in flash memory. Though everything seems to work fine at first glance, I still get annoyed by the irritating sound coming from the motor. I even wrote a post on the TI forum (https://e2e.ti.com/support/motor-drivers/f/38/p/921831/3412724#3412724) but the issue is still unresolved. I will investigate it further someday, however right now I'm out of ideas. 

My first approach to paste soldering using a stencil. I'm really happy with the result although the paste was not a high quality one.
Finished PCB
I do not know what happened here. Wasn't expecting much from 13$ 4-layer PCBs, but the vias' shape look really bad, the soldermask is superthin and gets scraped off really easily. The overall quality is really low and is appropriate only for prototyping.

Right now I'm working on a mechanical casing and planetary gear for the motor module. I managed to mill some prototype parts and it looks promising, however I'll tell more when the first prototype is ready. The biggest issue for now is the backlash of the planetary gear extracted from cordless drill. On a 3d printed prototype, I get roughly 1.5* of backlash when the motor shaft is stalled. I believe I'll be able to take it down to 1* or less with a bit of precise machining. Even though it seems much when I remember that triple stage planetary reducer for a drill cost me about 5$ each I guess it is a decent outcome anyway. Below a few random photos from prototyping process:

3d - printed motor module prototype
PCB cap from the top - notice the milled radiator fins for cooling the MOSFETs and driver IC
Bottom of the cap with two cable slots.
removing the stator from the original mount. If you want to read more about the milling machine itself: https://pwwprojects.blogspot.com/

When I'm ready with a fully machined prototype I'll write an update ;) 

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