Heat Transfer of Motors / Active Cooling

[Nickick]

Hi,

I’m working on a fun variant of solo12, (which is actually more different than similar by now), but uses roughly the same actuator design. Unfortunately due to various modifications etc. the weight of my robot is quite a bit higher (I still need to measure it properly, but a little more than double solo8. Maybe 4kg?).

Due to this the current drawn by my motors when standing is in the range of 7A, which is way too high without any form of active cooling. Brief tests suggested that even 5A continuous is too much for PLA-based modules after 3 minutes, but I think switching to a better material won’t be enough for 7A. Not to mention that this means that if a motor takes on extra weight for some reason it will very quickly burn the phase wires.

Just wondering if anyone has had any success with adding fans/alternative active cooling, or measured any heat transfer properties of the motors (specifically, h, the heat transfer coefficient), so I can calculate what kind of fan I should need.

Alternatively if anyone has made an upgrade with more powerful knee motors, or a 1:16 gear ratio rather than 1:9 that I could check out?

[fgrimminger]

Hi,
sounds interesting - do you want to share a picture or screenshot of your robot?

So far we haven’t had overheating problems with Solo12 in our lab - that’s because the robot is pretty lightweight and because our experiments typically only take a couple of minutes.

We were concerned about the thermal behavior when designing the robot - so that’s why I left the 3d printed structure below the motor coils wide open. (picture below)

The idea was to use a closed body structure (like for Solo8v1) and to add one central fan that would move air into the body and then down into the leg modules.
Since the leg modules are pretty much closed most of the air would need to come out of the openings below the motor coils and cool them. You could also reduce the opening diameter of the hip actuator modules to force more air across the knee actuator which obviously sees the highest loads.

Standing taller (with the knees less bent or straight) would of course reduce the current draw of the knee motors significantly.

We don’t have a design with higher gear reduction or more powerful motors.

Best wishes. Felix