Best motor for reaction wheel project?

I’ve been reading a few of the reaction wheel posts on this site, and I think I’m getting closer to an answer but still uncertain.
Here’s my situation: I have two 30cm wheels , rigidly connected to an axle that houses a 3S lipo. This is the body of my robot. On the outside of each wheel is a motor and a reaction wheel. These reaction wheels are meant to provide the drive to the body, so it rolls forwards or backwards on its bigger wheels.
The problem: I’ve tried some brushless drone motors I had lying around emax rs2205 - and these yeet the bugger forwards really frickin fast … but I have no fine-grained control. Also, I need a bidirectional ESC. Considering the G431B-ESC1, it looks better for such control than a drone ESC, although I need to use an encoder.
Question: can I just place a sensor like an AS5600 at the right point near the motor and use that (or two) for encoder feedback? Or should it really be constructed in? I’m thinking of Reaction wheel bicycle - applications - SimpleFOC Community - rem666 used an AS5600, but tehe original motor does not appear to have this built in? So it must be placed?

Another motor I tried was a brushed DC motor, at 500rpm. With the original reaction wheel size I used, 15cm diameter, this … barely rocks the robot, let alone moves it. I imagine this is because body weight is so high and reaction wheel inertia is so low compared - I have added bolts for weight, but perhaps it isnt enough. Is this just a ridiculous proposition at all? My next attempt is to try a reaction wheel just slghtly smaller than the main rolling wheel, to capitalise on the r-squared term of the moment of inertia.

Question: How have other people solved such problems? Namely, that of moving a large mass with a reaction wheel? Often I see the balancing portion be quite lightweight, and the battery elsewhere.

Welcome to SimpleFOC, @dmck !

yes, this is not a problem, though I would encourage you to use a better (SPI or ABZ based) sensor if you can. But others have made it work with AS5600, so why not. You have to attach the magnet rigidly to the motor shaft somehow, and place the sensor the right distance from the magnet, and things should work.

I can’t really answer this :-/ perhaps others here know more about it… but I am wondering why? Is your robot intended to work without gravity? This seems at odds with designing it based on wheels… :man_shrugging:

But anyway, if it is working too fast with your emax motors with a standard ESC, it should be possible, once you have a well-tuned SimpleFOC based driver stage, to control them quite precisely to get that speed under control…

You mentioned my bike. In the video description you can read what motor I use.
Drone motors are not suitable for this.

oh, I thought AS5600 was SPI-based. What would you recommend then? And do you know of a guide on where/how to attach to the motor, like correct placement etc, or is this just a guess and check thing?
I’m not sure I understand your question about gravity - it sounds like you’re curious as to why I’m moving a large mass (the battery + motors). I’m trying to use reaction wheels to drive a robot, as opposed to … regular wheels. Hence having it be able to roll forwards and backwards - the reaction wheels will give the entire body angular momentum, and the wheels then naturally roll. Not an optimal solution, but more of an interesting application of reaction wheels

@Rem666 I saw the motor you mentioned, and have struggled to find that available online - ditto many other motors that seem suitable (which is why I was hoping to just use what I had lying around, instead of trying to source from ebay and hope that the product delivered isn’t broken - perhaps I am too skeptical of ebay?)
The drone motors are similar to gimbal motors, aren’t they? And it’s just the ESC that lacks fine control? Or are the drone motors actually constructed differently in such a way that means this will be too hard?

Drone motors and gimbal motors is not the same thing. Gimbal motors have lower KV and higher winding resistance.

so I understand that lower kv means higher torque, but can you explain how higher winding resistance affects the situation? Does this lower the current used and therefore the heat, which is important since the motors don’t have a massive fan on them?

You need to read more about how simpleFOC works.

Generally speaking higher winding resistance is associated with lower KV motors, like Gimbal type motors.

Such a motor does not necessarily need current control, because the currents cannot rise so fast or so high that they can break the driver / motor.

It will also tend to be “less twitchy”, e.g. easier to control because it is not moving so quickly and the currents are low.