Well, now we are getting in nebulous territory indeed, so let’s start from the use case of motor control of the lens rings from my first post. The rough requirements are:
- Move the ring(s).
- Don’t burn or break if you hit the movement limit.
- Provide enough precision to be usable.
- Don’t be huge and/or expensive.
Let’s flesh these out a bit more.
We need to turn the rings of the lens, which requires a torque of 0.0052 Nm if I 've done the math right in my first post. However, this is not torque of the motor, it’s torque on the ring. The connection can be geared and the ratio will have to do with how close is placed to the ring and how it is coupled (gear, belt etc). The speed of rotation is not terribly important, the use case requires fine control and modest speeds so it is conceivable that a tiny gear and many revolutions on a somewhat slow motor are perfectly fine. My thinking is that I will likely start with very slow speeds and see about speeding up.
The size is kind of important. I can fit three typical 9g servos, which are around 22mm x 12mm around the lens. It would be great if I can be in that ballpark, especially since the smaller the motor is, the closer I can get it to the lens ring and the smaller I can make the gear on its shaft, if I decide to go for gears meshing directly (which is the simplest approach).
Price. You can get a cheap and cheerful small servo for single digit dollars / euros. Obviously, this won’t be the case here but I would prefer not to go too crazy. An upper limit limit of around 30 euros per motor seems like a reasonable value.
Now, given the above, I have been looking around the threads suggested above and in this thread, @runger mentions the EMAX RS1106.
Now, if this is actually usable, it would be beyond wonderful. It is tiny, easy to source and so crazy cheap it can actually compete with a servo (well, price of the simpleFOC notwithstanding). However, I have no idea of its phase resistance and I 'm fairly certain it will be super low, in all kV versions. Now, I am planning on using the SimpleFOCMini V1.1 and its product page says in scary letters that:
SimpleFOCMini has been designed for gimbals motors with internal resistance around 10 Ohms. Using this board with high-power drone motors may burn the DRV8313 chip integrated on the board. The chip can handle up to 3Amps of current for short periods of time, but in for long-term operation (without the heat-sink) the current should stay under 2 Amps.
It is possible to use this board with low resistance motors but it requires a bit of experience and it is not recommended for beginners. Ask community about it!
So, if using the EMAX RS1106, I will almost certainly be operating with a wildly lower resistance motor than the SimpleFOCMini expects. I am not terribly sure how much experience would be required to “use this board with low resistance motors” as the note says but I would be willing to give it a shot, given the other characteristics (size, availability and price) of the EMAX RS1106 motor.