I’m a big fan of stepper motors because they are cheap compared to BLDCs, especially for low speed, high torque applications like this motor which is only $30, compared to hundreds for a BLDC.
I’ve been running my steppers on Trinamic drivers and am a huge fan of the TMC2209 due to its quiet operation.
However, I recently learned about FOC and my understanding is that because FOC always maintains a 90-degree angle between rotator and stator, higher torque can be achieved. That really seems to be the one advantage compared to stepping mode, but it’s a huge advantage.
However, I cannot find any data or info on how much more torque is produced between the two methods. Does anyone know of a good source for this? I’ve looked over this comprehensive paper and didn’t see anything either.
The torque you get can be calculated from the power output and efficiency. You can estimate efficiency by calculating the amount of wasted current, which can be calculated from the angle by which the electrical/magnetic angle deviates from the optimal. In other words, you have to know what the operating conditions of your motor were before you switch to FOC control were.
I also like stepper motors as they are more standard and common and easier to get, and yes cheaper for the same torque at low speeds, however for higher speeds gimbal motors and smaller motors for drones and so on are actually quite inexpensive. You can get them for a couple bucks each on ali express, however they are always different and you can rarely get the same ones twice, which makes manufacturing serious stuff with them impractical, but it’s fine for the hobbyist. I have like 20 motors because I kept buying them then couldn’t get more so I had to switch to different motors.
I now use motors from JdPower, gimbal motors which are quite nice but about $30 each. They are inherently smaller so yes they will have a lower torque at a given speed however it’s more practical to develop faster RPMs and thus more reasonable power outputs. For me personally I also require silent operation. I have used the TMC2209 chips and they are quite nice within their limits although I wish they would write a driver, the one for arduino doesn’t work.
The actual torque required to miss steps will not change. Also the TMC2209 has features that allow you to do something very similar to FOC, it allows you to monitor how close the motor is to skipping steps. If you adjust the current to keep it close to the region where it is going to skip steps, you have basically the same thing, a crude form of sensorless FOC. Whether you can pull this off within timing constraints etc. IDK. They have various features like Coolstep which might allow you to do this. That would save the bother of a sensor.
Sensors are a couple more bucks and I am finding the magnetic sensors do require calibration etc. so they are not that trivial to use.