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Another improvement and torque measurement

A project log for Custom stepper motor driver for FFB Wheels

Why do we have to rely on expensive drivers when we can make our own?

Nikiss999Nikiss999 09/19/2020 at 21:590 Comments

Did some Nm testing. At 25% strength wheel was able to lift a 2 liter bottle at 12 cm from center of the shaft. That is about 2.4 Nm. Don't have concrete results yet but that should be about 10 Nm at full strength. For now.

Turns out that bts7960 is not up to the task for closed loop current control. I made another diy bridge and current control now is much better. Current control is still not perfect. But good news is that torque unevenness is much Much better now. Didn't have a lot of time to calibrate it properly. This also solved the problem with fast rotation. Now the strength when steering quickly is not reduced. In fact if I didn't know that the problem existed I'd never notice it.

Notchiness is still there. However below 50% strength or 5 Nm you can only feel the "tip" as a notch. Everything between steps is butter smooth.

Driving with now improved wheel was a blast. Everything below 5 Nm is a meme. It is just not strong enough. 5Nm to 7.5 Nm is good. 7.5 Nm to 10 Nm is really strong. At 7.5 you feel road texture and it is the sweet-spot. More than that and you start struggling to make corrections. But it's too much fun to drive at 10 Nm.

In summary:
- Notchiness got lowered by let's say 70%
- Speedy corrections and rally driving is not reducing strength anymore
- 7.5 Nm is the sweetspot

Flux weakening will be one of the next research steps. It reduces torque and increases power consumption but greatly increases rotational speed. However I'm still not sure if it affects notchiness between steps. If it breaks FOC which is used right now then there's no other solution but to use power supply with more than 12 Volts.

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