My mind keeps on working and I stumbled upon something new to me, universal motors.
These motors are everywhere, also in 2kW power tools like 230mm angle grinders. I took a look at my 230mm angle grinder, rated 2000W and 6000 RPM. The gear ratio is 3.67:1 so when the grinding wheel spins at 6000 RPM, the motor spins at 22000 RPM.
Since a characteristic of the universal motor is high starting/stall torque, I was thinking, what would happen if a "designed for 22000 RPM"-motor was loaded enough to only spin at 3000 RPM? Would the motor overheat or would it easily handle this because the torque goes up as speed goes down? I my use-case, the motor spins up the propeller to be balanced, then runs for a few seconds at measuring speed e.g. 3000 RPM. So the motor is running for max 20 seconds at a time.
The DC treadmill motor has a price tag of $164 as a new spare part for a discontinued treadmill.
A brand new Makita 230mm angle grinder rated 2000W has a price tag of $98.
So the universal motor from an angle grinder is cheaper to get a hold on.
What I'm considering here is that for the propeller balancer sensor to pick up any imbalance in the propeller, the imbalance would need to have enough force to vibrate the whole motor. It will of course require a larger imbalance to vibrate a heavier motor, so I'm thinking with a lower weight motor, I will be able to pick up on smaller imbalances, hence improving my final propeller balance. I think the treadmill motor is heavier than the angle grinder motor, but I will need to verify this. Maybe it's just the flywheel on the treadmill motor that adds the weight, but this is also something to consider, do I really need the flywheel? It might provide for a smoother rotation, but it adds weight which counteracts vibration.