Testing the RPM of motors for various loads

Hello World!(pardon the cliche)

My college team and I are trying to develop small AUVs whose thrusters are much smaller than commercially available. We have a prototype ready and would like to test the RPM of the motor underwater for various loads. Is there any method to measure the RPM/torque of small motors(small shafts)?

Hi @bolozubaankesari, welcome to the forum :slight_smile:

Sounds like an interesting project! :smiley:

There are several methods for measuring motor torque and/or RPM, but the most appropriate one(s) will depend on the context. To start with:

  • what kind of motors are you using? (brushed DC are easy to measure the current of, which should be approximately linear to torque, but other motor types are a bit more complex)
  • what do you mean by “various loads”?
  • will you be testing with a propeller attached, or are you able to test without stirring up the water?
  • do you have a rough idea of the expected RPMs? (it may be possible to measure with a phone camera, either from above looking at a line on the shaft, or from the side through a clear container/tank wall or just in with the motor with a water-proof phone, or alternatively you may want/need to measure the rotations with a magnet and sensor)
  1. Brushed DC motors.
    2,3. Propellers of varying rotational inertia.
  2. The rated rpm from the manufacturer is known to be 50k rpm. We find this very hard to believe hence want to test it ourselves.