I wish to rotate a rectangular platform about its length. It is attached to a shaft that runs through the length of the platform at width/2. How can I compute the torque of the motor required to rotate and hold this platform. The platform has uniformly distributed weight on it. I want to rotate it upto 45 degrees only. I am not entirely sure if I should go fo a high torque DC motor or a stepper motor.


1 Answer 1


I have a hard time picturing your setup, but let us think about what torque is... the units can be foot X lbs or inch X lbs or N X M. The point is torque is weight multiplied by a distance. If your setup is super fancy then you will have to get into vectors; but if you simply have a platform at some distance from a shaft, here is how I would go about it:

  1. weigh the platform, or at the very least get a ballpark weight.
  2. measure the distance from the shaft to the wight

These two basic measurements should give you the torque value. Some other considerations are:

  • is your motor connected to the shaft through gearing? if you add gears (which you will need to do to transfer the power from the motor to the shaft) you might as well gear it to be able to get a smaller (cheaper/more common) motor.
  • You can buy motors from ebay that are already coupled to a gearbox, that will allow you to make crazy torque. Search for "right angle gear" on ebay, for ex: https://www.ebay.com/itm/DC-24V-50Rpm-Electric-Gear-Motor-Right-Angle-Reversible-High-Torque-for-DIY/172563602882?hash=item282d979dc2:g:FvkAAOSwGG5aJjUR
  • if you are holding the platform, a worm gearbox will hold the weight without the motor needing to eat power.
  • There are other things on my mind, like starting torque vs. running torque, vectors, gearing, footprint, and more, but I feel like I'm going off on a tangent. I keep doing that.

Good luck with your project.


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