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Wednesday, October 23, 2019
The Motion Control Community Forum, sponsored by Control Technology Corporation.
Determining Specs Needed for Motor Size
Need to determine motor sizing for homemade design.


I have an ongoing design that incorporates somarily into mechanical design, background in CNC. I'm not an electrical engineer but understand electrical principles. I've designed a large apparatus, which does not require precise locationing. Its quite a heavy mass, however it is fully counterbalanced, so the motor only has to overcome the friction of moving it, and holding position. It drives a roller screw mechanism, with 2 fixed points at each end. Two of these actuators work on the fulcrum end of the counterweight, and the entire mass rotates within the center of a large spherical bearing that is either oil, or pneumatically lubricated (tbd). Between the two actuators the mass is able to position the central axis +/- 20 degrees. However the total mass is approx 30,000 pounds including the counterweight. The spherical bearing point in between is around 70" in diameter. The actuator screws are 2" dia. Any suggestions? Hydraulics are not an option because of noise, heat, and leakage.

I don't think the mass is so much the issue, as any motor could move any mass given enough time and lack of friction. The issue is going to be inertia, rate of acceleration (and deceleration?). Probably want to use a VFD, some hefty braking, etc. It's going to be a large motor, guessing around 100hp or so, depending on acceleration, inertia etc.

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You first start with the moment of inertia, and masses being actuated, the time and rpms required to estimate the required accelerating, and breaking torques required.

Any mechanical design handbook will get you started, or just call a motor application engineer at your supplier. Some firms will put you in contact with the right resources and you will be good to go.