When to use a shaft, or connect directly to motor shaft. 1

[meanderngineer]

Hello Everyone,

I was wondering if anyone had any experience regarding the benefits of using a shaft to rotate a device. Basically, I have a probe that is oriented vertically and that will be moving over a device; you can visualize this as if it were a plain and vertically oriented cylinder. If we assume the cylinder is of perfect form, I want to rotate it so that it's vertical axis will not adopt any angle during the movement. I was wondering if using a continuous rotation servo in conjunction with a shaft / bearings held any significant advantages over attaching the probe directly to the servo. I imagine the bearings would add additional constraints to the rotational motion and may increase stability, but if I use a motor with internal bearings this may be redundant / unnecessary. There will be no significant radial, axial, or torquing forces applied to the cylindrical probe, it does all of its work without making physical contact to the devices it tests.

 

[MikeHalloran]

Electric motor manufacturers use the cheapest bearings they can get away with.

For serious motors, even orienting the shaft vertically may cause early bearing failure, because they don't ordinarily size the bearings for even the thrust necessary to hold the rotor up.

Expecting an undersized pair of bearings to demonstrate no trajectory error on a cylinder extending far outside the rotor length is not likely to produce results that you will find satisfactory.



Mike Halloran
Pembroke Pines, FL, USA