Torque Required to Rock a Box

[dgt32]

Hi All,

Im using a stepper motor to pull down essentially a heavy box (~60lbs) that has rocking legs. The box is rests on a base. The stepper motor will be rigidly attached to the base or the ground. Im trying to figure out how much torque the stepper motor needs to be rated for, before sufficient oversizing. Please excuse the crude drawing. Would it just be the distance x times the weight? Are there more assumptions that need to be made?

 

[3DDave]

Almost none. If the motor applies a load a the natural frequency then it will produce a rocking motion. Which is why rocking chairs are easy to use rather than being hard exercise.

 

[hydtools]

You need to account for the restoring moment of the weight which will be zero at initial rest as shown. The restoring moment will be the weight multiplied be the horizontal distance it is displaced from zero.

Ted