Re: [CAD_CAM_EDM_DRO] How do you compare steppers to servos

Jeffrey T. Birt wrote:

>> A stepper works by making the rotor follow a
>> magnetic field generated by the coils.
>>
>
>
>
> As does any electrical motor. I'm not I follow the point your trying to
> make.
>

A stepper motor has a characteristic deflection figure (torque vs.
deflection), or conversely,
stiffness. If you apply a torque to it, it will deflect. At
standstill, if the holding torque is
applied, the motor will deflect over a full step and then just keep
going. So, you can figure the
stiffness of any standard stepper motor (at standstill) as equal to
holding torque/(.005 of a full rotation).
Or, holding torque / one step. You can't do anything to adjust that
except buy a motor with more torque.
The deflection when running scales the same as the torque curve.

A servo can be as stiff as your control algorithm allows, up to the
maximum torque you have set the limit at.
If you double the loop gain, you double the stiffness. Generally,
increasing encoder resolution allows you to
make the loop stiffer while still being stable.

Jon