Re: [CAD_CAM_EDM_DRO] Mixing servos & stepper in same system

Marv Frankel wrote:

>Guys,
> I'm stilll doing R & D on my system components, and it was
>suggested that I use a stepper to drive the knee's X axis, rather than
>a servo, because of the steppers better low speed torque. Is there any
>problem doing that, or would it accomplish the same thing by using the
>higher speed servo, and just increase the gear ratio.
>
>

Servos generally have full torque available up to top speed, where a
stepper loses torque
rapidly at higher speeds. With the servo, if you need more torque, a
sprocket change will
fix it, at the cost of lower top speed. With the stepper, changing the
belt improves holding
torque, but makes the running torque fall off even faster at the
leadscrew. So, I would
recommend servos for difficult applications. Since the motor will have
to resist the
steady weight of the knee, you might want to make sure your motor is
plenty large
enough to dissipate the heat, and that the Gecko drive (I'm guessing) is
well heat sinked.
And, you are likely to need a fail-safe brake that grabs the motor shaft
when you go to
e-stop mode or power off. That's only necessary for ballscrews.

Jon