Re: [CAD_CAM_EDM_DRO] Re: stepper vs servo

Alan Marconett KM6VV wrote:

> Hi Jon, Mariss,
>
> Is there a standard comparison (rule of thumb?) between servo torque
> required for a machine, and stepper torque required? What would your
> 4.4 (in/lb) continuous and 15 in/lb (peak) servos translate to for
> steppers? I'd think it would be more the 240 oz/in steppers!

Well, there's the rub, or one of them, at least. Steppers are rated in
HOLDING torque, while a much more useful parameter is running torque.
In fact, what you need is running torque at the highest speed you plan to
use, for a safety margin. A 650 Oz-In holding torque stepper may be good
for 50 oz-In running torque at 500 RPM! The problem is that the motor
manufacturer can't rate the motors at speed without referring to a specific
driver. So, if you need to know the real running torque for a particular motor/

driver combination, you need to get that info from the driver maker, if he
has tested that combo. There are some numbers and charts available,
but obviously, not every combo has been tested, and only a few of those
are published.

> What servos should I be looking for to drive my RF-31? I think I recall
> 650 oz/in being recommended.

See above as for why such overkill seems to be needed. This sounds
reasonable.

Jon