> > Servos also don't lose torque at speed, the faster you drive a 
> > stepper, the less torque it has.
> 
> What kind of electric motor doesn't lose torque with increasing speed?
> Doesn't a typical electric motor have an almost linear drop 
> of torque with increasing speed? Highest torque (stall 
> torque) at (almost) 0 speed, 0 torque at the shaft at max. 
> speed (when all the power is used to overcome internal 
> friction and other losses)?
> 
> The characteristics of a complete servo are of course also 
> determined by the controller, but the controller only can 
> reduce the max. torque the motor can deliver at any given 
> speed, it can't increase it.
> 
> Gerhard


Yes, the torque of a servo goes down with speed, I meant that you can tune
the system so the torque is constant regardless of speed.  Servos have a
much higher RPM than steppers, so when geared down it gives them a flatter
torque curve.  A servo can do high speed & high torque, a stepper can't.
Given two similar spec motors, the servo will usually work better.

Servos have better acceleration/deceleration preformance than steppers too.
Nicer curves.

A bad habit of steppers is resonance.  All steppers have a particular speed
where this happens, and they stall or miss steps.  Varies with load, just to
liven thing up.

Steppers have an advantage in that when the controller goes nuts, they stop.
Servos just keep going, and crash your new $200 cutter into a clamp.

Regardless, steppers are cheap and easy to drive.  Yay for steppers.

Tony

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