Any shops carry servos at a reasonable price?

John

--- Tony Smith <ajsmith@rivernet.com.au> wrote:

> > > 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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