Not true.
If you look at stepping motor specs they usually state a "maximum pull-in rate", this is the max step frequency at which the motor can go from stationary to rotating, in one step - at its rated voltage. For the types of motors often used here, this is often about 1,000 full steps/sec.
There are two approaches to going faster - much faster.
The first is to use acceleration/deceleration - ie ramp the step rate smoothly from near zero to a very high value, and then decelerate smoothly. If the acceleration is not overly aggressive speeds 5X the pull-in rate can be achieved - and without missing steps or stalling. And by the way. this is exactly the technique used by Synta in the Synscan mounts - you will hear them accelerate/decelerate smoothly.
The second approach is much more brutal - and poses a safety hazard - and requires an understanding of the motor winding as an inductor at high step frequencies. Basically:
As the step rate increases the motor winding behaviour is increasingly that of an inductor - its impedance increases, reducing the current flow, and at the same time generating significant back-EMF spikes. If you treat the motor as a constant-power device, ie dissipating a constant amount of heat from the winding, it implies increasing the voltage applied to the winding with increasing frequency - using a constant-current power supply. Using this approach I have seen motors with windings rated for 4V running at as much as 30,000 steps/sec - with over 50V DC applied to the winding. There are two issues with this, however:
- the back-EMF spikes generated from the windings can exceed several hundred volts and is lethal; and
- if the motor stalls the inrush current will vaporise the winding in milliseconds.
Edited by luxo II, 26 March 2025 - 03:44 AM.