[amsat-bb] Re: inquiry about homebrew az-el systems

[Phil Karn]

On 03/08/2013 01:31 PM, PA3GUO wrote:

> Things I learned and included in my software:
> - thresholds are needed to avoid the system oscillating around a target position
> - corrections need to be made due to overshoot (after a stop command the rotor takes time to actually stop

These are exactly the problems that can be neatly addressed with a 
variable speed drive rather than the classic bang-bang. If you want a 
fixed position, you use a control algorithm that slows the motor as it 
reaches it so it won't overshoot (or at least not as much) and stops at 
exactly the position you want.

But since you're most likely tracking a moving satellite, you can simply 
vary the speed of the drive to match the actual speed of the satellite 
and then you'll never have to stop. You'll have a small error in 
velocity and position but again, with the right control law those errors 
can be made very small.