[RadioTelescope] Suggestions for safe operation

[Andrew Williams]

Harry McNally wrote:

> In order to remotely power the system, a relay on the UWA built interface
> board controls the power (by switching the active mains wire) to the large
> stepper motor power supply. Two buttons on the UWA interface board allow the
> supply to be manually powered on and off and I assume the remote (parallel
> port) input provides a similar mechanism for when the dish is unattended.

Running the active mains wire to the logic board was a crazy design 
decision - the relay should have been near the power supply, as you've 
suggested.

> Once those modifications are in place and have been inspected and/or tested by
> UWA safety people, I think anyone can gleefully (and safely) hack on the
> control box.

Personally, I'd recommend dumping the existing custom logic board 
entirely, and driving the commercial motor controller boards directly. 
All they need is a logic level on one input to set direction, and pulses 
on another input to step, and you can do all of that better with a 
microcontroller. It looks like the board just gates a fixed-rate clock 
to the stepper pulse lines, and you get much, much better response if 
you ramp the velocity to limit the acceleration (and better yet if you 
ramp the acceleration to limit the 'jerk').

Are the steppers wired up in unipolar mode (half of each phase energised 
at any given time), bipolar series, or bipolar parallel? The wiki has 
gone, so I can't re-read the controller specs. What voltage is the 
stepper motor power supply, and what value (and power rating) are those 
four big resistors on top of it? I'm guessing each pair of resistors is 
in series with one of the motor power supply lines? They would be the 
'Rs' series resistors in the wiring diagrams in the motor data sheets. 
The protection diodes are probably built into the controller, but might 
be external.

Andrew