ST4 guiding speed

[alistairsam]

Hi,

I've built a picaxe mcu based stepper motor controller for a home built equatorial fork, and am adding ST4 autoguiding to it.

I traced the ST4 pins on a qhy5 guide camera and interfaced it to a picaxe microcontroller and LED. I chose "mount on camera" in PHD and can now get the ST4 pulses to speed up or slow down RA.

What I wanted to know is if someone can explain the normal behaviour of a Hand controller, that is while tracking is on and the motor is tracking at sidereal rate, what happens when you press the east or west button, does the speed of the motor increase or decrease by 50% or is the amount different?

I can vary the amount of correction easily enough in the code.
I just don't want the speed corrections to be too small or too large.

I'm not sure if the manual for any mount explains this.

[Merlin66]

Pressing the East button speeds up the motor. Up to x1 "siderial rate" changes; pressing the West slows or stops the motor, to get greater rates of change i.e. > x1 siderial you need to reverse the motor.

[alistairsam]

Hi,
is this on a specific mount or is it common for most mounts?
I'd imagine the rate to be different as gear ratios would be different amongst mounts, So whilst a small change in speed may be sufficient for one, another might need a larger change due to a higher gear ratio.

I was using 0.5x sidereal as the change increment but will try 1x. My gear ratio is around 1178:1 with 1/32 microstepping.
to achieve sidereal rate, my step freq is 87 steps/sec.

So I'd have to change that to 174steps/sec for an East Pulse or 0 for a West Pulse?

[Merlin66]

The actual pulses per rev of the shaft will vary obviously depending on the gearing.
Whatever # of pulses you need to achieve proper siderial rate - then x1 siderial corrections would require twice as many pulses in one direction and zero in the other.