Re:ATM Computer Control help needed

[Andrew.Martyn@dao.defence.gov.au]

>I am busy building a microprocessor controlled stepper driven equatorial
>mount and I have some questions....

I have built my own microsprocessor controlled drive using a Z80 chip
driving a stepper motor. I have several drive rates for driving the
scope. Normally the drive trundles along at sidereal rate. I have slow
and fast momentary push buttons which when pushed slow or speed up the
drive by 10% and then revert to sidereal rate when released. If I push
both these buttons at once, it switches from the sidereal rate to the
lunar rate until the system is reset.

I have one other pushbutton that invokes a PEC mode that varies the
speed of the drive automatically according to prerecorded variations of
the worm wheel. The slow and fast buttons can also be used in this mode
of operation.

I have found that 10% variation in the speed was about ideal as on the
equator a 1 second push equates to a correction of 1.5 arcsec. I doubt
if variations less than this would allow fast enough correction.

One more point I would add on stepper motors is to be wary of the
vibration they may introduce. I found that my high torque motor
introduced vibrations which blurred fine detail at high powers. Vibration
can be a real problem in an all metal mount. I got rid of this by using
rubber on the motor mounting, reducing the voltage supplied to the motor
(and thus torque), and wood damping in the tube.

Andrew Martyn
Canberra
Australia