Slack is not too much of a problem if you use worm drives and avoid the Lego gearbox, then most of the slack is in the Lego motor gear train.
The weight of the camera/ scope usually means that the tilting gears are always in contact even after changes in direction (unless your tilting axle is very stiff!).
When panning, you can build in an extra motor movement at each change in direction to take up the slack.
You can get a good estimate of the amount to take up using the MK 1 eyeball by writing a short program which just reverses the motor on command and displays the rotation count.
Run in one direction, stop and note the count, reverse until the rig starts moving again, stop and note the new count.
Last edited by h-g-t
on 28 Jul 2013, 13:06, edited 1 time in total.
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