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Old 27-02-2012, 11:15 AM
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OzRob (Rob)
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OzRob is offline
Join Date: May 2009
Location: Thailand
Posts: 446
Originally Posted by rally View Post

The Robofocus and others that use the same/similar motor/gearbox hardware - (eg Cercis Astro) doesnt know its absolute position.
There is no feedback system - ie no rotary encoders on the output.

The controller relies on the fact that the stepper motor has in fact stepped when its been asked to.
If it has stepped, then the step is accurate and all is well, but if the load is too great or there is some interference then its possible that the controller tells the motor to step, but it it doesnt actually make the step because the motor is stalled with the load and then you will have some problems as the controller now thinks it has made the step and the controllers positional information is now wrong.
If that occurs repeatedly on every focus cycle, the focus position incrementally gets worse each time.

This can occur with very heavy loads at/near Zenith when the focus system gearing is not high enough to overcome this maximum load position or worse yet even slips.
You can adjust the motor power as an option, but that only helps so much.

If you are having problems keep this in mind.

Also bear in mind that these systems usually rely on the same effect to calibrate their "home" position, so they make a very large move in one direction to close up your focuser till it reaches a hard stop, the motor still keeps going, but there is no movement.
If the hard stop position is actually more like a soft stop (ie its somehow flexible or changing) then the the focusing system may be unreliable.


I believe that there is a more powerful motor available now for the Robofocus if you have a lot of weight.
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