Re: Backlash correction during calibration

Suresh Mohan

Thank you for the detailed response Rolando

On 21-Jan-2020, at 12:35 AM, uncarollo2 <chris1011@...> via Groups.Io <chris1011@...> wrote:

If you can't feel any movement when you wiggle the scope or the counterweight shaft, then the worm gears in both axes are in full mesh, and you don't want to further improve upon that.

There is about 1/2 second reversal delay in the Dec gearbox. It cannot be made any less than that. This delay is at 1x Sidereal guide speed setting. If you try to do the calibration at 0.5x then it will take twice as long, and at 0.25x it will take 4 times as long. That is the reason we recommend using 1x guide rate for calibration and also for guiding because the mount will be much more responsive at that setting.

In the guider program you can set the aggressiveness to something less than 100%. If you set it to 50% it will take twice as long for the guide star to return to the zero line or twice as long to do a Dec reversal. At 25% it takes 4 times as long. You have to remember that when you dial in a low value of aggressiveness.

I assume you use PHD2 for guiding. So, the proper setup of the calibration and guiding parameters is essential. I would suggest that for calibration that you set the time for each move at a high enough level so that the mount will be able to reverse quickly with just 1 or 2 pulses. I would set the pulse length to at least 500msec or even 1000msec. There is no reason to set it below that time frame. You can also specify a small amount of backlash compensation, and PHD2 is quite good at applying it properly without causing overshoot and oscillations.

After setting the parameters for calibration and guiding, my suggestion is to run Guiding Assistant and set the backlash and all the other settings per the suggestions. Don't try to guide faster than once per second, and in fact a good compromise is to do 3 second guide intervals. If you want, you can take a 1 second exposure of the guide star and dial in a 3 second or longer delay before the next guide exposure. This will prevent hunting back and forth and allow the mount time to settle after each guide move.

Doing the right settings for accurate guiding is a bit of an art, but once you have a good set of parameters, the mount should respond in a proper manner and give you good guiding results.


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