John,

Rotator problems again.

We have a 2" pyxis that works well when we use the pyxis software to rotate it. It is set to reverse rotation. Attached is a log file that has ccdap commanding it to go to 329 PA and it ends up at 240. Any ideas about this?

Cheers, Pete

ccdap20091011_210657.log (9 KB, 6 downloads) log file

Hi Pete,

Notice that your rotator offset is 270.9E. PA 329 is 31 degrees from 0(360). 270.9 (271) - 31 = 240. So to get to a PA of 329 with an offset of 270, the rotator needs to be sent to 240. HTH .....

Frank,

Where is the rotator offset stored? Can I clear that to 0?

Pete

Hi Pete,

The offset is the value of your PA when you performed your initialization, so that value is important for calculating the guiding vectors as you use the rotator and to position the rotator to the correct/selected PA for your target. The offset calculations for the target PA are handled by the software, so in order to change that value, you would need to move your rotator to your preferred offset and re-initialize the system. If you want a "0" offset, then you need to align your camera with the RA/DEC axes with the rotator also at its "0" position and initialize on the same side of the meridian that you used for the camera alignment. However, as John has mentioned many times, it is recommended that you offset approx. 10 degrees from the cardinal points when doing your initialization. With a good initialization, the software will put you on target at the correct PA, regardless of the rotator offset. HTH .......

Pete,

Frank explained this perfectly. Why would you want the rotator offset to be 0? It is like requiring the tic count for your RA axis encoder on your mount to be 0 when you are pointing at RA 00:00:00.0. Once initialized, the rotator offset has no utility or meaning - only PA does.

The Pyxis can not "wrap your cords around the axle" since its range of rotation is limited to 0 to 360 so there is nothing to worry about.

Make sense?

Frank, John,

Got it. Makes total sense. Now I understand what happened. The pyxis slipped on the focuser barrel, I readjusted it manually, but didn't reinitialize afterwards.

Cheers,

Pete

Pete,

I have the 3" Pyxis and the camera is mounted at about 50 degrees when the Pyxis is at zero. The offset is due to an adapter I am using. Point is CCDAP handles it fine and the Pyxis doesn't rotate the full 360 degrees in one direction.

Also, the Pyxis can slip if the load is too high. This is more common with the 2" than the 3". It takes a lot more torque to make it slip once it's not moving. My unit was just upgraded last month at Optec. One of the things they check is the torque produced. I opted for a 15 volt power supply to up the torque on my unit. I don't know if Optec has any upgrades for the 2", but they are very reasonable when it comes to servicing older units.

Even if your Pyxis "slips", you don't need to reinitialize CCDAP. All you need to do is "home" your Pyxis. Either through the Pyxis driver or simply by removing power from the unit.