EQ4 RA tracking problem - any suggestions welcomed

[[1ponders]]

I recently purchased a secondhand EQ4 mount (GP Clone by the looks of it) with dual drives. I have only now been able to put this mount to the astrophotography test. It looks like it has the potential except for one little irksome factor, the RA drive runs too slow/fast (?). I haven't really checked which yet, but the star was definately drifting 'up' at quite a rate. (I was using an SBIG in a refractor without a diagonal with the base of the SBIG in line with the RA direction of travel. I'm not used to how the SBIG orientates yet as it was first light for it as well :) ) Since then I haven't had the opportunity to check it with a camera I am more familiar with using.

There was a thread a short while ago about a similar problem but I have been unable to find it. Not being an electrical guru I don't really know where to start. Does anyone have any suggestions on what might be going on?

[Karls48]

Hi Paul. Almost all new mount motor controllers use microcontroler IC OTP (one time programming) type. Those have software burned in and it cannot be reprogrammed. Some use crystal, some resonator to provide accurate timing for CPU. If the crystal is oscillating too slow or too fast that would affect tracking speed. Also, if the tracking speed is slow it is possible that tightness the driving train is a culprit.

[[1ponders]]

Thanks for the info Karl. I'll check the tightness of the drive, though the amount of backlash would seem to indicate that it isn't overly tight. I'm looking forward to a bit of clear sky so I can check whether it is slow of fast.

[[1ponders]]

If it is slow I was also wondering if the 12>6V adapter I am using is not putting out the full 6V or if it is not able to draw enough current through the adapter?

[Karls48]

That’s possible too. Also bad connection in the DC plug will cause voltage drop. RA motor itself could be faulty. But you are right, when troubleshooting electronics, always start with power supply.

[[1ponders]]

I checked the two 12 to 6V adapters I have and the one I was using the other night was only showing 5.8V while the one I will try tonight showed 6.5V. Hopefully that will make a difference (and not make it run too fast :P )

[[1ponders]]

Well I did a bit of experimenting tonight and it didn't matter which adapter I used I didn't get the problem I was having the other night. I did work out which direction the drift was though, RA+. Then it dawned on me, clutch slippage. :doh: I had the scope pointed directly east at about 25 deg with a whoppin' great SBIG and filter wheel at the end of a 100mm f10 refractor on a poor little EQ4 mount. :doh:

Another bonus of the nights exercise I now have the periodic error measured so I can play around with that now. I think it's time to do the Astroboy CG5 turbocharge to this little mount ;)

The two images below are from each of the adapters. The PE looks pretty constant, though horrendously large :P . I'd be interested to find out what is making it gradually climb though.

Ignore the pink Dec graphs, I hadn't polar aligned accurately to start with and then with the second one I had only adjusted to altitude and as the mount pointed higher the azimuth drift error started to creep in. Mind you if you look at the second graph carefully and read the .csv file generated you will see that up until around 1100 sec there was less than 3 arcsec drift in Dec (approx 0.15 arcsec/min). Ya gotta love K3CCDTools for drift aligning :D