I've been using my NEQ6 with PHD2, and a couple of nights ago I see a graph that clearly shows a short-frequency, cyclical dec error. I have recently re-lubed the Dec axes, and (attempted) to fine tune it again as per astro-baby. Anyone had similar experience?
PHD "cyclical" Dec errors
Posted 09 December 2019 - 10:32 PM
My graph looks somewhat like this when there are strong variable winds. I have an 8" reflector, so it reacts to gusts.
Posted 10 December 2019 - 01:20 AM
In addition to winds like what Gipht mentioned, another possibility is excessively large Dec backlash.
Posted 10 December 2019 - 01:40 AM
Posted 10 December 2019 - 02:58 AM
The graph has the look of backlash to me also.
Have you tried running the PHD2 Guiding Assistant tool ? It tests for and reports DEC backlash.
-- David F.
Posted 10 December 2019 - 07:25 AM
I did run the guiding assistant. the backlash was about 780ms which I then accounted for in PHD. It was not a particularly windy day, so I don't think it's the wind (I was using my SV105T which is fairly compact) and I checked all the cables to make sure there are no snags. It seems more like gear slippage, no? I did try to tighten up the contact between the Dec motor and the gear. Maybe that? The thing is that the error is happening in far less than a full cycle of the Dec motor/gears. Feels like there's something loose.
Posted 10 December 2019 - 08:48 AM
I would think if this was from wind you would see similar large excursions in RA. Perhaps your Dec clutch isn't fully tightened, or your balance is off.
Posted 10 December 2019 - 04:15 PM
The graph shows a definite time correlation between RA and Dec drifts. To me, this point to a general mount “disturbance”, which could be due to wind or cable drag.
Posted 10 December 2019 - 04:36 PM
I did notice the correlation also, especially on my longer guide time. But the disturbances in RA is far less than DEC, so something disturbing DEC more than RA? I will double check the snags.
Posted 10 December 2019 - 05:34 PM
If you in guide in RA only as a test, does it show disturbances in RA still? If not the disturbances are introduced by the DEC axis...might give you a place to start looking.
Posted 11 December 2019 - 08:46 PM
good point - I'll test it when I get some clear skies