ChrisEll

UPDATED: A bit more info on the motor pinion... it's a 9 tooth, 0.4 module gear. The motor shaft is 2.3mm in diameter and the pinion is simply hammered on to the end. The motor shaft is not splined or keyed... the pinion is held in place by friction. It's a nasty cheap looking cog, no proper bore and no grub screw which accounts for the off-centre motion. I would be disappointed to see such a gear in a Hornby locomotive never mind a £800 mount. So my plan now is to find a suitable replacement if possible. Radio controlled car/planes/helicopter parts seem to be the best bet.

A post re PE at different frequencies: http://ccdware.infopop.cc/eve/forums/a/tpc/f/401101098/m/3097074586 "Looking at the frequency spectrum tab, it looks like there are integral peaks at 1x, 2x, 6x, 18x, and 54x. I think you could correct all except for the 54x peak, as it's frequency (11 seconds, may be two fast to correct)." Not what I want to hear...

Just read your thread, very informative! Looks like your AVX has been through the wars I need to be careful how much I tinker with mine... it's got to remain in a newish, resellable condition!

Ok I was getting a bit muddled with worm and RA bearings... got it now It seems tricky to get the exact size RA bearings, I heard that some people's RA axis stick out a bit more at the top and holes need to be drilled, like yourself.

Thanks for the bearings info. Did they fit perfectly or did you have to drill an access hole for the RA tension ring grub screws? No, not swapped the worms.

The gearbox is certainly interesting to poke in Also see if your motor's pinion spins a bit eccentrically looking from end-on... both mine do :/ I can't believe this is a good thing. Anyway I swapped my 2 motors over and tested last night and the RA guiding wobble is still there Fast running out of ideas now... it's not PHD2 cos the wobble is still there when guiding is off, so it's probably the mount, maybe RA bearings? (another long shot)

Anyone with a deep interest in motor encoders should read this: https://www.cloudynights.com/topic/551524-celestron-as-gt-ra-encoder/

After discovering a periodic signal (once every 11 seconds) in my guiding in the RA axis I did a bit of digging and found the motor pinion rotates 1 rev/11 sec at sidereal rate. By motor pinion I don't mean the big brass spur gear visible with you take the cover off... I mean the output from the motor before the reduction gearbox. When I spin the motor at a fast speed you can easily see that the pinion wobbles about which is not a good thing. The pinion is simply hammered onto the somewhat thin drive shaft rather than held in place by a grub screw. Dec motor wobbles the same. On the Celestron website there are photos of the CGX and CGEM motors and they look exactly the same... this may suggest the wobbly pinion is not an issue :/ I then opened up the encoder. Nothing odd there but the optical wheel was worryingly grubby so I cleaned it with a damp cotton bud. There were markings on the PCB: "E8300 Rev.A RoHS". Time to open up the gearbox. Inside are 4 pairs of cogs. The gear ratios are: Motor pinion (9 teeth) -> 2nd gear (27 teeth) ==> 1:3 3rd gear (11 teeth) -> 4th gear (33 teeth) ==> 1:3 5th gear (11 teeth) -> 6th gear (33 teeth) ==> 1:3 7th gear (16 teeth) -> 8th gear (32 teeth) ==> 1:2 Overall reduction 54:1 Motor output speed 1 rev/ 11 sec Worm period: 11*54 = 594 seconds Note 2nd, 3rd and 4th cogs are plastic, possibly ok due to the low torque at that stage although someone here on SGL has experienced a split gear. I found that cleaning off all the excess grease results in a much smoother gearbox. I was tempted to open the motor casing itself but thought better of it So I was left with what to do about my RA high freguency periodic error... in the end it seemed a good idea to swap the Dec and RA motors over to see if that would help, especially as I had everything in pieces. Also my RA motor has had a hard life so far... my RA axis had been very, very tight - so tight I could not turn the worm by hand. This was due the tension ring being ridiculously overtightened and also the worm mounting bottom bolts being completely loose so the worm was not seated against on the ring gear properly. I only recently fixed this. I'm surprised the motor had not burnt out or a plastic gear split. I'm hoping it may have developed a slight problem and that the swap will help, though I admit it's a long shot. So will test shortly and see what the outcome is