ChrisEll

For those wishing to tune their AVX further check out my other mod:

13 minutes ago, Astrowal said:

For the most part it's been pretty accurate visually. I do have a Celestron 9.25 sct attached to it. Could be the weight of the scope that's throwing it off for astrophotography. 

It is quite stiff though, so stiff that I could balance it with my eyes closed. 

 

That's a big scope for imaging on the AVX... I had a 8" SCT and it was a struggle! I then got a SW ED80 refractor which was an improvement, being lighter and having a shorter focal length.

38 minutes ago, Astrowal said:

Thanks for replying Chris. 

One more thing, when loosening the RA axis should I follow the same method of rotation (anticlockwise) then pull/push then adjust so that there is no play then tighten the grub screws? 

Just an insight, Iam a newbie to astronomy but very passionate about seeing this through. Also just recently tried astrophotography and I can safely say iam addicted! I was warned about the Avx mount but chose not to listen. Appreciate all the help though on anything to help make guiding smoother. 

That sounds fine to me.

Yes I got addicted to imaging but now finished my journey.

The AVX is capable of good results, just needs some tweaking which is probably true of all of the cheaper GOTO mounts.

There are many reasons not to have the axes too tight... you will be able to balance better, less stress and load on the motors, gears, and bearings and yes it may improve guiding.

Another thought: only operate the mount when the mount is properly balanced otherwise you will overly stress the motors and gears.

On 03/05/2019 at 03:21, swordfishy said:

Howdy. I have a similar issue with a CGEM mount. 2 motors with 2 plastic gears missing teeth. I cannot find a source for the plastic gears, willing to go brass if I must. Any idea where a good place to look may be?

You probably have to buy a whole motor replacement for each... i've not come across any gearboxes which are the same as the ones for the those motors.

The broken teeth seem to suggest the RA and Dec axes are far too tight... the axes are not well assembled and tend to be overly tight. They can be easily corrected.

Inspired by the great images above I gave it another go, this time trying to be a bit more patient and less heavy-handed! I've not tried deconvolution yet but will do. Thanks to @NigeB for uploading.

Couldn't resist having a go...

I had problems removing an M42 adapter off a filter wheel yesterday, tried rubber gloves and WD40 but no good. In the end I used my trusty plumber's pliers, taking care to mask off the area with masking tape to avoid scuffing. If you're not familiar with this tool one arm slides over the other until you get a decent purchase on the thing you want to grip... a very useful tool!

A similar issue with an EQ3 Pro mount

22 hours ago, newbie alert said:

You could try this..

http://www.astrokraken.fr/dovetail-adapter-for-dslr-flash-grip-a132406226

Interesting device but I would be concerned about flexure with that.

Perhaps some kind of vixen saddle bar that has 2 attachments, one for the DSLR and one for the guide scope. This link is probably not what you need but gives you an idea.

https://www.firstlightoptics.com/adm-vixen-type-v-series/adm-v-series-side-by-side-mounting-system.html

However rather than waste money on one of those consider a small ED refractor that can be had for around £200.

I bought mine here:

http://www.dancingwingshobby.com/free-shipping-rc-model-metal-pinion-gear-04m-23mmhole-diameter-8t-9t-10t-12t-13t-14t-15t-18t-20t-24t-height5mm-10mm-12mm_p0558.html

Takes about 2 weeks. They come in fives, so I have some spare, so PM me and I'll pop one in the post if you like

Anyway have a look first and see if your pinion does run off-centre... I thought you said it was all ok?

My AVX motor pinion replacement finally arrived. The only suitable gear I found were 5mm in height with no boss or grub screw. This meant bonding the new gear to the motor with glue. 

First job was to check it's the right diameter bore, so I removed the optical wheel off the back end of the motor and tried the gear there... perfect fit. I removed the RA motor, PEC sensor and control panel all as one piece, much easier than removing the motor from the control PCB. Also you can spin the motor using the handset. So the motor went in the vice and after many failed attempts to lever off the pinion with a screwdriver I eventually removed it by gripping the motor in my left hand rather than the vice. The pinion was hammered on very tight and was only held in place by friction... no keying or splines.

Next to prep the bonding surfaces... I scored some lines inside the gear hole to give the glue something to grip onto, ditto the motor shaft. Quick clean then I put a small piece of masking tape at the base of the motor shaft (make sure the gearbox base can sit back on the motor without the masking tape interfering). This prevents any wayward glue entering the motor and also I can use it to help position the new pinion at the correct height. I put the gearbox base back on with the 2nd gear to get the correct height - I jiggled the masking tape accordingly. The new pinion is 5mm in height so only 3mm of it will actually bond to the motor shaft, not ideal but hopefully enough.

Now to glue it on. I used Loctite 638, a "high strength retaining compound". I smeared some onto the motor shaft and inside the pinion using a tiny screwdriver, then a small blob into the hole and fitted the gear to the required height. I expected to have a bit of time to jiggle it and double check the height but the glue set very quickly and I was not able to move it. Luckily it was at the right height. I spun the motor using the handset to check the gear ran true which it did, much better than the original pinion. I left it for an hour and then scooped out the small pool of residual glue from the top of the pinion... this is not going to set and it's good to get rid of it now to help the curing process (Loctite only cures in small spaces in the absence of air). Left overnight.

Next day I reassembled everything and switched on the mount. I could see the RA gears start to turn very slowly. I manually slewed the mount in ever increasing speeds, finally reaching 9... it worked fine. More slewing and then I left it on for the day at sidereal speed. I also loaded the mount with scope, camera, etc. (this is only a 5kg payload, the AVX can handle up to 16kg... I should test with a max payload sometime).

So after all that here are the results. The high frequency periodic error is gone and the RA RMS has dropped considerably. Success! 

N.B. In case you need to remove the gear for any reason here's how: you need to apply heat to the Loctite, so hold the gear in a match flame for about 3 seconds then pull the gear off immediately.

N.B.B. No need to do this mod on the Dec motor.
 

41 minutes ago, Redscouse said:

Again, forgive my stupidity; What does dithering do/mean in astro terms?

Dithering randomly nudges the scope position very slightly inbetween exposures... this means the sensor is not sitting over the same bit of sky all the time and so sensor noise can be removed more effectively. I use DigicamControl and you can tell it to dither between shots, handy!

9 minutes ago, knobby said:

Slightly off topic but will dithering only in RA be of any benefit ?

I hope so cos I only dither in RA, too much Dec backlash. But having said that I've recently been Dec guiding in one direction and I imagine that should cope with Dec dithering better.

1 hour ago, Fspp369 said:

hi

just been looking at your avx  strip-down…

on the pics of the worm drives they don't show locknuts on the end of the backlash adjusters… are they supposed to be there?

great article btw.

Not sure which pics you're referring to... maybe to @Shelster1973 's posts?

Those are all useful links which I have visited many times!

Quick update on the AVX motor pinion situation... I am waiting for some pinions to arrive. In the meantime I've been experimenting with different ways to fix the pinion to the motor shaft... the new pinions do not have a boss and grub screw so will need to be glued on with something like Loctite or JB Weld. Hopefully I'll have something interesting to post in a few weeks.

I've just put a post up on how to adjust AVX axes.

Here's a quick guide to adjusting the tightness on the Dec and RA axes on the AVX mount. Freeing up the axes means better guiding, less wear on gears and motors (some gears in the drivetrain are plastic), lower worm PE and you will be able to balance more precisely.

Dec axis: 

Remove the counterweight bar and cup to reveal the tension ring. To adjust this first loosen the 2 grub screws at its side... there is a small access hole at the side of the housing. You'll need a tiny allen key to do this. Then use a slightly larger, stiffer allen key and insert this into the access hole and against the grub screw so that the tension ring is wedged tight against the allen key - this serves to hold the tension ring in place as you turn the axis, no need for a special tool! Now rotate the mount saddle anti-clockwise to loosen the tension ring until you feel some vertical play (grab hold of the saddle and move up and and down to test). Slowly tighten until there's no play. Tighten grub screws.

RA axis: 

Remove the plastic cup at the end of the axis. The RA tension ring has 3 grub screws and the access hole is hidden by the control panel cover (3 screws hold this in place). My RA axis was very tight and needed a few turns of the axis before I got any vertical play.

For those wishing to improve their AVX further I recommend adjusting the worm housings in both axes.

2 hours ago, knobby said:

Please !

Ok, I will put a post up over the weekend.

15 hours ago, iapa said:

I envy you guys knowledge of how to take the AVX apart - I've no idea where to start.

Both RA and DEC are tight to the point of not even completing a half revolution when taken to horizontal and left to drop

Adjusting the RA and Dec axes tightness is really quite straightforward, no need to take anything apart (well, not too much!). I'd be happy to create a post on the subject if you're interested.

Here's a diagram of the AVX gearbox ratios, courtesy of Peter Wolsley.

More chat about AVX/CGEM motors and high frequency PE can be found at: https://groups.google.com/forum/#!topic/open-phd-guiding/-O5nY0xae2w

Does your motor pinion wobble when you rotate it with hand controller?