CG5-ASGT belt conversion, jumping on bandwagon

[billhinge]

Been following the various mount belt conversions on the internet so decided to give it a whirl, how hard can it be?

Just put in the order at beltingonline for the following which keeps the existing gear ratio and gear centre to centre distances

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2 x 15 Tooth HTD3 Pulley (15-3M-09F) (HP15-3M-09F)  = £14.23
Modify Bore? 5mm
Grubscrew Holes? 2off M3
2 x 3mm HTD® Timing Belts (4573)  = £3.91
Width in mm 9
Belt Length in mm 111
Tension Cords Glass Fibre
Material Neoprene Black Rubber
2 x 24 Tooth HTD3 Pulley (24-3M-09F) (HP24-3M-09F)  = £11.43
Modify Bore? Not Required
Grubscrew Holes? 2off M3
Keyway? Not Required

Should be here in about 4 days post permitting

I contacted beltingonline and got quotes for AT3, T2.5 and HTD3 but decided to go down the HTD3 route - AT3 was very expensive !!!

For info, if anyone is curious I found this useful chart showing belt differences http://www.mycncuk.com/forums/attachments/linear-rotary-motion/9931d1377980211-best-timing-belt-pulleys-type-minimum-backlash-belts.png

I'll also have to reverse the polarity on the motors of course but had a quick look and shouldn't be difficult

I'm also replacing worm bearings on Dec axis with good ceramics while I'm at it, already done RA axis  

let you know how I get on when done

[billhinge]

Belt and pulleys have arrived, test fitted on Dec shafts the other night  and they fit perfectly, the pulleys I bought have guides to keep the belt straight on the pulley

Have updated Dec worm bearings with ceramics and worm turns much more freely

Plan to do the belt mod Thursday or Friday when I finish for chritsmas- may have a play with Pec tool first to do a before and after if I work out how it works

Celestron confirmed motor polarity needs reversing

"Thank you for contacting Celestron.

The polarity would have to be reversed as there is no menu in the hand control to reverse the motor direction permanently."

(you can change the direction of the handset arrow buttons apparently which prompted the question)

[msh1]

any chance you could do a walk through because i been think about doing mine but not sure where to start 

[billhinge]

sure, as soon as I get it working I'll post how I did it (or didn't    )

[billhinge]

I've been working on electronics and computer projects recently ...

I finally got around to removing the DEC & RA spur gears and replacing with belts and pulleys, the upgrade does work but obviously everything turns the wrong way - wasn't too difficult

challenge for next weekend is to reverse the motor polarity (may need a bit of soldering ??)  

I also accidentally decoupled the glass encoder disk when I was looking inside the DEC motor. The CG5 definitely didn't like it

Thankfully I think I managed to remount it using a couple of pairs of tweezers and it seems OK again

[msh1]

glad its going ok any pics sounds like a very interesting project 

[billhinge]

Will do, but it will be next weekend, I have tried everything connected to power and it does work. I haven't put all the wires and circuit boards back in the housings yet so can do some pics

I'll show my motor  and mount damping solutions as well 

[billhinge]

Unexpected result...

I thought simply switching the motor wires around would be enough the make the motor run backwards - works on my maxons

However, when I tried this by switching the crimped wires at the Dec circuit board end what actually happens is that the motor loses rate control, everything is at rate 9

Switching the wires back fixes the problem

Any ideas?

[1parsec]

Unexpected result...

I thought simply switching the motor wires around would be enough the make the motor run backwards - works on my maxons

However, when I tried this by switching the crimped wires at the Dec circuit board end what actually happens is that the motor loses rate control, everything is at rate 9

Switching the wires back fixes the problem

Any ideas?

Hi,

 If you've only swapped the motor wires the mount is 'running away from' rather than towards the command position.

You mentioned the mount has encoders. .The encoder should have 2 channels  A + B.  There might be a index channel too.  You'll need to swap the A and B wires .

If the encoder isn't labelled, you'll probably need an oscilloscope to find the  A + B signals.  They should be square waves, 90 degrees out of phase.

Dave.

[billhinge]

Thanks Dave

I got the same answer on cloudy nights, I found the wiring diag for the us robotics encoder that celestron apparently used  so I'll give it a go

[billhinge]

Got it working now. On my CG-5 the encoder A & B pins are 1 and 2 (green and  white in the pic) and motor are 5 & 6 (purple & blue)

reversing the motor and A & B encoder pins turns the motor as desired

[billhinge]

Done the RA as well now, same cable layout  and belt mod appears to be working well

Next steps, put the casing back on. Just received notification that my Starsense has been dispatched !

[1parsec]

Got it working now. On my CG-5 the encoder A & B pins are 1 and 2 (green and  white in the pic) and motor are 5 & 6 (purple & blue)

reversing the motor and A & B encoder pins turns the motor as desired

Well done, an excellent result.  What oscilloscope is that you used ?

Dave.

[billhinge]

Hi Dave

Its the scanaplus logic analyser

http://www.ikalogic.com/ikalogic-products/scanaplus-9-channels-100mhz-logic-analyzer/

[msh1]

have you taken any pics yet or will you do a tutorial when it works I'm following this project 

[billhinge]

No pics yet, I should be able to do some tomorrow - I'll show my novel wiring (works and is easy, no soldering required)

[billhinge]

Here are some pictures.

Things to note, I used male female jumper wire to connect the CG5 cables to the crimp connectors, tested that everything was working then used hot glue to make sure everything stayed put. I noticed noise on the encoder ground line from the motor so I made the motor wires a twisted pair to cut down on EMI interference

Also notice I bunged up all the crevices I could find with bluetak (old hi-fi trick to reduce vibration) - everything feels more solid now

Notice I used a 50mm m5 screw to hold the motor bracket, this comes through to the centre of the Dec axis. I'm waiting on delivery of some 60mm hex screws, there will be two going through to the bluetak. When I've done that they will be covered in more bluetak - this should hopefully minimise any vibrations from the motor. I also used anti vibration washers on most screws

All the worm bearings have been replaced by ceramics and the black grease is tungsten disulphide in light oil

[billhinge]

Just fitted a new Dec motor from Lee at Green-Witch (excellent service), if its not my imagination it seems smoother and quieter than the old one

Certainly seems quieter than the remaining RA motor to me least, the RA was quieter than the old Dec motor if I recall correctly

Maybe Celestron have improved their motor design ?

RA housing now fitted, just the Dec cover to put back now and the belt mod should be done ready for testing with my new Starsense when weather permits