EQ6 Belt Mod (Belting Online)

[sharkmelley]

I've been wanting to do a belt mode for my EQ6 for some time now but other discussion threads have scared me off with talk about the need to bore out the toothed pulleys to larger diameters and modifications required to the worm housings, lengthening the slots of the motor mounting plates etc.

I'm not an engineer and wouldn't know where to start, nor what to ask for, so it was with great relief that I came across a kit of ready made parts at BeltingOnline:
http://www.beltingonline.com/heq6-belt-mod-drive-kit-12220
This kit also preserves the 12:47 gear ratio which means the EQ6 goto handset will continue to work correctly. 

Since I haven't come across an easily accessible set of instructions for fitting the kit so I thought I'd share my experience.  Happily I can report that none of the scary modifications mentioned above were required.

The kit arrived within a few days of my order, despite the website saying there is 15 working day lead time for manufacturing - I guess they had a batch ready prepared.  Attached is a photo of the kit of parts (confusing labelled HEQ6 instead of EQ6).

I followed AstroBaby's excellent instructions for strip down and reassembly with the main differences for reassembly noted below.

You will need a 1.5mm hex key for the grub screws on the new pulleys - don't start the job without one. It's a different size to the grub screws on the existing EQ6 gears.

The worm axle has a shoulder where the toothed pulley goes on. Assemble without tightening the grub screw (remember to assemble with the belt in place!) then tighten the grub screw until the pulley still slides on the axle but the grub screw hits the shoulder and prevents it going further towards the worm.  Then tighten the grub screw in this position.

At this point I noticed that the pulley flange just touched the bottom of the housing as it rotated, so I needed to remove half a millimeter from the flange height.  So I put it the pulley on a 10mm drill bit (packed out with masking tape - see photo) and spun it against some P80 wet'n'dry paper then some P180 to remove the rough edges. I only needed to do this for the DEC axis - the RA axis was absolutely fine.

The pinion gear on the motor was easily removed after loosening the grub screws.  Measuring distances from the flat side edge of the mount I worked out I needed approx 6-7mm of visible tooth appearing above the motor's mounting plate - see photo.  But it is necessary to temporarily remove the mounting plate to tighten the grub screw.

Once the worm housing is attached to the mount, it is fiddly to put the motor back in place so the belt goes around the motor's pulley.  I used a bent piece of wire to do this - see photo. For this reason I found it necessary to assemble both the DEC and RA motors in place before putting completely reassembling the main DEC axis - because then the useful large circular holes in the housing are blocked. It took a few attempts before I achieved success.

To tighten the belts I tightened one of the motors mounting bolts and twisted a screwdriver blade between the motors and housing until the belts felt taut and then tightened the 2nd bolt.  Then ran the motors for a while on fast slew to seat the belts, then retightened both belts.

That's it really.  I'm just waiting for a clear night so I can record the periodic error and compare with the horrendous charts I already have.  More importantly, to check if the guiding performance has improved. I have 2 EQ6 mounts side by side in the observatory and currently their guiding performance is more or less identical - so I can easily compare the modded mount against the unmodded mount, guding on the same star.

[pete_l]

That's it really.  I'm just waiting for a clear night so I can record the periodic error and compare with the horrendous charts I already have.  More importantly, to check if the guiding performance has improved. I have 2 EQ6 mounts side by side in the observatory and currently their guiding performance is more or less identical - so I can easily compare the modded mount against the unmodded mount, guding on the same star.

Sounds like a great project. The before and after comparisons should be very interesting.

[JamesF]

Sounds like a great project. The before and after comparisons should be very interesting.

They will indeed.  I look forward to seeing the results.

James

[r3i]

Good write up of the installation of the kit.

I've also recently bought one of these kits but had a couple of problems with it. When attempting to install the worm gear I noticed that the diameter of the hub (where the grub screw fits) was far too large.  The diameter of the hub on the new gear was 26mm whereas the existing gear was 20mm.  I contacted Belting who were very helpful - I returned the gears back to them and they turned them down and got them back to me in a couple of days.  Interestingly they said they'd sold a few of these kits without coming across this problem so perhaps there are different versions of worm housing? The dimensions of mine matched the schematic drawn up by George in this post: http://stargazerslounge.com/topic/100401-eq6-belt-mod/?p=1174534

I also then encountered the same issue that you did, i.e. the flange diameter is slightly too large to fit into the worm housing on the DEC axis.  Like you, the RA axis looks OK.  I've still got to file the flange down to fit so have yet to complete the modification.  I measured the diameter of the flange to be 42mm, the original gear has a diameter of 39mm, so knocking down its diameter to 41mm or 40mm sounds about right.

I'll be interested so see how the mod performs on your mount when (if) clear skies return.

Thanks once again for the information - it will be very useful when I finally get round to fitting mine.

[sharkmelley]

I've also recently bought one of these kits but had a couple of problems with it. When attempting to install the worm gear I noticed that the diameter of the hub (where the grub screw fits) was far too large.  The diameter of the hub on the new gear was 26mm whereas the existing gear was 20mm. 

Interesting.  I didn't measure my gears before installing them but looking at my photo of the gear sitting on the drill bit and assuming the flange is just over 40mm diameter then the hub diameter on mine was probably around 20mm.   My kit arrived just a few days ago so maybe it has been updated slightly.

[Gina]

Yes, great write-up of the mod and I too will be interested in the results

I've tried drilling out timing pulleys etc. and have had little success - they always come out either eccentric or out of alignment.  Hopeless for this project so I've never tried - putting up with pretty dreadful PE and the horrible grinding noise from the gears.  I may get a lathe sometime and then I can do this sort of job from scratch with bog standard pulleys.  But with just a bench pillar drill it's a no-no.

[r3i]

Interesting.  I didn't measure my gears before installing them but looking at my photo of the gear sitting on the drill bit and assuming the flange is just over 40mm diameter then the hub diameter on mine was probably around 20mm.   My kit arrived just a few days ago so maybe it has been updated slightly.

Yes I'd agree that on your pic they look like 20mm.  Perhaps they'd just not turned mine down far enough in the first place - story of my life, things never run smoothly

[1parsec]

Yes, good write up.

It will be worth double checking the position and clearance of the belt going through the slot though.

I'm working on a EQ6 belt kit  ( 47T & 12T 2.5mm pitch )  and the drawings I've made show that the belts will just touch the ends of the slots.

If the belt does touch the sides, it will generate particles that will find their way in to the worm wheel.

The red shaded area in the attached drawings show the problem. It's difficult to see where the belt is positioned

during assembly as it is the inside wall of the worm case that is hidden from view.

I will be adding a couple of idler rollers in the belt path to 'nip' the belt path as it goes through the slot to be

absolutely certain there's enough clearance.  That will do away with the hassle of needing to modify the slots in the casting.

The idlers will also make the belt wrap a full 180 degrees around the small motor 12T pulley like the HEQ5 belt mod I've done.

Dave.

[dark knight]

Can't wait to hear the results, if proves beneficial I could well end up doing this mod myself too.

[sharkmelley]

Hi Dave,

That's a beautiful set of detailed drawings you have produced! 

As far as I could tell (and as you say it is not at all easy to see clearly) the belt was not touching any part of the casing forming the slot.  However, you've definitely got me worried now!  I will certainly look for any signs of dust from chaffing, by removing the side panel and later on perform a partial disassembly to double check.  As you say, I wouldn't want dust in the worms and certainly don't want to compromise the lifetime of the belt.

Mark

[1parsec]

Hi Dave,

That's a beautiful set of detailed drawings you have produced! 

As far as I could tell (and as you say it is not at all easy to see clearly) the belt was not touching any part of the casing forming the slot.  However, you've definitely got me worried now!  I will certainly look for any signs of dust from chaffing, by removing the side panel and later on perform a partial disassembly to double check.  As you say, I wouldn't want dust in the worms and certainly don't want to compromise the lifetime of the belt.

Mark

Sorry Mark, I didn't intend to worry you     As you say, it should be easy enough to check and keep an eye on.  

If there is contact it will be the RA belt that will probably show signs first as that is closer to the casting that the DEC. 

Dave.

[r3i]

Superb CAD drawings Dave.  Presumably the idler rollers will be fitted to the motor mounting plate?  Do you envisage any difficulties in getting the pulley fitted around all the wheels?

[1parsec]

Superb CAD drawings Dave.  Presumably the idler rollers will be fitted to the motor mounting plate?  Do you envisage any difficulties in getting the pulley fitted around all the wheels?

I will machine  new motor mounting plates and an idler plates. Red layer is the motor plate and green is the idler plate on the drawing.

You'll be able to put the idler plate in position and feed the belt through the idlers to leave the belt with a loop.

The idlers will help to hold the belt in position while the motor plate & motor is positioned and tension applied.

Sorry Mark for hi-jacking your thread   - I'll move to a new thread with further info.

[sharkmelley]

Sorry Mark for hi-jacking your thread   - I'll move to a new thread with further info.

No problem - it all looks very interesting.  And thanks for posting those wonderful CAD drawings - very helpful.

Mark

[r3i]

I will machine  new motor mounting plates and an idler plates. Red layer is the motor plate and green is the idler plate on the drawing.

You'll be able to put the idler plate in position and feed the belt through the idlers to leave the belt with a loop.

The idlers will help to hold the belt in position while the motor plate & motor is positioned and tension applied.

Sorry Mark for hi-jacking your thread   - I'll move to a new thread with further info.

Sounds good - looking forward to seeing it progress.

[sharkmelley]

I now have some results and it is a bit of a mixed picture.  The overall peak to peak periodic error has improved only slightly.  I've attached the PE charts below - you can clearly see the 478.69 sec period worm cycle and the the superimposed 122.2 sec period coming from the motor rotation. 

Following the belt mod, the amplitude of this 122.2 sec cycle has reduced quite considerably - the second set of graphs show the PE for one rotation of the motor, obtained by averaging 30 cycles of the motor rotation.  The infamous 10.2 sec period is quite noticeable on these - this is the time taken for one tooth (the motor pinion gear has 12 teeth).  It is this period that causes the greatest difficulty to the guiding - much more so than the motor period or the worm period.

Anyway, the good news is that the guiding performance on the fully loaded EQ6 mount has improved by a factor of 2.  By fully laden I mean a Celestron C11 + guidescope/guidecam + DSLR which totals around 17-18kg plus the 4 x 5kg counterweights!

Tonight I had the unmodified EQ6 side by side with the modified EQ6, both simultaneously guiding on the same star.  The unmodified mount had an RMS guiding error of 1.1 arcsec whilst the modified mount had an RMS guiding error 0.5 arcsec.

So I'm reasonably pleased with this result.  I suppose I was never going to obtain Paramount ME performance!

Mark

[r3i]

As you say, you're never going to get it down to +/-2 arcsecs but there is definitely a significant improvement in many respects and I think you've clearly demonstrated that it's a modification worth pursuing.

[sharkmelley]

The goal, in my case, is not necessarily to get the PE down but to make it so it can be guided out.  This belt mod seems to have just about achieved that, by removing the inter gear jitter arising from the gear teeth - especially the transfer gear.

I've still got to do a bit more analysis on the results.

Mark

[Gina]

Yes, it's the affect on guiding accuracy that matters - PE is just an interim measurement that can affect it.