We completely cnc machine the 12T and 47T pulleys from start to finish from bar stock and get excellent concentricity on the mounting bore to the tooth profile.
Hi Dave,
have you heard of a "PE Sync" problem with the 12T/47T ratio ?
I came across this thread where he mentions it and therefore has gone for a 4:1 ratio.
I know its been mentioned that this mod will work without any modification to tracking rate in eqmod, but I'm keen on using PEC as well. not sure if this is going to be an issue.
perhaps this needs a different thread but I came across this from another forum where the standard worm is replaced with the aeroquest machined worm with higher precision than the stock ones and aren't that expensive for the eq6. PE of +/- 4 arc secs is what's claimed but I think that's for a matched pair of worm and gear. http://www.aeroquest-machining.com/pricing.php
Hi Dave,
have you heard of a "PE Sync" problem with the 12T/47T ratio ?
I came across this thread where he mentions it and therefore has gone for a 4:1 ratio.
I know its been mentioned that this mod will work without any modification to tracking rate in eqmod, but I'm keen on using PEC as well. not sure if this is going to be an issue. http://www.iceinspace.com.au/forum/s...17&postcount=1
Can you please clarify.
found the ratio's of the spurs
- stepper gear (12 teeth)
- transfer gear (36 teeth)
- worm gear (47 teeth)
and the 47T/12T has the same effective reduction, but not sure what this sync issue is.
Cheers
Alistair
Hi Alistair,
The standard ratio is 47:12 which is what our belt mod uses.
It allows the handset still to be used and also EQMOD.
A belt kit using the non-standard ratio would mean the mount would have to be operated using EQMOD. The handset would not work.
Periodic correction reduces any repeating cyclic errors for the drive train .
Handset periodic correction will only work with the 47:12 ratio.
EQMOD periodic correction will work with any ratio.
If you use a 48:12 ratio any error from the motor pulley are in sync with the main worm cycle, which can also be corrected by periodic error correction.
I think this observation has come from some of the earlier belt mods that were done by modifying standard parts. It's difficult to bore the pulleys concentric. The motor pulleys wobble !
An eccentric pulley on the motor can be corrected if it uses the 48:12 (or any other divisible ratio) so not a total disaster.
However if the pulleys are made to a good precision it won't matter if they are 47:12 or 48:12, infact 47:12 would be prefered as you still retain the use of the handset and if you want to sell the mount in the future to some one who doesn't use EQmod.
So to summarise the only difference between the ratios is you can't correct for motor pulley error with 47:12 ratio.
However the error from the motor is usually small any way and even smaller with our kit.
I have a track log taken a month or so ago of my NEQ6 mount with the standard gear train
and have been waiting for a clear opportunity to grab some data with the belts fitted.
Tonight was clear and here is the comparison of the 2 set ups. Gears.jpg & Belt.jpg
The overlay image of the 2 traces is shown with the Gears in red and Belt in blue. Overlay.jpg
The final image are the results in spreadsheet form for direct comparison. Sheet.jpg
All the main figures show a 30 to 35% improvement with the belts fitted.
The residual errors look to be more random and are probably from the worm
bearings and the variable tooth to tooth wheel errors.
That looks good Dave,
Do you think changing the worm bearings really help as is done in most hypertune mods?
Would be good if you can do some pointing tests as well, especially repeat slews to the same star.
A plate solve after the slew should give you the error or difference.
I'm going to replace the worm bearings and make 2 tests.
I have 2 types of bearings on order, standard SKF and a higher precision grade.
I'll replace the factory worm bearings with the new types and run a test with each.
I've not seen any results of a such a comparison . It will be useful to know.
The mount is in my workshop so it will be next time when I do a pointing test.
Hi Dave,
Do you have the part numbers for the work bearings
Hi Alistair,
The worm bearings are 608 type. The standard I've ordered is SKF608 2RS with a tolerance of 10 micron inner race radial run out.
I've asked the supplier to order a P5 precision bearing with 4micron run out but I don't know the manufacturer yet.. probably FAG or NSK.
Thanks,
Dave.
The kit arrived today, I think it took less than a week. Now to get some lithium grease, clear up a table and get started.
I've been imaging a bit with the NEQ6 with 20min subs and I had to discard 6 of them cause the guiding would be perfect, then all of a sudden, there'd be a spike ruining the sub. Its odd that it didn't happen in the other 4 x 20min subs but happened only in the later ones. it doesn't happen in shorter ones.
Is this the jump that you'll were mentioning earlier in this thread that's inherent with neq6's?
I will get the worm bearing as well. I wonder if their energy efficient ones would be any better as they are low friction, not that it matters too much. did you get the part number for the precision worm bearing?
Hi Alistair,
I haven't done the pointing test yet, I have the bearing comparisons to do.
What's the size of pointing error you are getting now ? If it's high it will be down to the worm clearances and balance of the scope.(assuming the gears are locked tight on their shafts etc)
I always set my scope with a slight imbalance so the worm is always loaded to one side of the gear.
The precision bearings are from a German manufacturer, code- IBC 608.2Z.P5 Any of the premium manufacturers should be able to supply a P5 or better grade bearing.
It's the P5 that denotes the level of precision. Lower number = higher precision.
If the bearings prove to show an improvement, I will add these as an additional option to go with the belt kit.
Thanks
Dave.
Alistair,
Here's my quick slew test.
I took an image at a reference position and slewed the scope about 15 degrees away. Then slewed from different directions back to the ref pos and took images.
Most slews returned close. The east and west directions being very good at 8 and 9 arc sec offset.
The north direction gave the greatest error of 175 arc sec but I this was probably down to that I'd not been too fussy setting the Dec worm backlash since the mount was last stripped down and that it's going to be stripped again for further bearing tests.
Cheers, Dave.
That's close enough and plate solving and centering would take care of those small errors.
Do you remember what it was like with the spurs?
so the worm and gear mesh makes a big difference as well with pointing?
Have you tried the backlash tab in Pempro?
that takes an image while issuing slews and shows the backlash.
I know there's a lot mentioned about grease for the bearings and I know its not part of the belt mod, but what would you recommend? I believe white lithium isn't recommended, but bearing grease with PTFE or superlube with PTFE?
so the worm and gear mesh makes a big difference as well with pointing?
Have you tried the backlash tab in Pempro?
I know there's a lot mentioned about grease for the bearings and I know its not part of the belt mod, but what would you recommend? I believe white lithium isn't recommended, but bearing grease with PTFE or superlube with PTFE?
Cheers
Alistair
Hi Alistair,
I don't have any measurements with the original gears.
The worm gear mesh is the main reason for pointing problems.
If you can feel movement when gently trying to rotate the RA with the counterweight shaft that's the worm clearance.
I set my mount so that there's just the smallest of clearances with out the mesh being closed and no tighter.
I don't use Pempro so I've not tried that test.
There's a lot of opinion on the net to what grease is best.
Lithium + ptfe is commonly quoted but may not be suitable for very hot environments/climates . A continuous high average temp may cause the grease to dry out requiring regreasing. I've never had this problem though.
I'm yet to install the pulley and belts but wanted to know if you've noticed a small improvement in the size of your stars with long exposures.
Reason I ask is that guide corrections would normally be subject to the minor backlash in the spur gears, whereas with timing belts and pulleys, as this is eliminated, in theory the corrections would be a lot more quicker and more responsive?
any thoughts? FWHM measurements would be interesting. Another parameter to add to the list.
I will focus on the worm/gear mesh though.
Hi Dave,
I'm yet to install the pulley and belts but wanted to know if you've noticed a small improvement in the size of your stars with long exposures.
Reason I ask is that guide corrections would normally be subject to the minor backlash in the spur gears, whereas with timing belts and pulleys, as this is eliminated, in theory the corrections would be a lot more quicker and more responsive?
any thoughts? FWHM measurements would be interesting. Another parameter to add to the list.
I will focus on the worm/gear mesh though.
Cheers
Alistair
Hi Alistair,
I've not made that comparison but rather concentrated on the PE track logs.
They give the best indication on tracking performance.
An improvement in the tracking should give a corresponding improvement in the guiding performance and star profiles.
The size of the guider corrections will be smaller and as you've mentioned more responsive too.
I finally finished installing the belt kit on my neq6 yesterday and gave it a test run.
its a lot quieter and responsive and going by the pec data captured after the mod, its a huge improvement over the previous 30 arc sec PE.
the improvement could be the worm mesh adjustment as well that I did from scratch.
I took a few days for the mod, cleaned out all the bearings, adjusted the worm mesh after a lot of trial and error, and that has paid off. any imbalance shows up as the axes rotate more freely.
I captured this PE data with a star at the meridian through thin clouds.
couple of gotchas with the mod. when inserting the RA worm wheel into the body, you need to insert it as straight as possible. I tried it with the body fixed on the tripod as per Rowan's instructions, but I didn't insert it straight and it got wedged solid. took me half a day to get out. no damage though.
I then inserted it with the body vertical, and that went a lot easier.
that tip to use the plastic sheet with the allen key for the motors was brilliant.
couple of minor things,
when installing the worm end covers, tightening them causes the shaft to bind a bit. so I installed the cover first and then inserted the shaft and bearing and that helped as I could adjust the nut at the other end.
need to keep the timing pulley loose on the shaft before inserting, else it won't go in.
I was following the instructions step by step, and there is a warning early on to watch out for the thrust bearing accidentally falling. that needs to be one step earlier cause I read it after the bearing fell :-)
Overall pretty happy, and will post some results for repeated slews and target centering.
Just finished the belt drive modification myself tonight. I had previously hyper tuned the eq6 and was quite happy with it but I thought that this modification would assist in a better PEC and/or guiding. It's certainly quieter in slewing and I will have to wait for the clouds to disappear before trialling it out.
The mount was capable of 30 and 60 min guided subs prior to this with perfectly round stars so I guess I'll have a trial with pempro to see what difference it has made.
The kit from Rowan was easy to do as long as the instructions are followed.
Agree that the tip with plastic sheet and Allen key was invaluable.
Allan
I did the belt mod a few weeks ago and just realized I must've inserted the delrin spacers incorrectly.
There's close to a mm gap between the RA scale and the float cover and 0.5mm in the Dec scale and I'm not able to remove backlash entirely.
so will have to strip it down again.
anyone have any pics or notes on where the spacers go for the neq6 for both axes?
I'll do the height measurements as per astrobaby's site, but if delrin shims are required, where do you source them from?
