EQ6 belt drive modification

[chrisshillito]

PS, re washers, does anyone have a source for teflon sheet between 0.25 and 0.5mm thick?

PTFE SHEET 0.25MMTHK A4 SHEET SIZE | eBay

I ordered one of these and it arrived next day with together with an extra off-cut slipped in for free! They do 0.5mm sheets as well.

Chris.

[chrisshillito]

Neil, sorry for hi-jacking this thread... I was going to post the question regarding different ratios on the HEQ5 thread I started, but then Chris had outlined all the settings and aspects of different ratios in this thread...

Malcolm,

In my opinion you haven't hijacked the thread at all. George may have started this particular thread with only the EQ6 in mind but the HEQ5 is so closely related to the EQ6Pro that many of the issues George, and now Neil, have faced will apply equally to those contemplating similar mods on HEQ5s. Personally I'd much rather concentrate all this info in one place than have it distributed, and indeed duplicated, amongst separate threads covering each and every variation that is attempted.

Chris

[MG1]

Cheers Chris I'm over to the bay right now...was worried I was going to have to fork out for a whole massive sheet!

Btw, has everyone doing this mod recorded their PE prior to and changes? Just thinking we could have a good sample here to establish what sort of improvements can be gleaned?

I've attached my lastest (Hypertune a year on - no fine tuning yet) PHD log...I'm about to go through the PECPrep tutorials again and will report what sort of PE I'm starting with...although I may need to do some gear meshing first as I think something was making a funny noise...

fingers crossed

PHD_log_06Nov11.txt

[chrisshillito]

...was worried I was going to have to fork out for a whole massive sheet!

Well even if you did I'm sure with the addition of a cheap compass cutter you could soon get your money back by knocking out packs of "supertune" type spacers!

Btw, has everyone doing this mod recorded their PE prior to and changes? Just thinking we could have a good sample here to establish what sort of improvements can be gleaned?

Yes, I've got plenty of examples of my mounts PE (an inevitable consequence of continual PECPrep development!) My PE was actually quite smooth and fairly repeatable (amplitude around +/- 15 arcsecs) and I can't say I've had any problems with it even though its 5 years old and has never been serviced. Still going to have a bash at this belt mod though

Chris.

[George]

Neil, sorry for hi-jacking this thread... I was going to post the question regarding different ratios on the HEQ5 thread I started, but then Chris had outlined all the settings and aspects of different ratios in this thread...

As for kits..the one thing I've found is it can be either difficult to find a decent machinist that will bore out and turn them down to the correct size properly (so they don't wobble or rub), and /or find a machinist that doesn't charge the earth to do the work (I was charge £40 which was more than I paid for the parts). The other factor for looking at "kits" is that purchasing in bulk reduces the cost of the parts, thus "hopefully" makes it cheaper for other members. It also make for a convenient solution for other members who haven't got the time to get the parts machined.

I'm sure if I do end up persuading the boss that I need this lathe, and then have the capital to bulk buy the pulleys etc then I'll also offer them for EQ6 owners.

Having said that, I'm sure there are other members with access to or own lathes etc and could well do the same... It would certainly save me a lot of bother and the expense of a lather and all the gubbins that go with them

Actually Ive given this a lot of thought and I'm actively looking at lathes and looking at supplying ready to use kits , if you can service the EQ6 then doing the mod is a doddle.

The 12 tooth pulley is the biggest problem in its present form ie aluminum with a steel shaft insert as there is very little of the steel left after machining as a few of us have found out. Im in the process of making inquiries with suppliers on either a solid aluminum or steel 12 tooth pulley. Alternative would be to have custom pulleys fabricated or oversize the bore and use a bore reducing insert (which Ive had todo with my focuser pulleys) if the demand is there putting together a reasonably priced belt conversion kit should not be a problem.

Watch this space

[MG1]

George gave this link but i haven't tried them, my machinist was a couple of quid cheaper.

HPC Gears, modifications page

If the teflon sheets are for a hypertune then there is a guy in the states that will send you a pack of teflon washers for 13 dollars enough to do a tune up...i never looked into getting the sheets. His contact details are on astrobaby website in the hypertuning section.

I bought two sets from him last week.

Ah yes Doug.... I purchased from him last year when I did my hypertune. I still have a few spare spacers, but thought i might be able to source the 0.015" sheet over here. Unfortunately it's only available in metric @ .25 and the .05mm. Never mind, Doug is a really nice guy and so I have no qualms sending a few more $$ his way.

Ta!

Slight side step, but did someone mention lapping/ polishing earlier on? Any links for suitable paste/ instruction would be of interest....I feel a EQTwK sticky should maybe take shape to bring all of this stuff together.

CS

[MG1]

apologies for another post...especially as I'm so late to the party, but is there any advantage to other ratios such as utilising a 10t and 50t pulleys?

Or is it size size constraints, designed to not require housing mods that has driven the 12t/48t combo?

Again apols if this has been asked already, although having read through from the start I must have missed it if it has.

CS

[fwm891]

Use jewellers rouge to polish your (gear) teeth! It stains virtually everything so not a job for the kitchen table. Alternately use cerium oxide - cleaner working.

Both are quite slow working on metals - avoid silicon carbides even in fine paste form (aka valve grinding paste) the word grinding there means everything!

Note: if your lapping worm/wheel combos then remember that the softer metal (usually the wheel) will have some of the polishing medium embed itself in, so all the time your using the scope the worm/wheel are suffering accelerated wear!

[malc-c]

apologies for another post...especially as I'm so late to the party, but is there any advantage to other ratios such as utilising a 10t and 50t pulleys?

Or is it size size constraints, designed to not require housing mods that has driven the 12t/48t combo?

Again apols if this has been asked already, although having read through from the start I must have missed it if it has.

CS

Part of the problem (for both mounts) the the diameter of the pulley that sits on the worm shaft as it has to fit within the same space as the original gear. You'll also find it difficult to locate a 50t pulley, most suppliers seem to do 48t and 60t but nothing in-between.

[MG1]

Cheers Malcolm, I always forget about the limitations placed by real-world availability of components!

D'oh!

[MG1]

Use jewellers rouge to polish your (gear) teeth! It stains virtually everything so not a job for the kitchen table. Alternately use cerium oxide - cleaner working.

Both are quite slow working on metals - avoid silicon carbides even in fine paste form (aka valve grinding paste) the word grinding there means everything!

Note: if your lapping worm/wheel combos then remember that the softer metal (usually the wheel) will have some of the polishing medium embed itself in, so all the time your using the scope the worm/wheel are suffering accelerated wear!

So is it then just a case of cleaning up the gears, reassembling with rouge in lieu of grease and running the motors continuously?

I'm guessing there is a little more finesse involved

[George]

I used (shock horror) fine grinding paste I connected a drill to the worm shaft and ran it 10 times in each direction and then checked progress using a magnifiying eye glass. This was repeated 3 or 4 times until I got a polished and easy to turn worm, it was then washed off with white spirit and then another thorough washing with degergent and a nail brush.

Provided you don't go mad and take your time and make those inspections I don't see what it matters what you use as a grinding medium, Ive heard good reports about Solvolautosol (think that's how its spelt) which is a alloy wheel polish.

[jimao22]

Total Steps = 8640000

Worm Steps = 64000

Tracking offset = -28

For a 4:1 ratio on an HEQ5 you would need to set EQMOD up with:

Total Steps = 6912000

Worm Steps = 51200

Tracking offset = -211

For Chris - I want to know how do you determine the parameters from above, especially the so called "tracking offset". For an EQ6/ 4:1 this is 13 - why?

[chrisshillito]

OK, I'll try to explain where the numbers come from.

An EQ6Pro uses motors with 200 steps per revolution and the mount controller is able to split this into a further 64 microsteps. With a 4:1 gearing the number of microsteps per worm rotation is therefore is:

64 * 200 * 4 = 51200

An EQ6Pro has a worm wheel with 180 teeth so the total number of microsteps for a single rotation of the axis is:

51200 * 180 = 9216000

A standard EQ6Pro has 9024000 steps per revolution. The change in gearing to 4:1 means that without adjustment the mount will no longer track at sidereal rate of 15 arcsec per sec but instead will track at 15 * 9024000/9216000 = 14.6875 arcsecs/sec.

A correction of 0.3125 arcsec/sec therefore needs to be applied. Each increment of tracking compensation gives approx 0.02419 arcsec/s change in rate. 0.3125/0.02419 = 12.91 . As tracking compensation can only be an integer value we use 13. The way the mount works is that once we know the amount of correction needed for sidereal we can apply the same correction factor to fix any other rate.

Looks like I messed up on the HEQ5 4:1 ratio, the tracking offset should have been -189.

Chris.

[jimao22]

Ok! I understood !

Now, if we should use integers (13 instead of 12.91), doesn't induce this aproximation some errors on the system, especialy when traking for a long time (the whole night)? Is just an academic question, hope not to disturb to much.

But sometime is good to know the theoretical bases of what we are using, to avoid mistakes or make some improvments in the future.

[malc-c]

I would of thought that Synta would of made a gear train that was in sympathy with the number of steps the controller can get out of the motors, thus taking out the need to "compensate" in software. But then I guess programming a PIC micro to do the offset is cheaper than having to manufacture specialist gears or pulleys

[chrisshillito]

Yes, there will be a slight tracking error due to the use of integers but this kind of compromise is quite typical in embedded controllers where memory storage, code space and execution time are at a premium. The mount firmware is designed to operate at accurately sidereal using its standard gearing - move away from that and you loose some degree of accuracy. However using the integer 13 rather 12.91 will result in a tracking error of only 0.0021771 arcsecs per sec which works out to only 8 arcsec per hour. The reality is that other errors in the system (polar alignment, flexure, mirror flop etc.) will probably present more much significant problems and if you are guiding anyway its really not a problem.

Chris

[chrisshillito]

I would of thought that Synta would of made a gear train that was in sympathy with the number of steps the controller can get out of the motors, thus taking out the need to "compensate" in software. But then I guess programming a PIC micro to do the offset is cheaper than having to manufacture specialist gears or pulleys

It isn't really feasible for a pretty basic PIC controller like the motor controller uses to be able to provide spot on tracking accuracy for every possible rate from 0.1 x sidereal to 800 x sidereal.

What synta have done therefore is to design their hardware/firmware such that it is optimally tuned to delivering accurate tracking at sidereal rate using their standard gearings. At any other rate there is likely to be a small offset. Because we are moving away from the standard gearing this is something we must accept - but it really shouldn't be problem.

Chris.

[jimao22]

So, if using autoguider, the 64 arcseconds error for a whole night for instance, is compensated by autoguiding system, right?

But what about the alignment, is it affected some how by this small error?

[chrisshillito]

If autoguidng the autoguider will issue a correction as soon as any drifted amount exceeds whatever thresholds you have set in the guider.

I can't see why a tracking error should ever affect alignment or gotos. You manually centre the alignment star on a reticule eyepiece and in the time it takes to sync it its not going to drift very far! - Periodic error is after all a much faster moving error signal and no-one seems to have any problems with that affecting alignment.

Chris.

[jimao22]

Ok, Chris, good enough.

Thank you very much, you are one of my favourites peoples from the astronomy area, realy.

[fwm891]

George, Chris and others,

Many thanks for this thread. I've just completed my belt mod to my NEQ6. It's so quiet I have to look to see if its running..

I've had it running without loading (mount only) going e-w & n-s with meridian flips thrown in:D.

Next step is to realign the polar axis. Be interesting to see what PHD tells me about backlash which took ages before the mod...

Thanks again

Francis:D:D:D

[Earl]

Daft question, but does the EQ 6 still have the chirpy whistle when tracking after the belt mod?

[fwm891]

Mine's frighteningly quiet!

[yesyes]

Makes you wonder why a belt drive is not factory fitted....