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EQ6 belt drive modification


George

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Looks like the firmware may have been hacked to account for a change in the gear ratios. See the last sentence in the penultimate paragraph here:

Stepper Motor Replacement Parts EQ5 HEQ5 EQ6 Pro Atlas Sirius Telescope Mounts - Astronomy Forums | Telescope Forums & Reviews | Astronomy Community

I can't find any other reference to it being done on-line though.

James

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I find myself idly wondering this evening if the knowledge of the gear ratio is built into the hardware or the firmware. If it's the latter (which would seem logical to me) then it might be possible to "hack" the firmware so it accounts for the changed gear ratio. Could be something of a slog to identify which bits need changing though.

James

Its built into the mount controller firmware. The synscan reads the mount characteristics from there during initialisation. In this way you don't need different sysncan firmware for each mount type. When in "custom" mode EQMOD ignores what the mount itself is telling it and applies its own custom set of parameters which subsequently modify the data passed to the mount when setting tracking/slewing rates or in moving an axis an angular amount.

Patching the motor controller firmware may be a possibility - especially with the latest revision motor controller boards that can have their firmware upgraded. Alternatively it would be possible to design a simple interface unit, siting between synscan and mount, that intercepted the messages asking for mount characteristics and sent back custom replies.

Chris.

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Yes. The handcontroller/EQMOD does all the clever astronomical stuff. The motor controller really doesn't know it is controlling a telescope mount at all. It is essentially just a stepper motor driver with a communications interface to command it to "move x steps clockwise" or "start moving x steps per second clockwise" and messages to read the current stepper positions / status.

Chris.

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OK, just got home from work and took the covers off my HEQ5 and did some measuring with a rule and came up with the attached.

One thing I noticed in the above picture and measurements was that the intermediate gear is different between the RA and DEC drive chain. wouldn't that means that the mount moves at different rates on both axis ??, and if so should I take that into account when working out ratios ??? :D

Edit: isn't google a wonderful thing... found this Gear Ratio Calculations

so it seem that any idler gear has no effect on the ration between the driver and driven gears. I think I mis-counted and the main gears are 46T which gives a 5.111 ratio. where did you guys get the 3.9xx ratio from for SW If this is the case could it explain poor tracking / slewing off target when moving to EQ Mod ?

Looking at the current gear it's 3mm thick, is that too thin for a belt? Given the position of the gear I'm guessing that provided the new pulley remains on or less than 10mm thick, it would work, provided I can get a pulley with a long enough shank to attach to the motor shaft to keep the belt level.

Would welcome suggestions (George ?)

post-23388-133877677702_thumb.jpg

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Malcolm,

The different mounts have different intermediate gearings.

EQ6Pro / NEQ6 uses a 47/12 ratio and a 180 tooth worm gear overall ratio 705:1

HEQ5Pro uses a 47/9 ratio and a 135 toothed worm gear - overall ratio 705:1

EQMOD knows about all this and tracks/slews correctly with all synscan models/upgrades.

So, if you were to perform the belt mod you would either have to source 47 and 9 tooth pulleys or go for the EQMOD custom mount setup and use a 5:1 pulley ratio (12 and 60 tooth?) - thereby gaining the advantage of better PEC response. EQMOD doesn't currently have a dropdown selection to preset the various parameters to the for the HEQ5 5:1 ratio but I can easily add this (as things stand you would have to manually calculate and enter them).

Chris.

Edited by chrisshillito
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Ha forgot about the final worm.... thanks for clearing that up Chris, and sorry for my ignorance regarding the backend of EQMod. So given that the final drive is different, and the smaller gear on the HEQ5, do I still need to maintain the 5.222:1 ratio when buying the pulleys or do i stick to 4:1 and then select this in EQMOD ??

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Its up to you - you can either stick with the same ratio (if you can source the 47 toothed gear) or you can go for a 5:1 ratio

For a 5:1 ratio on an HEQ5 you would need to set EQMOD up with the following parameters:

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

However with the 4:1 ratio you would be operating a long way away from the original values the mount is designed around and you may find that the max slews at a much faster top rate (this isn't controlled by EQMOD - the mount makes its own mind up how fast to go when slewing to a target and of course it doens't know you've changed the gearing!)

[Edit] Just for completeness I'll give the HEQ5 6:1 values

Total Steps = 10368000

Worm Steps = 76800

Tracking offset = 80

Chris.

Edited by chrisshillito
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I shopped around and whilst there were other companies, so that seemed to offer pulleys in single tooth increments from 10T up to 100T, they were a lot more expensive, so I used the same company as George

Products

------------------------------------------------------

1 x MXL Rubber Timing Belt, 80 T (BMXL080) = £2.76

1 x MXL Rubber Timing Belt, 90 T (BMXL090) = £2.82

2 x Aluminium MXL Pulley, 12T, 3mm Bore (PL012AL) = £6.92

2 x Aluminium MXL Pulley, 60T, 5mm Bore (PL060AL) = £14.26

------------------------------------------------------

Sub-Total: £26.76

Shipping: £0.00

VAT 20.0%: £5.35

Total: £32.11

I had my observatory pier adapter made by a local company, and I'm sure the chap will bore out the pulleys for me for the cost of a beer or two :D

The only thing that concerns me is the thickness of the pulleys, which would mean using P'billys suggestion of some form of spacer / gasket type arrangement. The alternative would be to have the some of the "hub" milled off thus reducing the thickness of that gasket. However given the fact the SW gears are 10mm wide, and as the belt is 6mm wide, that would only leave 4mm on the hub in which to fit the grub screws... I think this is going to be one of those "suck it and see" type projects that you wing it as it goes.

Rather than hi-jack this thread I'll start my own when the part arrive

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Well if it all goes pearshaped then I've only wasted £30 for the parts.

George, what did you use to pull the gear off the motor shafts ?

On the stepper shaft gear there are 2 hex grubs, just loosen off and it should come easily, if not wrap something soft round it and wiggle free with grips......same with worm shaft gear.

Alternatively have a gander on Astrobabys site

BTW on the Motionco site the dimensions of all the pulleys are listed so you should be able to work out what space you have, there's room for quite a bit of material removal on the 48 tooth pulley, the dimensions I listed in the 1st post are only bare clearance measurements for the EQ6 and I could have taken a bit more off if needed.

Edited by George
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Thanks George. Ive opted for 60T pulley on the worm, these are 38.8mm which is less than the current gear, plus there is a couple of mill clearance around the housing. I'm more concerned with belt tension as the 80T belt was as close as I could get to the 44.5 gap between centres

That said, I've just re-meshed the gears and given them a good dollop of lithium grease and they are as quiet and smooth running as I've ever heard them, and I bought the mount "serviced" by the previous user !

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George,

I have a complete set of SKF bearings, very smooth, and the belt mod kit. I will take the pullies to the machinist tomorrow and start stripping the mount.

Did you need to machine out the RA in the end, to provide more belt tension?

Thanks

Neil C

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George,

I have a complete set of SKF bearings, very smooth, and the belt mod kit. I will take the pullies to the machinist tomorrow and start stripping the mount.

Did you need to machine out the RA in the end, to provide more belt tension?

Thanks

Neil C

No Neil, no modifications to the actual mount castings. Both stepper back plate screw slots need lengthening slightly, 2 minute job with a small round file.

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George,

The 12 pully that needs boring out to 5mm, when you drill it basically it removes all of the center section leaving just the main pully. My machinist was querying it but i told him just to bore it out any way.

I take it yours is fine like that?

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On the stepper shaft gear there are 2 hex grubs, just loosen off and it should come easily, if not wrap something soft round it and wiggle free with grips......same with worm shaft gear.

Alternatively have a gander on Astrobabys site

Had a gander at that site, but can't see any mention of removing the gear. On the HEQ5 motors there are no grub screws, and it would appear that the shaft is stepped to take the cog :)

Not sure how to pull the cog off without damage (bear in mind I may need to return to factory settings should the belt drive not work)

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Heating the gear should allow it to be pulled off. Should expand faster than the shaft if its a friction fit (friction fits sound a bit too over engineered for these mounts!)

Edited by fwm891
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The top of the shaft has a hole in that I though was a grub screw, but it had no hex form to it so the alley key just spins round... but it does look as if the shaft has a step turned at the end and the cog is fixed (probably by cooling the shaft first)

I don't want to force it so that I risk damage to the motor or gear, juts in case i need to return to gear drive

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Hmm... I agree, it certainly looks like a "shrink fit". You might get away with heating the pinion as that looks like brass on a steel shaft. If I remember correctly, brass has a higher coefficient of expansion than steel. Of course, when assembled the steel shaft would be cold and the pinion would be heated then slipped on. Whether this would be a cheaper assembly method I'm not sure - saves the cost of drilling and tapping for a grub screw but requires much greater precision.

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