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HEQ5 - Experiments with belt drive

malc-c

By malc-c
in DIY Astronomer

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  • 2 weeks later...
malc-c

malc-c

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I'm still looking at alternatives that give a better fixing of the 60t pulley to the axis shaft. Its early days yet, but I'm waiting to hear back from a couple of companies who hopefully might be able to help.

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  • 1 month later...
malc-c

malc-c

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Further Update:

Having now identified potential issues I thought I would invest in a further set of pulleys and belts to prove / dis-prove this mod once and for all.

One of the issues was with the belts offered by Motionco in that they only offer 80t or 90t, where you really need something in between on the RA motor. This, hopefully will be resolved as I sourced the belts from Beltingonline - I have 85, 87 and 88t belts so hopefully will have one that will suit.

The other issue was that of securing the 60t pulley so that it didn't get pulled off the end of the axis shafts. The option I've gone for is to have the grub screw running through the tooth section, which should give a better purchase on the shaft.

However, before I started this second attempt I needed to find someone with a lathe who would undertake the work required, and following on from seeing the excellent turning that Tony (Freff) had done, approached him via PM's. Whilst Tony had reservations we struck a deal and I sent the parts off to him. A few weeks later and after several conversations via e-mail and phone Tony returned the machined parts to me. I'm gobsmacked by the quality - I can see my face in them !! I would therefore like to publicly thank Tony for his help with this project. - Thanks Tony !

The parts require lot more machining than the EQ6 mod. You need to take the tooth section down to 7mm, and turn down almost all of the hub, then drill and tap a hole through the tooth section, and finally bore the central hole out to just under 9mm (9mm being close enough).

I'll post up some pictures later of Tony's excellent work, and hope to be fitting them in the mount tomorrow morning.

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malc-c

malc-c

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OK after a mare of a morning of playing about with this here are my conclusions:

The mod is feasible if you want to go to a lot of trouble. It's not as straight forward as the EQ6 mod seems to be for the following reasons:

1) - Even reducing the large pulley to 7mm, the motor pulley and the drive pulley sit too proud to secure the cover plate.

2) - To overcome the 1st issue you need to fabricate a "gasket" at least 4mm thick to give clearance. This then means that the 6 securing screws need to be replaced with longer ones.

3) - Belt tension is an issue with the RA motor. Due to the mount casing there is less space in which to move the motor. It is recommended that the slots in the motor mounting plate be elongated to give as much freedom to achieve decent tension.

4) - Getting the correct tension can be an issue. I've tried three belts, For the RA an 80t is too short, and an 85t is too long. My guess is that an 82t belt would be ideal, but I didn't have one (85, 87,88 and 90 belts). The DEC axis has more play, and I've used a 90t belt, but this then lead to a further issue. My guess is that a 85t belt would be more suitable. Again I elongated the slots in the motor plate to assist in belt tension.

5) - When I used the 90t belt I managed to get good tension, but then noticed that the view through the polar scope was obscured.

6) - Having the toothed pulley drilled and tapped doesn't caused any issue with the belt. Gluing as suggested above could be an alternative.

7) - Pulley ratio of 5:1 dictates a 12t motor pulley, and boring this out to 5mm without any run out which causes the pulley to wobble is asking a lot of the machinist. Whilst the drive still works with an off centre or out of true pulley, it's not ideal. A 4:1 ratio would give a 15t pulley for the motor, which may have just enough meat on the hub to overcome this issue.

Anyone wishing to try their hand at this modification, and overcome these issues here are the links to the suppliers I used.

Timing pulleys - MXL type

MXL Pitch Pulleys : Beltingonline.com, Supplier of power transmission and conveying products

motionco_Pulleys & Belts_Aluminium MXL Timing Pulleys_Buy Online

Timing belts - MXL - 1/4"

MXL Pitch Rubber Timing Belts [4580] : Beltingonline.com, Supplier of power transmission and conveying products

I'm off to hunt for that Allen Key that I dropped, bounced three times on the cushion flooring and then fell down the small gap between the pier and the floor so I can put my mount back together. Whilst it's cost me upwards of £100 for the multiple sets of pulleys and machine time and I'm no where near having the mount converted (and my not even bother considering the hassle I've had) it's been an interesting project. One thing I have noticed is that there is quite a lot of slop on the RA worm shaft, which I don't thing the belt mod would do much to correct. The one BIG advantage of the belt mod would be the lack of noise that gets transmitted through the gearing from the ramping up and down of the stepper motors.

So there you go....the mod is doable but not without a lot of fuffing about. If anyone else wants to have a go then please feel free to post their findings to this WIP thread.

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  • 4 weeks later...
malc-c

malc-c

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Update:

Well today I finally got round to doing the belt modification on the HEQ5. The stumbling block was finding something to make the "gasket" from and to get some suitable bolts for the increased depth that causes.

The free play in the worm on the RA was also adjusted once the motors were removed.

I purchased a selection of 1/4" belts from 80t - 90t. The DEC drive required an 85 tooth belt, whilst the RA an 82 tooth. The fitting went well, until during the initial tests the flange of the motor pulley came off. This was one of Tony's concerns as boring out the hub to 5mm leaves little metal left on the gear. Fortunately I still had one of the original set the local machinist made for me, and used that.

To create the spacer / gasket I used a cheap basic mouse mat, picked up from Staples for a couple of quid... used a scalpel and carefully cut out the desired shape. The finished result can be seen from the attached images.

I've now set a 5:1 ratio configuration in EQAscom and hopefully the clear spell that has just arrived will allow me to re-align the mount and try a basic PHD track before I have to go out tonight (typical - the 1st clear night in a week and I have to go out !!)

So now I have joined the elite club of having a mount that no longer goes "granch" at the end of a fast slew :D

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Freff

Freff

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Hi Malcolm, glad you have it working ok. I have been to unwell over the last 3 weeks to do anything with the gasket. I couldn't do much until the new year anyway.

I thought the flange would soon come away, I also believe the splines will also part from the hub sooner rather than later.

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malc-c

malc-c

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Tony,sorry to hear you have been unwell.

Don't worry about the gasket, the mat seems to be doing the job. I'll let you know how it pans out with the hub. I'm still messing about with PHD, at the momnet, and so far can't actually see much improvement over the graphs I got with the gearing.... seems that tthe only benefit of doing this mod is a slightly quieter slew with out graunching on spool upand down.... jury is still out at the moment

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Freff

Freff

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Are you basing your image results on the PHD graph. Why I ask is because it may not be your mount that's giving poor images.

I have poor (well far from perpect) PHD and Maxim guide graphs, yet my stars are round over 5min subs. I know several imagers that get great images from poor graph results.

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malc-c

malc-c

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Tony, I agree it's all too common to get hung up on these graphs... I'm really just trying to compare them with previous ones to see if it makes any difference by doing this mod. Mind you with the wind gusting to 22mph here, even with some protection offered by the observatory, it's not ideal for imaging !

This is the best result I've had so far... I'm hoping to try and get one long exposure in before I have to go out (typical !) to see how sharp the stars are...

post-23388-133877710209_thumb.png

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Freff

Freff

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Malcolm, that graph is typical of what I get with the EQ6/MN190 and a 102mm guide scope. Stars are very acceptable.

If you can better your graph for peace of mind, then that's another issue eliminated. You may be pleasantly surprised at your mounts performance anyway.

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malc-c

malc-c

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Well I slewed the scope round to M45 and took the attached 600 sec exposure at 800ISO - apart from the vignetting at the edges, I think that's OK - and the graph wasn't near the smoothness of the one shown above !

Cricky, just seen the time.... should be off out by now !

post-23388-133877710214_thumb.jpg

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malc-c

malc-c

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Hee hee... managed to get out of going out :D

One last image..... 1200 seconds (20min) @ 800 ISO. Then re-sized for forum and autoleveled in PS.

Stars seem round enough given the conditions (latest guest of 27mph !!) I'm hoing to load the PHD log files to the forum and hope that Chris can cast his trained eye over the PEC curve

post-23388-133877710222_thumb.jpg

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malc-c

malc-c

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Awesome work there Malc. When you have a minute, could you just round on what parts you used in the end? I wouldn't mind trying this at some point in the summer.

Thanks

No worries :D

The belts came from BeltingOnline

1 x MXL Pitch Rubber Timing Belt

Width in mm 6.35

Belt Length in mm 166.62

Tension Cords Kevlar

Material Neoprene Black Rubber

1 x MXL Pitch Rubber Timing Belts

Width in mm 6.35

Belt Length in mm 172.72

Tension Cords Kevlar

Material Neoprene Black Rubber

Total cost £2.99 + £2.50 postage + VAT

The original pulleys came from motionco

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

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

Plus £2.39 for a mousemat for the gasket and you'll need 6 x screws that are approx 5mm longer than the stock cover screws.

Total outlay for parts was £34.39 or there-about's

You then need to have the 12t pulley bored out to 5mm, and the 60t pulley to 9mm. I had the 60t faced down to 7mm with the hub reduced to 2mm, so that the original hole left from the grub screw is removed. I can't stress how important it is to make sure the machining is done to tight tolerances. As you would of seen from my post above, boring the 12t out to 5mm doesn't leave much, and the part can fail. The cost of having these parts machined can be anything from £20 to £40 depending where you go... I was lucky, and struck a deal with Tony who was kind enough to give up his time for a nominal exchange to be redeemed at next years SGL7 :)

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