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Offline petevasey

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Dome Motorisation
« on: 12:38:48, 09 March, 2017 »
Ah yes, work.  Bit of a problem that.  There is of course a solution .  Well two really. Retire early with a reasonable works pension.  Or get old and retire 'cos they don't want you working any more.  Or win the lottery.  Oh, yes, that makes three, but winning the lottery is a really long shot  ;)

I am retired, well at 73 I should jolly well hope so!  Meets options one and two   :yes:   But because my obs has a standard dome with slot, and would be very difficult to motorise, I still have to be around during any session to rotate the dome.  Of course there's loss of sleep to contend with, but with the persistent cloud this winter there hasn't been much of that - plenty of cloudy nights to catch up on lost sleep.   :snore:

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #1 on: 14:03:22, 09 March, 2017 »
Peter

 Have you looked into options for motorising your dome. Mine is one of the older Pulsar domes (with he big draft gap!) and I have a windscreen wiper motor with a rubber wheel. Easy way is to just nudge it round slowly and hope. Slightly more complex is to use a tilt compensated compass to read the dome azimuth and then use an Arduino to compare that to where it should be (Ascom POTH or in my case SkyX) and nudge the motor to suit. There are a lot of off the shelf solutions but they are eye waveringly expensive for what they do. I reckon mine cost me no more that £50 all in and nearly half of that was the motor controller. Motorising it really changed the game for me.

Chris
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Offline petevasey

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Re: Dome Motorisation
« Reply #2 on: 11:34:30, 10 March, 2017 »
Thanks for the interest, Chris.  My dome is timber and plywood and quite heavy.  See my observatory page:

http://www.madpc.co.uk/~peterv/astroplover/equipnbits/Observatory.htm

If you look at some of the pics lower down you will see there is a substantial rim which could accept a drive.  But the dome needs a good strong push, and I doubt a pure friction drive would do the job.  Maybe toothed belt glued and stapled to the rim with a geared motor to drive it at sidereal rate.  Strong spring to hold it onto the belt, with a lever to pull it out of contact for rapid manual movement to the initial position.  But would it need to reverse for imaging certain parts of the sky, maybe between Polaris and the zenith?

With the gradual deterioration of the dome due to rot etc., I may need to replace it before I'm too decrepit to continue the hobby.  In which case I'd probably get a 9 ft Pulsar with drive system.  But a jury rig could be fun  ;)

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #3 on: 12:26:10, 10 March, 2017 »
Peter

I think you would be surprised at how much a friction drive can generate. I have to try hard to stop my dome from moving and then the rubber wheels slip rather than the motor stalling. I have sandpaper stuff glued onto the face of mine and there are two rubber wheels wheels that are slightly offset and just grip the lip.

I did try making some Acorn Gear based runner out of plywood but it didn't go well. To get enough depth, the ply is not flexible enough in one thickness so you end up making a sandwich of several layers of 6mm and it is hard then to get the holes to line up perfectly. I kind of ran out of patience after a few strips. It is a reasonable option though and could work well on your timber dome. A windscreen wiper motor has more than enough torque but you do need a motor controller that will handle the amps is can take so something like http://www.robotshop.com/uk/30a-5-30v-single-brushed-dc-motor-driver.html. The Acorn gear could easily be fitted with a rotary encoder and you are only one step then away from total automation.

You really want the drive to be adjustable up to +/- 1 x sidereal as it does vary depending on where in the sky you are pointing.

Chris
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Offline petevasey

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Re: Dome Motorisation
« Reply #4 on: 17:38:39, 10 March, 2017 »
Hi, Chris,

There is no lip on my dome to nip between rollers, and I don't know if I could apply enough pressure for a roller to work.  But maybe worth a try.  I've been looking at this motor:

http://www.ebay.co.uk/itm/High-torque-Turbo-worm-Geared-motor-DC-motor-GW370-12V-0-6rpm-/261481630429  I've asked the seller for dimensions.

They quote 25 Kg-cm torque, so a 25 mm diameter wheel should provide enough shove to get things moving.  The rim is around 7' 6" diameter i.e. 7200 mm circumference.  So in 24 hours for a full rotation I would need 92 revolutions of the drive wheel i.e. 0.064 RPM.  So if the motor drives at 0.5 RPM on load, it would need to run for a minute or so every 8 minutes.  Should be possible to build a simple (adjustable) timer to do that.  Maybe worth a go - not a lot of money involved.  But need a wheel with a high coefficient of friction!

Cheers,

Peter. 
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline petevasey

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Re: Dome Motorisation
« Reply #5 on: 00:30:32, 11 March, 2017 »
Came across this timer unit on ebay - looks like it might do the business - useful to have a visible indication of the on/off times.  This is a 'tiny URL' - the original was over 300 characters!  So I don't know how long this will be active.  There are a few sellers of this, this is about the cheapest.

http://tinyurl.com/zh4sptm

Only problem is the instructions are somewhat obscure.  But might be fun working it out.  Probably no worse than a digital watch  ;)

Chris, where did you get your wheels, and what size are they?

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #6 on: 09:03:37, 11 March, 2017 »
Peter

I got my rubber wheels off some equipment casters off eBay I had to butcher the castors to get the wheels off but they work a treat, something like http://www.rosscastors.co.uk/75mm-swivel-castor-grey-rubber-wheel.html?gclid=Cj0KEQiA3Y7GBRD29f-7kYuO1-ABEiQAodAvwIcGhTTkq4OgKhazS3B6tkALtZ5MbaEl_NN-T-1yek8aAkSD8P8HAQ. I still wonder if with a timber dome like yours you would be better off with an Acorn gear something akin to http://www.morningstarobs.com/dome-automation.html. An easy way of making the Acorn gear is http://www.ebay.co.uk/itm/A2-Stainless-Steel-Dome-Acorn-Nuts-M3-M4-M5-M6-M8-M10-M12-M14-M16-M18-M20-/310413439000, that just leaves you needing to make the track.

One other option is http://www.dppobservatory.net/DomeAutomation/DomeDriver.php. This would give you full Ascom dome control, though it is a little more complex. I had it running but my motor is mounted on the rotating part of the dome and I could not find an easy way of making it wireless. As such I used an Arduino and PWM motor controller and use Bluetooth to send Azimuth data from the PC to the Arduino. The Arduino then fires up the motor controller to carry out the required move.

Chris
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Offline petevasey

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Re: Dome Motorisation
« Reply #7 on: 10:17:04, 11 March, 2017 »
Thanks again, Chris.

That Morning Star system is seriously complex - not the sort of thing I'd want to tackle - I'm not interested in full automation.  I've been looking at castors, and have seen some with quite small wheels.  Just might be a bit of a problem fitting to the motor shaft.  But read on.

I wasn't sure what you meant by an 'Acorn' gear, but that is now clear.  I don't think I'd need to make a track - the wooden rim goes right round in an unbroken circle, and is quite thick, so it would just (!) be a matter of drilling suitable diameter holes a small way into the rim at an appropriate spacing.  But in order to use that system I'd need a relatively large diameter drive wheel, so the little motor I show above wouldn't have sufficient torque - a reduction gear would be required - more complication.

To try a friction drive,  I've come across some dimensions for that motor unit, and it would appear that a 35mm diameter wheel would be big enough to clear the casing.  IF the 25 Kg-cm figure is correct that would give me a pull of 14.5 Kg - enough to move the dome.  I might be able to find a suitable size castor, but it could be just as easy to make a wheel on my little lathe.  Then I could make the bore a good fit secured with a grub screw.  To rubber face it, maybe a section of bicycle inner tube stretched over the wheel and glued would do the job.

The motors are so cheap that if one isn't quite up to the job, why not two  ;)  Maybe I'll get one and experiment....

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #8 on: 12:44:09, 11 March, 2017 »
Peter

I did lots of experiments before finding a solution that worked. As you say bits are cheap. If a friction drive doesn't work you could then go the Acorn route. 12v windscreen wiper motors can be had off of eBay for around £15-20 and they have immense torque. Ive just put some new liquid waterproofing membrane down on the floor of my obsy so I can't get in it at the moment but when its dry I'll look up the motor controller I used. Very easy to control from an arduino with a dozen or so lines of code.

If you do end up going the Acorn route I would still make a ply track as it will wear and need replacing. My dome is only 2.1m diameter so the radius was too small for 12mm ply hence having to try a sandwich of multiple strips of 6mm, glued together. I got about half way round and gave it up when the rubber friction roller idea developed. Its the route I would take if doing it again as with a rotary encoder you could get absolute positioning. The tilt compensated compass does work ok with the refractors but with the RC the dome slit is a little narrow, giving little tolerance. The electronic compass is liable to a bit of jitter and though my code does an average of 5 readings, it can still wander about a little.

Chris

ps I also tried a solution with timing gear belt glued to dome lip, that one didn't end well!
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Offline petevasey

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Re: Dome Motorisation
« Reply #9 on: 16:41:04, 11 March, 2017 »
Thanks again Chris.

After checking hands on in my Obs, I realise that the friction wheel system just isn't going to work.  The lateral wheels all press on the outer overhanging rim of the dome, so pushing against the inner rim increases the drag, and even with a high friction pad it slips easily.

Maybe I should buy the Exploradome track and an Acorn wheel - their track for the 8' would go nicely on my inner rim.  I certainly wouldn't get their drive motor - as you say, windscreen wiper motors are readily available.  But their speed seems to be around 60RPM unlike the 11RPM for the Exploradome motor.  And a 6" gear will rotate the dome fully in 15 revolutions.  So how do you stop things from going too fast?  Is it simply a matter of the 'on' pulse being just a few seconds and the 'off' pulse several minutes?

So for example would this

http://www.ebay.co.uk/itm/Black-Front-Wiper-Windscreen-Motor-Fits-Vauxhall-ASTRA-G-Mk4-1998-2004-23000826-/152183133532?hash=item236ed2555c:g:V3UAAOSwTuJYt5iZ

be driven by this

http://www.robotshop.com/uk/cytron-13a-5-30v-single-dc-motor-controller.html

perhaps using the on-off unit I linked earlier.

Although the 30 amp unit you mentioned has a built in PWM generator, it might not have a wide enough range.  Or maybe I should get an Arduino unit and learn how to use it.  I see there is one suggested on the controller web page.  Then I could have switches for preset speeds in either direction.  But a bit daunting - although I've programmed in Delphi, it's a whole new ball game for Arduino.

I guess I'm asking you to rather lead me by the hand - I'll understand if you don't want to go any further.

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #10 on: 16:59:58, 11 March, 2017 »
Peter

Give me 24 hours for the waterproof membrane to dry and i'll be able to get back in my obsy and find out what motor controller I used. It uses PWM for speed control so I have three speed settings, fast for big dome rotations (360 degrees takes about 40 seconds), when it gets close to final position it slows to medium and then slow. That stops any overshoots and reverses.

If you have programmed in Delphi you should find the Arduino pretty simple. Its effectively C++ with a few syntax anomalies but to be honest there are so many libraries about to use the actual amount of coding is minimal. Mine is no more that 50 lines and a lot of that is the decision logic as to the shortest direction to slew the dome and a table of corrections for the tilt compensated compass.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
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Offline petevasey

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Re: Dome Motorisation
« Reply #11 on: 17:16:58, 11 March, 2017 »
Thanks again, Chris.

In the meantime what do you think about this motor? - a decently long output shaft to either fit an Acorn wheel directly, or an adapter which I could make on my lathe threaded and with a taper to fit tightly on the splines.  Then I would use grub screws into the splines for final fixing - don't want it to unscrew when reversed   ;)

https://www.amazon.co.uk/AUDI-SKODA-WIPER-MOTOR-FRONT-x/dp/B00GI909AS/ref=pd_sbs_263_6?_encoding=UTF8&psc=1&refRID=SDNK34Z38ZHZYJFDENND

Cheers,

Peter.
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #12 on: 19:03:02, 11 March, 2017 »
Peter

Looks very much the same as the motor in this video https://www.youtube.com/watch?v=iSgxv-tcwoA. For £15 it would be a good start I would have thought.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline petevasey

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Re: Dome Motorisation
« Reply #13 on: 20:35:35, 11 March, 2017 »
Hi again, Chris,

That's working well isn't it!    And you say ' For £15 it would be a good start I would have thought.'  I think so too, so I've taken the plunge and ordered one!  I'll be able to tell pretty quickly if it will do the job.  If not, well, what the hell  ;)  If so, then Arduino here I come!  Every year there's a Maker Faire in Newcastle (http://www.makerfaireuk.com ) - I've always been fascinated by the things people use Arduino for, but I never had an application to justify playing with one.  Now....

Cheers,

Peter,
Telescopes: GSO RC10 Truss, Meade S5000 127, TMB 105, TS65 Quad, Solarscope SV50
Binoculars: Canon 15x50 IS
Camera lenses: Canon 400L f5.6, Canon 70-200L f4 zoom, various old M42 thread
Cameras: QSI 683wsg, SX AO, LodestarX2, Artemis285, Canon 350D (modded), Canon 700D, GPCAM2 (colour), GPCAM2 (mono), LE Vesta Pro, Toucam.
Mounts:  Gemini G41 with Pulsar controller. EQ6 Pro, EQ3-2 with Autostar. Star Adventurer
Observatory: 8' Astronomydome

Offline chris.bailey

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Re: Dome Motorisation
« Reply #14 on: 20:46:17, 11 March, 2017 »
Peter

I have coded quite a few things with them so should be able to help. The motor controller will be the deciding factor on how its coded.

Its running a bit fast in that video for my comfort but it shows the Acorn gear system doing its stuff.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

 

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