Bert
sage
Reged: 02/17/06
Posts: 429
Loc: Australia
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Some of you may know about the Chronos Mount that uses Harmonic Drives.
Here is a video if you do not know what a Harmonic drive is.
http://www.youtube.com/watch?v=q1v7a0jsp1I
Here is an animation that is self explanatory 6MB
http://d1355990.i49.quadrahosting.com.au/2009_10/gearanimation.wmv
These harmonic drives have ZERO backlash!
Most if not all EQ mounts use gearboxes. My mount does not as it has belt drives to eliminate the gearbox. Image below. This has the effect of eliminating any micro jumps due to the gearbox.
I am seriously thinking of getting a dead or alive G11 or Titan and modifying it to incorporate these drives between the motors and worms be they servo or stepper.
Bert
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David Pavlich
Postmaster
Reged: 05/18/05
Posts: 8655
Loc: Mandeville, LA USA 30.22 X 90....
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Pretty neat! Thanks for posting it.
David
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Proud Member; PAS NOLA,
"If we knew what we were doing, it wouldn't be called research..."
A. Einstein
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E_Look
Pooh-Bah
Reged: 03/06/08
Posts: 1206
Loc: near New York
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Yes! That was educational! No gears, so smooth motion. I guess by changing the eccentricity of the parts, different rotational rates can be achieved.
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Ed
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amateur
sage
Reged: 06/15/06
Posts: 300
Loc: The Netherlands
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I think in a telescope drive:
- the worm gear is for getting a high gear ratio
- the stepper+gears are just for driving the worm (no major gear reduction)
So when applying a harmonic drive in a telescope, I would put the harmonic drive directly on the main RA axis and drive it from a stepper motor (optionally via a belt drive).
This seems to be an example of harmonic drive telescope mount.
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gordianknot
professor emeritus
Reged: 09/04/05
Posts: 542
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Most comparably priced high end mounts like those from AP and Bisque use anti-backlash gears (spring loaded worm). I get the impression that backlash is already a solved problem in high end mounts, but I don't claim to be an expert.
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Phil Cowell
sage
Reged: 05/24/07
Posts: 376
Loc: Southern Tier NY
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The spring loaded gear reduces but doesn't completely remove backlash. Chronos do a very sweet harmonic drive mount which appears to be an order of magnitude on from the current GEMs on the market. I haven't used one but have one on my next mount list for when the market has fully recovered (might be a long wait). [url] www.chronosmount.com [/url]
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If it'll fit on a sig you don't have enough
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SkyscraperJim
professor emeritus
Reged: 07/29/07
Posts: 537
Loc: Providence, RI
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There is also the ASA Direct Drive mount. http://www.astrosysteme.at/eng/monts.html
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Jim
TMB/APM 130/780 (#185) on G11
TMB/APM/Lomo 80/600
Tele Vue Pronto (#3533) on Half Hitch
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Bert
sage
Reged: 02/17/06
Posts: 429
Loc: Australia
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In answer to all replies I was just putting forward an alternative to all gearboxes that have unpredictable 'jumps'.
A smooth PE in our autoguided universe is easy to control. It is the random jumps from gearboxes that are almost impossible to deal with.
Bert
Edited by Bert (10/11/09 07:07 AM)
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E_Look
Pooh-Bah
Reged: 03/06/08
Posts: 1206
Loc: near New York
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I don't think I've heard of stepper motors giving trouble in terms of unpredictable jumps, but then, I don't think I ever ran one for several hours straight.
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Ed
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urke
member
Reged: 04/11/07
Posts: 73
Loc: Slovenia
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Stepper motor itself not, HEQ5/EQ6 STD. stepper motors have reduction gears, I think this causes problem, as I know conrad gearbox project solves this (rajiva).
HEQ5/EQ6 PRO has better stepper motors (no gearbox!), but some backlash comes from transfer gears.
I've been thinking putting stepper motors direct on worm shaft, that changes gear ratio so steppers would need to work about 7X slower (slewing, GO-TO).
For now, I'm working on project: spring loaded worms (DEC and RA) and transmission gear enhancement, the goal is to minimize backlash, mount is HEQ5 PRO
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Orion|opticsUK Europa 203 f4.5 De-Luxe 1/8PV + Baader MPCC
HEQ-5 SynScan PRO v3.x
Canon EOS 350D (Baader UV/IR mod), Philips SPC900NC (LXmod), QHY5 monochrome
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