EWhytsell
super member
Reged: 06/15/08
Posts: 157
Loc: North Central Ohio
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I had to send my CG-5 back to the factory for repair and I dusted off my old super polaris mount. Does anyone else have motors that pulse so hard that they shake the image?
It sucks because this mount can guide perfectly,and by that I mean I just finished some 300mm telephoto piggy back imaging with it and I shot for over 1 hour at veil nebula and from frame to frame there is ZERO drift.
If only the motors didn't shake I'd have a great mount and I'd probably throw my CG-5 in the dump.
Evan
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Classic C8 Super Polaris upgraded to CG-5 mount
Canon 40D unmodded
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ccs_hello
Carpal Tunnel
Reged: 07/03/04
Posts: 2781
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Evan,
Old drive controller in that era used full-step or half-step for tracking movement. That was the state of the art at that time.
Newer drive system uses microstepping to reduce the jitter.
Clear Skies!
ccs_hello
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EWhytsell
super member
Reged: 06/15/08
Posts: 157
Loc: North Central Ohio
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I'm pretty good with small electronic motors since its my day job. I was just hoping someone knew a trick to eliminate the shake that occurs each time to motor pulses because this mount stays locked perfectly on target all night and it sucks to have to use my newer less accurate mount.
Oh well maybe I'll get a wide field scope to put on the SP and do some really neat wide field imaging.
I wonder if an external flywheel might help? We use them at work to smooth out our high speed steppers. I'd almost attempt to build a drive for it, but I don't have much time anymore.
Evan
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Classic C8 Super Polaris upgraded to CG-5 mount
Canon 40D unmodded
Edited by EWhytsell (08/09/08 06:51 PM)
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steveeb
super member
Reged: 05/06/08
Posts: 196
Loc: Murrieta, CA
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I just bought an MT-1 and a SD-1 but have yet to install them. I tested the motor and the pulses at 1x speed are faint. I don't think they are strong enough to shake the mount.
Maybe you should think about selling the CG-5 (instead of trashing it) and using the money on new Vixen motors.
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Steve
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ccs_hello
Carpal Tunnel
Reged: 07/03/04
Posts: 2781
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Evan,
Vixen SP also has the worm ratio of 144:1 thus many after-market kit for CG-5 might be adapted to it.
Orion Telescope (USA) in its "second", has a GOTO kit for its SVP for sale at $399. This type of later generation of drive system has microstepping capability to smooth out jitter.
Another option is to find an old LXD55 (which is uisng Autostar drive system) and do a transplant.
P.S. the magic is the drive electronics, half-step driving for a stepper unavoidably will cause jitter.
P.S.2, DIY microstepping mod is possible, but is rather involved.
Clear Skies!
ccs_hello
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Exit-pupil
super member
Reged: 11/13/07
Posts: 187
Loc: Eastern Long Island, NY
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Evan,
Not sure if this is the problem, but drive motors work smoother when they have some resistance to pull against rather than having weight "helping" them along, which will make them (and your scope) shudder. You might check the balance and adjust it so the motor has a little work to do to move the scope.
Jono
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BRisley
super member
Reged: 09/04/06
Posts: 170
Loc: SW Florida
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I had the original sky sensor with the pulse motors on my SP. Even the manual said that the motors are a problem at any med to high mags. I picked up an MT1 and MD-6 (early predecessor of the SD-1?) and a JMI/Celestron dec motor which I mounted using the gears from the sky sensor instead of the belt so I could keep the clutch. Tracks beautifully. I setup last night, did a polar scope alignment, and put it on Jupiter with a C-8 and a 7mm. Left it for 15 minutes. Still tracking when I came back. Spent time collimating, never saw a jitter and motor moved very smooth when scanning over the moon with the 7mm.
I am using 3 of the CW's, as I sometimes piggyback a Cometron 62 or 80. I also use a Meade 1200 focuser. Drive just keeps on chugging!
I tried a roboscope using DS motors and autostar, never could get it to work good, never got a good alignment. Gave up on goto and went back to the MT1 and haven't looked back.
Brian
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EWhytsell
super member
Reged: 06/15/08
Posts: 157
Loc: North Central Ohio
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Nice tip BRisley. Maybe I'll look into that. I already started working out a new motor drive system in my head since last night as well:-) I work on copy machines and other office stuff so I have lots of motors, driver boards, and gear parts laying around all over.
I wonder what would happen if I gear reduced a motor I can get down from like 15,000rpms down to sidereal rate:-) That would be very smooth I would think.
Evan
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Classic C8 Super Polaris upgraded to CG-5 mount
Canon 40D unmodded
Edited by EWhytsell (08/10/08 10:26 PM)
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ccs_hello
Carpal Tunnel
Reged: 07/03/04
Posts: 2781
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Quote:
...
I wonder what would happen if I gear reduced a motor I can get down from like 15,000rpms down to sidereal rate:-) That would be very smooth I would think.
Evan
Evan,
15,000 PRM motor is definitely not a stepper. A DC perm-mag motor need a closed-loop servo to maintain its position/speed accuracy. The nature of such motor is it is not "stepping" thus no jitter/shudder. But the work is rather involved.
Your existing stepper-based drive system's control circuit can be compeletely redone to be microsteppeing.
Either way, it is a one-off situation. A commercial solution might be more useful for many common souls.
Clear Skies!
ccs_hello
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John Carruthers
Skiprat
Reged: 02/02/07
Posts: 1681
Loc: Kent, UK
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AWR do a microstep drive,
http://www.awrtech.co.uk/tdsumry.htm
might help tidy it up?
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Jc
ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light )
6" F7 spec
127mm F9.4 Refractor
10 x 50 bin
ETX80 (finder)
Canon 20D
and a curious mind
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tim53
sage
Reged: 12/17/04
Posts: 317
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I bought my Super Polaris in 1986 at RTMC, right after the Halley bubble burst in the commercial market. (I won't tell you what I paid for it!).
I bought the Skysensor in 1987, a year after the bubble burst.
I have friends who had Skysensors from the year before, and they had the coarse steps and oscillation at high mags. I never have, and I still don't know whether it was the motors or the controller in the skysensor that changed.
One option I'm looking at nowadays to upgrade to a modern goto system and autoguiding capability is the Ioptron GotoNova. It's still pretty new, so I want to be sure the bugs are worked out before I make the change.
The old skysensor works fine, but it can't slew fast, and it can't autoguide. ...and it drains a car battery in a matter of hours!
-Tim.
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"We`re just waiting looking skyward as the days come down.
Someone promised there`d be answers, if we stayed around."
-Orchestral Maneuvers in the Dark, "The Romance of the Telescope"
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EWhytsell
super member
Reged: 06/15/08
Posts: 157
Loc: North Central Ohio
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offtopic: 15krpms is a sorta fast stepper in my field. 60krpm is a really fast one, but it's not designed for a load maybe just a few ounces.
Very good tips guys. One more major concern. Right now the PE of the drive is literally 0. If I replace the motors with something else I'm guessing that I'll likely cause PE to happen right?
Anyone happen to know what scope size (focal length) would be low enough power that it probably wouldn't detect the drive ticks? My Canon 40D piggybacked with a 300mmf5.6 lens never detects any shake, but that is like a 50mm aperture or probably less.
Thanks,
Evan
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Classic C8 Super Polaris upgraded to CG-5 mount
Canon 40D unmodded
Edited by EWhytsell (08/11/08 05:44 PM)
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ccs_hello
Carpal Tunnel
Reged: 07/03/04
Posts: 2781
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Evan,
My experience on typical 200 steps/rev hybrid-stepper is they cannot be easily driven beyond 1000 RPM, even with gradual ramp-up. Over-voltage can do faster but excessive amount of heat. Per factory datasheet, torque drops significantly.
E.g., for SynScan 800x fast slew, it's about half as that.
Old classic EQ6 (non-Syntrek) has a similar jitter problem. Darren H. (astroesq) has a microcontroller/firmware mod which changes fro factory half-stepping during tracking to a microstepping design.
There are ways to mod your classic Vixen-SP controller to be microstepping, but it will be a one-off job.
Clear Skies!
ccs_hello
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