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Ovision upgrade

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#1 Hilmi

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Posted 15 May 2013 - 12:52 PM

I had earlier thought I had my PE under control for a while. Turns out that 360mm isnt exactly optimal for measuring PE. When I got my 8" RC scope I was getting nasty stars again. I measured the PE and this is what I got

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#2 Hilmi

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Posted 15 May 2013 - 12:54 PM

I cant guide now since my ccd camera is dead and needs repair. So I figured its as good an excuse as any to get an ovision upgrade. I just got the excel sheet from them and here is the plot of the worm they are shipping to me. The Excel sheet was all in french. I am assuming this is the correct plot to look at. My french vocabulary consists of a couple dirty words and counting to 5 so couldnt figure out what they were going on about.

Im guessing this will let me image unguided till my ccd is back. Especially after I program the PEC. The installation instructions keep on telling you that it is easy to damage the worm. I hope I dont damage mine durring installation

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#3 David Ault

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Posted 15 May 2013 - 02:15 PM

Hi Hilmi,

Congratulations on the new worm. Hopefully it works really well for you. Sorry to hear about your CCD though.

Any of the high precision brass worms can be easily damaged. I think the number one thing to look out for is making sure that the gears are meshed properly before any force is applied to the system. The steel worm wheel can easily notch or bend the brass causing irregularities in tracking.

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#4 EFT

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Posted 16 May 2013 - 10:39 AM

Hard to say whether you will be able to do unguided or not and how long you will be able to go. In general, the G11, like most mounts, are not that great at unguided. You need to remember that the worm is not the only source of error in this case and, while the worm is very important, the graph is not all that clean and your ability to go unguided will depend on the image scale and the object brightness. If all it took to get the total error of the mount down to +/-4.5 arcsec was to add a higher precision worm, then that is what everyone would do and there would be no issue. Obviously, that is not the case.

#5 Hilmi

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Posted 16 May 2013 - 11:55 AM

I guess we will know once I get it installed. Stay tuned

#6 orlyandico

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Posted 16 May 2013 - 12:08 PM

My *cough* extensive studies of this issue seem to point to:

1) the worm is the source of most of the PE if it is > about 8" p-p

2) the motor gearbox contributes significant PE; we know on the CGEM it can be as high as 25" p-p (can be more than the worm fundamental) but for good-quality Japanese gearboxes the gearbox PE would be around 5" p-p

3) a really good gearbox would have perhaps 2" p-p

So at the end of the day, something like an Ovision worm with PEC applied would only have say 2" p-p of PE... but the gearbox PE is still there. I believe this is why some G11 users replace the regular motor with a Maxon.

#7 Startraffic

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Posted 16 May 2013 - 01:18 PM

Orly,
Maxons are now standard with Gemini-2, if you but the whole upgrade. In fact, they now a a newer Maxon motor that provides more torque than the old one.

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#8 Bart

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Posted 17 May 2013 - 07:04 AM

When did Losmandy start using the Maxon motors as regular OEM parts?

#9 Raginar

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Posted 17 May 2013 - 09:22 AM

It's been in the last 6 to 9 months. They're nice motors; very loud though.

#10 Joe C

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Posted 17 May 2013 - 09:58 AM

You are correct that with PE applied, a very low P-P with the Ovision is seen. However, the Maxon now High Torque motors are only for added torque to handle additional moment arms and loads with a bit more ease. The gearboxes are completely different and are at times upgraded to Mclennan gear boxes that have metal rather than plastic gears and tend to be a bit more precise.

So at the end of the day, something like an Ovision worm with PEC applied would only have say 2" p-p of PE... but the gearbox PE is still there. I believe this is why some G11 users replace the regular motor with a Maxon.



#11 orlyandico

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Posted 17 May 2013 - 01:17 PM

Hmmm.. well thing is you can buy Maxons with Maxon gearboxes. I have some Dunker servo motors and the gearboxes are really tight. Dunker (German) and Maxon (Swiss) make really, really nice motors and gearheads.

I used to believe that Astro-Physics used Maxon gearboxes, but it seems that they manufacture their own gearhead reducers, although they do use Maxon motors.

If Losmandy is using Maxon motors but the same old gearboxes, you'd get better responsivity (less cogging) but the gearbox PE wouldn't change.

And yes, thanks for mentioning the Maclellan gearboxes. That was at the tip of my fingers but I conflated them with the Maxon motors.

#12 Hilmi

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Posted 17 May 2013 - 02:02 PM

I actually read a test somebody once did. I cant recall the link. Basically changing out the gearbox brought down the G11 PE by 1 arc second. So for the sake of example that ovision test run is +/- 4 arcseconds it can go down to +/- 3 with upgraded gearboxes. This is about as low as can reasonably be expected at this price point. Im thinking of getting the gearboxes myself if only to cut down on the unbearably loud noise.

#13 JSeay86

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Posted 17 May 2013 - 03:36 PM

Hi Hilmi,

Congrats on the Ovision worm, your graph looks very similar to mine. My Ovision worm is also about +/- 4 arcsec peak to peak. I noticed significant improvements after the change. With a little care during the install you should be fine. Of course, remove all scopes from the mount, and use a gauge block or similar to get each side of the worm the same distance from the flat on the housing that surrounds the larger ring worm gear.

I noticed some chatter and play in the stock gearboxes, and I am now in the middle of a McLennan gearbox and high torque motor conversion. This was not as straightforward as I had hoped, but the newer gearboxes feel MUCH smoother and I enjoy the tinkering. The conversion required several modifications:

- Reaming out the ID bore of the motor pinion supplied with the McLennan gearbox (stock pinion gear is for 3mm motor shaft, and the shaft size of the new high torque motors is 0.125 inches)

- Enlarging the mounting holes on the McLennan gearboxes. I used a 3.95mm diameter drill bit here.

- Expanding the screw holes on the gear box covers to fit the new motor position (slightly different).

- I ordered new Oldham style couplers from Ruland that fit the new gearbox output shaft and also the worm gear shaft. I have read about the Ruland coupler conversion but I don't think that it has much effect on the end performance. The Oldham style should be fine in my opinion. I have the Ruland part numbers for the couplers if anyone needs them.

- Finally, I installed a small stainless steel shim between the M2.5 mounting screws and the screw slot on the new high torque motors. The other option is to drill and tap the gearboxes to accommodate 4-40 screws like those used with the stock Losmandy gearboxes. I chose the shims instead to avoid opening up the gearboxes to drill and tap.

I will be testing everything over the next several weeks and report the results.

Also, follow the link below. I think this is the website for the gearbox conversion you are referring to.

G11 Gearbox and Coupler conversion

#14 Hilmi

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Posted 17 May 2013 - 03:42 PM

You mind posting a photo tutorial along with links for shopping? There is a website out there with steps, but it sounds a bit different from what you are doing.

Also having difficulty getting hold of the gearboxes. The sites that seem to provide them for international shipping are quoting a 60 days lead time.

Same goes for the pinion puller. Could you post a link to where you got yours?

#15 JSeay86

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Posted 17 May 2013 - 03:44 PM

Hi Hilmi,

I just updated the prior post with a link to the website you are referring to I believe. I am out of the country right now, but I can take some images when I return home outlining some of the steps required for the gearbox conversion.

#16 JSeay86

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Posted 17 May 2013 - 03:48 PM

THIS might also be the website you are referring to for the gearbox conversion. He does not mention having to ream out the pinion gears, so I think the older McLennan gearboxes or Losmandy motors used a slightly different size.

#17 wolfman_4_ever

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Posted 17 May 2013 - 06:19 PM

A TDM would take care of that PE as well as your headaches. I can jack up my ra adjustments with a 60+ p2p pe and the TDM knocks it down to below 1.

#18 Hilmi

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Posted 18 May 2013 - 12:57 AM

I had seriously considered the TDM and this was my conclusion:

TDM up sides:
-Fixes tracking issues with one device with high level of precision
-One purchase to eliminate all the issues
TDM Downside":
-Costs a lot
-Adds more wires to an already complex set up
-Lose access to polar scope unless you are willing to disassembel and re-assemble everything on a regular basis

Upgrading gears and worm upside
-Fixes the root of the problem, therefore even if I add a TDM to this set up later, I will get even better performance
-Will reduce the noise from the plastic gearbox
-Costs far less

Downsides:
-Needs tinkering to get right (especially gearbox upgrade)
-Warranty implications??? <-Mine is out of warranty.

#19 orlyandico

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Posted 18 May 2013 - 03:16 AM

The TDM will also fix PE problems regardless of whether you are east- or west-heavy. This would make balance less problematic / critical.

#20 Jesus Munoz

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Posted 18 May 2013 - 01:01 PM

The TDM will also fix PE problems regardless of whether you are east- or west-heavy. This would make balance less problematic / critical.


What is TDM?

#21 Hilmi

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Posted 18 May 2013 - 01:45 PM

It is an encoder that measures pe on the axis and corrects for it in real time via guide port. A bit expensive bit rhe price has come down a bit.

Edit: TDM is short for Telescope Drive Master

#22 Hilmi

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Posted 19 May 2013 - 01:56 AM

I just placed my order for 2 gearboxes from RS Components. They expect the gearboxes to arrive in 10 days time. Local custom is for shops to over promise and under deliver, so I will assume they will take 2 weeks to deliver. I have also ordered a pinion puller and some brass tubing from eBay. One ships from the US and the other from UK so I guess the US shipment will be late due to the new postal security checks. So overall I think I will have everything needed to upgrade the gearboxes in 3 weeks time. I'll see how it goes from there.

I'm not sure how I will ream the pinion as my Dremel Bits are metric. I have a Dremel press attachment, so I should be able to drill straight down, but I'm not sure how to secure the gear so it doesn't slide or rotate without damaging it. I guess one way to do that would be to make a hole on a piece of wood to place the gear in. I guess the hole should be a tight fit but not so tight as to damage the gear teeth.

#23 Hilmi

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Posted 19 May 2013 - 06:43 AM

Finally, I installed a small stainless steel shim between the M2.5 mounting screws and the screw slot on the new high torque motors. The other option is to drill and tap the gearboxes to accommodate 4-40 screws like those used with the stock Losmandy gearboxes. I chose the shims instead to avoid opening up the gearboxes to drill and tap.


I'm a bit confused about this step, especially when I looked at some online directions that said the following about the same step.

As the new screws are slightly undersized, put a wrap or two of tape around them where they fit through the motor housing.
The motor is in a very slightly different position, so only tighten the gearbox cover screws after you have fitted the motor.



So I figure a picture is worth a thousand words. What exactly is it you are talking about? I'd like to understand before I place my order for the screws.

#24 Geo.

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Posted 19 May 2013 - 08:33 AM

2) the motor gearbox contributes significant PE; we know on the CGEM it can be as high as 25" p-p (can be more than the worm fundamental) but for good-quality Japanese gearboxes the gearbox PE would be around 5" p-p


Orly, any idea of what reduction Celestron is using for the CGEM?

#25 orlyandico

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Posted 19 May 2013 - 11:41 AM

Hi George, do you mean the gearhead reduction? it's 57.xxxx (some weird irrational ratio) in the Igarashi gearbox.

Hilmi - do not try to ream out the holes with your dremel drill press!!!!!! get someone with a LATHE to do the reaming for you.

Trust me, I tried reaming out the 5mm holes in my AP600's spur gears to 6mm myself. The holes came out not perfectly square and it increased the periodic error. I had to buy new spur gears from AP (good thing they still sell parts for a 25-year old mount!)






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