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Safe Remote Operation

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#1 nitegeezer



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Posted 20 June 2013 - 02:44 PM

I am considering operating my LX200GPS remotely so I can do imaging without all the setup I do now. The concern I have is that I have heard of scopes going into a constant high speed slew and hitting the hard stops and getting damaged. Is this just a concern with the Classic or does the GPS version also have this problem? Is there anything that I need to do so I don't take a chance of damaging one of the drives?

#2 P26


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Posted 20 June 2013 - 09:17 PM

This doesn't happen with the Classic. It's a function of the GPS & later versions using the GPS basics. The only solution I've heard of is adding a webcam to the setup so that you may confirm scope orientation visually and throw a remote master switch if you get a runaway. Not very sophisticated, but there it is.

#3 jrcrilly


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Posted 21 June 2013 - 12:12 AM

It can happen to the Classic. It can happen to ANY servo-controlled mount (which is almost all mounts) if an open loop condition occurs and the system doesn't catch it and shut down; that's a characteristic of servos. The most common cause on the Classic LX200 is dirty controls on the servo board. I've seen and repaired several of them that were running away, either intermittently or consistently. Never saw it on a GPS model but I think that's just because they aren't as old; the controls are similar.

#4 nitegeezer



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Posted 21 June 2013 - 01:08 AM

Are there any other failures other than a runaway that could cause damage?

If the runaway is the primary fault, I am thinking of putting an automatic power switch in the system. The power supply current during tracking should be fairly small compared to a slew or runaway current. For this a simple current monitor with a high limit is all that is needed. A bypass would be required whenever the scope needs to slew, but the monitor could be disabled any time an operator is present. Does anyone know of other conditions I should monitor to protect the scope and drives?

#5 Christopher Erickson

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Posted 21 June 2013 - 01:53 AM

Mounts with limit switches and/or absolute axis encoders are designed to prevent this kind of problem when running remotely.

All modern Astro-Physics mounts are optimized for remote operation. Additionally, the Astro-Physics 1100GTO and 1600GTO mounts can be had with absolute encoders but AP mounts are not cheap.

The Software Bisque Paramounts are also optimized for remote operation but are not cheap either.

The Celestron CGE has the needed switches and is about 1/3 the cost of an AP or SB mount. That might be an option.

Some people have added limit switches to LX200GPS scopes. I don't have any links to share at the moment. You could always work up your own.

If you were to set up the LX200GPS worm block play-limit-screws so the mount axis motor would stall instead of cause the worm teeth to skip over each other, the CPU would detect the servo motor stall and stop the motor and report an error. Also set the clutches tight enough to make the motor stall instead of slip the clutch.

This problem/challenge exists regardless of the motor type involved. The cure is having some kind of absolute axis position sensing ability. Either via limit switches or better-yet, by absolute encoders.

One of the best features of the modern Astro-Physics mounts (Mach1, 900GTO, 1100GTO, 1200GTO, 1600GTO and 3600GTO) is that they keep their sky-position awareness regardless of how they were powered down. When they are powered back up, they get time from an internal real-time-clock and they know exactly where the mount was pointing when it was shut down. They have a "brownout feature" where they detect the loss of the main 12VDC power and are able to save their current axis positions to NVRAM before the power drops to zero. Pretty-darn nice feature!

I hope this helps.

#6 GrassyPond



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Posted 21 June 2013 - 09:21 AM

I am lucky, as I have never had a run away while operating remotely.

I do have video in the dome so that I can see what is going on, and I do have remote power management so that I can kill the power to ths scope if it starts acting up, but I have never used it in the 6 years it has been setup.

Operating the scope remotely is a whole other deal. I use ASCOM as my LesveDome driver requires POTH to function properly. I have constant problems Parking and Unparking the scope in this configuration. Frequently I will simply use the "hand pad" in the Autostar software and then move the dome manually to where the scope is pointing.

I hope this gives you some help.

#7 Lorence



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Posted 21 June 2013 - 01:50 PM

Are there any other failures other than a runaway that could cause damage?

You can shut down the system and forget to power down the mount. It will run until it bottoms out and keep running. I did that once and got away with it. Reconfigured the system power so that the mount will always power down.

You have to plan for something going wrong eventually, no matter how many people tell you they have not had a problem.

I never had a runaway until I had a runaway. In my case I can see and hear what is going on in the observatory and if all else fails I can power the entire setup down buy simply unplugging two UPS units in my house.

Setting up a remote system is easy, setting up a reliable remote system isn't.

#8 Mittag56


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Posted 21 June 2013 - 03:50 PM

My LX200 10 inch is 15 feet away and I have to use kill switch...I purchased one of those rf remote power switches...and keep it in my hand....only had to use a couple times..but easyer than tripping over stuff to get to extension cords...would love to monitor with a camera or better yet wire on some switches..

#9 nitegeezer



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Posted 24 June 2013 - 01:58 PM

I was just looking at DigiKey and they sell a variety of breakers at fairly low current ratings. The power supply current when tracking should be fairly low. If I were to measure the current when the scope is manually slewing at 8X, and then add a circuit breaker that would trip just above this current, is there any known failure that this would not catch? I know I would have to include a bypass switch for when I was changing objects and thus slewing at a rate higher than 8X, but during photos where I would like to step away from the scope I think this would provide the necessary protection. Motors when stalled at the hard stop should draw a lot of current, more that high speed slewing, so I guess the question is whether the breaker would trip faster than human reaction time. Am I missing something?

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