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Meade LXD 500- tracking speed.

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#1 Franklink

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Posted 25 June 2010 - 12:04 AM

I recently purchased an (admittedly) old Meade LXD 500 (w/ motor drives) for some wide field AP. I fitted my EOS 500D to it using an adaptor, and I set out tonight (motor drives installed) to see how it tracks.

I found that when I turned on tracking and shot a 30 second exposure with an 85mm lens, there was significant star trailing. I turned off the drive and shot 30 seconds to compare. The (tracked) star trails were half as long as the untracked star trails. This tells me that the mount is moving at 50% the correct speed. I confirmed with the live view that the mount was not keeping up with the sky.

This could be due to multiple reasons:

1. Voltage.
The motors have "15v" printed on them, and I am using a 12 volt power supply. However, 12 volts is within the range said by the instruction manual. My power supply was full charged.

2. Balance. The setup could have been improperly balanced. However, I checked, and the setup could hold horizontal without the lockdowns.'

3. Software. The software could need calibrating to get the motors to track properly. I "trained the drives" and hit "calibrate motor" at least twice, to no ado. However, I did not completely reset the software.

Can you guys think of any other reason why the mount would be sluggish?


Regards,
franklin

#2 rmollise

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Posted 25 June 2010 - 07:07 AM

This could be due to multiple reasons:

1. Voltage.
The motors have "15v" printed on them, and I am using a 12 volt power supply. However, 12 volts is within the range said by the instruction manual. My power supply was full charged.

2. Balance. The setup could have been improperly balanced. However, I checked, and the setup could hold horizontal without the lockdowns.'

3. Software. The software could need calibrating to get the motors to track properly. I "trained the drives" and hit "calibrate motor" at least twice, to no ado. However, I did not completely reset the software.

Can you guys think of any other reason why the mount would be sluggish?


Regards,
franklin


1. Nope...the nominal output of a 12vdc battery is just right.

2. Possible.

3. You might reset it...

BUT...the primary reasons you're getting star trails are likely...

Poor polar alignment. Did you drift align.

Periodic error in the gears.

#3 JayKSC

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Posted 25 June 2010 - 07:09 AM

Franklin,

I used to own one of these mounts with the Meade #1702 drives years ago. Overall, I liked the mount and drives well enough for visual observing. For imaging, though, today's inexpensive mounts will likely put the LXD500 to shame. I highly suspect that the 12 volt feed is a likely culprit here. I remember the drive motors were fickle things. I also remember that they had a little bit of slip to them when they first started up. Did you start your exposure before engaging the drives? If so, a little backlash at the time the drives engage might be to blame. You also didn't mention how you tracked or set-up the polar alignment? When I did some astro-imaging, I always found the polar alignment to be the biggest hassle. This is why I always would manually guide (this was in the days when autoguiders were new and super fancy).

Hope that these comments may help.

- Jay
South Florida

#4 jrcrilly

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Posted 25 June 2010 - 07:53 AM

I "trained the drives" and hit "calibrate motor" at least twice, to no ado. However, I did not completely reset the software.


I don't remember that controller having either of those functions. Is it possible that someone has substituted an old Starfinder goto system on the mount (it will fit and I've done that)? If so, the ratios are different from standard and will need to be entered manually. Unless that is done the tracking rate will be incorrect.

#5 Franklink

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Posted 25 June 2010 - 12:20 PM

Yes! It is an Autostar system controller. How might I enter the gear ratios manually?

#6 jrcrilly

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Posted 25 June 2010 - 12:35 PM

Yes! It is an Autostar system controller. How might I enter the gear ratios manually?


It's probably under Telescope Setup. It's been a few years. I don't remember what the ratios are for that mount.

#7 Franklink

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Posted 25 June 2010 - 01:10 PM

The formula for this specific motor is:

0.0456296 x (number of worm gear teeth) = Autostar ratio.

I'm searching for the number of teeth on a LXD 500, but can't seem to find it anywhere....

#8 jrcrilly

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Posted 25 June 2010 - 01:14 PM

144 would be worth trying (I believe that all the Vixen clone mounts use 144 tooth worm wheels).

#9 Franklink

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Posted 25 June 2010 - 02:08 PM

I put in the proper ratio (6.5706624) , and it tracks at the correct rate. I put the tracking motor on for 10 minutes, and the dial indicated that the mount had moved 10 minutes of RA.

I will test it photographically tonight!






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