From: Milton Aupperle <milton@outcastsoft.com>
Date: June 2, 2008 1:54:07 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Tracking anomaly
Hi KirkusMcGurkus;
On 2-Jun-08, at 1:01 PM, KirkusMcGurkus wrote:
I have 2 OTAs that I use on a Meade LXD75 mount. A 6"SN and a 10". I
have zero problems tracking a guide star with the 6" on the mount.
AstroIIDC works like a charm.
However, with the 10", I have a specific problem with tracking. The
guide star will slowly drifts outside of the green cross (along the
yellow line - Dec.?) then after several seconds it snaps back and
tracks fine for a minute or so. Then it slowly drifts outside the
green cross again, etc.
I'm assuming this is probably due to the weight of the 10" along with
the extra counterweights and the ability of AstroIIDC to drive the
mount motors?
It's more likely that the motors are struggling to move the mount and probably the gears are slipping when it drifts out and then re-engaging. So Astro IIDC may be sending commands to correct it, but the mount isn't able to respond. Have a look at the Guide log too which may shed some light on it. What you would probably see is multiple RA corrections in a row and the guide star keeps drifting away.
Total weight on the mount is roughly 60lbs.
Gack, that is way too much. My HEQ5 mount is rated for around 30 lbs pounds and even a Losmandy G11 is only rated for 60 lbs.
According to the what I have been able to find, maximum weight for an LXD75 is 30 lbs:
http://www.optcorp.com/product.aspx?pid=9012
Do you think my assumption is correct?
I think it's the weight load is grossly exceeding the mount's capacity.
As a rule of thumb for accurate guiding, you are only supposed to load the mount to around 50% to 70% of the recommended capacity, including weights.
I unfortunately discovered this 6 months after I bought my HEQ5 and was planning on buying a C9.25 OTA. With the weight load I'd be over the capacity of the mount for good guiding, so I ordered the carbon Fiber C8 (saves around 2 lbs of weight over the aluminum tube). I was tempted by the HEQ6 mount, however I would not be able to fit an HEQ6 into my trunk without completely removing the head assembly each time, so it turned out to be the best choice in my situation.
Can you think of anything I can
do to help fix this?
Umm not really. You can try re-balancing the counter weights on the mount which might help. Making it a bit heavier on the west side (if your in the northern hemisphere / for southern hemisphere it's the east side) . I've noticed that with the HEQ5 and the C8 (total payload of maybe 24 lbs), that guiding on the east side of the N/S meridian was a bit more ragged than on the west side. I rebalanced the weights and that basically solved it for me.
HTH..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta T2R0N5
1-(403)-229-9456
www.outcastsoft.com