Unbalanced mount

[jambouk]

If an equatorial mount is quite unbalance (more so than the unbalancing the imagers sometimes purposefully do), will that affect its GOTO accuracy and/or tracking, or does it just put undue strain on the motors and gearing system, or both?

Thanks

James

[Mav359]

I forgot to balance my mount in RA once and switched on and tried to slew and it sounded like an old 80's ford ready to blow up, bouncing all over the place it was Scary

In short, both, forget the guiding issue though you're more likley to bust the mount. With the exception of the very slight imballance for imagining there isn't really any need for it not to be balanced.

[m37]

I would also like to know how much difference this makes. Surely rotating the camera and oag and guide cam to frame a target is throwing the balance off a bit too in one axis...

[Mav359]

I wouldn't describe that as "quite Unbalanced" though

If your balanced correctly in RA and in DEC then i would be astonished if just rotating the Camera and OAG was enough to cause a guiding issue, others wiser then me might say different but on my CGEM mount which is an EQ6 that wouldn't be enough to throw anything out in guiding.

[YKSE]

I agree with Alan totally, the mount should always be well balanced, even for visual use only.

A simple analogy can performed, if you take out your counter weight bar, hold it in the middle and point it to somewhere. then try to hold it near one end, and point to the same target. You'll surely notice the extra stress and shaking in your hand in latter case. An unblance mount will not only decrease accuracy in alignment and tracking, it will most likely bust the mount if it's kept like that.

[jambouk]

Ok. That's interesting and useful, thank you.

James

[Zakalwe]

I doubt if you'd bust it. If the torque requirement exceeds what the steppers can but out then they'll stop. They make a hell of a racket when they do, but they won't be damaged. The same thing happens if the OTA hits the tripod legs.

Running it unbalanced for a long time (think years) will probably wear the worm and gears much quicker, but lets be honest...has anyone ever worn a mount out (and if you live under the seemingly permanent skies where I live, then it's highly unlikely!)

[jambouk]

Zakalwe, interesting. But do you think a grossly unbalanced mount which actually slews will be less accurate in goto and tracking than a well balanced mount?

James

[ollypenrice]

I agree with Zakalwe. Go To might just be marginally affected by credible imbalance (ie not insanely out of balance) but it would have to be bad to have much effect. Rotating cameras, adjusting focus? No, we all do that without rebalancing.

Olly

[Zakalwe]

Zakalwe, interesting. But do you think a grossly unbalanced mount which actually slews will be less accurate in goto and tracking than a well balanced mount?

James

I would think that it depends on the amount of backlash in the gearing. If there is little or no backlash, then as long as the motors can move the OTA, the GOTO accuracy should be OK. If there is a lot of backlash, then the mount might "lurch" as it goes over the meridian. This would absolutely affect the GOTO accuracy.   That would apply if the mount was unbalanced or not.

Moving the camera and OAG? It depends. The OAG and camera (on a Newt) have their weight away from the centre of the scope's axis. Similarly, if you balanced the OTA with the focuser racked the whole way in, and then you had to rack it out a few inches to focus then it might unbalance things a bit.  I always run my kit unbalanced anyway to keep the gears meshed. Perfectly balanced the whole lot tends to "bounce" on the gears and ruin subs (even with guiding).

[Ant-33]

With the exception of the very slight imballance for imagining there isn't really any need for it not to be balanced.

Not sure I understand this. Is this because of not re-balancing after adding the camera or something else? I always try to balance with all the gear in place, so... what difference does imaging make?

[jambouk]

I think some imagers purposefully have their kit slightly unbalanced so there is always some tension on the gears to minimise backlash (slack).

James

[Ant-33]

I think some imagers purposefully have their kit slightly unbalanced so there is always some tension on the gears to minimise backlash (slack).

James

That makes sense - thank you. I suppose I've always relied on the fact that my ability to balance the gear isn't so good that my gears are chattering

[ollypenrice]

Im

[jambouk]

Im

.... falling asleep at the computer?