automating imaging - flips and balance

[troypiggo]

I'm trying to get a bit more automated with my imaging. Been using CCDCommander and MaxIm successfully. The only thing now I'm struggling with is balance and guiding after a meridian flip. The software takes care of the flip fine, takes an image after it's flipped, plate solves, recentres target etc. Where it's struggling is guiding, and it's because of the RA balance.

Typically I'd slightly have more weight on the east side of mount to keep some weight on the gears. I do this by having the counterweights slightly lower when imaging in the east, then slide them up a touch when imaging in the west.

But for automation and handling meridian flips, how do you guys address this without having to change weights/balance?

Thinking outside the box, I was contemplating having things balanced slightly scope-heavy, and when imaging in the east balancing something on the weights, then when it flips, this slight extra weight (whatever it is) falls off for when shooting in west. Silly?

My mount is an EQ6.

[RickS]

Troy,

My solution to this problem was to get an Astro-Physics mount :lol:

I have heard of people tipping water or sand out of a bottle attached to the counterweight shaft, so the idea of dropping off a small weight when you flip seems like it is worth exploring.

Cheers,
Rick.

[troypiggo]

I predicted someone was going to say "Get a PMX/PME/AP mount!" :)

I'm thinking a small sandbag type thing would work all right. Maybe one of those little ankle weight thingies, but don't tie it around, just leave in a loose horseshoe type shape so it can slide/fall off.

[bojan]

How about automating the balance shift (stepper motor moves a small weight according to where the balance must be?

[troypiggo]

Aside from my technical incompetence... ok, well that's all that's holding me back from that. :)

[bojan]

One of those should sense the position of the mount:
https://www.sparkfun.com/products/10289

The rest could be a DC motor (that moves the weight by means of worm drive, from old video recorder for example) with limit switches, driven in direction according to a position of above switch.. the weight does not have to be huge.. 100g should be enough.
But, I think the way better approach is exact balance - too many things can go wrong even without automatic counterbalancing.

[peter_4059]

Troy,

I'm thinking you should rig up an egg timer on the counter weight shaft. As the shaft approaches horizontal the egg timer approaches vertical and the sand changes position to shift the balance.

I'll pm you with a sketch.

[mithrandir]

Can you do something like this (http://www.flickr.com/photos/averen1/6166581565/) G11 east heavy counterweight? The corp wraps around the RA shaft, over a guide roller and down to a weight. If you were concerned about wind swinging the weight around you could run it through a length of PVC pipe.

[multiweb]

I thought that if you guide with MAXIM DL it will take that into account and compensate with guiding so you don't have to recalibrate past the meridian (like PHD).

[bojan]

This is an excellent idea.
However, I still think exact balancing is better.

[mithrandir]

The trouble with exact balance is that play in the RA gearing means it alternates between pushing, coasting and pulling. While coasting the motors have no control over the pointing. You can't completely remove all play because differential expansion would cause binding in cold weather and too loose in hot weather. Keeping it east heavy means it is always pushing.

[Geoff45]

An AP mount is one option, but more practical is something I saw on the Losmandy Yahoo group. You'll have to do a search there, although it might be in the files section.Basically you wrap a cord around the RA axis and have it coming off the east side with a weight on the end. The beauty of this is that the torque remains constant as the hour angle varies.
Geoff
Note added: should have read the earlier post describing this. However there are pics on the Losmandy site, so I'll leave this post as a pointer

[bojan]

Yes, in principle this is correct, but don't forget the resistance due to grease, and a friction in bearings..
This should be enough to prevent the effect you are talking about.

[troypiggo]

Maxim takes into account the flip for guiding, but what we're talking about is a mechanical need for the gears to be loaded as per Andrew's explanation.



That looks interesting. Might look into something like that.



Thanks for the suggestion. I might need to image longer than 3 minutes though.



It's not. Definitely need that slight east bias balance.

[White Rabbit]

You could rigg an arm coming off the counter weight shaft, and suspend a small weight from stand just next to the mount. You could arrange it so that when flip occurs the counter weight swings past and picks up or deposits the small weight. Needs a bit more fleshing out but would be relatively simple to work out with some experimentation.

[RobF]

Fascinating to hear the proposed engineering solutions. I've found the reality with my chinese mounts (particularly with the Newt on) is that balance after a flip and tracking quality also depends on the DEC you're point at. If I'm going to leave the rig running automated with a few flips possible I'll balance it neutral and accept the possibility of some tracking drift. Once you start doing automated runs over a few nights an unexpected benefit is you get so much data you can afford to throw out more problem frames and the mathematics of integration means you gradually throw out pixels due to poor tracking. Sort of a "brute force" mathematical approach to increase the probability of tightly imaging a given piece of object detail.

I've been mulling over these things a bit since Ivo gave his great talk at the AIC last year. For those of us unable to get into quality mounts at the moment, you can still do a lot to lean things in your favour if you understand the limitations of your rig and how to work with it. Automated runs for much more data definitely one way of doing it. Heck, I treat any data collected after I'm in bed as a bonus anyway ;) :D

[cfranks]

3 years ago, I modified my G11 exactly like the reference although the weight is on the other side. Southern Hemisphere and all that. It has worked perfectly before and after flips. Nearly gave me heart failure a couple of times, brushing past I bumped the G11 tripod leg with the weight. BONG!!! My weight is about 3 Kg so the wind has little or no effect. My scope, cameras etc are properly balanced on the mount and the weight just removes backlash.

Charles