More EQ3-2 DEC axis fettling

[JamesF]

I've never been happy with the backlash in the DEC axis on my EQ3-2, but I've never really been able to work out how to measure what was going on so that I could do anything about improving it. Until today, that is...

I have no idea why this has never occurred to me before, but it struck me today that I could fix my collimation laser to the saddle of the mount (black insulting tape worked fine for me) and use the movement of the red dot on a wall to measure the motion. In fact, I set the mount up on my workbench and aimed the laser at an inspection mirror I fixed to the wall opposite so the red dot ended up on the wall next to me, the light having travelled forty feet or thereabouts and having the advantage that the apparent movement would be doubled, making it easier to see.

I've already tweaked the end float and mesh of the DEC axis as well as I could by hand, so I disconnected the DEC motor, fitted a slow-mo control and turned the spindle back and forth. There's a bit of give in the length of the slow-mo control, but as far as I could see the red dot started moving as soon as I could feel that the worm started to move, even when changing direction. No reason to be displeased so far.

I then reconnected the motor, plugged it all in and repeated the process with the motor. Even at the 8x speed setting I found that when changing direction it took around twelve seconds for the saddle to actually start moving. I'm therefore led to believe that what backlash I now have is pretty much all in the motor gearbox which I know wasn't great, but never realised was quite that bad.

I'm now very tempted to measure the gearbox reduction ratio (though I'm not entirely sure how yet -- probably with a couple of pointers on the input and output shafts to allow me to count turns) and then remove the gearbox entirely, fitting a belt drive and gears with a similar reduction ratio (assuming it's possible to get close with just a pair of gears).

James

[Steve Ward]

The Dec side of my 3-2 is much the same I find , the RA is fine though , I've never bothered tampering with it as I only use it for my Solar shots and the occasional widefield shot.

For anything else I use the HEQ5Pro.

Horses for courses ?

Steve.

[JamesF]

Well, I'd like to have it work better than it does. I realise that if I got the polar alignment right then generally DEC axis motion shouldn't be an issue anyhow, but until I get my obsy set up I am somewhat at the mercy of small children running around and wives who think patios aren't for drilling holes in, so I often need a bit of tweaking for solar images just to keep the image on the sensor (my camera sensor is 2848 pixels high and the way I'm working at the moment the Sun is about 2700 in diameter, so there's not a lot of room for movement). It would be nice to use it as a guided wide-field imaging platform, too. There's no fundamental reason that shouldn't be possible as long as the mount can be relied upon to behave well.

James

[Steve Ward]

If you get things aligned so the drift is up or down in the frame and you've little room for error . . just rotate your camera 90 degrees so any drift is left/right , gives you much more time between tweaking in the dodgy Dec side and a lot less mess than stripping a mount . . . .

Works for me when I'm away from my reference marks on the patio , you can just rotate the frame orientation later in processing.

Steve.