G11 with gemini need help - Page 2

JohnG (John) · #21 19-02-2006, 11:39 AM

Ahhhh, my spelling went out the door.

JohnG

Striker (Tony) · #22 19-02-2006, 04:20 PM

I just played around with the gears.....I did adjust the Dec a little so maybe I have fixed the backlash but I didn't see too much wrong with the Ra axis...anyway I loosened them off and retightened everything...so I will wait till I test next clear night.

It's a simple but affective gearing method on the G11....I can see that being a much improved system over the conventional geared mounts.

Thanks for your help John...I will let you know how I go.

[1ponders] (Paul) · #23 19-02-2006, 04:27 PM

Tony after you retightend the gears were you still able to turn the worm gear by hand?

JohnG (John) · #24 19-02-2006, 04:44 PM

Tony

A couple of important things, did you do a complete rotation by hand as mentioned in Paul's post, it is critical that you do that so you know you have the worm adjusted correctly, you will feel the highs and lows when you do that. Were the Oldham Coupler grub screws loose?.

When you run the system, make sure you keep an eye on your motors, the Gemini servo's will heat up quickly if the worm is too tight, if they are getting warm to touch there are 2 possibilities, 1. the worm is too tight, you will get a Motor Stalled or Tracking Stopped messages on the Gemini HC, turn the unit off immediately or you will fry the motors. 2. Slow your slew speed down, I think the default is 1200, drop it down to 800 and see what happens. This is where the balance between gearmesh and backlash comes into play, you have to balance each out, it takes a little time and practice but it is worth it in the end.

JohnG

Striker (Tony) · #25 19-02-2006, 08:35 PM

No I didn't turn it by hand.....to do that I imagine you would have to pull the motors off and the holders.

I have already dropped the max slew speed down to 600....I dont need any quicker then that.....I usualy only work on 1 target a night so fast slew is not needed.

[1ponders] (Paul) · #26 19-02-2006, 08:39 PM

Probably a good idea to take the servo motors off and try turning it by hand. Without doing that you can't know whether you have meshed the gears tight enough or too tight. Nor can you find where the "tight" spots on the gears are. I'ts not a big job and can make a big difference.

JohnG (John) · #27 19-02-2006, 09:15 PM

Paul
Unfortunately taking the motors (servo's) off a Gemini equiped mount is a little more complicated than the standard digital drive, there are a number of small parts that are fragile and could quite easily break.

Tony
Whilst what I am going to suggest is not ideal it should give you an idea if the worm is binding or not. Turn the Gemini on (you can do this indoors or whenever), counterweight down, do a warm restart, disregard the aliagnment procedure, press the directional buttons and let the mount slew to it's east and west limits, you should hear a warning squeal when you are near the limits, run it back and forth a few times and listen to the servo pitch, if the worm is binding you will hear the servo start to labour and the tone change, do the same in DEC as well, you should be able to go nearly all the way round in DEC, in RA this is not ideal but it will cover 180 degrees of the main gear, you are limited there by the built in limiters. The best way of course is to remove the servo's, that is something you have got to decide.

JohnG

[1ponders] (Paul) · #28 19-02-2006, 09:38 PM

Whoops, sorry Tony

John, for the other 180 deg of the RA would it work if Tony were to do as you suggested for a few swings and finishing at the western extreme end of the RA movement (assuming he's pointing at the SCP), then loosen the RA clutch and push the scope in RA to the opposite end and redo the swings. Would that enable him to cover all the worm and gears?

JohnG (John) · #29 19-02-2006, 09:46 PM

Yes, it should, your not doing any sort of aliagnment anyway, you can do this indoors, the only thing is that Tony is going to have to do is a Cold Start, any aliagnment model that has been built will be lost, it would also be a good time to check the east and west limits as the default limits are quite conservative.

Good thinking

JohnG

[1ponders] (Paul) · #30 19-02-2006, 09:48 PM

Don't worry John. Tony has had plenty of practice of remodelling after cold starts, hey Tony

JohnG (John) · #31 19-02-2006, 09:55 PM

Same here, I do them in my sleep, fact of life with a Gemini.
At least I got my A and E numbers down to 2 and 0 now. I don't want to tear down the GM-8 but will have to soon for the G-11, ah well back to cold starts again.

JohnG

RAJAH235 · #32 19-02-2006, 10:36 PM

FWIW, speaking from a strictly mechanical pov, the so called "Oldham Coupler" is a 'self aligning universal joint'... ( in other words, it moves in both axes).
We used a similar coupling in our radio controlled IC power boats, between the motor & prop shaft. Bit more substantial of course.. HTH.

L.

JohnG (John) · #33 19-02-2006, 10:41 PM

There you go, I knew someone would describe it a bit better.
Thanks for that.

JohnG

Striker (Tony) · #34 20-02-2006, 12:29 PM

Thanks both John and Paul.....Yes I have no trouble cold starting...I have done it approx 20 times now.
I would rather get all this sorted out now and then I would have to do the cold start and remodeling anyway....that does not take long

The idea is to have everything set up and working properly then do all your modelling.....sounds logical.

I will do what you said and slew over 180 degrees then loosen the clutch and cover the other 180degrees..that sounds simple....

I have a fealing that the Dec axis which I tightened may be a bit tight as it has a higher pitch to that of the RA axis....will test and adjust today.

Thanks guys.

JohnG (John) · #35 20-02-2006, 05:40 PM

Hey Tony

Don't forget to let us know how it went, might take a couple of goes but it will be worth it.

JohnG

Striker (Tony) · #36 21-02-2006, 03:14 PM

John.

I did take the motors out and adjusting so I could easily turn the worm by hand with no obvious sticky points on both axis's.

Had an opertunity early last night before the showers come over just to test the mount after the adjustment.

I am pleased to say that I now do not have any backlash what so ever on either axis.....but I still have reasonably bad Pec on the RA axis...not as bad but still considerable....I gave the mount a good going slewing at high speeds with no motor lock ups and had no motor over heating issues..all looks good except for the pec......is it possible the small worm has a ever so slight bend in it.

JohnG (John) · #37 21-02-2006, 03:37 PM

Hi Tony

OK, if you can turn the worm easily with your hand it is still probably not in tight enough, I don't know if you have tried this but get a set of feeler gauges and try the spacing the right hand worm block with various thickness gauges, you have to place the feeler gauge between the right hand block and the mount itself, most opinions I have read suggest you leave the left hand block in place and use your fingers to hold the right hand block in against the worm and mount face, have a look at that diagram I posted. Another way mentioned on the Losmandy Group is to use a small G cramp to hold the block. It is a matter of adjusting, correcting, you should be able to feel the highs and lows of the main gear, I doubt very much that the worm itself is bent, you should have the new high precission worm anyway. Unfortunately itis trial and error, you have to get balance right between backlash and gearmesh, once you do that your PEC should improve dramatically.
Something I use to turn the worm is a bit of 1/2 inch dowell with a groove cut in the end, makes it a whole lot easier on the fingers. Not such a hard thing to dismantle is it.

JohnG

Striker (Tony) · #38 21-02-2006, 04:47 PM

I will keep playing with it....keep you posted.

Atleast I only need to play with the RA now as the Dec looks good with no backlash.

JohnG (John) · #39 21-02-2006, 04:54 PM

Bout the only other thing I can think of, and I asume that you are doing this anyway, is to have the mount weighted so it is pushing against the worm ie slightly unbalanced.

JohnG

[1ponders] (Paul) · #40 21-02-2006, 05:27 PM

Tony is there much endplay in the worm? Is there much movement left a right of the worm gear in the block?

Also could it just be a bad spot on the gear? Have you tried guiding on different sections of the gear (not the worm but the main gear itself)

Btw Tony what do you mean by "reasonably bad pec" How do you measure it?