Priority 1 question. GM8 and G11 digital drive question

[[1ponders]]

I need to replace a Gemini tonight or tomorrow afternoon at the latest, on a G11. I was going to use my G11 Digital drive in the interim. Unfortunately it doesn't want to power up :mad2: There is a problem with the power socket. My GM8 Digital drive though is working fine. I know the GM8 digital drive rate is different to the G11 , but is there a quick flick switch I can use that will convert the 8 rate to the 11 drive rate?

[JohnG]

Paul

Did you replace the Servo Motors with the original Steppers.....

As far as I know, there is no switch in the Digital Cotrol Box, it is either a GM-8 or G-11, they are unique to each mount.

Cheers

[[1ponders]]

I was going to replace the servos John, but if i can't get the G11 DD going I'm up the creek atm. :(

I thought they might have been unique to each, but I had to check. Looks like I'll be looking for a quick turnaround fix tomorrow from a local electronics tech to get the G11 DD going again.

Thanks John.

[gbeal]

Somewhere in the dark dim brain cells I recall a chip difference inside, as the gears are a different size??
Standby I'll find out from Robbery Beck, he is the Losmandy legend.
I'll be back mate

[JohnG]

I have a gut feeling that there is a little fuse inside the cover of the control box, may pay you to check that or the power lead, unusual that the control box won't power up.

[Robby]

Hey Ponders,
Unfortunately there is no magic switch. To get a GM8 controller to work on a G11 or vice versa you have to change the internal crystal.
The G11 crystal is twice the speed of the GM8.

The other solution would be to use the GM8 controller on your G11 and ask population of China to all push at once against the Great Wall, thus slowing the rotation of the Earth to approximately half it's current rate, and thus allowing you to image for the "now extended" night. Once morning arrives, get the same Chinese to push on the other side of the Great Wall.. Easy :D

As to the power problem. I have found in the past that the power connectors on the DDB's are a bit dodgy. Might be worth pulling of the cover and checking the soldering joints on them.

Cheers for now.

[Apocrisiary]

Paul I know there is a jumper setting to change the direction of the drive for N vs S hemisphere.
Not sure if there is a similar jumpser setting for G11 vs GM8. The period of the worm on the GM8 is 8 minutes and for the G11 is 4 minutes.
I asked Scott and might get an answer by tomorrow morning at earliest.

[[1ponders]]

The power has been a bit d1ckie for a while John. There is a bent pin on the side of the socket, but I've always been able to get it to power up before. I haven't used it for months thanks to the weather. I'll have a look for the fuse.

There is a difference in the chip Gary. Everything looks the same inside each box except one ICs (? Luddite at work here) has an '8' written on it and in the other box it has an '11'. I don't know if those chips can be swapped over or not.

[[1ponders]]

cant find any fuse.

bugger thanks Robby. Hey are you still thinking of coming over for AF?

You know me and electronics Robby. :lol: I'll take it to work and get the pros to have a look at it tomorrow. I'm fairly sure its only a socket problem cos once it's going its np.

That's what I was looking for Apocrisiary, no such joy unfortunately

[[1ponders]]

While where at it, I'm doing this cos the gemini on another g11 isn't working properly. I keep getting RA motor stalls and the message RA lags. That's when the Gemini will actually power up. The LED comes on but the characteristic Beep doesn't sound and the handpaddle doesn't light up. I brought this up in another thread a while ago but even after sending it away still no joy. Could it be a power cable problem? I've tested the cable and it's putting through 16.22 V (using a variable V regulated powersource) but I don't know what is happening when under load.

[Apocrisiary]

I'm not sure Paul....you know how long I tried to get it to stall in the shop here.
Cheers,
Michael
BINTEL;)

[[1ponders]]

:lol: Thanks Michael. :lol:

The reason I'm asking Michael is the only thing I didn't send down was the power cable. And as soon as we put it all back together, we got a few good slews in, did a dozen or so stars to redo our model and she stalled. Since then if we turn it off it won't start back up again. The led comes on and that is all. If we turn it off for half an hour or so then with fingers crossed it starts up, but immediately shows a motor stall as soon as I try to slew to something.

[Robby]

Dam G11 controllers and motor stalls! It a common problem. my guess is that the design is a bit marginal and the driver chips are slightly overloaded, and over time this causes an increase in the drive impedance.
But then it could be a power cable that is too long, or not fat enough. Measuring the voltage is only useful if you can measure it at the controller when the motors are stalling. It might be drouping.
Not much the chinese can do about that I'm afraid :) Although they could probably make a better and cheaper DDB.....

Still thinking about AF. I would be quite keen, so better start saving now, and you guys better keep your swine flu in check...

Cheers

[[1ponders]]

Would be good if you could come over. If you want to keep the swine flu at bay just use oinkment. :P

We've had problems in the past with the mount stalling when the slew rate was too high. It was running on 13.8 V at the time. I bought a variable 5 amp power source and started running it at 15V which seemed to fix it for a while. Then it really started to stall badly and nothing I try seems to work. It only stalls in RA and not Dec. I've swapped motors, cables done everything I could think of, even running with the worms loosened right off and the damn thing still stalls.,

[netwolf]

Paul, pm sent. Give me a bell and i will express it. But mine when last i tested stalls at 16x. I sold the other spare one i had that worked fine.

[Bassnut]

I was plauged by stall probs on a G11 for a while, I bet its a balance problem or the worm gear is jamed too close to the RA gear?. Can you you easily rotate the RA worm manually?.

[JohnG]

Re the motor lag and motor stalls, I can't remember if we spoke about this before, have you checked the worm adjustment, sounds like it could be a little tight, backlash should be about 1-2 mm at the end of the counterweight shaft.

Cheers

[[1ponders]]

Hi Fred and John.

I've checked and rechecked the balance, I've had plenty of practice with my own G11 and GM8 so I'm confident there. Definitely not a worm binding as the motor stalls even when the worm is completely loosened off. But we also now have the issue of the Gemini not even booting up, which to me is saying I've got some sort of power issue.

[Bassnut]

I think Gemini senses a stall/lag by no/slow responses from the motor encoder rather than over current, so if you can, check the encoder coupling and wiring. You say you swapped motors, but did you try swapping the motor cable too?.

[JohnG]

The only other thing I can think of is that one of the two red power leads in the power cable might be faulty, bad solder or possibly broken within the power lead itself, the only way to check that would be to put a multi meter on it.

[[1ponders]]

Fred, I'm not sure how to go about that, but as for the cables, yes I've swapped cables, I've swapped motors and still the same issue, RA stalls. If I use either motor on the DEC, np

I've thought about that John, I've checked the solder and it looks ok. I put a multi meter on the cable tonight and it checked out simply carrying the voltage, but it wasn't under load. I'm a fair Luddite when it comes to electronics so I'm not sure how to go about that.

[Bassnut]

Well, swaping the motors also swaps the encoders, so sounds like your screwed. PM Peter Ward, see what he thinks.