GOTO AZ motor slipping?

[Kon]

During my imaging last night, the AZ motor of my 12" Syncan GOTO stopped tracking; I could hear the motor working but not tracking and I could use the hand controller to move the telescope so the motor is operating ok. Is it just slipping? The clutch was tighten and I had no issues until last night with it.  I opened the housing but I am lost beyond that. The brass rode is rotating with the controller. I can see another black disk under the whole system.  I found some info online that I could tighten the nut at the top. Before I do anything silly, are there any suggestions?

[michael8554]

The "brass rod" is the worm, meshing with the shiny wormwheel.

If the mount slews in Az with the hand controller, then the clutch and motor must be working - right ?

Is it tracking in Az as setup in the image ?

Put a finger mark in the grease on the wormwheel adjacent to the worm, and check that the wormwheel has moved after 10 minutes.

Michael

[Kon]

4 minutes ago, michael8554 said:

If the mount slews in Az with the hand controller, then the clutch and motor must be working - right ?

Yes correct, the motors seem to be fine.

4 minutes ago, michael8554 said:

s it tracking in Az as setup in the image ?

Put a finger mark in the grease on the wormwheel adjacent to the worm, and check that the wormwheel has moved after 10 minutes.

I just opened the housing and yes I did do this test last night but no movement. I can hear the motor trying to track, there is some noise (when it was tracking ok it was quietter, more like a humming noise). It is more of rougher sound now; not loud, i need to be close to the base to hear it..

[michael8554]

1.  "Yes correct, the motors seem to be fine."

You don't agree the clutch is okay ?

2.  "I can hear the motor trying to track"

Perhaps the motor has enough oomph to start a high-speed slew.

But not enough to overcome the friction of the system, bearings etc,  when tracking.

Are you able to remove the motor and worm assembly, and check the worm runs quietly without a load ?

And that the wormwheel rotates freely without binding or much resistance ?

What power supply ?

Michael

 

 

[Kon]

1 minute ago, michael8554 said:

1.  "Yes correct, the motors seem to be fine."

You don't agree the clutch is okay ?

2.  "I can hear the motor trying to track"

Perhaps the motor has enough oomph to start a high-speed slew.

But not enough to overcome the friction of the system, bearings etc,  when tracking.

Are you able to remove the motor and worm assembly, and check the worm runs quietly without a load ?

And that the wormwheel rotates freely without binding or much resistance ?

What power supply ?

Michael

 

 

Yes clutch too, sorry.

I am powering from the mains. It's a bit odd as it was tracking ok and I stopped to have a break and when i went back it wouldn't. I could try undo the nut and take the wormwheel off and see if the motor still makes the noise.

[michael8554]

"I am powering from the mains."

But how ?

The spec is "11 to 15V @ 2amp."

Users are recommending 13.8V @ 5Amp.

And it needs to be a Regulated power supply.

Michael

 

[Kon]

6 minutes ago, michael8554 said:

"I am powering from the mains."

But how ?

The spec is "11 to 15V @ 2amp."

Users are recommending 13.8V @ 5Amp.

And it needs to be a Regulated power supply.

Michael

 

I bought it second hand, and it came with a mains adaptor (12V 0.9A), I assumed from Skywatcher (from manual: 10 to 15 V DC 1Amp), plugged to the mains. But why tracking ok for the past couple of months if it was a power issue?

[Carbon Brush]

Going back to the original report, the worm is turning, which suggests clutch slip.
Driving at high speed might overcome some of the slip.

A good test is to remove the scope tube and just leave a flag (bit of paper) on the mount and see if it tracks.
If all is well on light load, you have a slipping clutch.

Skywatcher clutches are not the best in the world.
If the clutch is slipping, tighten the nut by a small amount. Say 1/10 turn and see what happens.

I would also get rid of the small (uknown origin) plug top PSU.
Put a decent supply (like a Nevada) on there and you know you have a good supply.
Explaining why an unknown and under-rated PSU is risking problems requires more than a one line answer🙂

HTH, David.

[Kon]

11 minutes ago, Carbon Brush said:

Going back to the original report, the worm is turning, which suggests clutch slip.
Driving at high speed might overcome some of the slip.

A good test is to remove the scope tube and just leave a flag (bit of paper) on the mount and see if it tracks.
If all is well on light load, you have a slipping clutch.

Skywatcher clutches are not the best in the world.
If the clutch is slipping, tighten the nut by a small amount. Say 1/10 turn and see what happens.

I would also get rid of the small (uknown origin) plug top PSU.
Put a decent supply (like a Nevada) on there and you know you have a good supply.
Explaining why an unknown and under-rated PSU is risking problems requires more than a one line answer🙂

HTH, David.

Thansk for the suggestions. Michael suggested similar thing, but without the tube I do not see any tracking either, unless the nut is undone more than i thought so it is completely slipping.

I will definitely look into getting a a new power supply.

[Clarkey]

If the Dobs are anything like the 'normal' skywatcher mounts then the meshing between the drive wheel and the worm could be a touch tight. This is then causing the motor to stall - hence the rough sounds. On the standard mounts the worm can be adjusted in and out (mainly to allow for poor manufacturing tolerances). I'm not sure if this is possible on the Dob? Is the whole motor /gear/worm assembly moveable?

[Kon]

10 minutes ago, Clarkey said:

If the Dobs are anything like the 'normal' skywatcher mounts then the meshing between the drive wheel and the worm could be a touch tight. This is then causing the motor to stall - hence the rough sounds. On the standard mounts the worm can be adjusted in and out (mainly to allow for poor manufacturing tolerances). I'm not sure if this is possible on the Dob? Is the whole motor /gear/worm assembly moveable?

Hard to tell if it is movable but I see a black screw at 6 oclcok in my photo that is adjusted to a sping, I wonder if that has to do with tolerance? It will be some investigating job tonight.

[Clarkey]

Found this online for a 14" Orion. Does not solve your problem as such, but it does show the whole assembly being dismantled. The motor appears to be spring loaded.

 

[Kon]

7 minutes ago, Clarkey said:

Found this online for a 14" Orion. Does not solve your problem as such, but it does show the whole assembly being dismantled. The motor appears to be spring loaded.

 

Perfect, thanks. I was looking for something like this. It gives me confidence to properly open it up now and see what is going on.

[Kon]

1. I opened up the azimuth motor compartment and check everything for slipping. I could see wormwheel running fine It didn't solve the problems.

2. I opened the gear box, all ok. It didn't solve the problem.

3. The motor itself seems to function ok but could it be something to do with the encoder? I can see the wormwheel running but the large disc or platform is not turning. It can turn with the hand controller. So if it is not slipping is it likely the stepper does not provide enough torque? Ie is it gone?

Thoughts on a replacement for it, assuming it's the culprit?

Edited April 19 by Kon

[Peter Drew]

If the brass worm is turning then the wormwheel must also be turning which points to clutch slip as already diagnosed.      🙂

[Kon]

6 minutes ago, Peter Drew said:

If the brass worm is turning then the wormwheel must also be turning which points to clutch slip as already diagnosed.      🙂

I opened up last night and it all looks ok. One thing I noticed is that there was a lot of grease on the small  spacers just under the big nut. Would that be causing it? Do they need the grease?

So why at high speed with the controller is it ok to turn?

Edited April 19 by Kon

[bosun21]

Have you tried moving it with the HC at the various speeds? Perhaps slippage could occur at slow rates 1-3.

[Peter Drew]

It probably needs at least some grease as the clutch has to be able to slip in the event of something impeding the rotation.  The "trick" is to adjust the slippage torque to avoid slippage in normal use but also to avoid locking up.  Try tightening the nut a small amount.     🙂    

[Geoff Lister]

Some years ago, with my 250PX, I had problems with slewing and tracking in the Az axis. It turned out to be one of the encoder ribbon cable connectors adrift from its position on the control board's pins. The ribbon cable layout may have been defined before the ferrite rings had been added (probably to pass regulatory EMC tests) and there was little slack in the cables. It was difficult to spot the poor connection, as it was under the control board. The problems went away once I had re-seated the plug, and has been fine since.

The clutch friction is a compromise between (1) good motor drive, and (2) manual operation without using the handset.

Geoff

 

[Kon]

1 hour ago, bosun21 said:

Have you tried moving it with the HC at the various speeds? Perhaps slippage could occur at slow rates 1-3.

2+3 seem to work.

[Kon]

2 hours ago, Peter Drew said:

It probably needs at least some grease as the clutch has to be able to slip in the event of something impeding the rotation.  The "trick" is to adjust the slippage torque to avoid slippage in normal use but also to avoid locking up.  Try tightening the nut a small amount.     🙂    

Thanks. It seems that I have lost torque to turn the wormwheel and brass when 'tracking' although at higher speed it works; this is with no clutch and large wheel?. Hmmm

 

After shutting down and restarting it turns with and without the wheel?? Most peculiar 

Edited April 19 by Kon

[Kon]

48 minutes ago, Geoff Lister said:

Some years ago, with my 250PX, I had problems with slewing and tracking in the Az axis. It turned out to be one of the encoder ribbon cable connectors adrift from its position on the control board's pins. The ribbon cable layout may have been defined before the ferrite rings had been added (probably to pass regulatory EMC tests) and there was little slack in the cables. It was difficult to spot the poor connection, as it was under the control board. The problems went away once I had re-seated the plug, and has been fine since.

The clutch friction is a compromise between (1) good motor drive, and (2) manual operation without using the handset.

Geoff

 

In these photos, what I am looking for?

[Jim L]

How is the balance of the scope? The clutch can only lift so much, and heavy eyepieces, etc., might be too much for it to handle. If that’s the case, a counterweight on the lower half of the scope might be the solution.

[Kon]

21 minutes ago, Jim L said:

How is the balance of the scope? The clutch can only lift so much, and heavy eyepieces, etc., might be too much for it to handle. If that’s the case, a counterweight on the lower half of the scope might be the solution.

Balance is ok. I had no issues tracking for the past 3 months I had it and it just stop tracking at the azimuth.

[Geoff Lister]

7 hours ago, Kon said:

In these photos, what I am looking for?

It's probably almost a decade ago, so my memory is a bit vague. The 4-way white ribbon cable shows how it is looped through the ferrite ring, although it seems to be long enough. It is possible that mine is of a slightly earlier design, without the plastic surround to the board half of the connector - in my case, if I remember correctly, just a row of pins sticking up from the board. I think the position/speed control loop uses the motor position encoder (this was the one with the poor connection), and the axis encoder registers the "real" position of the OTA. The mount has no idea of position, it just counts clockwise or anticlockwise pulses from the motor assemby. The handset starts at zero (Az = north, Alt = OTA horizontal) from power-up and counts the pulses to calculate position; the rest, including alignment with the stars, is done in handset software. I believe that my symptoms were most severe at the lower slew rates, and made it almost impossible to do a 2-star initial alignment.

I had problems with a slipping Alt axis, but I tightened the Nylock nut in the centre of the OTA attachment casting, and added a bit of weight at the primary mirror end of the main tube.

Geoff