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New PMC-8 problem


CYRIL BONNETT
 


My PMC-8  After only two short sessions the belt on the RA has started to slip.

can it be adjusted?




hubbell_jerry@...
 

Hi Cyril, I am sorry you are having this problem. I will try and talk you through a possible solution, but you may end up talking to customer service at Explore Scientific. In what way is the belt slipping? On the EXOS 2 PMC-Eight mount the belt is a toothed belt and pulley system between the motor and the worm. Is it just slipping off the edge of the larger pulley of the two? If you can upload a picture that would be most helpful.

Thanks

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


CYRIL BONNETT
 

Hi

Thanks, the belt started to slip on the RA after starting to slewing to an object near the horizon and then slewing back up to Polaris, it continued to slip a few times more so we halted to investigate.

The belt on the RA is much looser than that on the Dec. motor. We slewed it to another low  object and watched the RA belt ,when it changed direction it took up the slack in the belt and jumped a few teeth on the stepper motor cog. I have attached a couple of pics hoping that it shows how much slack is in the belt.

I checked the balancing of the scope  today just to make sure it’s okay and have now spoken to the supplier, Telescope House/Bresser UK and they have assured me that it is simple to tension the belt.

 

Cyril

From: ESPMC-Eight@... [mailto:ESPMC-Eight@...]
Sent: 08 January 2018 20:25
To: ESPMC-Eight@...
Subject: [ESPMC-Eight] Re: New PMC-8 problem

 

 

Hi Cyril, I am sorry you are having this problem. I will try and talk you through a possible solution, but you may end up talking to customer service at Explore Scientific. In what way is the belt slipping? On the EXOS 2 PMC-Eight mount the belt is a toothed belt and pulley system between the motor and the worm. Is it just slipping off the edge of the larger pulley of the two? If you can upload a picture that would be most helpful.

 

Thanks

 

Jerry Hubbell

Director Electrical Engineering

Explore Scientific, LLC.


hubbell_jerry@...
 

Hi Cyril,  okay it sounds like you have it figured out. That's good to hear. I am not sure why it was delivered with such a slack belt, the motor adjustment must be a little loose to where it is easy to move. It is very simple to adjust, and it probably is a good thing to understand so that you can adjust it in the future.

Thanks for the clarification.


CYRIL BONNETT
 

Hi Jerry

The reason the belt is slack is the steeper motor’s frame measures 19.6mm while it’s slide on the mount measures 21mm, 1.4mm is quite a bit of slack for the slide. Tightening the bolt (to the right) causes the stepper motor’s  frame to twist in the slide  slackening the belt.

 

Cyril

 

From: ESPMC-Eight@... [mailto:ESPMC-Eight@...]
Sent: 08 January 2018 22:44
To: ESPMC-Eight@...
Subject: RE: [ESPMC-Eight] Re: New PMC-8 problem

 

 

Hi Cyril,  okay it sounds like you have it figured out. That's good to hear. I am not sure why it was delivered with such a slack belt, the motor adjustment must be a little loose to where it is easy to move. It is very simple to adjust, and it probably is a good thing to understand so that you can adjust it in the future.

 

Thanks for the clarification.


CYRIL BONNETT
 

Sorted with some shim.

 

From: ESPMC-Eight@... [mailto:ESPMC-Eight@...]
Sent: 09 January 2018 22:03
To: ESPMC-Eight@...
Subject: RE: [ESPMC-Eight] Re: New PMC-8 problem

 

 

Hi Jerry

The reason the belt is slack is the steeper motor’s frame measures 19.6mm while it’s slide on the mount measures 21mm, 1.4mm is quite a bit of slack for the slide. Tightening the bolt (to the right) causes the stepper motor’s  frame to twist in the slide  slackening the belt.

 

Cyril

 

From: ESPMC-Eight@... [mailto:ESPMC-Eight@...]
Sent: 08 January 2018 22:44
To: ESPMC-Eight@...
Subject: RE: [ESPMC-Eight] Re: New PMC-8 problem

 

 

Hi Cyril,  okay it sounds like you have it figured out. That's good to hear. I am not sure why it was delivered with such a slack belt, the motor adjustment must be a little loose to where it is easy to move. It is very simple to adjust, and it probably is a good thing to understand so that you can adjust it in the future.

 

Thanks for the clarification.


r_hoskin@...
 

Cyril,

Do you have a photo of the fix?

- Bob


CYRIL BONNETT
 

Hi

The drive started to jump when slew from an object near to the horizon, we found that the belt on the RA was jumping a few cogs on the stepper motor, so we asked how to fix it.

This is the reply from Bresser UK and the attached pics.

 

Dear Cyril,

 

We’ve had the following guide to adjustment of the mount’s belt tension from the head of technical at Explore Scientific Europe.  Please see the attached photos and refer to the adjustment guide below:

 

“it´s very simple. Please see attached pictures and do as follows:

 

1. Remove the clip-in housing cover and the 4 housing screws with a Phillips screw driver.

2. Take off the upper motor housing.

3. Unloose the central motor screw with the delivered 3/16” hex key.

4. Move the complete motor outside to give some more tension to the belt-drive and re-tighten the motor screw.

5. Turn the motor shaft by hand and double-check the belt tension.

6. Put the housing parts together and install also the small housing cover.

 

Done.”

 

I had a problem though that when I tightened the motor screw the stepper motor housing frame would twist. I actually got it wrong in my first post so I decided to investigate and pulled it apart.

The motor drive screw goes through the mount and has a elongated hole, when tightening the motor screw into the S/M housing frame it wants to straighten up and so twists the housing/frame to the left with the bolt head coming up hard against the left side of the hole in the mount.

With the plastic covering on I could not get the belt tension right so I took the plastic covering off and managed to get the belt to tension okay. The metal to metal contact kept it in position.

I didn’t want to leave the plastic cover off so with a bit of thought!!! I decided to replace  the plastic cover and try some shim  between the S/M housing frame and the mount body at the cog end.

I think the real problem is that when you tighten the motor drive screw you compress the plastic housing, which is held on by 4 small dome headed socket screws to the stepper motor frame, until these bolt heads come into contact with the mount , you can see the marks on one side, which allows it then to slip.

You can just see the shims in front of the right hand screw in RA Drive shim.jpg

 

Bit long but hope you understand it.

Cyril

 

From: ESPMC-Eight@... [mailto:ESPMC-Eight@...]
Sent: 11 January 2018 13:27
To: ESPMC-Eight@...
Subject: RE: [ESPMC-Eight] Re: New PMC-8 problem

 

 

Cyril,

Do you have a photo of the fix?

- Bob


CYRIL BONNETT
 

Hi Bob

Further to my last reply, I took another look at it and decided to file a bit of the tops of the four small domed head socket screws that hold the bottom plastic casing on.

This solved the problem, the plastic now compresses enough for a metal to metal contact (stepper motor bracket to mount body) so the shims are not now needed.

 

Cyril

 

 

From: ESPMC-Eight@... [mailto:ESPMC-Eight@...]
Sent: 11 January 2018 13:27
To: ESPMC-Eight@...
Subject: RE: [ESPMC-Eight] Re: New PMC-8 problem

 

 

Cyril,

Do you have a photo of the fix?

- Bob


r_hoskin@...
 

Thanks, Cyril!

I haven't had this happen myself (still working on other matters), but good to see problem statement and solution packaged up together, if it does.

- Bob