Rowan Belt Mod HEQ5 help

[Simon Pepper]

Hi all

i have modded my HEQ5 and for couple weeks worked a great then I noticed a knocking sound so stripped it down checked everything looked good job sorted fixed again. Couple weeks later same again any ideas what could be causing this? It’s like instead of a nice smooth rotation it’s more of like a jump knock rotation. I have tried different tensions on the belt. I think it’s something to do with the part that connects to the motor when it runs the belt gets tighter when I turn it off and pressure the belt it turns the motor back and the belt gets looser I can’t figure it out. Has anyone else seen heard or had this? Please photos and video put the sound up. Thanks 

[Simon Pepper]

Apologies for the heavy breathing just ran up the stairs 😂

An update if I take the belt off I don’t have this issue so something to do with the belt??? 

Edited August 18, 2022 by Simon Pepper

[Swoop1]

Not fitted a belt mod yet myself but, could either of the pulleys be slipping on their shafts or is the tensioner sticking?

[teoria_del_big_bang]

At the moment i do not know what is causing this.
I do not fully understand your explanation (give me time 🙂 ) but if the belt is getting tighter then slacker as the motor rotates it almost sounds like either the motor shaft or one of the spindles of the big gear or tensioner is bent (but lets hope not).

To help can you take a picture mote straight on to the gears, from the above image it looks like the belts teeth come very close to the teeth at the other side where I have ringed in red.

If these teeth ever touch each other then it would cause a knocking sound.

Also can you make a short video of these gears and belt when the mount is slewing at high speed, that would help to see them moving at speed.

EDIT: Sorry only just noticed the video you attached to OP. That is quite a loud almost ticking noise but still not sure what is the cause.
I would still like the image and a video of a fast slew if you can do so safely.

Steve

Edited August 18, 2022 by teoria_del_big_bang

[Knighty2112]

Not done the mod (but plan to do so pretty soon), but is the belt tension correctly set? In the instructions it looks like the motor housing is positioned more to the right than your seems to be? Should only be 2mm movement on belt. If too slack then the belt can slip out of the teethed pulleys.

 

[Simon Pepper]

On full speed slew there is no issue runs fine I can’t do that and video at the same time as I am using the phone to slew it. I am charging another phone so I can do this soon. The belt tension is good but when it starts to track it gets tighter if I turn off tracking and press the belt there is less flex then if I press harder it makes that same clunk noise and goes back to looser the correct tension it’s like it’s riding up on a tooth but I have checked the whole belt it’s not that I can see had the magnifying glass out as well! As soon as the belt is removed it’s tracking fine. The teeth are not touching at the bottom. More to follow when other phone charged thanks 

[Knighty2112]

Is the issue only seen on the RA motor side? If so maybe get a replacement belt just in case the belt you fitted has either stretched somewhat, or was faulty in some way. 

[Simon Pepper]

It’s just the RA but the DEC doesn’t track… if the belts are the same size I could try swapping them…

[teoria_del_big_bang]

Did you buy the mount new, or 2nd hand ?
I only ask because what you are describing makes it sound like the problem is in the mount not the modification.
This is only my thoughts (although I was an engineer for over 40 years and still am but semi retired now) but the motor is a stepper motor and so does not actually run smoothly but goes in very small steps, and you can hear this on any HEQ5 at night when very quiet there is a very feint ticking noise (nothing like your video).
But it looks like when the motor steps the large gear attached to the mechanism of the mount does not move (to begin with) but tension builds up in the belt (as you describe) then when the motor has done a few steps the tension gets enough to move the bigger gear which goes in one big movement and then causes the audible noise you hear.
Another reason I suspect this is that there is a large reduction ratio between the stepper motor and mount mechanism so one revolution of the large gear nees many revolutions of the motor so in a good mount the movement of the large gear when moving very slowly looks almost smooth and very slow but the video shows it moving in steps and quite big steps, certainly not one step of the motor.

Remove the belt and see how smooth you can turn the big gear, you may even feel that is notchy in its movement but it should be very smooth.

Steve 

Edited August 18, 2022 by teoria_del_big_bang

[Simon Pepper]

1 hour ago, Knighty2112 said:

Not done the mod (but plan to do so pretty soon), but is the belt tension correctly set? In the instructions it looks like the motor housing is positioned more to the right than your seems to be? Should only be 2mm movement on belt. If too slack then the belt can slip out of the teethed pulleys.

 

Hi knighty that one is the DEC mine is the RA issue not the one he is pointing at 

[teoria_del_big_bang]

8 minutes ago, Simon Pepper said:

It’s just the RA but the DEC doesn’t track… if the belts are the same size I could try swapping them…

I guess its a quick way to prove its not the belt or gears as both axes use the same parts so you could swap everything from one axis to the other but from all you have said so far I really do think it is in the mount. Maybe just a bit stiff and with the original gear mechanism where there is no way to build tension up like you can in the belt you could not hear any noise with the gears.
What was the tracking like before the modification did you think it was not particularly good in the PHD2 data ?

Steve

[Simon Pepper]

Hi Both

mount was brand new in 2020 so about 2.5 years old. Tracking was about 1.2 I had bad backlash I sorted that and immediately installed the mod got down to 0.4 then the ticking started lol. It was fine before the mod other than backlash and struggled to get under 1. I will go swap out the belts give me 5 mins to revert. Thanks 

[Simon Pepper]

Hold on!!!! The DEC big cog turns effortlessly the RA one requires force! 

[Simon Pepper]

So the red one is smooth easy to turn the blue one is tight I have to put a lot of effort in 

Edited August 18, 2022 by Simon Pepper

[malc-c]

Watching the video it doesn't seem to be the teeth on the belt interfering with itself as the amount the motor and axis pully moves is less than the distance between two teeth.  To me it sounds as if the stepper motor is cogging.  You've stated you have remove dthe belt and the knocking sound goes away, which could suggest it's a belt issue.  Have you confirmed that the RA axis is free enough and not binding.  Watching the video it seems as if the larger pulley is moving, but then cogs back, without showing signs of slipping, so it could be binding thats the issue

Ok seems you're already on that when our posts crossed

Edited August 18, 2022 by malc-c
crossed post

[teoria_del_big_bang]

5 minutes ago, Simon Pepper said:

Hold on!!!! The DEC big cog turns effortlessly the RA one requires force! 

That was my suspicion.
Why it should be like that on an almost new mount is very odd, I guess remove the big gear and see if there was anything binding after adding the new gear.
After that it is a bit of delving inside the mount to see why it is so tight.
I have a modded HEQ5 stored away now, not used for a long while, but can get it out to check anything if you need it. I cannot remember if Ra id as free to turn as DEC but I wouldn't think too much different , certainly shouldn't require a lot of force to move it.

Steve

[Knighty2112]

27 minutes ago, Simon Pepper said:

Hi knighty that one is the DEC mine is the RA issue not the one he is pointing at 

Yeah, realised that after I posted it. 

[Simon Pepper]

Ok the only thing I can think is that when I removed the backlash I went too far and it’s binding? I have never taken that apart before so no idea why it’s so tight. If it’s possible to burn out the RA motor well I will be surprised if I have not after all this time. Incredible I was getting 0.4 tbh! I will come back once I have opened it up. Thanks 

[Clarkey]

My HEQ5 was similar. It turned out I had marginally over-tightened the worm drive end float bearings. This sounds similar. I have actually just changed all the bearing on my HEQ5 and it is a similar age to yours. To be honest only the worm drive bearings needed changing, but as I was dismantling everything I decided to do them all.

[Clarkey]

Just now, Simon Pepper said:

backlash I went too far and it’s binding

Yes. That is what I did.

 

[teoria_del_big_bang]

1 minute ago, Simon Pepper said:

Ok the only thing I can think is that when I removed the backlash I went too far and it’s binding? I have never taken that apart before so no idea why it’s so tight. If it’s possible to burn out the RA motor well I will be surprised if I have not after all this time. Incredible I was getting 0.4 tbh! I will come back once I have opened it up. Thanks 

I doubt you have damaged the motor if it is still moving.
Removing the backlash is tricky. Because in essence these are not high end mounts costing tens of thousands (but very good mounts for the price) some of the machining of the parts does leave a bit to be desired and I would think all of these mounts suffer a little around the worm gear and matching gear and you usually cannot remove all backlash because they will get tighter and slacker during one revolution of the big gear driven by the worm. So you can remove backlash at its tightest point but there will be some backlash at the slacker part. Otherwise removing all backlash at the slacker position will mean it will bing at the tighter point (If any of that makes any sense).
I also suspect that some mounts will be machined better than others and it is just pot luck how good the one you buy is, mine was like this with slack and tight spots.

Steve

[teoria_del_big_bang]

10 minutes ago, Clarkey said:

My HEQ5 was similar. It turned out I had marginally over-tightened the worm drive end float bearings. This sounds similar. I have actually just changed all the bearing on my HEQ5 and it is a similar age to yours. To be honest only the worm drive bearings needed changing, but as I was dismantling everything I decided to do them all.

I did exactly the same, I bought all the bearings before doing any stripping down and when I did only the worm bearings needed replacing but as I has already bought them replaced some otherwise perfgood bearings 🙂 

Steve

[Simon Pepper]

35 minutes ago, Clarkey said:

My HEQ5 was similar. It turned out I had marginally over-tightened the worm drive end float bearings. This sounds similar. I have actually just changed all the bearing on my HEQ5 and it is a similar age to yours. To be honest only the worm drive bearings needed changing, but as I was dismantling everything I decided to do them all.

So just to confirm this is the two little hex adjustments when the RA is rotated one under the power box? Just need to ease back a little? Thanks 

[Pitch Black Skies]

43 minutes ago, Simon Pepper said:

So just to confirm this is the two little hex adjustments when the RA is rotated one under the power box? Just need to ease back a little? Thanks 

This is a useful follow along.

[Varavall]

7 minutes ago, Pitch Black Skies said:

This is a useful follow along.

It is useful as far as it goes in locating the screws and adjusting the backlash. However, when the mount is loaded there is some flexure/torsion/compression within the mount, therefore binding can occur. If a small telescope is being mounted, then probably not a problem. From experience mounting a SW 200pds with guidescope, cameras, etc then beware, binding is likely, so personally I would check the backlash once the setup is complete. In my case the RA did bind, so a quick adjustment was required.