Belted HEQ5Pro - RA axis no longer rotates!

[vineyard]

Hello,

A lovely two nights (last night was particularly fine).  Sadly around midnight, when I was switching targets - going from the Rosette to Tadpole - it became clear that while EKOS/INDI thought the mount was slewing somewhere, the actual mount was not doing that physically.

I shut down for the night & reconfirmed the problem this morning.  Basically the RA axis (ie the one around which the scope and the counterweight rotate - want to make sure I'm not making a silly error in labelling!) doesn't rotate.

If I set the mount to go somewhere, the DEC axis rotates, the mount makes noises for the rotation of the RA axis (I can hear something moving inside it - it sounds almost like a flapping belt?) but the counterweights stay firmly pointing down.  I'm guessing something snapped or wore down?

On the guiding side as well, the RA was much more volatile than the DEC last couple of nights.  So this failure of something on the RA rotation would be consistent with that.

I'm going to open it up to have a look, but thought I would check if anyone had ever experienced anything like this before, and/or if they were any good resources to look at first?  I know of the astro-baby one for a non-belted version.  Is there something for belted HEQ5Pros, or is it not that dissimilar, or would I be doing something v silly by opening it up myself (I'm working on the basis that if the belted mod can be done retroactively at home, then checking it also ought to be possible)?

Worst-case, if it all goes pear-shaped, any recommendations for folks who can fix it (or folks to avoid pls!)?

Thank you - luckily managed to get some nice footage of Rosette & already have lots of data on Tadpole so not too big a loss - especially if this leads to an even better performing HEQ5Pro!

Cheers,

Vin

 

[Budgie1]

It doesn't take any knowledge to remove the side panel and have a look.

It sounds like the RA belt is either too loose or has snapped. If you need a new belt then FLO have them listed HERE, although they are currently out of stock.

This video is for fitting the Rowan Belt modification but shows how to check the correct tension on the belts. Also, make sure the belt and gears are correctly aligned and the gears are secure on the motor & worm gear shafts.

Top Tip: When refitting the side cover, don't tighten the screws too much because you can crack the cover.

 

Edited January 6, 2022 by Budgie1

[AstroKeith]

That 'still' from the start/title frame of the video above shows just how small the drive pulleys are on those belts. They are way smaller than I would have used as a designer but I guess they wanted to get as much reduction ratio as possible.

The upshot is a very tight radius around the pulley with about 4 teeth fully engaged? This means those thin transparent belts too, without any or much reinforcement (ie Kelvar or glass fibre). That is not good for belt wear.

[1parsec]

15 hours ago, AstroKeith said:

That 'still' from the start/title frame of the video above shows just how small the drive pulleys are on those belts. They are way smaller than I would have used as a designer but I guess they wanted to get as much reduction ratio as possible.

The upshot is a very tight radius around the pulley with about 4 teeth fully engaged? This means those thin transparent belts too, without any or much reinforcement (ie Kelvar or glass fibre). That is not good for belt wear.

The belts & pulleys replace factory fitted gears. Therefore the number of teeth of the pulleys has to match the original gearing to maintain the correct drive ratio of 9:47
So the design constraint is pretty much fixed at those number of teeth or the tracking rates would be wrong.
The belts are polyurethane and reinforced with steel tension members so wear is not an issue if the belts are tensioned correctly ie not over tensioned.

 

[teoria_del_big_bang]

Take the side plate off and look at the belts..
If they are not snapped, loose or worn in some way then you can strip down and refit everything as the Astrobaby write up. Everything else is the same except there are gears instead of the belts and toothed pulleys.

If you remove the belts then you should be able to turn the big pulley easily by hand, if not then something inside has gone wrong.

Steve

 

[teoria_del_big_bang]

Plenty of SGL members, including myself, have stripped these things down and refurbished them so plenty of help available, just post some pics when you get inside it if you have any difficulties.

Steve

[900SL]

23 hours ago, AstroKeith said:

That 'still' from the start/title frame of the video above shows just how small the drive pulleys are on those belts. They are way smaller than I would have used as a designer but I guess they wanted to get as much reduction ratio as possible.

The upshot is a very tight radius around the pulley with about 4 teeth fully engaged? This means those thin transparent belts too, without any or much reinforcement (ie Kelvar or glass fibre). That is not good for belt wear.

I replaced my Ducati desmo drive belts every two years, mind you they were under considerable load, speed and temperature. I'm sure those Rowan belts are fine. Wouldn't leave them parked up in one position for months though

 

 

[malc-c]

Before Rowan made the belt drive commercially available I messed about modifying my HEQ5 to belt drive over a decade ago.  The problem was there were no off the shelf pulleys that could maintain the stock ratio the gearing has so that it could be used with the handset.  My experiments with different ratios also highlighted a problem with commercially available pulleys, in that the smaller ones are press fitted in two parts an due to the small diameter would separate.  Dave over at Rowan overcame these two issues  by CNC's the two pulleys.  The smaller one being machined as a one piece pulley, and as far as I know there has never been any reports of this small pulley failing.

As others have said, just unscrew the cover plate and check that the belts are intact and the tension wheels are doing their job in keeping the belt engaged.   If they are then go back to basics and remove all the connections to the computer, connect the handset and with it set to speed 9 test the mount in all direction by pressing the direction keys on the handset.  Provided the handset doesn't display any "no response XXX axis" message, and the mount moves then this would prove there is no fault with the mount and the issue lays with the links between the Computer / mount and the software initiating the slew commands.   Now as you use a Linux platform I'm not best to offer advice on how to test, but I would start with confirming the driver (presumably something like a modified EQMOD) can talk to the mount via whatever EQDIER cable you use and then add next level of software control

[vineyard]

Thanks all - much appreciated.  Finally had a chance to open it up today, and yep the belt had slipped (see photo).  Taking the belt off and turning the big pulley wheel, everything was smooth.  On closer inspection, I don't think the two pulleys and the plastic idler (if thats what it is called) had been aligned properly whenever this was installed (I bought it pre-owned).  So the RA belt was riding over the lower lip of the plastic idler, and over time I think that has warped the shape of the belt & hence it slipped off eventually.  Certainly when you lay the belt flat you can see it is warped a bit (2nd photo).  The DEC belt was still v fine & properly set.  I corrected the alignment, & also managed to fiddle with the horizontal spacing to increase the tension enough for the RA to work, but it will only be a matter of time before the warped belt slips again (you could see it moving up and down the pulley depending on which way the pulley was rotating).  So I'm going to order a spare belt (maybe also some new alt-az adjustment bolts as well if they are stocked!).

Let's see how much this improves guiding 🤞🏾(btw I did also find the hyper tuning how-to-video from astrobloke on Youtube - that looks quite interesting, esp if it gives such a large RMS gain).

Cheers & thanks again all!

[vineyard]

Replacement belt arrived & installed.  Seems to work fine on an indoor dummy run, so it is back on the pier waiting for realignment and under-the-stars testing.  Thanks all - will keep fingers crossed & report back on what happens (hopefully it will work, but also quite curious to see if/how much RMS improves with better RA fine-motion 🤞🏾)

Apologies in advance everyone if that means clouds are on the way!

[malc-c]

I'm going to state the obvious here... I take it you also adjusted the alignment of the pulleys and tensioning wheel too... Otherwise you'll be back to square one again soon

[vineyard]

Thanks & yes @malc-c I made sure to do that - both axes seemed to be running the same way, so I'm keeping my fingers crossed - let's see what actual guiding stats are like!🤞🏾

[vineyard]

So far so good🤞🏾!  Took it for a spin last night - about 5 hrs of data, and best regular RMS yet (not sure what the avg was over the night, but was getting c 0.8 quite often w a 1m+ long setup that comes in at the max recommended load fro AP, so quite happy w that given weight & moment).  Curious to see what happens w a lighter wide-field setup.

That warped belt was really affecting things.  Reckon the RA can still be improved a bit (has a bigger variance than the DEC) so maybe s/t to work on later in the year on the hyper-tuning side.

Hopefully it stays like this for quite a while - thanks again all, much appreciated & yet another example of SGL community spirit 🙏🏾