HEQ5 Pro / Rowan mod problem

[gazza]

Hi,

I have a brand new HEQ5 Pro. I fitted it with a Rowan belt mod. The mod went without issues, however, the results have been less than good.

I had not measured the mount prior to fitting, so I don't have a point of comparison. The mount has significant (3-5 arc second) jumps that destroy guiding.

I ran a run of a couple of hours of Pempro and found that whilst the native PE is very good at around a total of 12 arc seconds or so (depending on the fit) that I have a regular jump at around 13.5 seconds - this equates to the tooth count on the main RA pulley. This shows up in the plot and also the fft.

I spent 2 nights at a dark sky 400km from home (what a waste) trying loose belts, tight belts EQmod variables, all to no avail.)

Should I revert to the original gears, or is there some adjustment I can make that I can try. This was a very disappointing result.

HEEEEEEELLLLLLLPPPPPP!

cheers

Gary

[sloz1664]

I think you may have pointed to the issue. It could be the main RA Pulley, maybe swarf or an issue with the mesh on the worm gear. Have a look at AstroBaby's HEQ5 stripdown guide.

http://www.astro-baby.com/heq5-rebuild/heq5-m1.htm

Steve

[vlaiv]

I had this issue, and it is easy to solve but will require a bit of fiddling with mod it self.

Here is the problem: belt is mashing improperly with gear on motor shaft. To identify and confirm that it is indeed so, just observe how the motor shaft is turning and belt on it and you will see that each 13.8s or so - tooth of belt runs onto tooth of gear.

Solution is applying more tension to belt itself by pulling motor away from worm gear shaft.

[LightBucket]

37 minutes ago, gazza said:

Hi,

I have a brand new HEQ5 Pro. I fitted it with a Rowan belt mod. The mod went without issues, however, the results have been less than good.

I had not measured the mount prior to fitting, so I don't have a point of comparison. The mount has significant (3-5 arc second) jumps that destroy guiding.

I ran a run of a couple of hours of Pempro and found that whilst the native PE is very good at around a total of 12 arc seconds or so (depending on the fit) that I have a regular jump at around 13.5 seconds - this equates to the tooth count on the main RA pulley. This shows up in the plot and also the fft.

I spent 2 nights at a dark sky 400km from home (what a waste) trying loose belts, tight belts EQmod variables, all to no avail.)

Should I revert to the original gears, or is there some adjustment I can make that I can try. This was a very disappointing result.

HEEEEEEELLLLLLLPPPPPP!

cheers

Gary

Have you tightened up the lock screws on the pulley against the flat on the shaft correctly, as if not it can jump and that could be your issue....just a thought  but stick with it as the belt mod will be much better than the gears when you get it sorted...

[Thalestris24]

Just to add - remember also that with a belt mod you want perfect balance i.e. no east heavy

[LightBucket]

1 minute ago, Thalestris24 said:

Just to add - remember also that with a belt mod you want perfect balance i.e. no east heavy

Yes good point, i forgot to mention balance, that needs to be perfect too

[gazza]

Hi,

thanks for the replies. Re the suggestions:

grub screws holding gear on are tight

Worm mesh seems fine

Scope was balanced

I tried several levels of tightness on the belt. The last adjustment (measurement in my attached screen grab) was with the belts fairly tight - about as suggested in the instructions. I will try making it even tighter and re measure as soon as weather allows. Very frustrating when the native pe is so good.....

I do note that ra has significant backlash when driven by the motors, so perhaps I have underestimated just how tight the belts need to be. There is no detectable backlash when trying to move the axis by hand.

Will report back...

Gary

[Skipper Billy]

The backlash might not be in the belt system - you still have the worm to crown wheel gears and that is the usual source of backlash.

If you are running in balance IE not east heavy it could just be rhythmically 'bouncing' across the backlash.

AstroBaby's guide will help you get rid of the backlash.  (Linked to above).

[LightBucket]

If the backlash was in the worm, it would be there when the mount is rocked with your hand, but you say it is not....so thats very strange...

[RichLD]

If there's no backlash at all in RA the worm may be meshing too tightly. Just a thought.

[1parsec]

Hi,

Take a look at these videos on YouTube.  

Skip to 2:04 and note the way the belt behaves when going forward and then in reverse.  The bottom side of the belt doesn't go loose when the motor reverses.

If you see the belt drop at all, when the motor runs clockwise, then the belt is too loose. 
Once you have the belt set up properly you'll not want to go back to gears.

Some mention the balance has to be perfect with belts.  It doesn't have to be.
It's better to have a very slight East heavy set up as this will prevent the worm wheel 'bouncing'  side to side in the backlash / clearance, the same as you would have with gears.

Also try running with a fraction more backlash in the worm-wheel mesh. You may have this set just a bit too tight.

 

 

 

 

This video also shows how much finger pressure is needed to tension the belt - not much needed. Skip to 26:40.
The bottom side of the belt again stays straight when the motor first runs @  27:45

 

One other point to check is to make sure the belt isn't rubbing heavily on the end of the pulley. This will be due to the pulley not aligned with the track of the belt as it passes past the idler roller.
see step 9 in the instructions.

 

[sloz1664]

1 hour ago, RichLD said:

If there's no backlash at all in RA the worm may be meshing too tightly. Just a thought.

If the worm is too tight you will stall the motors. I've  experienced this first hand whilst supertuning and belt modding my old EQ6.

Steve

[gazza]

Thanks again for further replies/vids. Have redone everything, but looks like 4-5 ays before another clear night for testing. Will report back once I've re measured....

cheers

Gary

[Thalestris24]

Hi again

I'm wondering whether you had a problem pre-belt installation? If so, I'd definitely check the worm adjustment, at least. It's a pain to adjust but worth it in the end plus you can test that bit indoors.

All the best

Louise

[gazza]

Hope I may have found the issue....

I opened up the mount to check my installation and found that when I slewed in one direction, the belt tracked perfectly, but in the opposite direction it dropped down the pulley on the motor such that the teeth on the belt rubbed against the side of the pulley, and also on the side of the idler. This was when slewed in the same direction as the motor would turn when tracking. The belt would only climb back up when slewed in the opposite direction. After half a dozen tries I found a tension on the belt that stopped this dropping. The belt had to be loosened slightly. The belt now stays away from the sides of the motor pulley.

Fingers crossed this is the problem......weather report shows clouds for a few days yet :-(

cheers

Gary

[gazza]

Finally had a chance to check the mount (weather issues) after readjusting. Still getting the same issue as in my first post. The belt is tracking perfectly in each direction, not rubbing anywhere, nothing is loose. The belt tension seems pretty right. I'm at a loss as to what to try now. I wish I had characterised the mount before fitting the belt drive kit.

cheers

Gary

[LightBucket]

Sounds to me like one of the pulleysis misaligned somewhere...

take apart and run slowly and see if any of the pulleys are out of line at all when running..

[gazza]

have checked the pulleys with a steel ruler - alignment is ok, and I ran it for a couple of hours after adjusting it to check all seemed OK. I've decided to remove the belt drive kit and revert to the gears and see what happens.i should have checked the mount before fitting the kit - I never even bothered to try the mount out. Just fitted the kit as it seemed a pretty standard mod to do to .Gary

[Skipper Billy]

It sounds like the motor might be slightly tilted which would cause the belt to wander off in opposite directions as the motor turns in different directions ??

Refitting the gears should reveal the root cause.

Good luck!

[vlaiv]

Before you revert to gears, you might want to try something out. Just take a big magnifying glass, let mount track normally and observe at close range how belt interacts with motor gear. Particularly pay attention to place where they come together.

RA wobble of 13.8 secs can be because there is tiny, and I mean tiny part of belt tooth coming onto gear tooth. Seriously tiny - hence magnifying glass - it can't be seen with naked eye that easily. Well probably can if you are young and able to focus on short distance, but if you have trouble focusing on 10cm away from your eyes - large magnifier will help a lot.

Edit, I'm talking about this part:

Mine was doing this when I had such problem:

So it was off by really tinny bit, much less then 1mm.

[gazza]

Hi vlaiv

How did you fix this - belt tension? Going to take mine apart again today

Gary

[vlaiv]

Yes, there are 2 parts to belt tension that you can adjust. First is motor assembly position in mount housing. And second is plate on motor it self.

I tightened motor plate to certain position before I knew I had a problem and I did not move it later because I think it would require taking the motor out. If you can have enough tension just by moving whole motor assembly relative to mount housing then there is no need to adjust plate on motor itself.

Best way to achieve good tension is to loosen 3 hex screws holding motor assembly and do two things - move motor as far away as you can from worm gear and also try to "twist" it a bit in such way to bring idler and opposite side of belt as close as possible. There is a little play in motor position both horizontal and vertical (in relation to slots where screws go). Use horizontal to move motor away and use vertical to give it that bit of "twist" I was talking about.

Here is a diagram to better explain what I mean:

By reducing the gap you are increasing motor - belt contact surface and also because some of the tension is provided by idler - increasing the tension.

On my mount I pulled and twisted motor as far as it would go. After that there was still some motion/bending in the belt when I applied slight pressure with my finger on it (as instruction manual states). When I first made mod, I thought that "normal" tension is enough and there was again some bending of belt when pressure is applied, but it turned out not to be tight enough. After tightening things up I could not tell the difference when pushing with my finger against the belt - it felt as before but I no longer had improper tooth mashing.

[gazza]

Thanks very much vlaiv, I will try this adjustment and report back how I go. Might be a while as the weather forecasts are terrible for as far out as they go.

cheers

Gary

[gazza]

Hi,

looks like I've got it pretty much sorted - I tightened the belt a fair bit more than I had before and the blips are down to around half an arc second according to Pempro - a massive improvement. I will probably tighten them a tad more to see if I can reduce this further, but the blips as they are should not be troublesome. I just wish I could get more than an hour or so before the clouds come in!

Thanks to all those who assisted me...

cheers

Gary

[Thalestris24]

Be careful not to overtighten! The kit instructions for tightness worked for me