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Walking on the Moon

Slight mishap, advice needed....


LightBucket
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Hi all,

well have been doing some testing on a new set up in my garage, and whilst doing a slew the weight bar on my EQ6 got wedged against my workbench, did not realise it was that close, anyaway the RA made a bit of a wining sound for about 3 or 4 seconds, as it was jammed, so would this have done any damage to the worm gear, as my mount is belt modded so no other gears in there....or would it just be the motor stalling, not sure which would happen first.....just a bit concerned, although seems to run fine since... :(

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Unlikely to have damaged the worm, the EQ6 is stepper motor driven and these motors don’t have a lot of torque, they just rattle really loudly if you stall them.

Next time you are out pop in your highest mag eyepiece that seeing allows, balance the OTA slightly East side heavy, centre a star and monitor it’s position for one revolution of the worm. I can’t remember the worm period for the EQ6 for certain, 479 seconds comes to mind but you would need to look that up, anyhow, watch the star during one worm revolution for any sudden sharp deviations in RA, if present that would indicate damage to the worm, slow displacement due to periodic error should be all you see. Rebalance the OTA for slightly West side heavy and repeat the observation.

I can’t count the times I’ve fallen asleep while using my old HEQ5 only to be woken by the sound of a rattling RA stepper motor as the counterweight bar tracked into the tripod legs, never caused any damage.

Now, if you struck something at high slew rates with a lot of mass attached to the mount, that may be a different story....

The test above should show up any problem but I doubt you’ll find anything wrong.

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I once left my EQ6 Pro running overnight with the telescope jammed against the obs wall :iamwithstupid:It didn't seem to result in any damage and still runs fine. There must be some safety clutch arrangement to cope with this.  :icon_biggrin:

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Thanks all,

It was slewing at the time So was moving at a high speed, also was fully loaded with 80mm scope, guide scope  and 2x 5kg weights.. 

so in these situations, is it the motor that stalls, before any gear slipping or belt jumping teeth...?? It certainly did not sound like metal on metal grinding, it was more like a higher pitch screech or squeal...so I guess the worm would not make that noise...

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4 hours ago, LightBucket said:

Thanks all,

It was slewing at the time So was moving at a high speed, also was fully loaded with 80mm scope, guide scope  and 2x 5kg weights.. 

so in these situations, is it the motor that stalls, before any gear slipping or belt jumping teeth...?? It certainly did not sound like metal on metal grinding, it was more like a higher pitch screech or squeal...so I guess the worm would not make that noise...

Well, it is a little complicated to explain, the transferred loads across a worm and gear coupling are unequal in direction.

I’m not too sure how to explain without resorting to jargon so forgive me for oversimplifying but I’ll have a try.

If the stepper motor is driving at a fixed speed, whatever that may be, and the mount hits a solid object then the RA gear stops dead while the worm keeps rotating. Most of the energy in the moving mass will be lost in physically lifting or compressing the tripod, slippage in the clutches, (which is why you should never over-tighten the clutches), and deformation of the OTA, counterweight bar, OTA attachment and whatever it was that got hit.

As the worm is now being driven against a stationary gear and the mechanical angle between the tooth of the gear and tooth of the worm is shallow then the load generated by the still rotating stepper on the worm and gear will increase slowly until the stepper reaches stalling point when the motor’s stator will begin to oscillate between magnetic poles creating a chattering sound. 

The higher the driving speed of the stepper then the higher the frequency of the noise and it would sound more of a ‘squeal’ at slew speeds and a ‘chatter’ at sidereal or ‘tracking’ speed. 

Because there is very little mass in a stepper motor the inertial loading generated between stepper motor and the stationary worm and gear is comparatively small and it would be very difficult to damage the teeth of worm or gear by stalling the stepper motor in this way.

As for a jumping belt, that is very unlikely because the belt moves so slowly in comparison to the speed of the stepper. The distance that one belt tooth moves through as it rotates requires several hundred stepper motor pulses. If the belt were to jump it would sound like a series of low frequency rat-a-tat ‘thumps’ that you could almost count in real time. As long as the belt is fitted correctly it is not likely to have jumped and neither would the belt gears slip on the stepper or worm shafts provided the grub screws were all tightened correctly.

The depth of cut of the gear teeth and corresponding depth of the worm teeth coupled with a rigid mounting between the two means it would need a huge amount of force to cause the two to move apart and skip over each other, the stepper motor used in this mount just doesn’t have enough torque or mass to do this.

In this type of accident it is really difficult to cause any harm to the mount but easy to damage the scope or whatever gets hit.

The most damage to a worm gear is caused when the loads reverse direction and the shallow angle betwen gear and worm works against you.

If you accidentally walk into a mount, it gets knocked over or you bash your head on it after stooping to pick something off the ground (can’t you just tell I must have done that.....more than once!...), and the OTA or counterweight bar becomes suddenly loaded then there is a lot of mass and energy behind that event and the load on the RA or DEC gear rapidly increases to push against the teeth of the worm (sometimes called ‘shock loading’) the angle between gear and worm is so shallow that in this direction the load will not force the worm to rotate but will tend to bend and break the teeth of the gear or the worm.

This is another reason why the mount clutches need only be ‘snugged up’ to prevent slipping in use, not tightened so much as if to hold the QE2 in dock.

I hope the above is not written too opaquely and will put your mind at ease. 

If you are still concerned then carry out the visual test I described in the earlier reply and it will quickly reveal anything untoward but from your description I think it very unlikely any damage would have occurred.

HTH.

 

Edited by Oddsocks
Spelling......grrrr
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21 minutes ago, Oddsocks said:

Well, it is a little complicated to explain, the transferred loads across a worm and gear coupling are unequal in direction.

I’m not too sure how to explain without resorting to jargon so forgive me for oversimplifying but I’ll have a try.

If the stepper motor is driving at a fixed speed, whatever that may be, and the mount hits a solid object then the RA gear stops dead while the worm keeps rotating. Most of the energy in the moving mass will be lost in physically lifting or compressing the tripod, slippage in the clutches, (which is why you should never over-tighten the clutches), and deformation of the OTA, counterweight bar, OTA attachment and whatever it was that got hit.

As the worm is now being driven against a stationary gear and the mechanical angle between the tooth of the gear and tooth of the worm is shallow then the load generated by the still rotating stepper on the worm and gear will increase slowly until the stepper reaches stalling point when the motor’s stator will begin to oscillate between magnetic poles creating a chattering sound. 

The higher the driving speed of the stepper then the higher the frequency of the noise and it would sound more of a ‘squeal’ at slew speeds and a ‘chatter’ at sidereal or ‘tracking’ speed. 

Because there is very little mass in a stepper motor the inertial loading generated between stepper motor and the stationary worm and gear is comparatively small and it would be very difficult to damage the teeth of worm or gear by stalling the stepper motor in this way.

As for a jumping belt, that is very unlikely because the belt moves so slowly in comparison to the speed of the stepper. The distance that one belt tooth moves through as it rotates requires several hundred stepper motor pulses. If the belt were to jump it would sound like a series of low frequency rat-a-tat ‘thumps’ that you could almost count in real time. As long as the belt is fitted correctly it is not likely to have jumped and neither would the belt gears slip on the stepper or worm shafts provided the grub screws were all tightened correctly.

The depth of cut of the gear teeth and corresponding depth of the worm teeth coupled with a rigid mounting between the two means it would need a huge amount of force to cause the two to move apart and skip over each other, the stepper motor used in this mount just doesn’t have enough torque or mass to do this.

In this type of accident it is really difficult to cause any harm to the mount but easy to damage the scope or whatever gets hit.

The most damage to a worm gear is caused when the loads reverse direction and the shallow angle betwen gear and worm works against you.

If you accidentally walk into a mount, it gets knocked over or you bash your head on it after stooping to pick something off the ground (can’t you just tell I must have done that.....more than once!...), and the OTA or counterweight bar becomes suddenly loaded then there is a lot of mass and energy behind that event and the load on the RA or DEC gear rapidly increases to push against the teeth of the worm (sometimes called ‘shock loading’) the angle between gear and worm is so shallow that in this direction the load will not force the worm to rotate but will tend to bend and break the teeth of the gear or the worm.

This is another reason why the mount clutches need only be ‘snugged up’ to prevent slipping in use, not tightened so much as if to hold the QE2 in dock.

I hope the above is not written too opaquely and will put your mind at ease. 

If you are still concerned then carry out the visual test I described in the earlier reply and it will quickly reveal anything untoward but from your description I think it very unlikely any damage would have occurred.

HTH.

 

Thanks very much, and yes I do understand most of what you have written, down to the paragraph about knocking the scope with your head or such like, that seems to contradict the rest, would that scenario not be “a better accident”, for want of a better expression, than the counterweight bar getting jammed at speed against a solid imovable object....?

There was certainly no metal against metal noise or thumping of the belt slipping as you say, just the motor stalling I think...

I have run the mount again today and done full rotations of the worm and seems perfectly fine... :)

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1 hour ago, LightBucket said:

I do understand most of what you have written, down to the paragraph about knocking the scope with your head or such like, that seems to contradict the rest, would that scenario not be “a better accident”, for want of a better expression, than the counterweight bar getting jammed at speed against a solid imovable object....?

No, this is not the case, because the loads across the worm are from opposite directions and of vastly different magnitudes in the two scenarios.

When the counterweight bar got jammed against a solid object and even though it is moving at speed only the low mass and torque or the stepper motor is still pressing against the teeth of the worm and gear. The 'immovable" object can not push back, if anything could be termed a 'better' accident this would be it.

When you suddenly bash against the scope with your head or fall over it in the dark etc then the mass behind that force is many times greater than the stepper motor was able to exert in the first scenario, together with the shallow angle at the point where the gear and worm come together such an accident pushes the gear against the worm with such a large force that damage can result, this is a 'bad' accident.

 

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1 hour ago, Oddsocks said:

No, this is not the case, because the loads across the worm are from opposite directions and of vastly different magnitudes in the two scenarios.

When the counterweight bar got jammed against a solid object and even though it is moving at speed only the low mass and torque or the stepper motor is still pressing against the teeth of the worm and gear. The 'immovable" object can not push back, if anything could be termed a 'better' accident this would be it.

When you suddenly bash against the scope with your head or fall over it in the dark etc then the mass behind that force is many times greater than the stepper motor was able to exert in the first scenario, together with the shallow angle at the point where the gear and worm come together such an accident pushes the gear against the worm with such a large force that damage can result, this is a 'bad' accident.

 

Got it, many thanks for your detailed explanations, makes a lot of sense now... :):)

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  • 2 weeks later...

Heeeeeeelllllpppppppppp

jusr set up my mount again for the first time since my little mishap, and have real issues, I turn the mount on in home position, pointing at Polaris for testing purposes, unpark, start and in planetarium software all good EQMOD shows point at Polaris, so I slew to the sun just for ease, and the mount slews, but it stops way off....about 90 degrees off, yet it shows in planetarium as being spot on....!!  So click park again, and goes perfectly back to home position, this is the same for anything I choose, it’s way off every time...yet goes to home perfectly, so the mount thinks it’s in the correct position but it’s not by a long way.....

Any ideas.... :(:(

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48 minutes ago, wxsatuser said:

I would clear the old synch data in EQMOD and start again by synching on several objects, if you have'nt already done so.

Hi,

yes when I do that it works until I switch mount off, then back on then it’s all out again....same as before, it’s not remembering...

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1 hour ago, wxsatuser said:

When you had your mishap did you turn the mount off without parking?

If you did have you resynched the encoders?

I certainly have not re synced the encoders as dont know how......! :(

Edited by LightBucket
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11 minutes ago, Oddsocks said:

Didn't think the bog-standard EQ6 had encoders or is this an AZ-EQ6?

It’s the EQ6 pro, I thought it had just on the RA axis...

but still can’t get my head around why when at it’s home position, today for testing I slewed to the sun, and it ended up pointing NW down at horizon instead of south up at sky...but when I click park it goes back to position perfectly, so it knows where its park / start postition is, so what so far away on first slew....I can’t get my head around, and am missing something simple....it was perfect a few weeks ago and always was close on first slew....

Edited by LightBucket
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13 minutes ago, LightBucket said:

It’s the EQ6 pro, I thought it had just on the RA axis...

but still can’t get my head around why when at it’s home position, today for testing I slewed to the sun, and it ended up pointing NW down at horizon instead of south up at sky...but when I click park it goes back to position perfectly, so it knows where its park / start postition is, so what so far away on first slew....I can’t get my head around, and am missing something simple....it was perfect a few weeks ago and always was close on first slew....

DST? MM/DD/YY?

Edited by tooth_dr
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I will have to look for a manual as I have not kept up with the latest Skywatcher models, AFAIK the old EQ6 PRO has no encoders and the new EQ6-R that Flo list doesn’t mention encoders.

Presumably you have taken account of the change to daylight saving time since the last time you used it?

Are you just working from the handset or using software on a computer?

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All the settings are correct as set by my GPS, am using EQMOD not the handset...

It was fine a few weeks ago, and if I slew to, sun for example, it’s miles off, so I use manual buttons in EQMOD to move then sync, it’s fine from then on, then I park and switch off, then turn back on unpark and slew to sun, and it’s miles off again, but it does go to the same place miles off.... :(

Edited by LightBucket
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Sounds more like a corrupted setting in EQMOD than a scope issue. I have little experience of EQMOD and don’t feel qualified to advise but it does sound like a summer/time winter/time issue to me. Is your PC set to auto-adjust to summer time?

To help fault finding I would disconnect the computer for now and connect the handset instead. If that works ok then you will know the mount is fine and the problem is with the computer/eqmod.

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13 minutes ago, Oddsocks said:

Sounds more like a corrupted setting in EQMOD than a scope issue. I have little experience of EQMOD and don’t feel qualified to advise but it does sound like a summer/time winter/time issue to me. Is your PC set to auto-adjust to summer time?

To help fault finding I would disconnect the computer for now and connect the handset instead. If that works ok then you will know the mount is fine and the problem is with the computer/eqmod.

I can assure you it’s nothing to do with incorrect settings, that much I do know as it was my first thought, and yes it is definitely a setting issue I think....

I have read a post by @steppenwolf that if you do a slew to a star, and it’s miles away, loosen the clutches and manually move, then a second star and centre this with handset, and same with a third star, and this should get good alignment, but then when I click park it won’t go back to the home position I had set, will it...and if I undo clutches and move, that will undo the work I have just done, so could I move with handset back to a home position, and then set as home, would that work.......this is what is frustrating me..

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14 hours ago, LightBucket said:

Heeeeeeelllllpppppppppp

jusr set up my mount again for the first time since my little mishap, and have real issues, I turn the mount on in home position, pointing at Polaris for testing purposes, unpark, start and in planetarium software all good EQMOD shows point at Polaris, so I slew to the sun just for ease, and the mount slews, but it stops way off....about 90 degrees off, yet it shows in planetarium as being spot on....!!  So click park again, and goes perfectly back to home position, this is the same for anything I choose, it’s way off every time...yet goes to home perfectly, so the mount thinks it’s in the correct position but it’s not by a long way.....

Any ideas.... :(:(

Just a thought here but if I'm reading you right, " home position pointing at Polaris ".
Can you clarify what you said here.

The home position does'nt point to Polaris it's just weights down scope up.
Have you checked that home is home with a spirit level as to the EQMOD docs?

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3 hours ago, wxsatuser said:

Just a thought here but if I'm reading you right, " home position pointing at Polaris ".
Can you clarify what you said here.

The home position does'nt point to Polaris it's just weights down scope up.
Have you checked that home is home with a spirit level as to the EQMOD docs?

Yes it’s just weights down scope up, in the rough direction of Polaris, this has been set in EQMOD and always returns there when I click park....so it knows where it starts from on a given night, so why is the first slew so far off....you would think it would go roughly in the right direction....and all dates, times, location and BST is set correctly....

I can’t help thinking it is something to do with the mount getting stoppped (incident mentioned above) while slewing as that was the RA axis and it’s that one that’s out, the DEC is fine...to get correct position I only have to move RA... 

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2 minutes ago, LightBucket said:

Yes it’s just weights down scope up, in the rough direction of Polaris, this has been set in EQMOD and always returns there when I click park....so it knows where it starts from on a given night, so why is the first slew so far off....you would think it would go roughly in the right direction....and all dates, times, location and BST is set correctly....

I can’t help thinking it is something to do with the mount getting stoppped (incident mentioned above) while slewing as that was the RA axis and it’s that one that’s out, the DEC is fine...to get correct position I only have to move RA... 

Can you confirm you have tried it with the handset and not EQMOD?

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