VintageBigBlue.org

 

Re: Permanently solving gear backlash


Jul 1, 2012

 


----------------------------

#51198 Jul 1, 2012

The usual method of overcoming backlash in the RA worm/wheel of Losmandy mounts

is to bias the mount counterweights, depending upon which side (east or west)

the OTA is on. The problem for remote or automated operation is that the

operator cannot be alongside the mount to do this every time there is a meridian

flip. Rainer came up with the brilliant idea of winding some cord around the RA

axis and suspending a weight on it so that the worm is always pushing against

the correct tooth of the gear wheel. The problem with this can be the suspended

weight knocking around.







I am wondering whether there is some kind of gearing - a friction wheel of some

sort, perhaps, which could do the same job and be mounted near the RA axis. Has

anyone seen or tried something like this to solve the RA backlash issue?







Greg







[Non-text portions of this message have been removed]



----------------------------

#51199 Jul 2, 2012

Hi Greg,



Why not just put the weight in a guide tube?





Gale



--- In Losmandy_users@yahoogroups.com, "Greg Crawford" g.c@...> wrote:

>

> The usual method of overcoming backlash in the RA worm/wheel of Losmandy mounts

> is to bias the mount counterweights, depending upon which side (east or west)

> the OTA is on. The problem for remote or automated operation is that the

> operator cannot be alongside the mount to do this every time there is a meridian

> flip. Rainer came up with the brilliant idea of winding some cord around the RA

> axis and suspending a weight on it so that the worm is always pushing against

> the correct tooth of the gear wheel. The problem with this can be the suspended

> weight knocking around.

>

>

>

> I am wondering whether there is some kind of gearing - a friction wheel of some

> sort, perhaps, which could do the same job and be mounted near the RA axis. Has

> anyone seen or tried something like this to solve the RA backlash issue?

>

>

>

> Greg

>

>

>

> [Non-text portions of this message have been removed]

>



----------------------------

#51200 Jul 2, 2012

I saw Rainer's solution and did something similar:

www.flickr.com/photos/averen1/sets/72157627714693494/



When this gets moved to a more permanent location I will likely replace the weight with a spring attached to the tripod or pier. In practice you really only need to have the weight move a little more than 1/2 the circumference of the RA housing so it's not moving around all that much (around 9.5 inches).



I've also devised other methods where the counterweight shaft would "pick up" a weight as it passed from the west to the east side of the mount. For the G11 this would be difficult to do since the counterweight shaft turns with the dec axis. You would have to align the capture mechanism up so that you could "drop off" the weight when the shaft went from east to west.



I think friction wheels would have more of a "stick/give" rotation which would create problems for tracking.



Jared

--- In Losmandy_users@yahoogroups.com, "Greg Crawford" g.c@...> wrote:

>

> The usual method of overcoming backlash in the RA worm/wheel of Losmandy mounts

> is to bias the mount counterweights, depending upon which side (east or west)

> the OTA is on. The problem for remote or automated operation is that the

> operator cannot be alongside the mount to do this every time there is a meridian

> flip. Rainer came up with the brilliant idea of winding some cord around the RA

> axis and suspending a weight on it so that the worm is always pushing against

> the correct tooth of the gear wheel. The problem with this can be the suspended

> weight knocking around.

>

>

>

> I am wondering whether there is some kind of gearing - a friction wheel of some

> sort, perhaps, which could do the same job and be mounted near the RA axis. Has

> anyone seen or tried something like this to solve the RA backlash issue?

>

>

>

> Greg

>

>

>

> [Non-text portions of this message have been removed]

>



----------------------------

#51201 Jul 2, 2012

Mount a PVC tube on the ground, then have the hanging weight inside, this way wind could not swing the weight around.



Clear Skies,

Oz

--- In Losmandy_users@yahoogroups.com, "Greg Crawford" g.c@...> wrote:

>

> The usual method of overcoming backlash in the RA worm/wheel of Losmandy mounts

> is to bias the mount counterweights, depending upon which side (east or west)

> the OTA is on. The problem for remote or automated operation is that the

> operator cannot be alongside the mount to do this every time there is a meridian

> flip. Rainer came up with the brilliant idea of winding some cord around the RA

> axis and suspending a weight on it so that the worm is always pushing against

> the correct tooth of the gear wheel. The problem with this can be the suspended

> weight knocking around.

>

>

>

> I am wondering whether there is some kind of gearing - a friction wheel of some

> sort, perhaps, which could do the same job and be mounted near the RA axis. Has

> anyone seen or tried something like this to solve the RA backlash issue?

>

>

>

> Greg

>

>

>

> [Non-text portions of this message have been removed]

>







----------------------------

#51202 Jul 2, 2012

I've been using a variation on the weight and cord concept with my GM8. It's been working well with a single 2.5 lbs weight. The weight will move in the breeze a little bit when things start blowing. However, the amount of vibration this creates is not noticeable - at least I can't see it in my subs.



When I was using the LW tripod, the tray and spreader bars got in the way of the weight. Once I switched to the HD tripod, this was no longer an issue.



The bigger problem that I have had with the setup is that I have to be very careful about cable snags because it's easy to remotely operate and do meridian flips.



Stephen



--- In Losmandy_users@yahoogroups.com, "Greg Crawford" g.c@...> wrote:

>

> The usual method of overcoming backlash in the RA worm/wheel of Losmandy mounts

> is to bias the mount counterweights, depending upon which side (east or west)

> the OTA is on. The problem for remote or automated operation is that the

> operator cannot be alongside the mount to do this every time there is a meridian

> flip. Rainer came up with the brilliant idea of winding some cord around the RA

> axis and suspending a weight on it so that the worm is always pushing against

> the correct tooth of the gear wheel. The problem with this can be the suspended

> weight knocking around.

>

>

>

> I am wondering whether there is some kind of gearing - a friction wheel of some

> sort, perhaps, which could do the same job and be mounted near the RA axis. Has

> anyone seen or tried something like this to solve the RA backlash issue?

>

>

>

> Greg

>

>

>

> [Non-text portions of this message have been removed]

>



----------------------------

#51207 Jul 2, 2012

Wouldn't spring loading of the worm against the worm wheel solve the backlash problem, and if so, why is it not implemented?

Is it a very difficult task to add it to Losmandy mounts?

Regards

John





[Non-text portions of this message have been removed]



----------------------------

#51208 Jul 2, 2012

I was wondering this as well.. "Weight on a string" seems a little cheesy on a

mount that costs this much.



Kevin









---------------

From: John majorobs14@...>

To: "Losmandy_users@yahoogroups.com" Losmandy_users@yahoogroups.com>

Sent: Mon, July 2, 2012 8:42:20 PM

Subject: [Losmandy_users] Re: Permanently solving gear backlash



.

Wouldn't spring loading of the worm against the worm wheel solve the backlash

problem, and if so, why is it not implemented?

Is it a very difficult task to add it to Losmandy mounts?

Regards

John



[Non-text portions of this message have been removed]









[Non-text portions of this message have been removed]



----------------------------

#51209 Jul 2, 2012

Hi Kevin,

What this actually does is keep the mount loaded to the east even after

a meridian flip and you don't have to stop and change the balance on the

CW shaft. I personally push my mount to its maximum weight limits as far

the payload recommendation. My worm blocks are preloaded and the mesh is

set properly and I may have maybe 1.5mm of backlash. My imaging scale is

at 0.66"/pixel and I have round stars and I run fully automated and

don't have to stop after the meridian flip and re-balance or mess with

it.The system is portable and not in an observatory so any wind my C-14

becomes a sail in the wind so to speak and with a slight gust of wind I

can see sometimes that that 1.5mm of back lash could cause my to enlarge

by as much a 2 pixels and give a slight elongation. If you were imaging

at 2"/pixel you might not notice much. But I know a lot of people who

push their mounts to the max and when you do that you surpass the

manufactures specs and leave yourself open to all kinds of issues.



Actually these mounts are not that expensive and are probably the best

buy for the money / per payload. I would have to pay at least 7.5K more

or in addition to get a mount that would carry the payload that mine is

rated at and you have to set the mesh on them as well.

JG













On 7/2/2012 8:35 PM, Kevin Cummins wrote:

>

> I was wondering this as well. "Weight on a string" seems a little

> cheesy on a

> mount that costs this much.

>

> Kevin

>

---------------

> From: John majorobs14@... mailto:majorobs14%40yahoo.com>>

> To: "Losmandy_users@yahoogroups.com

> mailto:Losmandy_users%40yahoogroups.com>"

> Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com>>

> Sent: Mon, July 2, 2012 8:42:20 PM

> Subject: [Losmandy_users] Re: Permanently solving gear backlash

>

>

> Wouldn't spring loading of the worm against the worm wheel solve the

> backlash

> problem, and if so, why is it not implemented?

> Is it a very difficult task to add it to Losmandy mounts?

> Regards

> John

>

> [Non-text portions of this message have been removed]

>

> [Non-text portions of this message have been removed]

>

>









[Non-text portions of this message have been removed]







----------------------------

#51216 Jul 3, 2012

> Wouldn't spring loading of the worm against the worm wheel solve the backlash problem, and if so, why is it not implemented?

> Is it a very difficult task to add it to Losmandy mounts?

> Regards

> John

>

>

> [Non-text portions of this message have been removed]

No, that just increases friction, and still leaves backlash. Even if the

worm is tight 'home' in the gear, with tooth form, there is still

backlash. Also adds the risk of the worm 'climbing' the gear when

loading increases. It also leads to tiny variations in the distance

between the worm axis, and the centre of the crownwheel, adding another

source of motion error.

'Proper' anti-backlash gears, have two crownwheels, sitting next to one

another, and a spring twisting them relative to one another, so one

rides against the front part of the worm tooth, and the other the rear.

Expensive to make. This provides exactly the same effect as adding the

spring loading, except the force is provided against the worm.



Best Wishes



----------------------------

#51218 Jul 3, 2012

Roger, I am trying to get my head around what you are describing. I don.t suppose you have a drawing of such a setup which you would be willing to share?







Greg











From: Losmandy_users@yahoogroups.com [mailto:Losmandy_users@yahoogroups.com] On Behalf Of R J Hamlett

Sent: Tuesday, 3 July 2012 11:04 PM

To: Losmandy_users@yahoogroups.com

Subject: [Losmandy_users] Re: Permanently solving gear backlash









>

> Wouldn't spring loading of the worm against the worm wheel solve the backlash problem, and if so, why is it not implemented?

> Is it a very difficult task to add it to Losmandy mounts?

> Regards

> John

>

>

> [Non-text portions of this message have been removed]

No, that just increases friction, and still leaves backlash. Even if the

worm is tight 'home' in the gear, with tooth form, there is still

backlash. Also adds the risk of the worm 'climbing' the gear when

loading increases. It also leads to tiny variations in the distance

between the worm axis, and the centre of the crownwheel, adding another

source of motion error.

'Proper' anti-backlash gears, have two crownwheels, sitting next to one

another, and a spring twisting them relative to one another, so one

rides against the front part of the worm tooth, and the other the rear.

Expensive to make. This provides exactly the same effect as adding the

spring loading, except the force is provided against the worm.



Best Wishes











[Non-text portions of this message have been removed]



----------------------------

#51269 Jul 9, 2012

Roger, I am trying to get my head around what you are describing. I don.t suppose you have a drawing of such a setup which you would be willing to share?

>

>

>

> Greg

>

Been out of internet connectivity for a couple of days, so couldn't answer.

Haven't been able to find a drawing on the web, but will try to describe

better:



Start with the main gear driven by the worm. Saw this into two thinner

layers. Attach shaft connections etc., to just one layer. Then have

second layer able to turn on the 'fixed' layer, by only a small amount

(normally held by a series of slots round the gear, with 'T' bolts).

Total movement, only a tiny fraction of a mm. Going from teeth on both

halves perfectly aligned to misaligned by this small amount. Then have a

spring mechanism turning the second plate relative to the first, towards

the 'misaligned' position. Then turn the second plate till it is 'in

line', and engage both with the worm. Release plate. The second plate

then moves to take up any slack in the gear.

Limitations - backlash only disappears so long as the torque being

transmitted is less than the force needed to compress the springs. Adds

friction. Costly to make.



Have seen variations of this used on stuff ranging from Victorian

scientific instruments, through to modern laser platforms.



Best Wishes

>

>

>

> From:Losmandy_users@yahoogroups.com [mailto:Losmandy_users@yahoogroups.com] On Behalf Of R J Hamlett

> Sent: Tuesday, 3 July 2012 11:04 PM

> To:Losmandy_users@yahoogroups.com

> Subject: [Losmandy_users] Re: Permanently solving gear backlash

>

>

>

>

>

>> Wouldn't spring loading of the worm against the worm wheel solve the backlash problem, and if so, why is it not implemented?

>> Is it a very difficult task to add it to Losmandy mounts?

>> Regards

>> John

>>

>>

>> [Non-text portions of this message have been removed]

> No, that just increases friction, and still leaves backlash. Even if the

> worm is tight 'home' in the gear, with tooth form, there is still

> backlash. Also adds the risk of the worm 'climbing' the gear when

> loading increases. It also leads to tiny variations in the distance

> between the worm axis, and the centre of the crownwheel, adding another

> source of motion error.

> 'Proper' anti-backlash gears, have two crownwheels, sitting next to one

> another, and a spring twisting them relative to one another, so one

> rides against the front part of the worm tooth, and the other the rear.

> Expensive to make. This provides exactly the same effect as adding the

> spring loading, except the force is provided against the worm.

>

> Best Wishes







----------------------------

#51270 Jul 9, 2012

I've seen what you describe online before...

sdp-si.com/eStore/..%5Css%5CPDF%5C81001209.pdf



Take care,

Howard

--- In Losmandy_users@yahoogroups.com, R J Hamlett ttelmah@...> wrote:

>

> > Roger, I am trying to get my head around what you are describing. I don...t suppose you have a drawing of such a setup which you would be willing to share?

> >

> >

> >

> > Greg

> >

> Been out of internet connectivity for a couple of days, so couldn't answer.

> Haven't been able to find a drawing on the web, but will try to describe

> better:

>

> Start with the main gear driven by the worm. Saw this into two thinner

> layers. Attach shaft connections etc., to just one layer. Then have

> second layer able to turn on the 'fixed' layer, by only a small amount

> (normally held by a series of slots round the gear, with 'T' bolts).

> Total movement, only a tiny fraction of a mm. Going from teeth on both

> halves perfectly aligned to misaligned by this small amount. Then have a

> spring mechanism turning the second plate relative to the first, towards

> the 'misaligned' position. Then turn the second plate till it is 'in

> line', and engage both with the worm. Release plate. The second plate

> then moves to take up any slack in the gear.

> Limitations - backlash only disappears so long as the torque being

> transmitted is less than the force needed to compress the springs. Adds

> friction. Costly to make.

>

> Have seen variations of this used on stuff ranging from Victorian

> scientific instruments, through to modern laser platforms.

>

> Best Wishes

>

> >

> >

> >

> > From:Losmandy_users@yahoogroups.com [mailto:Losmandy_users@yahoogroups.com] On Behalf Of R J Hamlett

> > Sent: Tuesday, 3 July 2012 11:04 PM

> > To:Losmandy_users@yahoogroups.com

> > Subject: [Losmandy_users] Re: Permanently solving gear backlash

> >

> >

> >

> >

> >

> >> Wouldn't spring loading of the worm against the worm wheel solve the backlash problem, and if so, why is it not implemented?

> >> Is it a very difficult task to add it to Losmandy mounts?

> >> Regards

> >> John

> >>

> >>

> >> [Non-text portions of this message have been removed]

> > No, that just increases friction, and still leaves backlash. Even if the

> > worm is tight 'home' in the gear, with tooth form, there is still

> > backlash. Also adds the risk of the worm 'climbing' the gear when

> > loading increases. It also leads to tiny variations in the distance

> > between the worm axis, and the centre of the crownwheel, adding another

> > source of motion error.

> > 'Proper' anti-backlash gears, have two crownwheels, sitting next to one

> > another, and a spring twisting them relative to one another, so one

> > rides against the front part of the worm tooth, and the other the rear.

> > Expensive to make. This provides exactly the same effect as adding the

> > spring loading, except the force is provided against the worm.

> >

> > Best Wishes

>



----------------------------

#51271 Jul 9, 2012

Thanks Roger and Howard. I don.t suppose there is any easy way to swap such a contraption into a G11?







Greg







From: Losmandy_users@yahoogroups.com [mailto:Losmandy_users@yahoogroups.com] On Behalf Of Howard Dutton

Sent: Monday, 9 July 2012 10:39 PM

To: Losmandy_users@yahoogroups.com

Subject: [Losmandy_users] Re: Permanently solving gear backlash











I've seen what you describe online before...

sdp-si.com/eStore/..%5Css%5CPDF%5C81001209.pdf



Take care,

Howard

--- In Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com> , R J Hamlett ttelmah@...> wrote:

>

> > Roger, I am trying to get my head around what you are describing. I don...t suppose you have a drawing of such a setup which you would be willing to share?

> >

> >

> >

> > Greg

> >

> Been out of internet connectivity for a couple of days, so couldn't answer.

> Haven't been able to find a drawing on the web, but will try to describe

> better:

>

> Start with the main gear driven by the worm. Saw this into two thinner

> layers. Attach shaft connections etc., to just one layer. Then have

> second layer able to turn on the 'fixed' layer, by only a small amount

> (normally held by a series of slots round the gear, with 'T' bolts).

> Total movement, only a tiny fraction of a mm. Going from teeth on both

> halves perfectly aligned to misaligned by this small amount. Then have a

> spring mechanism turning the second plate relative to the first, towards

> the 'misaligned' position. Then turn the second plate till it is 'in

> line', and engage both with the worm. Release plate. The second plate

> then moves to take up any slack in the gear.

> Limitations - backlash only disappears so long as the torque being

> transmitted is less than the force needed to compress the springs. Adds

> friction. Costly to make.

>

> Have seen variations of this used on stuff ranging from Victorian

> scientific instruments, through to modern laser platforms.

>

> Best Wishes

>

> >

> >

> >

> > From:Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com> [mailto:Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com> ] On Behalf Of R J Hamlett

> > Sent: Tuesday, 3 July 2012 11:04 PM

> > To:Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com>

> > Subject: [Losmandy_users] Re: Permanently solving gear backlash

> >

> >

> >

> >

> >

> >> Wouldn't spring loading of the worm against the worm wheel solve the backlash problem, and if so, why is it not implemented?

> >> Is it a very difficult task to add it to Losmandy mounts?

> >> Regards

> >> John

> >>

> >>

> >> [Non-text portions of this message have been removed]

> > No, that just increases friction, and still leaves backlash. Even if the

> > worm is tight 'home' in the gear, with tooth form, there is still

> > backlash. Also adds the risk of the worm 'climbing' the gear when

> > loading increases. It also leads to tiny variations in the distance

> > between the worm axis, and the centre of the crownwheel, adding another

> > source of motion error.

> > 'Proper' anti-backlash gears, have two crownwheels, sitting next to one

> > another, and a spring twisting them relative to one another, so one

> > rides against the front part of the worm tooth, and the other the rear.

> > Expensive to make. This provides exactly the same effect as adding the

> > spring loading, except the force is provided against the worm.

> >

> > Best Wishes

>











[Non-text portions of this message have been removed]







----------------------------

#51272 Jul 10, 2012

There are two problems:



1. The gears in the G-11 (or G-8 for that matter) have smooth

faces for the clutch mechanism. The anti-backlash springs and

the cavities to house them would be a problem with clearance.



2. The specific gears in the example are way too small. Look

a the Pitch Diameter (PD) values in the table.



Personally, I don't think this is that big an issue with the

G-11. Maybe if I was operating a remote observatory I would

feel differently. But that is a different price point for

the whole system anyway, not to mention a different style

of observing and imaging - I like being out with the gear.



Cheers,



Mark Christensen --- In Losmandy_users@yahoogroups.com, "Greg Crawford" g.c@...> wrote:

>

> Thanks Roger and Howard. I don...t suppose there is any easy way to swap such a contraption into a G11?

>

>

>

> Greg

>

>

>

> From: Losmandy_users@yahoogroups.com [mailto:Losmandy_users@yahoogroups.com] On Behalf Of Howard Dutton

> Sent: Monday, 9 July 2012 10:39 PM

> To: Losmandy_users@yahoogroups.com

> Subject: [Losmandy_users] Re: Permanently solving gear backlash

>

>

>

>

>

> I've seen what you describe online before...

> sdp-si.com/eStore/..%5Css%5CPDF%5C81001209.pdf

>

> Take care,

> Howard

>

> --- In Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com> , R J Hamlett ttelmah@> wrote:

> >

> > > Roger, I am trying to get my head around what you are describing. I don........t suppose you have a drawing of such a setup which you would be willing to share?

> > >

> > >

> > >

> > > Greg

> > >

> > Been out of internet connectivity for a couple of days, so couldn't answer.

> > Haven't been able to find a drawing on the web, but will try to describe

> > better:

> >

> > Start with the main gear driven by the worm. Saw this into two thinner

> > layers. Attach shaft connections etc., to just one layer. Then have

> > second layer able to turn on the 'fixed' layer, by only a small amount

> > (normally held by a series of slots round the gear, with 'T' bolts).

> > Total movement, only a tiny fraction of a mm. Going from teeth on both

> > halves perfectly aligned to misaligned by this small amount. Then have a

> > spring mechanism turning the second plate relative to the first, towards

> > the 'misaligned' position. Then turn the second plate till it is 'in

> > line', and engage both with the worm. Release plate. The second plate

> > then moves to take up any slack in the gear.

> > Limitations - backlash only disappears so long as the torque being

> > transmitted is less than the force needed to compress the springs. Adds

> > friction. Costly to make.

> >

> > Have seen variations of this used on stuff ranging from Victorian

> > scientific instruments, through to modern laser platforms.

> >

> > Best Wishes

> >

> > >

> > >

> > >

> > > From:Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com> [mailto:Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com> ] On Behalf Of R J Hamlett

> > > Sent: Tuesday, 3 July 2012 11:04 PM

> > > To:Losmandy_users@yahoogroups.com mailto:Losmandy_users%40yahoogroups.com>

> > > Subject: [Losmandy_users] Re: Permanently solving gear backlash

> > >

> > >

> > >

> > >

> > >

> > >> Wouldn't spring loading of the worm against the worm wheel solve the backlash problem, and if so, why is it not implemented?

> > >> Is it a very difficult task to add it to Losmandy mounts?

> > >> Regards

> > >> John

> > >>

> > >>

> > >> [Non-text portions of this message have been removed]

> > > No, that just increases friction, and still leaves backlash. Even if the

> > > worm is tight 'home' in the gear, with tooth form, there is still

> > > backlash. Also adds the risk of the worm 'climbing' the gear when

> > > loading increases. It also leads to tiny variations in the distance

> > > between the worm axis, and the centre of the crownwheel, adding another

> > > source of motion error.

> > > 'Proper' anti-backlash gears, have two crownwheels, sitting next to one

> > > another, and a spring twisting them relative to one another, so one

> > > rides against the front part of the worm tooth, and the other the rear.

> > > Expensive to make. This provides exactly the same effect as adding the

> > > spring loading, except the force is provided against the worm.

> > >

> > > Best Wishes

> >

>

>

>

>

>

> [Non-text portions of this message have been removed]

>



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