AZ Altitude Clutch Slip

[wibblefish]

I have a SW 90 short tube refractor mounted on an AZ Pronto. 

I am having some issues with altitude slipping either when doing slow mo or at times when the tripod is tapped / changing EP. This is worsened the higher the telescope goes towards the zenith.

I suspect it is due to the weight of the BST EP I am using but I was wondering if there is anything I can do to counteract it.

I have already moved the telescope as far forward on the dove tail as possible. I also tried to strap a weight on the front of the telescope but that seemed to make it worse though perhaps I added to much weight / to the wrong place.

Any suggestions would be appreciated! I have toyed with the idea of replacing the mount head but that feels a bit extreme (also not sure if it will actually fix it!).

 

[John]

Sounds like the same sort of issues that you get with the AZ-3 mount.

I think they are caused by the centre of gravity of the scope being above that of the altitude axis.

With the AZ-3 folks would add a counter weight on a bar to counteract the tendency of the scope to tip backwards when pointing upwards. The AZ-3 modification is detailed here:

https://stargazerslounge.com/topic/275499-finally-finished-my-az3-modification/

Maybe you could adapt it for the AZ Pronto ?

[wibblefish]

9 hours ago, John said:

Sounds like the same sort of issues that you get with the AZ-3 mount.

I think they are caused by the centre of gravity of the scope being above that of the altitude axis.

With the AZ-3 folks would add a counter weight on a bar to counteract the tendency of the scope to tip backwards when pointing upwards. The AZ-3 modification is detailed here:

https://stargazerslounge.com/topic/275499-finally-finished-my-az3-modification/

Maybe you could adapt it for the AZ Pronto ?

Thanks for the suggestion John I suspected it might be something like that. My counterweight attempt was to strap a wrist weight around the front part of the OTA but that then becomes precarious when elevated as it moves above the axis so I can see why the example in that post goes for something that will remain angled at the front.

Ultimately I guess upgrading the mount head to a more conventional side arm style AZ4 / AZ5 etc. would be a solution but I might see what spare nuts and bolts are hanging about in the garage to put some weight on the front (I guess it'd have to be the dovetail itself).

Someone else has mentioned pushing the telescope further forward on the rings also so I might see if that would help.

Edited February 12, 2021 by wibblefish

[happy-kat]

Slow mo controls are nice. Hopefully you'll find bits you can use in the garage to add a counter weight bar as those other mounts heads you mentioned don't have slow mo. A did similar to my az3 and it worked great and no slipage at high altitude angles and I liked to keep soft enough tension to use as a push to.

[wibblefish]

7 minutes ago, happy-kat said:

Slow mo controls are nice. Hopefully you'll find bits you can use in the garage to add a counter weight bar as those other mounts heads you mentioned don't have slow mo. A did similar to my az3 and it worked great and no slipage at high altitude angles and I liked to keep soft enough tension to use as a push to.

Yeah I like the slo-mo, the AZ5 does have it though but at £175 just for a mount head its almost the same price I paid for the whole telescope package so if I can find a cheap solution that'd be a lot better already spent plenty on new EP, diagonal, finders, filters etc as it is! Will try and McGuyver something together  

Edited February 12, 2021 by wibblefish

[John]

1 hour ago, wibblefish said:

...Someone else has mentioned pushing the telescope further forward on the rings also so I might see if that would help.

That does help a bit.

In this article a spring is used to a similar job to the counter weight on the AZ-3 mount:

https://astromart.com/reviews-and-articles/reviews/mounts/alt-azimuth/show/virtual-counterweight-for-az3-mounts

Maybe even some stout elastic or a bungee would help if you can find a suitable place to connect each end ?

 

Edited February 12, 2021 by John

[John]

Here is another approach. Here the scope position has been moved using a simple wooden adapter. This moves the centre of gravity of the scope tube downwards to match the centre of the altitude axis:

http://www.homebuiltastronomy.com/stool/EasyAltAzMountModification.htm

As you can see, you are not the only person to be affected by this sort of issue with this type of mount !

 

[wibblefish]

Thanks for the options @John I'll have to see what might work for the az-pronto I guess its just the way they behave so that's reassuring at least, will have to update when I work out a suitable plan

[Louis D]

Try poking around the bins at a home improvement store to see what sorts of angle brackets and mending straps they have.  With some nuts and bolts to connect everything and a nice heavy ankle weight on the end, you should be able to MacGyver something together for under $20 like the first link.

[wibblefish]

Just an update, I didnt have the right bits to actually do to much but pretty sure I could as there are a couple of useful countersunk holes in the middle of the dovetail I could attach a bolt and metal plate to hold weights.

For now I have moved the dovetail forward and telescope forward in the rings which seems to have improved things significantly.