SynScan AZ GOTO Odd Azimuth Slewing Behaviour

[PeterC65]

Sometimes my Sky-Watcher SynScan AZ GOTO behaves oddly.

It’s pointing in roughly the right direction for a target. I select that target on the hand controller. Instead of slewing in azimuth through the smallest angle from its current position to the target, it slews in the opposite direction and does a 360° pivot to find the target.

Last night I stopped the GOTO, aligned the scope by hand, then let the GOTO find the target and still it insisted on performing a pirouette.

The hand controller was running firmware v4.39.15 which I have now upgraded to the latest version (v4.39.20).

Mostly it slews sensibly but just sometimes it behaves like this.

Has anyone else noticed this behaviour? Is there a fix? Is there some way to tell that the mount is about to perform a pirouette?

[AstroNebulee]

1 hour ago, PeterC65 said:

Sometimes my Sky-Watcher SynScan AZ GOTO behaves oddly.

It’s pointing in roughly the right direction for a target. I select that target on the hand controller. Instead of slewing in azimuth through the smallest angle from its current position to the target, it slews in the opposite direction and does a 360° pivot to find the target.

Last night I stopped the GOTO, aligned the scope by hand, then let the GOTO find the target and still it insisted on performing a pirouette.

The hand controller was running firmware v4.39.15 which I have now upgraded to the latest version (v4.39.20).

Mostly it slews sensibly but just sometimes it behaves like this.

Has anyone else noticed this behaviour? Is there a fix? Is there some way to tell that the mount is about to perform a pirouette?

I don't use synscan and I maybe being thick here and probably am, but is it because the target is just near or past the meridian? It came to me in a flash of brilliance and will leave me ignorant 😂

[PeterC65]

30 minutes ago, AstroNebulee said:

I don't use synscan and I maybe being thick here and probably am, but is it because the target is just near or past the meridian? It came to me in a flash of brilliance and will leave me ignorant 😂

I don't think the problem is related to where the target is with respect to the Meridian. The mount usually crosses the Meridian when doing its pirouette, but not always. If anything, the problem seems to happen more often after doing an alignment where the alignment stars are quite far apart.

Edited February 11, 2022 by PeterC65

[Zermelo]

2 hours ago, PeterC65 said:

Sometimes my Sky-Watcher SynScan AZ GOTO behaves oddly.

It’s pointing in roughly the right direction for a target. I select that target on the hand controller. Instead of slewing in azimuth through the smallest angle from its current position to the target, it slews in the opposite direction and does a 360° pivot to find the target.

Last night I stopped the GOTO, aligned the scope by hand, then let the GOTO find the target and still it insisted on performing a pirouette.

The hand controller was running firmware v4.39.15 which I have now upgraded to the latest version (v4.39.20).

Mostly it slews sensibly but just sometimes it behaves like this.

Has anyone else noticed this behaviour? Is there a fix? Is there some way to tell that the mount is about to perform a pirouette?

Yes, I get this sometimes (I have a Star Discovery mount but it's still Synscan).

It took me a while to figure it out. I use Sky Safari with Synscan, and I usually slip the clutch (I always use the dual encoders), push the scope to somewhere in the right area, then do a GoTo for the last bit (from Sky Safari, but it makes no difference to this discussion).

Occasionally, I'd experience what you have - instead of moving the last few degrees, the mount would go all the way round the other way. If I cancelled it quickly and re-tried, it did the same. Re-aligning doesn't help.

Here's what I noticed. I have quite a long power cable from my tank to the mount. When it does its funny thing, it's because I've done a few targets in succession and not noticed that I've gone all the way around with the mount, and then some more. In those situations, I believe that something in the Synscan code is "unwinding" the extra rotation, returning the azimuth angle offset to 0<θ<360. That means it might travel the long way round.

Since I noticed that, I always keep an eye on the power cable, and when I'm moving the scope by hand I choose the direction so as not to cross the "360 boundary". It's a bug, but they're probably not going to change it.

 

 

[AstroNebulee]

1 hour ago, PeterC65 said:

I don't think the problem is related to where the target is with respect to the Meridian. The mount usually crosses the Meridian when doing its pirouette, but not always. If anything, the problem seems to happen more often after doing an alignment where the alignment stars are quite far apart.

No brilliance on my part just ignorance 🤐😂

[PeterC65]

2 hours ago, Zermelo said:

Yes, I get this sometimes (I have a Star Discovery mount but it's still Synscan).

It took me a while to figure it out. I use Sky Safari with Synscan, and I usually slip the clutch (I always use the dual encoders), push the scope to somewhere in the right area, then do a GoTo for the last bit (from Sky Safari, but it makes no difference to this discussion).

Occasionally, I'd experience what you have - instead of moving the last few degrees, the mount would go all the way round the other way. If I cancelled it quickly and re-tried, it did the same. Re-aligning doesn't help.

Here's what I noticed. I have quite a long power cable from my tank to the mount. When it does its funny thing, it's because I've done a few targets in succession and not noticed that I've gone all the way around with the mount, and then some more. In those situations, I believe that something in the Synscan code is "unwinding" the extra rotation, returning the azimuth angle offset to 0<θ<360. That means it might travel the long way round.

Since I noticed that, I always keep an eye on the power cable, and when I'm moving the scope by hand I choose the direction so as not to cross the "360 boundary". It's a bug, but they're probably not going to change it.

 

 

It's good to know that I'm not the only one experiencing this behaviour.

My SynScan AZ GOTO doesn't have clutches so I always use the hand controller to slew. There is a slip clutch on the altitude axis but moving that looses alignment so I've tightened it up and leave it alone.

When I first got this mount I had quite a short power lead to the tank and the first time it performed a pirouette the mount disconnected its power and lost consequently alignment. There was much swearing ...

I now have enough cable for a full pirouette and a half.

Last night I had this problem on my second target so it doesn't seem to be an accumulation effect, and judging by the power cable, the SynScan is not attempting to unwind. I expect there is a bug in the software that calculates the shortest azimuth path from current position to target position.

I just wanted to check that others have seen this and whether there is a fix or some insight as to how to prevent it.

For now I just have to manually (via the hand controller) unwind the mount (the power cable) after it's performed a pirouette.

 

[Zermelo]

58 minutes ago, PeterC65 said:

It's good to know that I'm not the only one experiencing this behaviour.

My SynScan AZ GOTO doesn't have clutches so I always use the hand controller to slew. There is a slip clutch on the altitude axis but moving that looses alignment so I've tightened it up and leave it alone.

When I first got this mount I had quite a short power lead to the tank and the first time it performed a pirouette the mount disconnected its power and lost consequently alignment. There was much swearing ...

I now have enough cable for a full pirouette and a half.

Last night I had this problem on my second target so it doesn't seem to be an accumulation effect, and judging by the power cable, the SynScan is not attempting to unwind. I expect there is a bug in the software that calculates the shortest azimuth path from current position to target position.

I just wanted to check that others have seen this and whether there is a fix or some insight as to how to prevent it.

For now I just have to manually (via the hand controller) unwind the mount (the power cable) after it's performed a pirouette.

 

Actually, I misspoke - my mount also has a clutch knob on the altitude only. But you can turn it by hand on the az axis anyway. So with the Star Discovery (but not the AZ-Goto, I suppose) you have the option of cancelling the slew and just moving the mount 360 degrees by hand, and then it behaves the way you expect. I have to do this sometimes when I've forgotten to keep track of the cable position (or on moonless nights).

Interesting that your symptoms seem to be a bit different. Since I worked out what mine was doing, it has been 100% consistent.

Perhaps Synscan is having an attack of the "Twisties":

https://www.bbc.co.uk/news/world-us-canada-57986166