I am asking on behalf of my clubs SC install. It is a 40" with a Nexus (not Pro). All GOTO's are via the Nexus. A couple of years ago just after a GOTO finished the SC would motor about 10 arcminutes from the target. Display on Nexus indication something like `0.10. It has progressively increased over the past year or so. Last outing it was nearly 1 degree. I can issue another GOTO and it will zero in a little better. Strange thing is it will nearly zero the target stops then proceed again to a position now that is 50+ arcminutes. Anybody got any ideas what the issue is? We are calling it overshoot. In it is acquiring the target then moving away.

Bob

Hello Bob,

?

Forgive me - I saw this and forgot to respond to it ...?

?

So - this sounds like a drive roller is slipping due to a loose grub screw. Check to see which axis is off first - then focus on the drive roller for that axis.?

?

Gary Myers

StellarCAT

?

?

?

?

?

I am asking on behalf of my clubs SC install. It is a 40" with a Nexus (not Pro). All GOTO's are via the Nexus. A couple of years ago just after a GOTO finished the SC would motor about 10 arcminutes from the target. Display on Nexus indication something like `0.10. It has progressively increased over the past year or so. Last outing it was nearly 1 degree. I can issue another GOTO and it will zero in a little better. Strange thing is it will nearly zero the target stops then proceed again to a position now that is 50+ arcminutes. Anybody got any ideas what the issue is? We are calling it overshoot. In it is acquiring the target then moving away.

Bob

Gary,

Thanks for the reply. I will check the drive rollers. It seems to split the error between the axes. I will check both. ?Hadn’t really thought about it being slipping as it goes to the target stops for about a half second then motors past. It is pretty much acquiring the target in the initial goto. No overshoot or undershoot there. Just immediately after acquisition, the motors start back up and drive past. I is like it has built in offset.

Bob

?

From: [email protected] <[email protected]> On Behalf Of K9RX - Gary via groups.io
Sent: Wednesday, January 8, 2025 2:23 PM
To: [email protected]; [email protected]
Subject: Re: [ServoCAT] Servo Cat moves after goto completes.

?

Hello Bob,

?

Forgive me - I saw this and forgot to respond to it ...?

?

So - this sounds like a drive roller is slipping due to a loose grub screw. Check to see which axis is off first - then focus on the drive roller for that axis.?

?

Gary Myers

StellarCAT

?

?

?

?

------ Original Message ------

From "bobrose500 via groups.io" <bobrose500@...>

To [email protected]

Date 1/2/2025 10:26:17 PM

Subject [ServoCAT] Servo Cat moves after goto completes.

?

I am asking on behalf of my clubs SC install. It is a 40" with a Nexus (not Pro). All GOTO's are via the Nexus. A couple of years ago just after a GOTO finished the SC would motor about 10 arcminutes from the target. Display on Nexus indication something like `0.10. It has progressively increased over the past year or so. Last outing it was nearly 1 degree. I can issue another GOTO and it will zero in a little better. Strange thing is it will nearly zero the target stops then proceed again to a position now that is 50+ arcminutes. Anybody got any ideas what the issue is? We are calling it overshoot. In it is acquiring the target then moving away.

Bob

The algorithm is designed, assuming you are using the latest version firmware, to always end up in the direction of sidereal tracking. So - it does a GOTO. Then it gets the offset again from the DSC and does a 2nd GOTO. If after the 2nd one the distance to the object is still more than ... I think it was 0.04°, it will do a third one, if it is within that it will not do another.?

?

But it then checks to see which direction the last move was - was it in the direction of sidereal or not. If not it will move the axis away in the direction opposite sidereal, more than the backlash value (typically 0.7° or so)... and then it will do one final GOTO. THIS should put it both at 0.00 on each axis as well as tracking immediately (no backlash to unwind).?

?

Thus you could and would see behavior like you are describing - but it should still end up < 0.05° away.?

?

g.

?

?

?

?

?

Gary,

Thanks for the reply. I will check the drive rollers. It seems to split the error between the axes. I will check both. ?Hadn’t really thought about it being slipping as it goes to the target stops for about a half second then motors past. It is pretty much acquiring the target in the initial goto. No overshoot or undershoot there. Just immediately after acquisition, the motors start back up and drive past. I is like it has built in offset.

Bob

?

From: [email protected] <[email protected]> On Behalf Of K9RX - Gary via groups.io
Sent: Wednesday, January 8, 2025 2:23 PM
To: [email protected]; [email protected]
Subject: Re: [ServoCAT] Servo Cat moves after goto completes.

?

Hello Bob,

?

Forgive me - I saw this and forgot to respond to it ...?

?

So - this sounds like a drive roller is slipping due to a loose grub screw. Check to see which axis is off first - then focus on the drive roller for that axis.?

?

Gary Myers

StellarCAT

?

?

?

?

------ Original Message ------

From "bobrose500 via groups.io" <bobrose500@...>

To [email protected]

Date 1/2/2025 10:26:17 PM

Subject [ServoCAT] Servo Cat moves after goto completes.

?

I am asking on behalf of my clubs SC install. It is a 40" with a Nexus (not Pro). All GOTO's are via the Nexus. A couple of years ago just after a GOTO finished the SC would motor about 10 arcminutes from the target. Display on Nexus indication something like `0.10. It has progressively increased over the past year or so. Last outing it was nearly 1 degree. I can issue another GOTO and it will zero in a little better. Strange thing is it will nearly zero the target stops then proceed again to a position now that is 50+ arcminutes. Anybody got any ideas what the issue is? We are calling it overshoot. In it is acquiring the target then moving away.

Bob

No, it goto’s essentially almost 0’s. Then moves and ends up something like 0.30:0.55. ?Back when we first noticed it, the numbers were around 0.10 :0.10. I might suspect the gears are getting play in them except after nearly getting it right, the motors wind back up and it moves decidedly away.

Firmware has not been updated in years. Probably should do that first.

Bob

?

From: [email protected] <[email protected]> On Behalf Of K9RX - Gary via groups.io
Sent: Wednesday, January 8, 2025 4:02 PM
To: [email protected]; [email protected]
Subject: Re: [ServoCAT] Servo Cat moves after goto completes.

?

The algorithm is designed, assuming you are using the latest version firmware, to always end up in the direction of sidereal tracking. So - it does a GOTO. Then it gets the offset again from the DSC and does a 2nd GOTO. If after the 2nd one the distance to the object is still more than ... I think it was 0.04°, it will do a third one, if it is within that it will not do another.?

?

But it then checks to see which direction the last move was - was it in the direction of sidereal or not. If not it will move the axis away in the direction opposite sidereal, more than the backlash value (typically 0.7° or so)... and then it will do one final GOTO. THIS should put it both at 0.00 on each axis as well as tracking immediately (no backlash to unwind).?

?

Thus you could and would see behavior like you are describing - but it should still end up < 0.05° away.?

?

g.

?

?

?

?

------ Original Message ------

From "bobrose500 via groups.io" <bobrose500@...>

To [email protected]

Date 1/8/2025 5:29:29 PM

Subject Re: [ServoCAT] Servo Cat moves after goto completes.

?

Gary,

Thanks for the reply. I will check the drive rollers. It seems to split the error between the axes. I will check both. ?Hadn’t really thought about it being slipping as it goes to the target stops for about a half second then motors past. It is pretty much acquiring the target in the initial goto. No overshoot or undershoot there. Just immediately after acquisition, the motors start back up and drive past. I is like it has built in offset.

Bob

?

From: [email protected] <[email protected]> On Behalf Of K9RX - Gary via groups.io
Sent: Wednesday, January 8, 2025 2:23 PM
To: [email protected]; [email protected]
Subject: Re: [ServoCAT] Servo Cat moves after goto completes.

?

Hello Bob,

?

Forgive me - I saw this and forgot to respond to it ...?

?

So - this sounds like a drive roller is slipping due to a loose grub screw. Check to see which axis is off first - then focus on the drive roller for that axis.?

?

Gary Myers

StellarCAT

?

?

?

?

------ Original Message ------

From "bobrose500 via groups.io" <bobrose500@...>

To [email protected]

Date 1/2/2025 10:26:17 PM

Subject [ServoCAT] Servo Cat moves after goto completes.

?

I am asking on behalf of my clubs SC install. It is a 40" with a Nexus (not Pro). All GOTO's are via the Nexus. A couple of years ago just after a GOTO finished the SC would motor about 10 arcminutes from the target. Display on Nexus indication something like `0.10. It has progressively increased over the past year or so. Last outing it was nearly 1 degree. I can issue another GOTO and it will zero in a little better. Strange thing is it will nearly zero the target stops then proceed again to a position now that is 50+ arcminutes. Anybody got any ideas what the issue is? We are calling it overshoot. In it is acquiring the target then moving away.

Bob

Bob,?

?

Sorry - I think you missed the point. IF it is the latest version firmware then my point is a) that is why you are seeing a lower value and yet it moves again and b) there is indeed a last mover after that...?

?

so if there's slippage in the drive rollers that would account for it.?

?

Also: the fact that it is getting worse suggests strongly it is a loose drive roller.?

?

But I would suggest you check the version. If it powers up and the red AUX light comes on before the green SLEW light (ignore the HC light for this) then it is the latest version. (if you have a Gen2 it might show the yellow SPm light before the green SLEW light)

?

g.

?

?

?

?

?

No, it goto’s essentially almost 0’s. Then moves and ends up something like 0.30:0.55. ?Back when we first noticed it, the numbers were around 0.10 :0.10. I might suspect the gears are getting play in them except after nearly getting it right, the motors wind back up and it moves decidedly away.

Firmware has not been updated in years. Probably should do that first.

Bob

?

From: [email protected] <[email protected]> On Behalf Of K9RX - Gary via groups.io
Sent: Wednesday, January 8, 2025 4:02 PM
To: [email protected]; [email protected]
Subject: Re: [ServoCAT] Servo Cat moves after goto completes.

?

The algorithm is designed, assuming you are using the latest version firmware, to always end up in the direction of sidereal tracking. So - it does a GOTO. Then it gets the offset again from the DSC and does a 2nd GOTO. If after the 2nd one the distance to the object is still more than ... I think it was 0.04°, it will do a third one, if it is within that it will not do another.?

?

But it then checks to see which direction the last move was - was it in the direction of sidereal or not. If not it will move the axis away in the direction opposite sidereal, more than the backlash value (typically 0.7° or so)... and then it will do one final GOTO. THIS should put it both at 0.00 on each axis as well as tracking immediately (no backlash to unwind).?

?

Thus you could and would see behavior like you are describing - but it should still end up < 0.05° away.?

?

g.

?

?

?

?

------ Original Message ------

From "bobrose500 via groups.io" <bobrose500@...>

To [email protected]

Date 1/8/2025 5:29:29 PM

Subject Re: [ServoCAT] Servo Cat moves after goto completes.

?

Gary,

Thanks for the reply. I will check the drive rollers. It seems to split the error between the axes. I will check both. ?Hadn’t really thought about it being slipping as it goes to the target stops for about a half second then motors past. It is pretty much acquiring the target in the initial goto. No overshoot or undershoot there. Just immediately after acquisition, the motors start back up and drive past. I is like it has built in offset.

Bob

?

From: [email protected] <[email protected]> On Behalf Of K9RX - Gary via groups.io
Sent: Wednesday, January 8, 2025 2:23 PM
To: [email protected]; [email protected]
Subject: Re: [ServoCAT] Servo Cat moves after goto completes.

?

Hello Bob,

?

Forgive me - I saw this and forgot to respond to it ...?

?

So - this sounds like a drive roller is slipping due to a loose grub screw. Check to see which axis is off first - then focus on the drive roller for that axis.?

?

Gary Myers

StellarCAT

?

?

?

?

------ Original Message ------

From "bobrose500 via groups.io" <bobrose500@...>

To [email protected]

Date 1/2/2025 10:26:17 PM

Subject [ServoCAT] Servo Cat moves after goto completes.

?

I am asking on behalf of my clubs SC install. It is a 40" with a Nexus (not Pro). All GOTO's are via the Nexus. A couple of years ago just after a GOTO finished the SC would motor about 10 arcminutes from the target. Display on Nexus indication something like `0.10. It has progressively increased over the past year or so. Last outing it was nearly 1 degree. I can issue another GOTO and it will zero in a little better. Strange thing is it will nearly zero the target stops then proceed again to a position now that is 50+ arcminutes. Anybody got any ideas what the issue is? We are calling it overshoot. In it is acquiring the target then moving away.

Bob