RA Problem


Gary Hug
 

Recently after nearly a decade of good use, Ive had an issue with the RA drive.
I've a SiTech Controller II and use it on a rather large and heavy fork mounted reflector scope. My number of RA motors ticks for 360 degree are in the range of 93,000,000 and I'm limited to just under 1 degree per second slews after ramping. No Problem with that.

The latest issue with the RA drive is when slewing to the west the slews are accurate and after briefly ramping up it does indeed obtain just under 1 degree slews.

The problem arises when I try to slew to the east (no matter where I am in relation to the meridian) The motor starts out ramping OK but after ramping the motor speed cuts back to about 1/2 or less and the results are it overshoots the target by a considerable distance. I changed out 3 different servo motors with the same results in each. I've also replaced the wiring and connectors.

The RA timing pulley is easily moved either east or west with little change in resistance. I'm assuming there is a problem with the encoder numbers somewhere. Either in sending or receiving or converting.

Probably something I'm not thinking about but at my age I throw embarrassment to the wind.


Thanks for reading,

Gary Hug


Russell R
 

Hi Gary,

What is your version of SiTech?
Assuming this is a worm gear drive and well lubed.
Have you checked the amp load in both directions in controller stuff?
Have you tested the motor with "test and tune" in Servo Config? Here you can check the encoder also?

Age is no embarrassment....unless you are under 30!  Your mileage may vary.

Russell R.


Don W
 

Hi Gary,

Check if you have configured the controller to "Keep above Horizon Limit when Slewing".  That control slows either servo to avoid going past the limit.  This is probably your problem.

Don W


Gary Hug
 

Hi Don,

I don't have the "Keep above Horizon Limit when Slewing", box checked.
The RA motor is only affected in one direction. It's like the motor moving forward runs at the correct speed but in reverse runs at a much lower speed and looses position. That's why I keep thinking it's losing ticks or not registering the encoder's output completely. Maybe an I/O problem?

Anyway thanks for your suggestion. You guys rock! (and I'm not saying that just because I work with asteroids.)

On 4/18/2021 12:05 PM, Don W wrote:
Hi Gary,
Check if you have configured the controller to "Keep above Horizon Limit when Slewing".  That control slows either servo to avoid going past the limit.  This is probably your problem.
Don W


Gary Hug
 

Hi Russell,
I'm using 95P and V97

My amp load in both RA directions is nearly the same and avg .3 to .5 at tracking mode.
I'll give test and tune another go and see if anything changes.

I'm definitely not under 30!

thanks for you suggestions,
cheers
Gary

On 4/18/2021 11:00 AM, Russell R via groups.io wrote:
Hi Gary,
What is your version of SiTech?
Assuming this is a worm gear drive and well lubed.
Have you checked the amp load in both directions in controller stuff? Have you tested the motor with "test and tune" in Servo Config? Here you can check the encoder also?
Age is no embarrassment....unless you are under 30!  Your mileage may vary.
Russell R.


Don W
 

Hi Gary,

There is the possibility that the brush type servo motor is simply failing.  You have had a heavy load for a lot of years.  Try running the servo if you can, free of load - disconnect the worm from the main gear and see if the servo moves at the same rate each way.  Also try moving the servo using Servo Config.exe rather than the SiTechexe.

Don W


Gary Hug
 

Hey Thanks Don.

I took your advice and while I was running the motor thru Servo Config. I also played with the motor parameters and sure enough after I took the motor off load and played with the parameters I was able to get the motor to run well in both directions. It appears I didn't do a very good job adjusting the motor when I replaced the old motor with a new one.
I'll put the new motor back on load and test it tonight. Thanks for your help.

cheers,
Gary

On 4/18/2021 6:18 PM, Don W wrote:
Hi Gary,*
*There is the possibility that the brush type servo motor is simply failing. You have had a heavy load for a lot of years.  Try running the servo if you can, free of load - disconnect the worm from the main gear and see if the servo moves at the same rate each way.  Also try moving the servo using Servo Config.exe rather than the SiTechexe.
Don W


Russell R
 

Gary,

When the motor starts to slow down after ramping up, does it sound like it's "growling" when running at ½ speed, then "frees up" when getting near the target?

If so, try slowing down the slew speed in Servo Config and see what happens.  This same thing happened to me, and when I dropped the slew speed a bit, it stopped doing that.

I am limited to just under 2° slew speed at 64M ticks. I was able to go over 2° for years, not sure if it had something to do with a updated version SiTech.exe.

You also mentioned you are in the range of 93M ticks, do you know the tick count exact?  That's a whole lot of tickin goin on. :-)

Russell R.


Gary Hug
 

Hi Russell,

No, there was no growling and it didn't stop the motor but as I told Don I wrongly made the assumption that my motor configuration was OK. It wasn't.
After going back and reworking the numbers I was able to hear the difference and the motor now looks and sounds the same in each direction. (actually the apparent speed of the east movement is now as fast as the west movement.) I never knew that one direction could be affected more than the other. At this point I'm eager to adjust both RA and DEC to finally bring the scope pointing accuracy to +/- and arc minute or so. It's just now getting dark enough to try. I'll send out a report toward morning on the results but I'm pretty sure it'll work now.

(93,754,919 RA ticks/360 degrees to be exact - at least until I refine that number thru tonight's calibration run.) The scope weighs roughly 1200 lbs.


Thanks to you and Don for the support. Also to Dan and Taij. Its great to have such support with a wonderful company like SiTech.

cheers
Gary

On 4/18/2021 6:55 PM, Russell R via groups.io wrote:
Gary,
When the motor starts to slow down after ramping up, does it sound like it's "growling" when running at ½ speed, then "frees up" when getting near the target?
If so, try slowing down the slew speed in Servo Config and see what happens. This same thing happened to me, and when I dropped the slew speed a bit, it stopped doing that.
I am limited to just under 2° slew speed at 64M ticks. I was able to go over 2° for years, not sure if it had something to do with a updated version SiTech.exe.
You also mentioned you are in the range of 93M ticks, do you know the tick count exact?  That's a whole lot of tickin goin on. :-)
Russell R.


CandCShaw
 

Gary,

Another cause for the motors to vary in speed is if you are using a custom Horizon (check "Use Horizon File Sitech.hrz" checked, and you have "Keep Horizon Limit while slewing" checked  Both are in the upper right area of the Config > ChangeConfig! . > MountParams tab.

Chuck

Chuck Shaw

On Sun, Apr 18, 2021 at 9:25 PM Gary Hug <garyhug@...> wrote:
Hi Russell,

No, there was no growling and it didn't stop the motor but as I told Don I
wrongly made the assumption that my motor configuration was OK. It wasn't.
After going back and reworking the numbers I was able to hear the difference and
the motor now looks and sounds the same in each direction.  (actually the
apparent speed of the east movement is now as fast as the west movement.) I
never knew that one direction could be affected more than the other.   At this
point I'm eager to adjust both RA and DEC to finally bring the scope pointing
accuracy to +/- and arc minute or so. It's just now getting dark enough to try.
  I'll send out a report toward morning on the results but I'm pretty sure it'll
work now.

(93,754,919 RA ticks/360 degrees to be exact - at least until I refine that
number thru tonight's calibration run.) The scope weighs roughly 1200 lbs.


Thanks to you and Don for the support.  Also to Dan and Taij.  Its great to have
such support with a wonderful company like SiTech.

cheers
Gary

On 4/18/2021 6:55 PM, Russell R via groups.io wrote:
> Gary,
>
> When the motor starts to slow down after ramping up, does it sound like it's
> "growling" when running at ½ speed, then "frees up" when getting near the target?
>
> If so, try slowing down the slew speed in Servo Config and see what happens. 
> This same thing happened to me, and when I dropped the slew speed a bit, it
> stopped doing that.
>
> I am limited to just under 2° slew speed at 64M ticks. I was able to go over 2°
> for years, not sure if it had something to do with a updated version SiTech.exe.
>
> You also mentioned you are in the range of 93M ticks, do you know the tick count
> exact?  That's a whole lot of tickin goin on. :-)
>
> Russell R.
>






Russell R
 

Gary,

That's good news!   1200#......Wow, maybe you could post a pic of that big boy.  

I could not agree more!!! 
Dan, Taj, Don, & Chuck are just awesome folks!  Dan really stands behind his products and tries to help solve everyone's individual nit-picky issues, even if he has to re-write the software.
Each one of these guys and others here, helped me along the way for sure.

Best,
Russell R.


Joshua Hufford
 

1200 Lbs. of scope? That requires some pictures!  :))

Josh

On Sun, Apr 18, 2021 at 9:57 PM Russell R via groups.io <rem.64=yahoo.com@groups.io> wrote:
Gary,

That's good news!   1200#......Wow, maybe you could post a pic of that big boy.  

I could not agree more!!! 
Dan, Taj, Don, & Chuck are just awesome folks!  Dan really stands behind his products and tries to help solve everyone's individual nit-picky issues, even if he has to re-write the software.
Each one of these guys and others here, helped me along the way for sure.

Best,
Russell R.


Gary Hug
 

Thanks Chuck,
And thanks to everyone on this SiTech.io group for such wonderful support.
The 'Little Blue 22' is functioning again.
cheers
Gary

On 4/18/2021 8:41 PM, CandCShaw wrote:
Gary,
Another cause for the motors to vary in speed is if you are using a custom Horizon (check "Use Horizon File Sitech.hrz" checked, and you have "Keep Horizon Limit while slewing" checked  Both are in the upper right area of the Config > ChangeConfig! . > MountParams tab.
Chuck
Chuck Shaw
On Sun, Apr 18, 2021 at 9:25 PM Gary Hug <garyhug@mercurywireless.net <mailto:garyhug@mercurywireless.net>> wrote:
Hi Russell,
No, there was no growling and it didn't stop the motor but as I told Don I
wrongly made the assumption that my motor configuration was OK. It wasn't.
After going back and reworking the numbers I was able to hear the difference
and
the motor now looks and sounds the same in each direction.  (actually the
apparent speed of the east movement is now as fast as the west movement.) I
never knew that one direction could be affected more than the other.   At this
point I'm eager to adjust both RA and DEC to finally bring the scope pointing
accuracy to +/- and arc minute or so. It's just now getting dark enough to try.
  I'll send out a report toward morning on the results but I'm pretty sure
it'll
work now.
(93,754,919 RA ticks/360 degrees to be exact - at least until I refine that
number thru tonight's calibration run.) The scope weighs roughly 1200 lbs.
Thanks to you and Don for the support.  Also to Dan and Taij.  Its great to
have
such support with a wonderful company like SiTech.
cheers
Gary
On 4/18/2021 6:55 PM, Russell R via groups.io <http://groups.io> wrote:
> Gary,
>
> When the motor starts to slow down after ramping up, does it sound like it's
> "growling" when running at ½ speed, then "frees up" when getting near the
target?
>
> If so, try slowing down the slew speed in Servo Config and see what happens.
> This same thing happened to me, and when I dropped the slew speed a bit, it
> stopped doing that.
>
> I am limited to just under 2° slew speed at 64M ticks. I was able to go
over 2°
> for years, not sure if it had something to do with a updated version
SiTech.exe.
>
> You also mentioned you are in the range of 93M ticks, do you know the
tick count
> exact?  That's a whole lot of tickin goin on. :-)
>
> Russell R.
>