changing the tracking rate


Gary Hug
 

I've been trying to get a different Pittman servo motor set up on the RA axis of my Newt Reflector. The encoder is 500 CPR and the motor is an 8000 Pittman brushed servo series. Its an older model Lo-Cog with 19.1 ratio gear-head but has never been used.

I was able, by trial and error, to slew to different parts of the sky and increase or decrease the number of encoder ticks/360 degree and got to a accuracy of about 15 arc minutes for slews up to 120 degrees. With a PXP model I should be able to bring that down to less than 5.

My tick count is approx. 83,500,000 which limits slews to only .75 degrees/ second. I'm fine with the slow slews and am accustomed to it.

The problem is my tracking rate (for imaging) seems to be twice what it should be. If I lower the ticks per 360 degree, I'll loose slewing accuracy.

I'm probably not remembering something about how to change the tracking rate without changing the ticks/revolution thereby losing the slewing accuracy? Or maybe something is getting counted (x2) somewhere along the way?

Any help would be appreciated,

& thanks for letting me ramble on.

Gary


Russell R
 

Gary,

My guess would be tick count is off.   Just has a reminder, that encoder is read in quadrature, 500 X 4 X 19.1 X gearing ratio.  
How do you increase or decrease ticks by slewing?  Maybe I don't understand.

Russell R.


Don W
 

Hi Gary,

In servoConfig.exe you can adjust the tracking rate, and you can set an adjustment rate that you can use with the HandPad.  I am copying the paragraphs from the Setup Manual here:

Setting Up the Equatorial Mode

Using the ServoConfig software, click on “Edit Parameters”, then “Auto Tracking”.  Click on the Equatorial mode radio button.  Set up the Equatorial rate.  If you know the number of effective encoder ticks for one revolution of the Right Ascension axis, enter that number in the green text box to the right.  After pressing the Enter key, the proper Equatorial rate will be calculated and will appear in the “equatorial rate” text box. (The number you entered in the green box will also change to accommodate the math the controller uses internally.  Not to worry, if you entered the correct ticks/rev, the slight change the controller needs will not mess things up for you!)  If you do not know the exact number to enter and want to experiment, a larger number will make the system track faster.

 

You can adjust the tracking rate up and down by pressing a certain sequence on the handpad (described in the next section).  The amount it is adjusted per handpad press is in the text box labeled “Equatorial Up/Down Adjust”. 

To raise the tracking speed, press the top left key, and while holding it down (think of it as an ALT key) press the up direction.

 

To lower the tracking speed, press the top left key, and while holding it down (think of it as an ALT key) press the down direction.

 

The up/down speed adjustment will not work if you have set up the local search feature (version 1.7 or later of the firmware).  To enable the UP/Down adjustments, you will have to enter a value of zero in the local search distance and speed parameters.

I don't know how many times you can adjust the speed.  But you can increase or decrease the setting.  I think the value in the green box for R/A Total Motor Encoder Ticks is independent of the setting elsewhere for ticks/rev.

Just to be sure, are you positive that your tick/rev are 83.5 million?  That is very high, and being high makes the mount track faster.  Please recheck your ticks calculation.
Don W

 


Gary Hug
 

What I meant to say was I was adjusting the ticks/360 degree rate according to the accuracy of the slews. As example if I plate solved some position in the east sky and slewed 120 degrees to the west but ended up at only moving 105 degrees to the west (that west position again being plate solved also) Then I know to increase the number of ticks needed by approximately 10%. Now if there are motor issues or ticks missing or slipping somewhere this won't work of course.

So I do need to do as you and Don suggest just to make sure the count is close to the predicted through the gear train.

I have a unique mount that uses basically a pinch roller for the drive mechanism or as I like to call it a 'high pressure friction drive'. The drive roller is a 1" slightly tapered shaft pressed against the outer surface of the 48" diameter 3/8" steel disk. So I start with a 48-1 ratio x a 30-1 gear reducer x 1.5 to 1 timing pulley arraignment x 2000 x 19.1 = 82,512,000 ticks per 360 degree.
My previous motor had a 10-1 gear ratio, but I changed the timing gear from 2-1 to a now 1.5-1. The scope is approx 1200 lbs including the mount, so the high gearing ratio gives me a greatly relaxed need for torque at the expense of speed reduction. I can turn the pulley next to the motor by one finger in both directions so the torque required by the motor is minimal.

cheers
Gary

On 4/26/2021 6:44 AM, Russell R via groups.io wrote:
Gary,
My guess would be tick count is off.   Just has a reminder, that encoder is read in quadrature, 500 X 4 X 19.1 X gearing ratio.
How do you increase or decrease ticks by slewing?  Maybe I don't understand.
Russell R.


Joshua Hufford
 

Gary, trying to correct for slewing errors by changing the tick count seems like an exercise in frustration to me. 

There is a tool in ServoConfig to determine the amount of ticks. If you can't get an exact figure using math this "should" get you close. If your slews are accurate but your tracking speed is off or the other way around, I'd look for the problem elsewhere, not by changing the tick count. 

My $.02

Josh

On Mon, Apr 26, 2021 at 3:06 PM Gary Hug <garyhug@...> wrote:
What I meant to say was I was adjusting the ticks/360 degree rate according to
the accuracy of the slews.  As example if I plate solved some position in the
east sky and slewed 120 degrees to the west but ended up at only moving 105
degrees to the west (that west position again being plate solved also) Then I
know to increase the number of ticks needed by approximately 10%.  Now if there
are motor issues or ticks missing or slipping somewhere this won't work of course.

So I do need to do as you and Don suggest just to make sure the count is close
to the predicted through the gear train.

I have a unique mount that uses basically a pinch roller for the drive mechanism
or as I like to call it a 'high pressure friction drive'.  The drive roller is a
1" slightly tapered shaft pressed against the outer surface of the  48" diameter
3/8" steel disk.  So I start with a 48-1 ratio x a 30-1 gear reducer x 1.5 to 1
timing pulley arraignment x 2000 x 19.1 = 82,512,000 ticks per 360 degree.
My previous motor had a 10-1 gear ratio, but I changed the timing gear from 2-1
to a now 1.5-1.  The scope is approx 1200 lbs including the mount, so the high
gearing ratio gives me a greatly relaxed need for torque at the expense of speed
reduction.  I can turn the pulley next to the motor by one finger in both
directions so the torque required by the motor is minimal.

cheers
Gary

On 4/26/2021 6:44 AM, Russell R via groups.io wrote:
> Gary,
>
> My guess would be tick count is off.   Just has a reminder, that encoder is read
> in quadrature, 500 X 4 X 19.1 X gearing ratio.
> How do you increase or decrease ticks by slewing?  Maybe I don't understand.
>
> Russell R.
>






Gary Hug
 

Yeah, I think your right, Joshua.

I'm beginning to suspect the motor or controller is dropping ticks. The other motor I had seemed to suddenly became faulty and that's why I changed it out but maybe it wasn't the motor. Maybe the controller needs tested out. I've had that Servo II controller in use for over a decade. Or more likely I've got my tracking rate messed up while my slew rates are relatively accurate. Don suggested checking my tracking rate adjustment,

"The up/down speed adjustment will not work if you have set up the local search feature (version 1.7 or later of the firmware). To enable the UP/Down adjustments, you will have to enter a value of zero in the local search distance and speed parameters."

I had some numbers in the ('local search' dialog box) so maybe by setting this number to zero will allow and up down tracking adjustment. I'll try it next time the wind is less than 20-40 MPH and its not raining. (Or what we call Full Moon (:>) )

Thanks for the suggestions guys,

cheers
Gary

On 4/26/2021 3:18 PM, Joshua Hufford wrote:
Gary, trying to correct for slewing errors by changing the tick count seems like an exercise in frustration to me.
There is a tool in ServoConfig to determine the amount of ticks. If you can't get an exact figure using math this "should" get you close. If your slews are accurate but your tracking speed is off or the other way around, I'd look for the problem elsewhere, not by changing the tick count.
My $.02
Josh
On Mon, Apr 26, 2021 at 3:06 PM Gary Hug <garyhug@mercurywireless.net <mailto:garyhug@mercurywireless.net>> wrote:
What I meant to say was I was adjusting the ticks/360 degree rate according to
the accuracy of the slews.  As example if I plate solved some position in the
east sky and slewed 120 degrees to the west but ended up at only moving 105
degrees to the west (that west position again being plate solved also) Then I
know to increase the number of ticks needed by approximately 10%.  Now if there
are motor issues or ticks missing or slipping somewhere this won't work of
course.
So I do need to do as you and Don suggest just to make sure the count is close
to the predicted through the gear train.
I have a unique mount that uses basically a pinch roller for the drive
mechanism
or as I like to call it a 'high pressure friction drive'.  The drive roller
is a
1" slightly tapered shaft pressed against the outer surface of the  48"
diameter
3/8" steel disk.  So I start with a 48-1 ratio x a 30-1 gear reducer x 1.5 to 1
timing pulley arraignment x 2000 x 19.1 = 82,512,000 ticks per 360 degree.
My previous motor had a 10-1 gear ratio, but I changed the timing gear from 2-1
to a now 1.5-1.  The scope is approx 1200 lbs including the mount, so the high
gearing ratio gives me a greatly relaxed need for torque at the expense of
speed
reduction.  I can turn the pulley next to the motor by one finger in both
directions so the torque required by the motor is minimal.
cheers
Gary
On 4/26/2021 6:44 AM, Russell R via groups.io <http://groups.io> wrote:
> Gary,
>
> My guess would be tick count is off.   Just has a reminder, that encoder
is read
> in quadrature, 500 X 4 X 19.1 X gearing ratio.
> How do you increase or decrease ticks by slewing?  Maybe I don't understand.
>
> Russell R.
>


Gary Hug
 

Yes, Thank you for the info. I did indeed have some numbers in local search box that I've now set to zero. I'm now able to change the tracking rate. As a test I took the tracking speed from 83500000 to 10000000 and the timing belt speed is greatly reduced. So while I'm not sure yet what numbers I'll end up with, I'm confident I can get there..

Thanks again guys,
I think Dan should double your salary (:>)

cheers
Gary

On 4/26/2021 11:13 AM, Don W wrote:
Hi Gary,
In servoConfig.exe you can adjust the tracking rate, and you can set an adjustment rate that you can use with the HandPad.  I am copying the paragraphs from the Setup Manual here:
*Setting Up the Equatorial Mode*
*Using the ServoConfig software, click on “Edit Parameters”, then “Auto Tracking”.Click on the Equatorial mode radio button.Set up the Equatorial rate.If you know the number of effective encoder ticks for one revolution of the Right Ascension axis, enter that number in the green text box to the right.After pressing the Enter key, the proper Equatorial rate will be calculated and will appear in the “equatorial rate” text box. (The number you entered in the green box will also change to accommodate the math the controller uses internally.Not to worry, if you entered the correct ticks/rev, the slight change the controller needs will not mess things up for you!) If you do not know the exact number to enter and want to experiment, a larger number will make the system track faster.*
**
*You can adjust the tracking rate up and down by pressing a certain sequence on the handpad (described in the next section).The amount it is adjusted per handpad press is in the text box labeled “Equatorial Up/Down Adjust”.
*
**
*To raise the tracking speed, press the top left key, and while holding it down (think of it as an ALT key) press the up direction.*
**
*To lower the tracking speed, press the top left key, and while holding it down (think of it as an ALT key) press the down direction.*
**
*The up/down speed adjustment will not work if you have set up the local search feature (version 1.7 or later of the firmware).To enable the UP/Down adjustments, you will have to enter a value of zero in the local search distance and speed parameters.*
I don't know how many times you can adjust the speed.  But you can increase or decrease the setting.  I think the value in the green box for R/A Total Motor Encoder Ticks is independent of the setting elsewhere for ticks/rev.
Just to be sure, are you positive that your tick/rev are 83.5 million?  That is very high, and being high makes the mount track faster.  Please recheck your ticks calculation.
Don W


Don W
 

Hi Gary,
Good luck adjusting your tracking rate.  But I am an unpaid "volunteer".
Don W


Gary Hug
 

Yeah I knew that; but just think of doubling that!!
(:>)
G

On 4/26/2021 7:37 PM, Don W wrote:
Hi Gary,
Good luck adjusting your tracking rate.  But I am an unpaid "volunteer".
Don W