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Jiggle when tracking

Antonio
 

Greetings

My Onstep is on  Arduino Mega 2560 with 8825 drivers and a proprietary "shield".

The image keeps "jiggling" (or jumping) when tracking.  Take a look at https://youtu.be/gkvGbBnexf8 .


My mount is an old CG4 with a 102 mm refractor, with counterweighs slightly against the RA motion to avoid worm slip.

The engines are Nema 17, 200 steps.

Since these "jigglings" are constant in any tube position, I think I can rule out mechanical problems.

The configuration file is Config.classic.h

Are there some configurations I could try to solve this problem?

Thanks,

Antônio

Howard Dutton
 

On Mon, Mar 16, 2020 at 07:40 AM, Antonio wrote:
My Onstep is on  Arduino Mega 2560 with 8825 drivers and a proprietary "shield".
The DRV8825 is notorious for not stepping smoothly, happens all too often, hence we don't recommend using them.

Khalid Baheyeldin
 

On Mon, Mar 16, 2020 at 10:52 AM, Howard Dutton wrote:
The DRV8825 is notorious for not stepping smoothly, happens all too often, hence we don't recommend using them.
Depending on how much current you are running the motor at, you may be able to use the LV8729, which are very smooth, and very cheap.
If the current is higher than ~ 1 Ampere, then try the S109 drivers.

SteveS
 

Antonio,
I use the 8825 drivers (for now) without that issue, you didnt mention if you tuned the currents to the driver chip currents?
SteveS
--
Three stones observatory 40° 46' 42"N 88° 12' 30" W

Howard Dutton
 

On Mon, Mar 16, 2020 at 08:56 AM, SteveS wrote:
I use the 8825 drivers (for now) without that issue, you didnt mention if you tuned the currents to the driver chip currents?
I too am assuming this is your shield board.

Question: long ago we discussed designing in the DRV8825 decay control, did that ever happen?

SteveS
 

I dont know if its mine or not, Antonio can respond.
I m using my board without issue, but as you know, I didn't include a set of test points or pads for doing the current adjustments so its difficult to do (learning curve on my part).
I m sure that Antonio would prefer to work the issue rather than purchase new gear so if I can help..
No, the newer motor control chips were coming on line at the time and everyone was shifting to those so the effort(and my focus ) didnt seem important.

--
Three stones observatory 40° 46' 42"N 88° 12' 30" W

Antonio
 

I replaced the driver unit and the problem remains.  No matter "the DRV8825 is notorious for not stepping smoothly (Howard)", a lot of users of an Onstep group where I buy the shield reports it fine.
They says my problem is mechanic but I inverted the cables (RA driver to DEC motor and the DEC driver to RA motor) aiming to get another mechanical configuration. (I know I can´t do that for good...), and the jiggle continues (of course, changing the direction and the frequence, since the gear of the DEC has a differente tooth number), but appears to be THE SAME error.


Em 16/03/2020 13:41, SteveS escreveu:

I dont know if its mine or not, Antonio can respond.
I m using my board without issue, but as you know, I didn't include a set of test points or pads for doing the current adjustments so its difficult to do (learning curve on my part).
I m sure that Antonio would prefer to work the issue rather than purchase new gear so if I can help..
No, the newer motor control chips were coming on line at the time and everyone was shifting to those so the effort(and my focus ) didnt seem important.

--
Three stones observatory 40° 46' 42"N 88° 12' 30" W

SteveS
 

Antonio,
Did you adjust the currents for your motor?
Have you tried removing the load from your mount, ie take off the OTA and balance weights, running the motors with no load just as a check?

SteveS


On Sat, Mar 21, 2020 at 10:59 AM Antonio <antonio.soares@...> wrote:

I replaced the driver unit and the problem remains.  No matter "the DRV8825 is notorious for not stepping smoothly (Howard)", a lot of users of an Onstep group where I buy the shield reports it fine.
They says my problem is mechanic but I inverted the cables (RA driver to DEC motor and the DEC driver to RA motor) aiming to get another mechanical configuration. (I know I can´t do that for good...), and the jiggle continues (of course, changing the direction and the frequence, since the gear of the DEC has a differente tooth number), but appears to be THE SAME error.


Em 16/03/2020 13:41, SteveS escreveu:
I dont know if its mine or not, Antonio can respond.
I m using my board without issue, but as you know, I didn't include a set of test points or pads for doing the current adjustments so its difficult to do (learning curve on my part).
I m sure that Antonio would prefer to work the issue rather than purchase new gear so if I can help..
No, the newer motor control chips were coming on line at the time and everyone was shifting to those so the effort(and my focus ) didnt seem important.

--
Three stones observatory 40° 46' 42"N 88° 12' 30" W


--
Three stones observatory 40° 46' 42"N 88° 12' 30" W

Aisling Lightworks
 

This looks like mechanical problem to me. It looks like it's taking time for the motor torque to overcome the friction of the gears. Are you well lubricated, well balanced, with proper backlash? Are you geared down enough and providing enough current and voltage to your motors to do the work you're assigning them?

Jorge Oliveira
 

Antônio, my onstep is the same as yours, the mount is the same as a CG4, mine so far has not presented any problem.  Traking and Goto are working perfectly.

Em dom, 22 de mar de 2020 12:49, Aisling Lightworks <stercust@...> escreveu:

This looks like mechanical problem to me. It looks like it's taking time for the motor torque to overcome the friction of the gears. Are you well lubricated, well balanced, with proper backlash? Are you geared down enough and providing enough current and voltage to your motors to do the work you're assigning them?

Khalid Baheyeldin
 

On Sun, Mar 22, 2020 at 12:07 PM, Jorge Oliveira wrote:
my onstep is the same as yours, the mount is the same as a CG4, mine so far has not presented any problem.  Traking and Goto are working perfectly.
Jorge,

Are you using DRV8825 as well? Which board?

Jorge Oliveira
 

Yes, we buy with the same person, the kit is the same as Antônio's.  I use the dvr8825 driver.  


Em dom, 22 de mar de 2020 13:09, Khalid Baheyeldin <kbahey@...> escreveu:

On Sun, Mar 22, 2020 at 12:07 PM, Jorge Oliveira wrote:
my onstep is the same as yours, the mount is the same as a CG4, mine so far has not presented any problem.  Traking and Goto are working perfectly.
Jorge,

Are you using DRV8825 as well? Which board?

Jorge Oliveira
 


Em dom, 22 de mar de 2020 14:08, Jorge Oliveira via Groups.Io <voyagervideo=gmail.com@groups.io> escreveu:

Yes, we buy with the same person, the kit is the same as Antônio's.  I use the dvr8825 driver.  


Em dom, 22 de mar de 2020 13:09, Khalid Baheyeldin <kbahey@...> escreveu:
On Sun, Mar 22, 2020 at 12:07 PM, Jorge Oliveira wrote:
my onstep is the same as yours, the mount is the same as a CG4, mine so far has not presented any problem.  Traking and Goto are working perfectly.
Jorge,

Are you using DRV8825 as well? Which board?

Khalid Baheyeldin
 

On Sun, Mar 22, 2020 at 01:08 PM, Jorge Oliveira wrote:
Yes, we buy with the same person, the kit is the same as Antônio's.  I use the dvr8825 driver. 
Thanks.
This means that Antonio's problem has to be in his mount.

Antonio
 


Is there a method for me to check the assembly?
Moving manually, it rotates smoothly, without backslash. I always put the counterweight a little against the movement of the RA.
On the endless axis of the RA, it was necessary to place an extension, but it was turned and has no gaps.

My only doubt is the engines: one is 4 Nm and the other is 3.5 Nm, but the seller assured me that it would not be a problem.


Em 22/03/2020 14:10, Jorge Oliveira escreveu:


Em dom, 22 de mar de 2020 14:08, Jorge Oliveira via Groups.Io <voyagervideo=gmail.com@groups.io> escreveu:
Yes, we buy with the same person, the kit is the same as Antônio's.  I use the dvr8825 driver.  


Em dom, 22 de mar de 2020 13:09, Khalid Baheyeldin <kbahey@...> escreveu:
On Sun, Mar 22, 2020 at 12:07 PM, Jorge Oliveira wrote:
my onstep is the same as yours, the mount is the same as a CG4, mine so far has not presented any problem.  Traking and Goto are working perfectly.
Jorge,

Are you using DRV8825 as well? Which board?

Aisling Lightworks
 

4Nm should be more than enough. My mount moves 25 Kg with ease using 59Ncm motors.

Aisling Lightworks
 

How much reduction does your assembly have? Are you coupled directly to your worm?

hitosi sato
 

Hi Antonio
I saw your video.
My impression is that the vibration is about a few Hz. Probably 2 to 5 Hz.
I think it is necessary to inquire both electrical and mechanical factors.
If that vibration is an electrical factor, how many steps does the motor move? Calculates backward from the overall reduction ratio.
If you want to check quickly, replace the 8825 for RA with the 8825 for DEC?
If it's a mechanical factor,
Probably because there is no necessary gap in the gear, it feels like hunting belt.
Especially, the gear tends to cause such vibration if there is no backlash.

hitoshi

Antonio
 

They have 60x20 tooth.  As I said... in the DEC there are a machinized extension, but firmly attached.
The jiggle occurs at +/- 2 seconds frequency no matter the position of the tube.

Em 22/03/2020 20:36, Aisling Lightworks escreveu:

How much reduction does your assembly have? Are you coupled directly to your worm?

Howard Dutton
 
Edited

On Sat, Mar 21, 2020 at 08:59 AM, Antonio wrote:
No matter "the DRV8825 is notorious for not stepping smoothly (Howard)", a lot of users of an Onstep group where I buy the shield reports it fine.
If this is a kit with motors included, where someone has confirmed the DRV8825's work reasonably well with these exact stepper motors then no problem, you're good.

If not the fact remains the DRV8825 has major issues and doesn't work well with a wide variety of stepper motors.  And generally speaking the drive ratios of your mount put you in the ball-park of full steps going by once every two seconds or so (if using 400 step motors) which is also consistent with this type of problem and/or the stepper driver current Vref not being tuned properly.

I'll continue to assume one of these issues are the problem until you provide some feedback to convince me otherwise.