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[engreric]

So I noticed something and was wondering if there was an explanation for it. If I set the Goto speed in the astroeq config to something like 200 and I set the EQMod slew rate to 200, the behavior of the motors is completely different.

EQmod slew with the control pad arrows for 200 will be smooth and quiet. CDC slew (goto at 200) on the other hand will be noisy and I get a lot of unwanted resonance out of the motor.

I've tried many different goto rates in the astroeq config, but all the ones I have tried are never as smooth and quiet as the EQMod slew with the controller...

Any ideas?

[TCWORLD]

For Go-To movements (and hence slews from CdC), the micro-stepping mode is changed to allow more torque and higher speed movements. You will see the same thing from EQMOD if you pick a slew rate higher than 200 as it requests the lower micro-stepping mode for these as well.

Normally this shouldn't cause an issue.

Could you upload a video of it to Youtube or somewhere so I can get an idea for how it is behaving.

[engreric]

Thanks So Much!

I will take some video when I get home. For now let me post the specs.

0.9 deg stepper, 68 oz/inch, Nema 17
http://cdn.sparkfun.com/datasheets/Robotics/42BYGHM809.PDF

RA: 4:1 reduction with GT2 pulleys and belt
DEC: 2.8:1 reduction with GT2 pulleys and belt

DRV8825, I also tried the A4988 but results were better with the DRV8825

I have them set to about 1.7A/phase (I'm using a good quality DMM and I have decent test equipment for any other measurement that could help)

Celestron CG-4... As far as I can tell, an EQ3-2
New version with steel tripod legs

The worst part of the resonance/vibration is during acceleration/deceleration. It seems that there are frequencies that the motors don't like during this (However, again this is only during CDC slews). Accel/Decel works great when it's only EQMod.

I will also test out the <200/>200 slew rates from EQMod. However I remember never wanting to go above 200 in EQMOD just for this reason. So what you are saying makes perfect sense.

[Smokie]

Hello,

i have the same problem ,goto in CdC is slow and the motors run noisy
slewing in EQmod is smooth and fast

have you found a sollution already?

gr,Henk

[engreric]

You have done a great job with AstroEQ and all together this is quite an amazing project you have kept going.

It's been a while since I've worked on this project but a recent injury has me back at fine tuning my telescope setup =)

A year later, all my previous posts are still valid and I'm back at trying to debug this.

Although I believe I've found the best settings for these motors with the Goto speed in the astroeq config, using the DRV8825 instead of the A4988, and the current limit I have set. I'm still not too happy when my motors are operating in the so called "NOISY" range. I'm willing to change motors and try other things to achieve the 100% smooth operation I've witnessed during slower speed EQMOD Control Pad Slewing.

Here are some tests using EQMOD Control Pad Slewing, first with the RA Axis then the DA Axis.

EQMOD Control Pad Slewing
RA - Axis

180 SLEW E - SMOOTH, W - SMOOTH
195 SLEW E - SMOOTH, W - SMOOTH
198 SLEW E - SMOOTH, W - SMOOTH
199 SLEW E - SMOOTH, W - NOISY
200 SLEW E - SMOOTH, W - NOISY
201 SLEW E - NOISY , W - NOISY
205 SLEW E - NOISY , W - NOISY
280 SLEW E - NOISY , W - NOISY

DEC - Axis
180 SLEW E - SMOOTH, W - SMOOTH
195 SLEW E - SMOOTH, W - SMOOTH
198 SLEW E - SMOOTH, W - SMOOTH
199 SLEW E - SMOOTH, W - SMOOTH
200 SLEW E - NOISY,  W - NOISY
201 SLEW E - NOISY,  W - NOISY
205 SLEW E - NOISY , W - NOISY
280 SLEW E - NOISY , W - NOISY

Things I'm noticing, if the noisy vs smooth operation is caused by stepping modes, then I notice that the RA axis has a difference between E and W at a couple of slew rates, 199 and 200. This difference is probably just caused in code by a > condition vs a >= condition or something to that degree. That isn't a big deal but I figure that I would mention it. I'm really just trying to chase after the Smooth vs Noisy operation of my steppers.

Now All Gotos within CDC result in the "NOISY" movement.

I am linking a video I just made on youtube to hopefully help out. The settings I have right now are definately tolerable although I'm worried that this noisy/resonate movement might result in losing steps during the deacceleration and acceleration phase of a movement, especially since I see the timing belt resonate which I did capture on video toward the end. Had I only ever seen the "noisy" operation I probably wouldn't be too interested in quietting it down, but because I know the 100% smooth operation is possible, I'm attempting to try and get all the movements like that. I'm an engineer trying to solve problems that people didn't even know they had (till I messed them up) =) JK

EQMOD Slews
https://youtu.be/aevdcVKxXMU

CDC Gotos
https://youtu.be/aaZtv6WAE4g

Any and all help is greatly appreciated, maybe the best answer is to change my motors from 0.9 deg steppers to 1.8 deg or change the type/torque/current rating. What do you think?

Thanks for all your great/hard work and help!

[TCWORLD]

What you are noticing is expected. Any EQMOD NESW button slew 200x or higher will be done in a high-speed mode. The same mode is used for Go-To movements.

In this mode the motors are switched into a different microstepping mode (which is 8 times larger step than the slow mode). So for example if you are using 1/32 stepping, high speed movements will be performed using 1/4 stepping. This is done to increase the motor torque in order to improve the ability to move quickly.

Once the movement is complete, it should switch back in to the slow mode.

Tom.

[engreric]

Tom, thanks for the response.

I'm glad that it looks as expected. I was wondering... given that I used relatively large steppers with a decent amount of current and torque, I might be able to achieve the same higher speed (as the >200 slew) but while still using the higher microstepping mode without losing steps. I know that this is outside of any feature or support that you would reasonably have to give, but if your not too busy and could point me to where in code I could force the microstepping mode for goto slews and slews >200 it would help me try it out.

Regardless, thanks for checking out my videos and helping. Right now I'm designing some 3d printed motor mounts for the CG4 / EQ3-2 mount, when they are done and tested I'll throw them up on thingiverse.

[TCWORLD]

I'll add it as an config option to the list of things to add to the next version that I've been planning on doing for the last two years. Once I finish my job in the states and get back to the UK in October I'll be able to test stuff out with my telescope and should have time to finish off developing the new firmware.

In the mean time if you find the decodeCommand(...) function in AstroEQ.cpp, then find the following line:

Code: [Select]

case 'G':
Uncomment the lines:

Code: [Select]

/*if (packetIn[0] == '0'){
     packetIn[0] = '2'; //don't allow a high torque goto. But do allow a high torque slew.
}*/
And add the lines:

Code: [Select]

if (packetIn[0] == '3'){
     packetIn[0] = '1'; //don't allow a high torque slew.
}
That should prevent it "changing gear" as it were.

When you compile it, make sure to use either UECIDE or the Arduino IDE version 1.0.5. The latest version of the Arduino IDE won't work.


Tom.

[TCWORLD]

As a side note, the reason why the East/West has a difference in when it jumps to high speed is that EQMOD adjusts the rate to account for tracking. If you have sidereal tracking enabled, then going west at 199x is adjusted by the sidereal rate to be 200x, whereas going east at 200x is adjusted by the sidereal rate to be 199x. The interesting effect of this is if you slew east at 1x speed the mount will stop moving - the slew is done by the Earth instead .

[engreric]

That's really interesting and makes complete sense. Thanks for the code changes and the version number, everything worked without any issues. I tried everything out and there seems to be no loss of steps, and the slew is now as smooth as can be. Thanks. I also got one of the 3d printed designs done for the dec axis and I redesigned my ra axis brackets as well. My mount has really come together and is much cleaner and quieter now.

I was going to ask you about accuracy. I've reduced my backlash as much as possible and really tuned everything.

I'm still off a bit and wanted to see if I was missing anything.

Right now, I do a polar alignment using my polar scope on the cg4. Then I goto a star around polaris, usually ursa major or cassiopeia. Then I let out the clutches, center the star, and tighten back up.

The next goto seems to be quite a bit off. Like around the 3rd ring of telrad. Is this the expected accuracy until I build up alignment/sync points? Could it be that I need a more precise polar alignment?

Thanks!

[TCWORLD]

Once polar aligned, you should do at least 3 star alignment. Slew to the first star, then release the clutches, centre, and lock the clutches again. Issue a sync to say the star is centred. Then slew to another star - but this time *don't* release the clutches. Use the NESW buttons to align the star, and then issue a sync to say it is now centred. Repeat for another star.

You should find that stars are then pretty well centred.

[Zh]

I also have this issue - very noisy and vibrating slewing... It would be very nice to have this feature as configuration option in next config utility version! 

[TCWORLD]

@Zh, I'll look into adding the option to the next version.