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Re: confusion over settings for stepper motors

Howard Dutton
 
Edited

On Sun, Dec 19, 2021 at 01:19 PM, <kevin_kevin_kevin@...> wrote:
3 degrees a second is still 1/2 a RPM, 7 degrees a second is quite a slew speed , 6 degrees a second is as fast a second hand on a clock,  do you really need yout telescope to move that fast ?
And I'd guess that those stepper motors specified loose about 80% of their torque at 1 deg/s, let alone 6 or 7 (7180:1 overall reduction.)


Re: confusion over settings for stepper motors

Khalid Baheyeldin
 

Regarding maximum goto speed.
On my small-ish Vixen SXD with a C8, 6 degrees/second is crazy fast, and feels
dangerous.
I usually stick to 3.5 deg/second as a good balance between speed and safety.

But again, we need one step at a time testing, before finding out what is the sweet spot.


Re: confusion over settings for stepper motors

Khalid Baheyeldin
 

The problem is that there are too many things changing at the same time
and responses from me and others are not keeping up with what is really
going on.

There is microsteps, steps per degree, maximum slewing speed, gear box
ratio, current when slewing, and so on ...

That is why I am recommending a step by step approach, changing only
one thing at at time.

Can we do this one step at a time?

Did you try these:
63,822.22222    = 200,    16,    20,    359
63,822.22222    = 200,    16,    20,    359
But with the lowest slewing speed on the SHC?
And what IRUN/IGOTO settings did you use?

If this is successful, you can retain the existing 20:1 gearbox.


Re: confusion over settings for stepper motors

Guy Brandenburg
 

Khaled, unfortunately, the settings you suggested did not help very much, if at all. The motors still freeze and scream while slewing. I'm using the SHC. I tried a a 3-star alignment and a plain old GoTo. Slewing by hand (ie pressing N, E, W, S and the > or + sign to get it to move faster) doesn't seem to be a problem. 

But when I try a GoTo and I watch the RA and DEC coordinates using a stopwatch, I calculate that the steppers think they are moving at either 1 degree per second or 1/2 degree per second, often while the shaft is in fact immobile (and screaming). 

The tracking rate seems OK, but that's not new. 

I hope that gearing up by using belts with 60:20 teeth ratio (stepper:worm) will help. No way am I replacing a Byers gear with something I cobble together. 

Look again at the images I shared.






Re: confusion over settings for stepper motors

kevin
 

3 degrees a second is still 1/2 a RPM, 7 degrees a second is quite a slew speed , 6 degrees a second is as fast a second hand on a clock,  do you really need yout telescope to move that fast ?


Re: confusion over settings for stepper motors

Khalid Baheyeldin
 

We need to be more methodical in the testing so that we don't keep running in circles. 

What slewing speed you put in Config.h is not what you end up with, depending on
many factors. So that is okay.

But 85096 steps per degree is a lot more than the 61200 recommended limit of OnStep.

Please use the settings that are closer that to that limit, which are in message

https://onstep.groups.io/g/main/message/40015

These use the 20:1 gear box.

Also change the IRUN and IGOTO to be 1400 and 1800 respectively.

Then set the max goto speed to the slowest that the SHC shows.

Test that, and see if there is stalling or not.

If that succeeds, then you can increase the speed from the SHC, and try
again to see if they stall or not.

Once you reach a speed that will not stall, stick to it and try the motors
in the real mount with the existing gear reduction.


Re: confusion over settings for stepper motors

kevin
 

Just looked at the photos,  the main shaft of the main worm gear ( the one with the 20:1 reduction gear on)  is presumably fitted at each end with bearings, do it extend through the side of the case where the silvery nut at the bottom of the picture is?


If so that may be a convenient place to attach a belt drive or direct coupling.


Re: confusion over settings for stepper motors

Guy Brandenburg
 

I have tried setting the slewing speed at 1 degree per second, 3 d/s, 5 d/s, and 7 degrees per second. Sometimes I get close to 3 deg/sec, but never anywhere near 7 degrees per second. 

Right now, in right ascension, with AxisStepsPerDegree set at 85096 and 64 microsteps, and the TMC5130 set at 1000 milliamps, the speed is three-eighths of a degree per second when I slew it manually by pushing either East or West at its fastest speed.

In Declination, with the same settings, I get 3 degrees per second in slewing, but in Config.H I asked for 7 d/s.

The steppers are no longer screaming. But the one for RA is pretty noisy.


Guy Brandenburg, Washington, DC  http://gfbrandenburg.wordpress.com/ http://guysmathastro.wordpress.com/
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Re: Push To - reuse intelliscope encoders

kevin
 

No Onstep though :-(
untill you add motors :-)  then you have goto instead of pushing. Videos on the web.


Re: I need advice on making a "star tracker" from a MiniPCB v2 and a drive design

kevin
 

If you are interested in a barn door ( also called scotch mount i think), this guy has buit one without a motor, just winds it by hand and has some really good photos. https://www.youtube.com/watch?v=P_qqLA0WKJg there are others, with a motorised nut and curved  threaded rod, like this one https://opticaleds.com/atm/making-a-curve-bolt-barn-door/ which could be used with onstep and one motor just to get a stepper running at sideral rate. it could also be used at a faster rate for a simple positioning if you have a long enought thread.
I havn't found the one using the skywatcher worm drive yet. obviously you can use others but that one is compleat, I saw the video an though that is an easy job which is why i have one in my shed as a future project.#  :-)


Re: confusion over settings for stepper motors

Khalid Baheyeldin
 

Guy,

Before ordering new things, please try what was said in this thread:

First, try to reduce the Goto speed from the hand (Slower and Slowest).

Then try the changes that I listed in my last message.


Re: Push To - reuse intelliscope encoders

AxG68K
 

Wait a sec... Thanks Kevin, that is exactly what I was looking for!  Perfect.   I just want to feed stellariuminfo just like the video. Fantastic.


Re: Push To - reuse intelliscope encoders

AxG68K
 

I have heard people doing it but I don't see any info out there.  What happens if your setup has steppers and encoders and you disconnect your motors? Wont the system still work? I just need to rig up a display that tells you your current position and delta.  I was hoping someone would replay with - "oh sure so easy. Check out my scope project."

AG


Re: I need advice on making a "star tracker" from a MiniPCB v2 and a drive design

kevin
 

Just a few of my thoughts on the subject. As usual, "it depends" :-)   in this case what driver you are using. As far as i know Onstep is"open loop" unless you start using encoders, however drivers with software control ( e.g some TMC, don't know about others) may screw up if it thinks there is a driver attached because it may wait for an acknowledgement for the message it sent at a "low level" in the serial data sortware.  I don't think Onstep expects any reply, or any wires to do so, from any of the other drivers. Config.h has the option for OFF as a driver so i suspect it just won't bother with it , or you could just tell it is a simple driver and not plug it in.
As you have a working Vixen GP system you could reflash it , or just (with power off)  unplug the driver ( not the motor)  , and see if it works OK.

Comercial star trackers  are basically what used to be called a "clock drive" on a equatorial mount. In the old days this was often clockwork or even a weight over a pully.  Most are a single axis which is aligned with the celestial pole and move it at 1 rev per celestial day. You need a fairly big reduction ratio on your gear set, you do the "goto" bit by moving the camera in 2 directions on a ball joint or use a single axis on the camera and do the other alignment with a clutch of driving the motor fast.  I don't know what the largest ratio you can get with  NEMA 17 with a planetary gear, i have seen 100:1 and people have used a pair of them as a simple goto mount but i think there wouldn't be small enough steps to stop the tracking being a bit jerky.
You might like to look at the " Skywatcher Dovetail L Bracket for Star Adventurer",about 50$ i think. The bit on the end is a worm drive and already has a camera mount screw. It may also have an inbuilt clutch but no idea about ratios, how well it would last etc, i have one in the shed if i can find it and you are particularly interested in details.  I saw somewhere someone had used it with a geared stepper to make a startracker.  It was probably a youtube video so i will see if i can find it later if you want.
The alternative is a "barn door tracker", cheap and easy to make  only does a segment of the sky but the gearing is high because it uses a threaded rod and geomety . To us it  with ONstep. I think instead of a driven  straight thread, which tecnically needs a  variable speed motor to do the tracking acuratly, you would use a stationary curved threaded rod and a motorised "nut" so that the motor ran at constant speed.


Re: confusion over settings for stepper motors

Howard Dutton
 

Guy,

What slew speed were you shooting for during your tests?


Re: Pulley ratio (same ratio with different pulley combinations)

Peter Boreland
 

George, I just want to point out the there is a 15T(5mm)/45T(6.35mm) combo available in GT2. This seems like the sweet spot if the 16T/48T proves to be too large for the reverse worm implementation. I have both setups on order and will report back

Peter


Re: Files upload

George Cushing
 

Ken, about the 492 Hurst/SATA wiring diagram. I am having trouble understanding all bends without studying it. I find this easier to understand this one.



.HTH, George


Re: confusion over settings for stepper motors

Guy Brandenburg
 

To answer some of the questions about our mount, take a look at my blog where I've posted a number of photos as well as videos. I've ordered a 3:1 reduction system with 6mm toothed belt.


 and
and


Guy Brandenburg, Washington, DC  http://gfbrandenburg.wordpress.com/ http://guysmathastro.wordpress.com/
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Re: ESP32 wireless SHC (wSHC)

Dave Schwartz
 

If you hack in some code to control an unused pin to control button backlighting, please do it in a robust way (i.e. allocate the pin with a define in the ESP32 pinmap) and contribute the code back to the repository so that anyone who implements backlighting can benefit from your work going forward.

On 2021-12-19 12:46 p.m., Martin Bonfiore wrote:
Dave,

Thanks for info.  Thanks for the pointer to the area in the code. Off to hack some code.


Re: confusion over settings for stepper motors

Guy Brandenburg
 

This photo shows how the Byers drive is arranged on Ealing mounts. At the bottom left, the spiral is attached directly to the motor (which you can't see). The tootheder behind the spiral 

Inline image
Here is a link to a blog post I just wrote that gives some more photos and a bit more information:





Guy Brandenburg, Washington, DC  http://gfbrandenburg.wordpress.com/ http://guysmathastro.wordpress.com/
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