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  #21  
Old 10-10-2020, 11:04 PM
Greggles (Gregory)
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Location: Sydney, Australia
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Thanks to every one for your replies,

I've completed some great testing with the new sectors which i will discuss after answering some of your questions.

All movement I a mentioning is East/West movement rather than north/South. So the direction it drifts when it is slow is the same direction it drifts when the motor is turned off.

Regarding polar alignment i have used solar noon method for my initial alignment then i further align at the beginning of every session with a illuminated cross hair EP.

I think the comments regarding polar axis being off is a strong possibility as per the results from testing.

Ok, so testing consisted of running the platform start till finish while constantly taking 10 sec exposures with a DSLR at prime focus with a 1.5 barlow. I completed 3 full runs of the platform.

Taking the continual exposures allowed me to go through every frame like a video and see how the platform was performing. Checking the time the first frame was taken and comparing it to the time of the frame were tracking slowed allowed me to get an accurate measure of when the slowing begins.

So what did testing show?

Well to summarise, the new sectors are working great and providing some excellent tracking. Although I think the new S109 driver will make a big difference when it comes as I'm pretty sure I'm seeing some missed steps.

More detailed:

- The platform tracks for 1 hour and 30 minutes.
- The platform tracks perfectly for 57 minutes. results consistent across all three tests.
- And too slow for the final 33 minutes.
- 10 second exposures are possible for photography although about 25% of frames may be throw away due to very slight speeding up and slowing down at times (missed steps, PE?)
- 8 seconds exposures are much better with less than 5% of frames being throw away.

Regarding the lowing of the platform for the last 33 minutes, I first thought I would code arduino to speed up for that time frame, however I don't think it would work as the exposures show its not simply slowing down rather inconsistent and sporadic movements and jolts. This strongly suggests slipping to me which may be a result of the polar axis being off as previously suggested.

At the moment I am going to enjoy my 57 minutes of quality tracking and when i get a chance ill look into the COG issue.

Cheers

Greg
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  #22  
Old 11-10-2020, 08:39 AM
Rod
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Join Date: Sep 2006
Location: Mount Martha
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Congratulations Greg,

Looks like you've achieved what you set out to. I think you were hoping for 10 second exposures and you are nearly able to do that. I think 57 minutes of good tracking is a great outcome. I don't know many platforms that do better than around 50 mins to an hour. The longer you run ithe more you are inviting errors due to slight imbalances as the scope moves up and sits at a greater angle.

I'll be interested to hear how the new driver performs.

Regarding the ? skipped steps. I think Bojan mentioned earlier that you had many more microsteps than needed. Would reducing the number of microsteps increase the torque a little and perhaps help with that small inconsistency you are seeing? I'm sure Bojan could answer that question.

Very impressive progress. It's been good to see how this develops.

Rod.
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  #23  
Old 11-10-2020, 01:18 PM
Greggles (Gregory)
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Hey Rod,

That's a great point. Going to give 1/16 another go but last time i used 1/16 i was getting some pretty intense noise/vibration which i think was leading to even more skipped steps due to resonance. How ever this was early on and a bit has changed in the platform since then.

Greg

Quote:
Originally Posted by Rod View Post
Congratulations Greg,

Looks like you've achieved what you set out to. I think you were hoping for 10 second exposures and you are nearly able to do that. I think 57 minutes of good tracking is a great outcome. I don't know many platforms that do better than around 50 mins to an hour. The longer you run ithe more you are inviting errors due to slight imbalances as the scope moves up and sits at a greater angle.

I'll be interested to hear how the new driver performs.

Regarding the ? skipped steps. I think Bojan mentioned earlier that you had many more microsteps than needed. Would reducing the number of microsteps increase the torque a little and perhaps help with that small inconsistency you are seeing? I'm sure Bojan could answer that question.

Very impressive progress. It's been good to see how this develops.

Rod.
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