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Old 19-08-2020, 10:05 PM
Greggles (Gregory)
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Eq1 RA Motor drive speed controller mod help

Hi everyone,

I have a DIY eq platform for my 10" dobsonian and the number one issue I have is getting the tracking speed perfect. It is run by a celestron eq1 ra motor drive the kind that's run by a 9v battery and rebadged by several other brands including saxon.

The problem is constantly having to bed down to fiddle with the tiny thin adjuster and going back and forth between it being too fast and too slow.

So my idea was to add some sort of speed controler to the unit with a larger more accurate dial and wire it so I can hold it never having to look away from the eyepeice while drift aligning.

Im quite lost, Any one know if this can be done?

Kind regards,

Gregory Americanos
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Old 20-08-2020, 04:57 AM
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Yes, it can be done.
The solution is to use OnStep (or something similar, but this system is currently the best in terms of ease of implementation and cost).
Once you determine the necessary parameters (mechanical transmission ratio between motor shaft and Ra axle), you will be in business.
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Old 20-08-2020, 07:29 AM
Greggles (Gregory)
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Quote:
Originally Posted by bojan View Post
Yes, it can be done.
The solution is to use OnStep (or something similar, but this system is currently the best in terms of ease of implementation and cost).
Once you determine the necessary parameters (mechanical transmission ratio between motor shaft and Ra axle), you will be in business.

Hey Bojan,

Thanks for your reply. Unfortunately from what I've read the onstep only works for stepper motors. From my understanding the eq1 ra motor drives are not stepper motors have attached a photos of my motor.
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Old 20-08-2020, 07:42 AM
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Originally Posted by Greggles View Post
Hey Bojan,

Thanks for your reply. Unfortunately from what I've read the onstep only works for stepper motors. From my understanding the eq1 ra motor drives are not stepper motors have attached a photos of my motor.
Of course, you are right.

You need to replace DC motor with stepper (plus driver).. there is a bit of mechanical fiddling, but then you will have stable system.
To stabilize the DC motor rate is possible, it can be done by adding some sort of encoder and couple it with stable oscillator in PLL ( I did it long time ago, using rotor from washing machine timer (it is 10-pole magnet) as encoder, tone head from tape recorder as sensor, CD4046 as PLL and reference oscillator).

If you are interested in this solution I can share it.. I think I wrote about it here on forum.


Also, you can find DC motors with optical encoder attached in old printers.. so plenty of solutions is out there.


But I still recommend doing it right - with OnStep.
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Old 20-08-2020, 07:48 AM
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Here is what I have done with my EQ3:
http://www.iceinspace.com.au/forum/s...&highlight=EQ3
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Old 20-08-2020, 07:58 AM
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...
To stabilize the DC motor rate is possible, it can be done by adding some sort of encoder and couple it with stable oscillator in PLL ( I did it long time ago, using rotor from washing machine timer (it is 10-pole magnet) as encoder, tone head from tape recorder as sensor, CD4046 as PLL and reference oscillator).

If you are interested in this solution I can share it.. I think I wrote about it here on forum......





Found it:
http://www.iceinspace.com.au/forum/s...&highlight=PLL (post #12).
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Old 22-08-2020, 10:40 PM
Greggles (Gregory)
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Thanks for all the info.

Your posts made me realise two things..

1 I'll have to go to a stepper motor eventually and
2 I am way out of my depth and have bo idea about how to get one working. I dont know why it confuses me so much.. hence why I went for direct drive system.

Anyway, I purchased new speed controller and attached it to the motor to give me a larger dial and greater accuracy. it's working well, just need to do a proper test with it on a clear night.

Cut the motors battery wires and placed the new speed controller between the battery and motor. Also extended the wiring so I can adjust while standing and looking through eyepeice. Happy to upload photos if any ones interested.

Will also report back once field tested.

Cheers

Greg
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Old 23-08-2020, 06:34 AM
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Greg,

DC motor without stabilization will not perform adequately for AP because of number of reasons, the main one is mechanical resistance (friction, grease stiffness, supply voltage etc, to name a few).
However, for visual, what you already have could be sufficient.

But.. sooner you go for steppers, the better. The investment will pay off quickly, and it will enable you to go even further than you originally though was possible.
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Old 23-08-2020, 07:47 AM
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[QUOTE=bojan;1488385]Greg,

DC motor without stabilization will not perform adequately for AP because of number of reasons, the main one is mechanical resistance (friction, grease stiffness, supply voltage etc, to name a few).
However, for visual, what you already have could be sufficient.

But.. sooner you go for steppers, the better. The investment will pay off quickly, and it will enable you to go even further than you originally though was possible.[/QUOTE

Understood. I'm going to look into it again and prepare. From memory my issue was always getting a stepper motor that was slow enough that I could set up for direct drive. I guess I'll have to look into gearing a motor down.

Wish me luck
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Old 23-08-2020, 09:03 AM
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Greg,

There is no need for special motors, standard NEMA17 (preferably 400step/rev) is widely used.

To achieve the required rot. rate and smooth movement for EQ platform, people are using various methods..

For example, threaded bolts and driven nut, shown on this website.
Or, here author used two bent threaded rods (lower on page) as worm wheel sector and third one (with same pitch) as worm, coupled with stepper motor directly or via suitable reduction (up to 1:2 is adequate).
The whole thing can be controlled with OnStep (or equivalent) electronics.
I wish you luck :-)

And you can always ask the question here, there will be plenty of help available from members of this forum.


Edit: first you have to calculate the required reduction. As a rule of thumb, aim for 0.2 arcsec/step.

Last edited by bojan; 23-08-2020 at 11:15 AM.
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Old 30-08-2020, 04:17 PM
Rod
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Hi Greg

I agree a stepper motor will be more accurate and consistent. You can also add nice features like automatic rewind.

I've made a couple of platforms. Friends have helped with the stepper motors and coding. However, I found the biggest source of tracking error was poor platform alignment and construction errors in the platform itself. The other issue I had was I got too fussy sometimes trying to get the perfect speed using a narrow field cross hair eyepiece. I found for visual use some speed error was not that noticeable when using moderate magnification.

With one of my platforms I spent ages adjusting speed. A friend then went over the platform. He ensured bearings were properly located and moving smoothly, removed any play in the motor connection etc. The improvement was dramatic.

You are probably a much better builder than I am. But I suggest you check these other potential sources of error (platform polar alignment and construction) before concluding motor speed is the issue.

Hope that helps. BTW please post some pictures. I for one would love to see what you have done.

Rod.
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Old 04-09-2020, 09:18 AM
Greggles (Gregory)
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Quote:
Originally Posted by Rod View Post
Hi Greg

I agree a stepper motor will be more accurate and consistent. You can also add nice features like automatic rewind.

I've made a couple of platforms. Friends have helped with the stepper motors and coding. However, I found the biggest source of tracking error was poor platform alignment and construction errors in the platform itself. The other issue I had was I got too fussy sometimes trying to get the perfect speed using a narrow field cross hair eyepiece. I found for visual use some speed error was not that noticeable when using moderate magnification.

With one of my platforms I spent ages adjusting speed. A friend then went over the platform. He ensured bearings were properly located and moving smoothly, removed any play in the motor connection etc. The improvement was dramatic.

You are probably a much better builder than I am. But I suggest you check these other potential sources of error (platform polar alignment and construction) before concluding motor speed is the issue.

Hope that helps. BTW please post some pictures. I for one would love to see what you have done.

Rod.
Hey Rod,

Apologies i missed this post.

Regarding my mods i got rid of the battery and and wires in a PWM form Jay car, photo attached, between the motor and a 12v power supply. unfortunately this was a wasted of time as it didn't give me the extra sensitivity/precision i needed. If the motor was moving slightly too fast turning the nob tiny bits at a time would do nothing the first few times then all of a sudden it would make a big change and slow motor right down! last night was a very frustrating night.

I will be removing the PWM today and making something to connect to the tiny built in potentiometer of the motor drive. I hear a peg works well but i couldn't get one that gripped on tight enough.

What type of mount do you have? I have a VNS and definitely not sure on the accuracy of my build. Having said that, i'm extremely confident that everything is where i want it to be based on my calculations, but were my calculations right? the main confusion I had was where was the pivoting point for the south segment to 90 degrees with the base and pivoting the segments in the other direction (don't know how to explain)

So I'm wondering if i should invest in the stepper motor of just remake a platform or both!

Stepper motors seems to be the quickest options as im pretty pressed for time with work and a newborn. And then if its still not quite right it kinda confirms the problem is the mount.

For stepper motor i'm looking at getting a high torque motor with a planetary gearbox so I can run it as a direct drive so I don't need to modify the platform. Although as mentioned the more i read the more I'm confused. lol
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Old 05-09-2020, 09:14 AM
Rod
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Quote:
What type of mount do you have? I have a VNS and definitely not sure on the accuracy of my build. Having said that, i'm extremely confident that everything is where i want it to be based on my calculations, but were my calculations right? the main confusion I had was where was the pivoting point for the south segment to 90 degrees with the base and pivoting the segments in the other direction (don't know how to explain)
Hi Greg,


I've built two styles of platforms. The first is similar to Ed Jones design:

There is a video description here

I used a tangent drive instead of the direct drive. The tangent drive was powered by a stepper motor. It rewinds automatically at the end of one hour's tracking. The circuit has a beeper which sounds to warn you rewinding is about to start. A different tone sounds when battery power is low. The code that runs the circuit also compensates for the small error introduced by using a linear drive. It's a nice system designed by the late Nils Olaf Carlin:

http://web.telia.com/~u41105032/Stepper/Stepper.htm

The other system I'm familar with is a group project we did at the ASV (Astronomical Society of Victoria). It used vertical sectors and a direct drive using a stepper motor. I'll post some photos in another post of the two platform designs for your interest.

How did you make the sectors on your platform? We used a jig to make ours. Ed Jones does his on a table saw with a sanding disk instead of the blade.

Did you calculate the centre of mass of your scope and mount? I ask because motor slippage in a direct drive could muck up the tracking if you did not.

I'm a bit confused by your last sentence above about the 'pivoting point for south segment'. In the southern hemisphere it is the South sector that would be vertical. A photo and a description of your alignment process would be useful.

The motor you have is used by a lot of people for their platforms so it should be possible to make it work. But I do agree that a stepper motor is likely to be better in the long term.

Regards,


Rod.
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Old 05-09-2020, 10:10 AM
Rod
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Hi Greg


The first 3 images are of the Ed Jones type platform with tangent drive. The second 3 are the group project platform designed by our Instrument making section director. Notice it has 2 vertical curved sectors. The stepper motor drives both sectors for added stability.



Regards


Rod
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Old 05-09-2020, 11:03 AM
Greggles (Gregory)
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Quote:
Originally Posted by Rod View Post
Hi Greg


The first 3 images are of the Ed Jones type platform with tangent drive. The second 3 are the group project platform designed by our Instrument making section director. Notice it has 2 vertical curved sectors. The stepper motor drives both sectors for added stability.



Regards


Rod
Hey Rod,

I made the sectors as per reinervogel website on VSN eq platforms and had them plasma cut from a CAD image.

my sentence regarding pivot points was in relation to making the segments rather than the eq platform working. In the photos I've attached you can see how its demonstrated to pivot the south segment to a right angle. the pivot point is in the centre of the segment. Where as i've seen other places demonstrate to pivot it from the tip. which would make the south segment sit a few CM further than where it is now.

Im nto sure if im making any sense.

I'm thinking of just re doing the platform as ed jones design. it seems easier to get it spot on.

I would like to point out that the platform works perfect for visual and i've managed to do a lot of photography with it but only 4 seconds exposure max. where as others with same platform reporting 10 seconds plus.

hopefully will get some extra accuracy with eds style platform.

P.s my scope is always in the same spot at home so i've used the solar noon method to find true south and then fine tune with drift method.

thanks for the info.
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Old 05-09-2020, 12:02 PM
Rod
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Hi Greg

Thanks for the info. It sounds like your platform is working better than I assumed. That's good news. The Ed Jones style is great. The only tricky bit as that are a few angles to cut. If you have a good table saw that shouldn't be a problem.

One thing I don't quite follow. Reiner Vogel uses a simple pivot for the smaller sector. Did you do that? I did some drawings once and concluded that would only be feasible for higher latitudes than we have in Melbourne or Sydney since you would have to extend the length of the platform significantly.

Congratulations on building a platform. I think they are a great ATM project.

Rod
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Old 05-09-2020, 03:10 PM
Greggles (Gregory)
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Hi Greg

Thanks for the info. It sounds like your platform is working better than I assumed. That's good news. The Ed Jones style is great. The only tricky bit as that are a few angles to cut. If you have a good table saw that shouldn't be a problem.

One thing I don't quite follow. Reiner Vogel uses a simple pivot for the smaller sector. Did you do that? I did some drawings once and concluded that would only be feasible for higher latitudes than we have in Melbourne or Sydney since you would have to extend the length of the platform significantly.

Congratulations on building a platform. I think they are a great ATM project.

Rod

Hi Rod,

Your spot on, the simple pivot would of made the platform way to long so I made that segment the same as what would be on Ed's design.

Here is my old thread of my build
http://www.iceinspace.com.au/forum/s...d.php?t=176305

Now just to decide new motor or new platform first

I have a table saw so not sure why I didnt just do that design from the start.

Also if you have instagram you can see photos I've got with it. Very happy with all my photos would just prefer at least 8 second exposures to save my cameras shutter count!

@astrogreggles

Cheers

Greg
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Old 05-09-2020, 04:25 PM
Rod
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Hi Greg

That's a nice looking platform! Personally I think it would be a shame to abandon all that work when perhaps a more accurate motor might help you. You'll probably go for a stepper drive anyway if you build another platform. So why not try the stepper system on your existing platform and even if it doesn't work you can use the motor on the new platform.

We use this stepper on our club platforms:

https://www.omc-stepperonline.com/cl...S19-1684S-PG27

I have one here I'd be happy to post you to try out. I fit works on your platform, keep it. Bojan might advise you on what he thinks of it for your purpose.

Rod
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Old 06-09-2020, 12:40 AM
Greggles (Gregory)
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Hi Greg

That's a nice looking platform! Personally I think it would be a shame to abandon all that work when perhaps a more accurate motor might help you. You'll probably go for a stepper drive anyway if you build another platform. So why not try the stepper system on your existing platform and even if it doesn't work you can use the motor on the new platform.

We use this stepper on our club platforms:

https://www.omc-stepperonline.com/cl...S19-1684S-PG27

I have one here I'd be happy to post you to try out. I fit works on your platform, keep it. Bojan might advise you on what he thinks of it for your purpose.

Rod


Thanks rod, yeah I do love my platform but could probably use a bit more sprucing up particularly in the two south segments. Currently plasma cut out of steel. Noticed it was slipping a bit tonight steel is quite hard, laser cut aluminium would be better.

The steel has smoothed out aluminium drive shaft so will need to rescuff for grip or try something else out. Might try wrapping it in electrical tape and see what effect that has.

Have emailed you re the motor. Very generous of you to offer that.

Cheers

Greg
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