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  #1  
Old 10-04-2015, 08:31 AM
garymck (Gary)
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Onstep Telescope Drive

Hi,

I have just built and fitted a really cheap telescope goto drive as in here:

http://www.stellarjourney.com/index....uipment_onstep

to my Losmandy G11 that previously had a Gemini 1 fitted. I was looking at options as I had a bent shaft in one of my G1 motors. These motors are not cheap. I was able to build a whole drive system including buying new 400 step steppers for about 2/3 the cost of 1 Gemini motor.

The new drive slews faster and quieter than the servos. The main benefit is that the steppers can connect directly to the worm on the G11. Last night I was able to do a quick PE test between the clouds and came up with a figure of +2.4, -2.5 arc secs (the mount has an Ovision worm) however the best part is that it none of the higher frequency hash associated with gearboxes. It was simply the smoothest PE curve I've seen outside of the premium mounts.

Might help someone else looking for a cheap drive.....

cheers
Gary
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Old 10-04-2015, 08:44 AM
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Thumbs up

Gary,
Thanks for the notice, this is really interesting.
For quite some time I was searching for suitable Arduino solution, but was not succesful so far.. This seem to be the excellent alternative to PicGoTo.

Last edited by bojan; 10-04-2015 at 08:56 AM.
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  #3  
Old 14-04-2015, 10:40 PM
bgilsrud (United States)
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Hi Gary,
Would you mind sharing what steppers you used? Also, how did you couple the motors to the worm? I'm seriously considering building this as well since I have a G-11 with a 492 digital drive and would really like goto's for astrophotography.

Thanks,
Ben
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  #4  
Old 16-04-2015, 12:35 PM
garymck (Gary)
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Hi
Steppers were these:

http://www.omc-stepperonline.com/09d...04s-p-122.html

They microstep beautifully at 9 volts. They do not work well at voltages much over this. To me this a is OK as it means that a power supply is really easy to find. Some motors need 24 volts which means lottsa $ for a power supply.

They are fitted to the G11 and have made a huge difference to my PE, not so much in the magnitude (though that is less) but all the high freqency gearbox noise has gone. Very smooth, very repeatable. Will be trying out PEC programming soon....

Couplers were these:
http://www.omc-stepperonline.com/5mm...c03-p-285.html
but they do need to be turned down on a lathe. If you can't do them PM me and we can organise something as I have a lathe.

cheers
Gary

Cheers
Gary
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  #5  
Old 07-11-2015, 01:48 PM
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Recently I decided to try OnStep..
It works but.... there are many issues with this system.
- Android controller is unreliable, and it seems there is no command to start tracking
- It works with CdC via ASCOM driver, trascking can be started from there, but it can't be sync-ed (I can't tell the scope "you are here!")
So, it seems both Android controller on a mobile device (connected via BT) and PC application (connected via USB) must be present to start the system.. but it seems the firmware is sometimes confused with commands from two ports.

I am talking to Howard Dutton (author), so we shall see how this will go..
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  #6  
Old 07-11-2016, 06:47 AM
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Last weekend I went back to OnStep system..
Everything that I complained about a year ago is now fixed

So, now I have controller that operates without computer or mobile... this is 90% of time.
But, when needed, just one USB cable provides the connection with laptop.
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  #7  
Old 08-11-2016, 03:54 PM
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Thanks for that
Looks like fun. Might have a crack at it !
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Old 19-11-2016, 07:54 AM
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Rac (Raymond)
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I use the Onstep system on my 20" Dob for visual and planetary imaging and it works great!
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  #9  
Old 20-11-2016, 05:35 AM
Baza (Barry)
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Rac, any photos or info about that drive system?
thanks
Barry
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  #10  
Old 20-11-2016, 06:45 AM
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Here:
http://www.stellarjourney.com/index....uipment_onstep

In my implementation, Arduino MEGA is in the box with buttons, Pololu drivers and motors are in the mount (so I can have any sort of electronics, including Bartels - which is still superior to other solutions in terms of functionality, but not in terms of portability).
The box itself works without laptop as well.

If you use Howard's Sky planetarium, only one USB cable is sufficient even if guiding used.
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Last edited by bojan; 20-11-2016 at 08:25 AM.
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  #11  
Old 20-11-2016, 05:03 PM
Baza (Barry)
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That's a very neat installation. Thanks Barry
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  #12  
Old 20-11-2016, 05:16 PM
Baza (Barry)
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double posted
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Old 21-11-2016, 03:14 PM
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My setup is not flash and it's made out of bits I had kicking around. I did it with the intention of changing it to all nice gear but it works so well that I have no problem with it the way it is. If I ever get around to making my 30" dob then I'll make it look a bit better on that scope.

I'm using a Teensy 3.2 with TMC2100 drivers and it's as smooth as servos! I recommend using a Teensy 3.2 and these drivers, I tried a mega2560 and all sorts of stepper drivers but nothing can beat the Teensy/tmc2100 combo!
I only ever use the Onstep App for controlling it apart from small 4 button remote wired into the guide port for moving the scope around.

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Old 21-11-2016, 06:10 PM
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It's flashy enough for me
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Old 22-11-2016, 04:26 AM
Baza (Barry)
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That look fabulous to me and really simple and inspirational. It has to be good to get images.
I was not aware of that drive system. Thanks for the info.

My system is Deepsky and too far along to change, no first light yet but it drives. I only worked out the secondary spider system last night. 16 inch dob.

Barry
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  #16  
Old 10-07-2017, 09:51 AM
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What driver and steppers has everyone used ? I was going to put on an old EQ mount to try it out. And couple directly onto the worm gear. That sound reasonable ?
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Old 10-07-2017, 10:10 AM
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I am using A4988 mounted on my own board, inside EQ6 (on connector I have STEP, DIR inputs, VCC_Out, enable etc), so I can use several interfaces (OnStep, SoundStepper, my own etc). No issues at all.
Steppers are 400spr, 1.4A (also from ebay)

To couple the motor directly to worm is a bit too rough IMO.. so maybe you should go with finer microsteps.... 64 perhaps? (A4988 has 16 microsteps), then it will be similar to mine.
Reduction with timing belt is not prohibitive, only couple of $$ more (thanks to 3D printer parts from China).

Last edited by bojan; 10-07-2017 at 10:36 AM.
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Old 10-07-2017, 10:38 AM
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Thanks Bojan. That driver does up to 32 microsteps. So what sort of stepping resolution does that give you on the EQ6.

And did you go with the arduino mega or the teensy. The mega is way cheaper and I'm used to arduinos so might use one of those.


Edit- the timing belt sounds like a good idea
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Old 10-07-2017, 10:45 AM
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I am getting 0.225 arcsec (for 16 usteps, 1/4 timing belt reduction inside EQ6), you will have 0.5625 (32usteps, direct to worm).

I used MEGA, for the same reasons... it is a bit bulky compared to teensy but it fits nicely into the box from Jaycar, together with push-buttons and connectors.
The power comes from mount and/or from laptop.
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Old 10-07-2017, 12:29 PM
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And another question, I haven't used stepper motors before. Should go with ~3V stepper motor if running off a 12V supply - gives it better performance with the chopper drivers.
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