Onstep Telescope Drive

[garymck]

Hi,

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

http://www.stellarjourney.com/index.php?r=site/equipment_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

[bojan]

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.

[bgilsrud]

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

[garymck]

Hi
Steppers were these:

http://www.omc-stepperonline.com/09deg-nema-17-bipolar-stepper-motor-2a-46ncm-17hm192004s-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-635mm-flexible-coupling-18x25mm-for-3d-printercnc-stepper-motor-stfc03-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

[bojan]

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..

[bojan]

Last weekend I went back to OnStep system..
Everything that I complained about a year ago is now fixed :thumbsup:

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.

[ChrisV]

Thanks for that
Looks like fun. Might have a crack at it !

[Rac]

I use the Onstep system on my 20" Dob for visual and planetary imaging and it works great!

[Baza]

Rac, any photos or info about that drive system?
thanks
Barry

[bojan]

Here:
http://www.stellarjourney.com/index.php?r=site/equipment_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.

[Baza]

That's a very neat installation. Thanks Barry

[Baza]

double posted

[Rac]

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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[bojan]

It's flashy enough for me :thumbsup:

[Baza]

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

[ChrisV]

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 ?

[bojan]

I am using A4988 (http://www.ebay.com.au/itm/5Pcs-A4988-Stepper-Motor-Driver-Module-Red-For-Reprap-Pololu-3D-Printer-/142416432522?epid=888859658&hash=item2128ae4d8a:g:SrMAAOSwLsBZQ 3lk) 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).

[ChrisV]

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

[bojan]

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.

[ChrisV]

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.

[bojan]

Yes, you will be driving motors from current source (and Pololu drivers are exactly that).
Those motors have 1~2ohms coil resistance and are rated for 1~2A.

[luka]

Chris, there are few other stepper alternatives. I used DRV8825 with 32x microstepping while SilentStepStick TMC2100 or TMC2130 will give you up to 128x microstepping. Note that such high microstepping may not work well with some motors and that they may skip steps.

Also I used these (https://www.sparkfun.com/products/10846) steppermotors for my EQ5.

[RobF]

Hey guys, do you think these Arduino stepper systems could ever evolve into encoder systems with sufficiently high res and functionality to assist with improved tracking and PE for established EQMOD (EQ6 etc) systems? :question:

[bojan]

Howard of OnStep said he will look into it, when he finds time for that... Not sure about AstroEQ.

Also, Maciel (of SoundStepper (https://sourceforge.net/projects/soundstepper/)) also mentioned he will try to do it when time permits.

In the meantime, Bartels system (http://www.bbastrodesigns.com/StepperSystem.html) (works on DOS) supports encoders (Ek box, for example, via RS232), however the encoder support was not designed to help with PE.

[ChrisV]

Okay. Ordered the 8825 driver and most of the stuff on ebay. So project might start August if it arrives by then. Have to temper my excitement till then.

[RobF]

Thanks Bojan - very interesting.

[ChrisV]

I finally got a breadboard onstep going using a Teensy 3.2 - seems to work with the android app. The other week I got an old EQ5 mount - it already had stepper motors mounted.

So the last thing to do is to put it on a proper PCB. Even better news I found a website that makes PCBs for ~ $0.50 each. Plus about $16 delivery - well its still cheap. <easyeda.com>

The other thing is that a pile of DIYers put their PCB designs on the website that you can use modify and get made by them. There's a few onstep designs there, including the miniPCB by Howard Dutton, plus some nice designs by others. Ordered 4 miniPCBs last week and they are now on their way!

[Rac]

I highly recommend you use the TMC2100 or TMC2130 drivers. when it comes to smoothness they are in a completely different league to any other driver.

I've been using Onstep now for a few years on my 20"dob for planetary imaging and I've now just Onstepped my NJP so it now has Wifi and bluetooth and it slews at over 3deg/sec instead of 1.

[ChrisV]

Definitely Raymond. I started with the 8825s, then a month ago got the TMC2100. The difference with this driver is unbelievable.

The PCBs arrived today !

[ChrisV]

Bojan and anyone else using a 3D printer

What is a good (and not too expensive) one? I've got no idea
Looking at building case, stepper brackets for this build - and for other stuff. So might need one that does ABS & PLA?

Chris

[bojan]

ABS requires heated bed, PLA does not.. so printer with heated bed will do both (and other materials).

[bojan]

I just noticed that Howard provided setup for RAMPS 1.4 shield.... IMO something that should have been done at the beginning.

See here:
https://groups.io/g/onstep/wiki/2D-RAMPS14

[Rac]

The main downside is the mega2560 falls far short of a Teensy 3.2-3.6 for speed. I also noticed smoothness under tracking was much improved when I moved to a Teensy. All my mounts now use a Teensy 3.6.

[bojan]

Hmmmm
I don't think the speed is an issue here - in my case ( I am using A4988 drivers, 16 /usteps), processor has to output a pulse every 15ms for tracking, which is not a large task, and it is timer interrupt driven. Slewing is much, much faster, and I never noticed any problems.

However, at the beginning when I experimented with other systems (SoundStepper) I did have a smoothness problem with A4988 drivers. I had to short the resistor, to obtain smooth motor operation (no missed pulses), see here. (http://www.iceinspace.com.au/forum/showpost.php?p=850244&postcount=53)
Most likely DRV8825 doesn't have that issue.

I like Teensy because it is smaller, so it may fit into smaller enclosure... but I don't like the price - So I am sticking with MEGA/RAMPS-1.4 for now, especially because i am using it for my CNC projects as well (3D printer, CNC mill, CNC lathe, laser engraver etc.).

[ChrisV]

Finally put together the onstep controller. Well nearly finished - just have to sort out fixing connectors near the steppers. I've built this on an EQ5 mount that I got here on IIS.

Built using the new miniPCB designed by Howard Dutton (used easyeda.com to get them made).

For the controller I've used TMC2130 stepper drivers which can do 32 microsteps during tracking. Used 200 step/rev NEMA14 steppers with 2.5:1 belt driven pulleys. With the 144:1 worm this gives 0.5arcsec/step during tracking (microstepping ON) and GOTOs of 4.9deg/sec (microstepping OFF). So reasonable accuracy with good GOTO speeds - the NEMA 14 stepper can just handle this (I might try some NEMA 17 steppers with 400 step/rev).

I have used bluetooth to control the mount (but will eventually put in the wifi adaptor). Star alignment done with the onstep android app, and then navigate with SkySafari.

Took it out on the weekend and did a quick Eta Carina = 58x 20sec subs (20min total, no guiding - captured with APT processed in PI). See attached pics of the full frame (x4 binned) and zoomed in (no binning) to show that the stars look reasonable with the pictured scope/camera which is 2arcsec/pix resolution.

Thanks for pointing me to the onstep build. This is going to be my portable mount for wide FOV imaging. Its pretty light - can carry the whole scope/camera/mount without too much of a struggle.

Chris

Edit: pics are
- 2x Eta Carina
- Inside the onstep controller box & stepper mounted on DEC axis
- Scope on the mount - black box is bluetooth onstep controller, white box is dew heater controller and 12V distribution & USB hub

[Baza]

Looks great to me. Nicely done.