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  #21  
Old 10-07-2017, 12:31 PM
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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.
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  #22  
Old 10-07-2017, 09:30 PM
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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 steppermotors for my EQ5.
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  #23  
Old 10-07-2017, 09:38 PM
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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?
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  #24  
Old 11-07-2017, 05:58 AM
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Quote:
Originally Posted by RobF View Post
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?
Howard of OnStep said he will look into it, when he finds time for that... Not sure about AstroEQ.

Also, Maciel (of SoundStepper) also mentioned he will try to do it when time permits.

In the meantime, Bartels system (works on DOS) supports encoders (Ek box, for example, via RS232), however the encoder support was not designed to help with PE.

Last edited by bojan; 11-07-2017 at 06:17 AM.
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  #25  
Old 11-07-2017, 08:31 AM
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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.
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  #26  
Old 11-07-2017, 07:44 PM
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Quote:
Originally Posted by bojan View Post
Howard of OnStep said he will look into it, when he finds time for that... Not sure about AstroEQ.

Also, Maciel (of SoundStepper) also mentioned he will try to do it when time permits.

In the meantime, Bartels system (works on DOS) supports encoders (Ek box, for example, via RS232), however the encoder support was not designed to help with PE.
Thanks Bojan - very interesting.
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  #27  
Old 02-12-2017, 09:40 PM
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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!
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  #28  
Old 03-12-2017, 09:20 AM
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Quote:
Originally Posted by ChrisV View Post
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.
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.
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  #29  
Old 03-12-2017, 07:11 PM
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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 !
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  #30  
Old 10-12-2017, 10:37 AM
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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

Quote:
Originally Posted by bojan View Post
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).
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  #31  
Old 18-12-2017, 05:57 AM
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ABS requires heated bed, PLA does not.. so printer with heated bed will do both (and other materials).
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  #32  
Old 27-12-2017, 05:42 PM
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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
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  #33  
Old 28-12-2017, 06:54 PM
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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.
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  #34  
Old 29-12-2017, 07:04 AM
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Quote:
Originally Posted by Rac View Post
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.
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.
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.).
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  #35  
Old 19-03-2018, 09:39 AM
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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
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Click for full-size image (EtaCarina_DSS_stacked58_DBE_6_final_zoom.jpg)
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Click for full-size image (Slide2_2.jpg)
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Click for full-size image (Slide3_2.jpg)
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Last edited by ChrisV; 19-03-2018 at 11:13 AM.
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  #36  
Old 22-03-2018, 06:39 AM
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Looks great to me. Nicely done.
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