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Old 01-12-2018, 01:22 PM
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pmrid (Peter)
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DIY Stepper motor focuser control

I know this is an oldie but a goodie.
I have a perfectly good JMI 2" Crayford (non-motorised) focuser and want to PC control it via stepper control. JMI have sold the farm to Farpoint Astro and have ceased manufacturing these products (as at the end of 2018). I had a look at Farpoint's site and the stand-alone motors for the JMI focusers are out of stock so the choices are between expensive and very expensive. Hence a recent order on EBay for one of these:

https://www.ebay.com.au/itm/181925257317

a DC 5v 4-phase 5-wire Stepper Motor+Driver Board+Remote Control Wireless RC.

Anyone have any experience with these? I know there's an old thread here:

http://www.iceinspace.com.au/forum/s...hlight=focuser

Bojan pointed towards a commercial version of the controller on the BangGood site but in, too, is out of stock. So EBay it was. Look pretty similar.

The questions I'd like to ask include:
1. Has anyone actually built the gear/belt drive mechanism to attach to a Crayfor-type focuser?

2. Has anyone figured out how to PC-control one of these? It would be nice to be able to put it all together somehow.

Peter
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Old 03-12-2018, 08:59 AM
brown_rb (Robert)
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https://sourceforge.net/projects/ard...et%20Examples/
might give you some ideas for mounting
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Old 03-12-2018, 09:34 AM
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I did this with the same motor, but no wireless.
http://www.iceinspace.com.au/forum/s...light=crayford
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Old 03-12-2018, 10:19 AM
garymck (Gary)
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What about this one...I have built 2 of them
https://www.cloudynights.com/topic/5...us-controller/
Cheers

Gary
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Old 04-12-2018, 05:44 AM
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pmrid (Peter)
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Thanks guys.

Helpful indeed. I've ordered the various Arduino boards mentioned in the Cloudynights thread - ordered them from Keyestudio direct with free shipping. The whole lot cost less than the single Leonardo board from Australian distributors. Amusing!!

I'll have a play with this lot and see where it takes me.

Thanks again.

Peter
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Old 04-12-2018, 08:30 AM
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Highly recommend the Arduino one on sourceforge.

That author has several Arduino based astronomy products.

https://sourceforge.net/u/brownrb/profile/

If you search a bit, I think there are some more gadgets he’s built that aren’t on that list. His documentation is incredible for an open source device.

I’ve just built version 2 of his focuser after I broke my Microtouch controller (long story). A replacement microtouch was going to cost me $700 landed in Australia. The Arduino based one was less than a tenth of that. I managed to get it working with the microtouch motor after some trial and error on the wiring.

Used the new controller on the weekend - perfect.

DT
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Old 04-12-2018, 04:28 PM
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G'day David.
Long time between shouts!
I'm sneaking up on this project very slowly and carefully. I thought I was being adventurous when I bought a Raspberry Pi. But Arduino is something else again. I've ordered the core elements most people seem to recommend - an Arduino Leonardo, a L298P, LCD1602 and a Temp Sensor DS18B20. For the massive investment of US$32.95. Buying locally would have been more than double. But while I wait for those bits to arrive, I am also expecting the imminent arrival of a couple of motors and control boards.

What eludes me for the moment is the mechanical issue of how to get the motor to drive my focuser - I ought to have bought a geared motor I suppose but that's definitely being wise after the event. Do you use belts or gears to drive your focuser? And how did you determine the appropriate gearing ratios?

Peter
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Old 04-12-2018, 09:49 PM
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+1 for myFocuserPro as suggested by David. It has a PC app, ascom driver and options to add temp sensor etc.

The site has all the instructions needed to sort out microstepping and gears. Make sure you read it. Mine is attached directly to the focuser using a flexible coupler. And 1/32 microstepping gave me 15 steps in the critical focus zone - more than enough.

It's really simple to make. I had an old freetronics Uno and soldered the few components needed onto the Uno. Used a NEMA14 200step/rev motor - I got one with 23N.cm holding torque which was enough to direct drive the focuser.
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  #9  
Old 05-12-2018, 04:22 AM
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Quote:
Originally Posted by ChrisV View Post
Used a NEMA14 200step/rev motor - I got one with 23N.cm holding torque which was enough to direct drive the focuser.
Thanks for the added vote for Mr. Brown's project.

I've now ordered a Nema 17 Stepper Motor 17HS13-0404S-PG27 with a 27:1 planetary gearbox. So with the f8 x 200 mm scope this is meant for, that should give me 40-odd steps within the CFZ.

Now we sit back and wait a bit while all these bits and pieces wing their way here from all over the globe.

Obviously I have a bit of reading to do in the meantime.

Peter
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Old 06-12-2018, 03:07 PM
AstroApprentice (Jason)
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stepper that can be manually turned

I recommend finding a stepper that can be manually turned when not powered if you want to do some unplugged visual as well as AP.
I have a Starizona MicroTouch on a FTF that works beautifully for AP, but has to be fully removed if you want to turn the focus knob manually for unplugged visual use - plus it requires the fine focus knob to be removed.
I also have a Moonlite motor that overcomes this issue with the use of a slip clutch to easily disengage motor - and at least I can keep the fine focus knob on other side.
My favourite design, however, at least from a versatility view point is my Avalon FOCS stepper that can be rotated manually when not powered ie simply unplug or switch off power. Plus it uses a belt to drive focuser knob so I don't lose use of the fine focus knob if I want to do some visual.
So if you can find a motor like theirs for your system, then it will be good for both AP & visual:
http://www.avalon-instruments.com/pr...e-focuser-focs
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Old 07-12-2018, 01:49 AM
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Hi Jason. I see your point about doing visual as well as AP. Those Avalon rigs look well designed and executed. No dealers in Oz though and the US$price at OPT (US$279) puts it well above A$400 landed here. These little Arduino modules are somewhat cheaper although not as "pretty".

Peter
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Old 07-12-2018, 06:54 AM
AstroApprentice (Jason)
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Hi Peter,
I agree arduino is a great option. I particularly like this mini one:
https://www.cloudynights.com/topic/4...ronic-focuser/
I just recommend finding a motor like the Avalon that can be rotated manually when not powered - Iím not sure why everyone doesnít use them, perhaps thereís a performance trade-off? Maybe I should compare performances between Avalon & Starizona on a FTF one day...
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Old 07-12-2018, 07:03 AM
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In absence of expesive solutions to manual issue, you can have a look at this thread.
Also, this (manual control of the focuser from comp) maye be useful.
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Old 07-12-2018, 08:16 AM
AstroApprentice (Jason)
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Hi Bojan,
Do you know why esteemed companies such as Moonlite and Starizona use stepper motors that can't be turned manually? ie is the Avalon motor that can be turned when not powered a new or inferior design?
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Old 09-12-2018, 07:45 PM
brown_rb (Robert)
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Why cannot be turned manually

If you disengage stepper and move manually then the focuser loses where it is, the focuser position is invalidated for the stepper. When you reconnect motor it still thinks ts in the same position - but its not (you moved it) and that is a sure fire recipe to ultimately do some serious damage to your focuser by exceeding travel limits.





Quote:
Originally Posted by AstroApprentice View Post
Hi Bojan,
Do you know why esteemed companies such as Moonlite and Starizona use stepper motors that can't be turned manually? ie is the Avalon motor that can be turned when not powered a new or inferior design?
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Old 09-12-2018, 08:00 PM
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Quote:
Originally Posted by AstroApprentice View Post
Hi Bojan,
Do you know why esteemed companies such as Moonlite and Starizona use stepper motors that can't be turned manually? ie is the Avalon motor that can be turned when not powered a new or inferior design?

It's probably a consequence of high transmission ratio.
The little motor I used also cant be turned (easily) when powered off, and definitely not when powered on.


I think neither of those designs are inferior per se... but if you can turn it somehow, it is much more practical.
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Old 14-12-2018, 02:12 AM
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pmrid (Peter)
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Quote:
Originally Posted by garymck View Post
What about this one...I have built 2 of them
https://www.cloudynights.com/topic/5...us-controller/
Cheers

Gary
Gary, may I tap into your experience with these - I'd already ordered the boards I need when I also discovered Robert Brown's focuser project. So since I'm already half-way down the track to the cloudynights project, I figured I might as well finish it. I'd like to clarify a couple of issues about powering the project though. I will be using a Nema17 27:1 geared motor which required 12VDC. But I'm a bit confused by the images on the cloudynights discussion. I wonder if you happen to have any images of your kits? The 12VDC input and the connections to the PC would help too.

Peter
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Old 14-12-2018, 06:50 AM
garymck (Gary)
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Quote:
Originally Posted by pmrid View Post
Gary, may I tap into your experience with these - I'd already ordered the boards I need when I also discovered Robert Brown's focuser project. So since I'm already half-way down the track to the cloudynights project, I figured I might as well finish it. I'd like to clarify a couple of issues about powering the project though. I will be using a Nema17 27:1 geared motor which required 12VDC. But I'm a bit confused by the images on the cloudynights discussion. I wonder if you happen to have any images of your kits? The 12VDC input and the connections to the PC would help too.

Peter
Hi Peter,
happy to help. I'm using the same motor as you, one thing that I found was that the motor became very hot when running at 12 volts (despite it's spec) so I dropped the power to 6 volts. The motor still has heaps of torque, but barely gets warm. Works a treat.

There is also a line in the firmware that may ned changing depending upon the display you purchased.

PM me your mobile number and which parts you need images of and I will
sms pics to you

cheers
Gary
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Old 14-12-2018, 08:44 AM
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pmrid (Peter)
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Quote:
Originally Posted by garymck View Post
Hi Peter,
happy to help. I'm using the same motor as you, one thing that I found was that the motor became very hot when running at 12 volts (despite it's spec) so I dropped the power to 6 volts. The motor still has heaps of torque, but barely gets warm. Works a treat.

There is also a line in the firmware that may ned changing depending upon the display you purchased.

PM me your mobile number and which parts you need images of and I will
sms pics to you

cheers
Gary
Thanks Gary. I sent a PM as you suggested but thought I might put this comment on the tread for others to reply - I thought that with these high-torgue motors such as the 27:1 NEMA17 you don't have to keep current to them all the time. The rotor inertia on these is 35gcm2 which ought to hold an elephant even when not powered.

Peter
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Old 14-12-2018, 09:43 AM
garymck (Gary)
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Peter,
the firmware does not turn off the power to the motors when they are staitonary - hence the motor getting hot. My guess is that some motors will move when unpowered so need to be kept energised to hold position - this would be the case with a motor with no gearbox for example.

Gary
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