I was reading through David's SharpSky stepper focuser controller thread the other day, and watching some of the videos on his site. Got me to wondering about the actual stepper motors moreso than the controller.
I have recently bought a Mount Hub Pro. It has a built-in stepper controller that is supposed to be ASCOM compliant with Moonlite and Robofocus motors. I bought it for the power, USB, and dew control features in one box, not so much for the focus.
But seeing David's video, I'm wondering if all I need is a cheap $15 (or thereabouts) 12V stepper motor and could make my own for use with the MHP. He makes it look so easy. Am I dreaming? Where would I start with figuring out the wiring connections between the MHP and the motor? I believe it's a DB9 type connector.
You can get a robo motor only from Peter Tan for $890 HKD.
Jase posted a link a while back which you might find interesting. LINK
These are cool because they have the gearbox all in one unit.
As for wiring a stepper directly, I guess you just need to check the wiring diagram. It shouldn't be to difficult I expect.
James
Thanks mate. Based on Jase's post and link, I'm beginning to see that there are stepper motors and there are stepper motors. Will have to research a bit more. He was supporting much more weight than I intend to. I've only got a QSI583 hanging off mine. So am wondering how important it is to pay $95 or whatever it is for the "super" motor.
Thanks mate. Based on Jase's post and link, I'm beginning to see that there are stepper motors and there are stepper motors. Will have to research a bit more. He was supporting much more weight than I intend to. I've only got a QSI583 hanging off mine. So am wondering how important it is to pay $95 or whatever it is for the "super" motor.
Hey Troy Bojan is someone you should talk to also as he is into stepper control in a big way.
I'm just about to start a stepper focus controller using a geared stepper but just using a hand paddle to adjust it so I don't bump the scope while adjusting focus.
Still using an SLR for imaging you see, but he Bojan that is will have some info for you I'd reckon.
Hi guys,
Have a look at this thread: http://www.iceinspace.com.au/forum/s...ad.php?t=90164
The Pololu drver is ~$15 per motor.
Motors from ebay are in the range of $5 ~ $15 (and steppers are just steppers - anything above ~20 (unless it's high torque, high current and/or high power.. but we don't need any of those here for driving telescopes) is rip off. Especially when the steppers can be found in a variety of old equipment (old 5.25" floppy drives, printers, photocopiers.. )
Or, try ebay, and search for "long motors" for example (manufacturer in China - I am using their motors (400steps/rev, $10 each) in my EQ6, with Pololu drivers, also from Ebay).
Or search for "NEMA17" or "1.8° stepper" or "0.9° stepper" or similar (this is the standardised size of the stepper motor).
Hope this helps
Thanks for the PM invite Troy, thought I would may a few comments if that's ok.
I designed my SharpSky digital focuser around the same motor technology that ML & Robo use that is 4 phase unipolar motors. The motors I use have five wires some unipolar motors have more wires for flexibility but once configured for 4 phase operation end up with five connections. You essentially end up with a common and then one wire per phase. The stepping sequence is very straight forward, basically a walking one or walking pair if two coils are to be driven at once. The big advantage of permanent magnet unipolar motors is that you only need a very simple driver (I used a Darlington driver IC) whereas bipolar motors require a much more sophisticated (and expensive) driver.
I use one of two motors both supplied from China. Both motors are very cheap one at about £4 and the other at about £7. Both motors have built in gear boxes and with my controller produce ~2048 steps per revolution but are capable of twice that. The second of the two motors really had grunt with a pull in torque of >147mN.m, The reason these motors are so cheap is that they are used in just about every air-conditioning unit on the planet are are made in the millions.
The motors do exhibit some backlash as they have gear boxes. This is not really an issue as I compensate for this in software and there is a parameter on the driver where the user can tweak the backlash compensation to suit their setup.
The SharpSky design uses a D-type connector and is pin compatible with ML/Robo and a couple of guys are using the design which such motors. Personally before shelling out lots on an expensive ML motor I would get hold of one/both of the motors listed below and give them I go. I fully expect that they will be more than adequate for Astro needs. Loads of imagers are using SharpSky with the smaller of the two motors and have reported great performance. If you really have a lot of kit to move maybe the larger motor would be better.
If you want any information regarding wiring or stepping sequences please ask away.
Smaller motor : 28BJY-48
Larger motor : 35BYJ-412B
Further to my last post and with regard to the Mount Hub Pro.
If the Mount Hub Pro is designed to drive ML/Robo motors the wiring for the motor is shown in the SharpSky build PDF document as SharpSky is also ML/Robo pin compatible. See section 11 of the document and this shows the wiring of the 9 way D-type and the colour coding of the two motors I listed in my previous post. If you wire these motors as shown and then use a pin to pin D-type straight through lead the motor will work just fine.
Hi guys,
Have a look at this thread: http://www.iceinspace.com.au/forum/s...ad.php?t=90164
The Pololu drver is ~$15 per motor.
Motors from ebay are in the range of $5 ~ $15 (and steppers are just steppers - anything above ~20 (unless it's high torque, high current and/or high power.. but we don't need any of those here for driving telescopes) is rip off. Especially when the steppers can be found in a variety of old equipment (old 5.25" floppy drives, printers, photocopiers.. )
Or, try ebay, and search for "long motors" for example (manufacturer in China - I am using their motors (400steps/rev, $10 each) in my EQ6, with Pololu drivers, also from Ebay).
Or search for "NEMA17" or "1.8° stepper" or "0.9° stepper" or similar (this is the standardised size of the stepper motor).
Hope this helps
Thanks for chiming in, bojan. Had a read of that thread, but most of it is quite technical and beyond my electronics knowledge. If I understand it correctly, and using lay terms, you're using a USB sound card to control a stepper motor. Read like you were having issues finding the right card/board?
Presumably with the MHP the hard part is done for me, and just need the right motor and wiring?
Further to my last post and with regard to the Mount Hub Pro.
If the Mount Hub Pro is designed to drive ML/Robo motors the wiring for the motor is shown in the SharpSky build PDF document as SharpSky is also ML/Robo pin compatible. See section 11 of the document and this shows the wiring of the 9 way D-type and the colour coding of the two motors I listed in my previous post. If you wire these motors as shown and then use a pin to pin D-type straight through lead the motor will work just fine.
...
The big advantage of permanent magnet unipolar motors is that you only need a very simple driver (I used a Darlington driver IC) whereas bipolar motors require a much more sophisticated (and expensive) backlash as they have gear boxes. This is not really an issue as I compensate for this in software and there is a parameter on the driver where the user can tweak the backlash compensation to suit their...
Do you get the impression that the MHP can handle the bipolar motors? Would these be zero backlash?
.... Read like you were having issues finding the right card/board?
Presumably with the MHP the hard part is done for me, and just need the right motor and wiring?
That was at the beginning, no issues here any more
and the software (SoundStepper, Maciel from Brasil is the author) supports Ascom and whatever you may ever want.
Yes, with MHP there shouldn't be any problems - small unipolar motor (5 or 6 wires) will work (as far as hardware is concerned...)
However I don't know anything about software side of it.
I see. Thanks. This unipolar/bipolar thing is confusing me. David's comment about backlash. Do the bipolar ones have this issue too? Trying to get a feel for cost/benefits of cheapies vs expensive motors.
Troy, the backlash is due to the gearbox only.
Bipolar/Unipolar steppers without gearheads do not exhibit this problem.
Oils aint oils and equally, steppers aint steppers.
Like almost everything else, some steppers are better than others with respect to positional accuracy and repeatability. http://www.euclidres.com/apps/steppe...r/stepper.html
It may be worth checking the datasheets for any steppers you are considering, if available.
No worries.
BTW, the accuracy of steppers is mainly due to the quality of the 'teeth' on the rotor and stator. Cheap stepper will be made from punched sheet steel. The steppers I have salvaged over the years from old floppy/harddrives had machined or ground teeth.
However I'm guessing the accuracy of the motor would not be such an issue with these gearheaded motors. Probably don't even need to microstep them if the gear reduction/steps per rev is high enough.
I see. Thanks. This unipolar/bipolar thing is confusing me. David's comment about backlash. Do the bipolar ones have this issue too? Trying to get a feel for cost/benefits of cheapies vs expensive motors.
Expensive and cheap... this depends more on manufacturer/distributor, less on the actual quality.
If stepper has ball bearings, and in general looks solid it is not bad, but it may be cheap. Even hybrid, NEMA17, 0.9° s/rev are ~$10 or so (from Long motors in China, for example).
Data sheet is a good indication on what you are dealing with.
