New Stepper control for Focuser

[Nico13]

Hi All,
Had an idea the other day when I came upon these steppers with control boards but wasn't 100% sure of the connections so with a bit of advice fron Bojan I hooked it up and away it went.

The aim is to build a Focus control to fit to the crayford for fine adjustment without bumping the scope.
As I'm still using an SLR for imaging this is a problem when trying to achieve good focus even with live view.

So this will when fitted allow very precise control, as with the encoder I used to control it (a volume encoder from a car radio) this is the type that just keeps going around when turned with no stops, it has 40:1 reduction because the gearbox in the stepper is a 60:1 for a start.

The result is plenty of torque. precise control, running at 5V with a holding current of 0.25A running of 0.2A

All I have to do now build a nice neat version of it and fit it up, still need to come up with a clutch or something for the drive as yet.

Here is a short Video (http://www.youtube.com/watch?v=vq_rrmu6ils&feature=plcp) to show control movement.

[adman]

Looks good ken! Where did you get the steppers and boards from...?

Adam

[alistairsam]

Nice work Nico,
Would you have a link to the controller and The stepper?
I like the simplicity and smoothness, should do the job well.
Is that a 7.5 deg stepper with a gearbox?

Just a suggestion
I'm a fan of micro stepping and I think you could get finer movement with a 1/16th controllerlike the allegro A4988 stepper controller, a 555, and your encoder switch with a 1.8 deg motor like this one
http://www.robotgear.com.au/Product.aspx/Details/459
This is the controller
http://www.robotgear.com.au/Product.aspx/Details/561

This video is a test of 1/32 micro stepping with a different controller where I'm sending a train of 6400 pulses for one rev. So one manual step pulse would yield very small movement and you could have one pulse per encoder tick.
http://m.youtube.com/watch?v=53tgJ4pwn1w

I know micro stepping yields lower torque, but current is adjustable and torque should be ample for a focuser.
I'll be making one with a simple lcd display that shows the number of steps.
Just need to think of a home position routine.

[Nico13]

Hi Adam,

I got mine from the Alibaba site but I think they're available on ebay as well cost with the board was under five bucks with free postage so I got three to play with just in case the smoke got out :eyepop: of one while testing.

Just do a search for ULN2003 on the bay and a number of different ones will pop up.

If you want the schematics for the additional circuitry let me know and will draw it up with resistor values etc.

[Nico13]

This isn't where I got mine from but it is the same stepper unit with all the specs.

LINK (http://www.ebay.com.au/itm/DC-5V-Stepper-Motor-Geared-Arduino-PIC-MCU-DIY-/260886562536?pt=LH_DefaultDomain_0&hash=item3cbe0d06e8)

[MrB]

Please first check via email with this vendor if they have stock.
I had a recent sweet/sour experience, not a biggie, just an issue with what their site says they have in stock and what they actually have at hand. Also the lack of any communication regarding my order being placed on back-order for two weeks.
Not enough to deter me from placing a second-chance order with them in future though.

[Nico13]

Yep love the idea of micro stepping as well and the stuff you linked to looks the bees knees. :thumbsup:
The bits I'm using will do the job although not a small step size, 5.6 deg I think it was, the gear reduction solves that issue but with the slight dissadvantage of a small amount of backlash in the gear set, not significant enough to cause a problem at my level of imageing though.

[adman]

Thanks ken, I'll do that when I am ready. I want to get my drive mechanism built first and test it by hand turning before I start to try to motorise it.

Adam

[alistairsam]

hmm, I've ordered only once or twice from them, had no issues so far.
This is another source
http://littlebirdelectronics.com/products/a4988-stepper-motor-driver-carrier
http://littlebirdelectronics.com/products/stepper-motor-bipolar-200-stepsrev-20x30mm-39v-600ma

[originaltrilogy]

This looks good.
I want to be making a barn door tracker and looking for cheap way to turn the handle instead of by hand.

Would this be possible?

[Nico13]

Yes this could be done, you would need to work out how fast you needed to turn the drive to allow you choose an encoder and stepper combination but that should be no real problem.

[ZeroID]

Re backlash: I'm looking at using a toothed belt system instead. Belt tightness can be easily adjusted to give almost no play and a reduction via the pulley sizes. The example I saw made even just used the standard knurled focusser knob as one of the drive wheels. Very simple to build and light as well.
Got plenty of motors and bits at home. Do some test builds soon and post results.

[Nico13]

Yep my thoughts also,
I to have a box of bits and steppers form all sorts of machines so will try a couple that I have that appear to have a very small step size, just have to sort the wiring and operating voltage as they are just bare leads and no labels.

[alistairsam]

I just ordered a moonlite focuser and am going to try coupling a 1.8deg stepper directly to the shaft on one side with a shaft coupler.
But ideal is a small timing belt as that could drive the focuser knurled knob directly.

Steve (Kinetic) made a nice slip clutch
Post #1 here
http://www.iceinspace.com.au/forum/showthread.php?t=51301&highlight=focuser+clutch

[2stroke]

Ken could you post the schematics for the additional circuitry, just ordered 3 myslef off ebay, what a bargain to have some fun with.

[Nico13]

No probs, :thumbsup:
Will have to make a couple of changes to the schematics I have to add in a couple of resistors needed but will get them done Saturday for you.

I don't have internet at home at the moment, :mad2: in the middle of provider change and they've left me with a five day gap with no service.

That's what they call a rapid transfer :question: :screwy:

I can still connect using my iPhone as a hot spot for a short period and that's ok though no emails until the new account is up and running.

[bojan]

Ken,
If I may step in, to speed the things up a bit.. I hope you don't mind :P
We started with this test circuit on my bench.
Values of resistors are not critical, they can be anywhere between 100 ohms and 10 kohms.

I am already using it on my focuser (with optical encoder - because I had couple of them) as a laptop-free alternative to my small application (that I posted some time ago on this forum).
It should be noted, that the smaller the resolution of the encoder, the finer positional accuracy of the focuser will be.
(My optical encoder has 96s/rev, and this gives me just about right transfer ratio)

[2stroke]

Cheers bojan, hope mine turn up for next weekend. These rainy day projects are keeping me busy to say the least lol

[Nico13]

Thanks for doing that Bojan, I have only just got fully back on line today your help with this is much appreciated.:thumbsup:

[ZeroID]

Be interested in seeing your schematic as well Ken. I can get stepping motors from scrapped copiers, printers etc at work. Already have quite a collection. If you need anything to play with let me know and I can post something over the ditch.

[2stroke]

Mine does run as great, if i turn the encoder to fast it doesn't move though it seems to register as leds flash quickly. Would this be because ive used only 1 1k resister for each double out, so theres a total of 3 instead of 6? Like pins 5 and 1 meet then go through a single 1k then onto leg A of the encoder? Lol maybe cause mine looks neater then kens wiring job, or the altronics encoders are poor quailty http://www.altronics.com.au/index.asp?area=item&id=S3350

[bojan]

This is because you reached the stepper motor max speed.
Higher voltage will help.. but not much.

[MrB]

I wonder if it's the start speed and not the max speed?
The encoder is only 20 pulse per rev. If it is one step per encoder pulse, even spinning it fast would not be many rpm for the motor.
Try ramping the speed up by starting slow on the encoder then increasing.
I'm guessing you are exceeding the motor's pull-in torque capability from a dead start?
This would also be helped by a higher voltage.

[Nico13]

LOL :rofl::rofl:hey whats wrong with my wiring job :question: it's the best mess I could make and it still worked ok, I was just following Bojans mud map :P :thumbsup: Thanks Bojan it wouldn't have worked without your help:thanx:

Version two will be a lot neater. (I hope) :lol::lol:

Mine does the same if you spin it quick but that's ok for this job I guess.

[2stroke]

Cheers guys lol i think ill play it safe just using a computer psu and i don't think that 5v 12v rail to make a 7v rail would be safe haha. Thanks for the schematics Bojan, well written and worked a treat, just wish i had some bread board though haha. Really need a sticky in this section with links to schematics and projects because god knows how many useful things are lost in the thousands of threads :(
I did mine in pretty yellow and black ken with shrink over connections. I still think your test version runs better, time to ghetto mine up hahaha.

[bojan]

Old thread, but updated design..
I added one IC (4001) to change the Full-step drive sequence with Wave-Drive.. resulting in 1/2 power consumption.

I am using older stepper driver on 2 of my telescopes for focusing - 10" Newt and Canon FD 400mm f/2.8 (http://www.iceinspace.com.au/forum/showthread.php?t=148460&highlight=ULN2003).
I will make contrpoller with new design for C11.

[bojan]

And, it is worth mentioning commercial version (https://www.banggood.com/4-Phase-5-Wire-Stepper-Motor-Driver-Board-Remote-Control-p-1026804.html?rmmds=search) of similar (but wireless) stepper driver on BangGood.