artaex: Now the complex part is transferring the motion of the motors to the roller blinds. I don't think I'll be able to use the cord that is included, because it has a fixed length and there's really no way to make them shorter apart from ordering custom ones. Even if I had custom ones, I would still need some special thing to put on my motors that fits the cord.
First off, I would ditch the steppers, and go for a worm-driven DC gear motor - that is, some form of a gear motor that can't be back-driven by the weight of the blinds. Likely, you would want something in the 30-60 RPM range on the output shaft (you could go higher - but not too high - then use PWM to slow things down). A worm-gear motor can't (generally) be back-driven at all; other gear motors might be able to, but at the RPMs needed, the gearing (spur or planetary - if not worm-driven) likely will have enough internal "hold" to keep things steady (after all, we're not lifting much weight).
Use an h-bridge to control it; if the RPM is low enough, then a simple two-relay system could be used, if PWM isn't needed.
You'll also likely want some limit switches - this will be needed whether using a gear motor or a stepper as you originally planned. Without the system knowing where the limits of travel are, you're going to have problems sooner or later.
artaex: Some of my thoughts: - Perhaps a gear system, but it would require a few 3D-printed parts and they might wear out quickly. - Pulleys? I can easily attach a pulley wheel to the motor's axel, but still requires a custom component to fit another pulley wheel to the roller blind's metal rod.
It's difficult to tell exactly - and correct me if I am wrong - but the chain as shown in the drawing is what makes the blinds go up and down, correct? I mean, I didn't see any provision for tilting slats - is that correct?
If so - then using that chain is what you'll want to use; however, if that chain is instead used for tilting slats, and a separate cord system is used for raising and lowering, things will be much more complicated.
artaex: Some important notes: - I have a 3D printer at hand, but I'm horrible at 3D modeling...
Then you may want to find somebody who is, to help you work on this project - if needed.
artaex: - I don't have much horizontal space. I can't directly fit the motor to the blind's metal rod. There's simply no room.
...which is why I am suggesting the chain. Again, if it controls the level of the blinds, and not something else.
artaex: - Manual operation is optional. I wouldn't mind if that would no longer be possible.
Good - because I can't see a way around that.
artaex: - If I replace the cord system, the blind will not stay at it's location, but instead roll down. Currently there's a spring in the cord system that keeps the blind in place at all times. I would need a powerless solution to keep it in its current position.
Well - again - if the "cord" (ie - the chain) is what is controlling the position of the blinds - then that is what you'll want to use.
First - you'll want to get rid of whatever spring you are talking about - you want to make this "free-running". Then - by using a geared DC motor of some type (as discussed earlier) - the blinds should stay in place once everything is connected.
For the chain, it should be able to be shortened; somewhere on the loop of chain should be a crimped "link" - like you would see on a ceiling fan or overhead-light pull-chain. This kind of chain (known as "ball chain" or "beaded chain") is very common, and is used for all kinds of stuff. That crimped link can be easily popped off, the chain shortened (using a pair of wire dikes), then clipped back together. There is, however, one issue with this - which I will get to in a moment.
Once you have the chain shortened, then all you need is some kind of pulley to attach to the gear motor, over which you can run the chain. Fortunately, such things do exist - heck, there's one inside the mechanism of that blind. You might be able to get such a pulley as a "spare part" - either from the blinds manufacturer, or from where you purchased it originally. Alternatively (though more expensively), you could purchase another set of blinds and remove the pulleys. Or - get the end-piece as a spare part.
Sometimes, you can find old blinds and such at a garage sale, tag sale, boot sale - ie, whatever they call such an informal selling in your area; or, check thrift shops and/or "recycled building and remodeling suppliers" if you have them.
You can find such pulleys brand-new - just google around for "ball chain pulley" or similar - you will need to know the pitch of the ball chain - sometimes, though, that can be more expense than it is worth.
Probably the best solution, though, would be the one you already have a tool for - 3D print it! When you google "ball chain pulley" you'll find a ton of links to various 3D models - here's one I found on Thingiverse:
Now I'm not saying that particular model will fit your chain - as noted on that model, it is for 3.5 mm pitch chain - but it looks really similar to standard ball chain. Otherwise, you'll need to find a model that will work for your chain. There seemed like there were more than a few such models out there.
Also note that model is seeming sized for a stepper similar to the one you are already planning to use; that said, make note of bore sizing and what-not - you might need to alter it for your motor (especially if you change over to a gear motor) - this will require modification of the model before printing it.
Now - for the point I noted before:
If you shorten the chain (and even if you don't, this could still be an issue) - that connector link would need to travel over the pulley - but such pulley aren't designed for that - it might slip off, or jam, or something else.
Instead, what you might need to do is create a continuous loop of ball chain. This isn't easy - basically, the balls of ball chain are composed of a crimped split-sphere of metal, crimped around a metal bar with two ends - that prevent slippage through the holes of the chain. You can (with care and patience) after cutting the chain - carefully split two of the balls with a thin blade of some kind, then use one of the spare metal bars (by again splitting and removing one from another section of the chain) as a link, and re-crimping (carefully, so as not to deform the balls) things together. This would all likely be best done under a magnifying glass of some sort (one of those magnifying lamps that jewelers use would be best). It would be a very tedious and patience-trying exercise, but not impossible.
It may also be possible to purchase such pre-made chains - again, do some googling.
Once you have you chain and pulley ready, it's just a matter of positioning the motor, mounting the chain, tensioning things properly (so the chain doesn't slip off) - then adding the remaining electronics, etc.
Hope this helps - or at least gives you some ideas or direction. Good luck!
Just wanted to also mentioned that the pulleys are also called "ball chain sprockets" - so, with that in mind - here's a couple of other items I found:
Also - this one was linked off the one I posted earlier:
It's kinda interesting in that it is a parametric OpenSCAD model - meaning you can alter some variables in the design file, and have it generate different pulleys based on your needs. This might help you fit your particular chain (though I don't know if chain pitch is one of the parameters). It does have various shaft mounting options, which may help with whatever motor you select. I would imagine that pulley size and/or shaft size would be parameters - but I am not sure.
Get Tubular Motors
Select Mount kits
Select wired or RF remote controller (433Mhz)
Cost ~$50 per windows.
Does the blind need to stop at mid positions or does it only need to full open/closed?
zoomkat: Does the blind need to stop at mid positions or does it only need to full open/closed?
full open/closed is handle by limit switch, stop at mid position is handle by break. It is all build in Tubular Motors.
ALEKO® AC Tubular Motor DM45RM for Retractable Patio Awning,
Perhaps an alternative to a ball chain pulley might be a 'V' pulley made from two facing halves with a thick rubber surface. Theoretically the string of balls would get somewhat trapped in the bottom of the V, providing enough friction to drive the chain. - Scotty
Tubular motor digram:
Single phase AC motor (120/220V, 50/60Hz)
Are you some kind of sales-rep making commission on sales of those motors?
Those tubular motors sound like an interesting idea - but I doubt that the OP is wanting to spend that kind of money; plus I would imagine that the idea of this being a project to use the Arduino on is also motivation.
That said - @artaex:
If you can find a DC gear motor with a concentric, centered output shaft (those with planetary gearing are best for this) that will fit inside the tube, you might be able to create a version of such a motor. Mount the motor so that the body is inside the tube, and (somehow) engages the tube, and then adapt the shaft so that it engages the bracket that mounts on the wall.
Get rid of any springs, plus the ball chain.
You'll need to figure out a way to get power to the motor (since it will be rotating) - the easiest might be to hook a wire from one terminal, and use a brush arrangement on the output shaft; the other terminal, lead a wire to the opposite end of the tube, and mount/attach it to the metallic shaft on that side. Then all you would need to do is apply power at the ends on the support shafts, and it will raise and lower.
...at least, in theory.
Are you some kind of sales-rep making commission on sales of those motors?
Those tubular motors sound like an interesting idea - but I doubt that the OP is wanting to spend that kind of money; plus I would imagine that the idea of this being a project to use the Arduino on is also motivation. ...
I am customer of remote controlled electric windows shield, tubular motor is used at electric windows shield might be older than computer age, very old technology. I used it as back plan for LCD glass window.
Looking at the picture of the shade hanging, I think I'd just go to one end and mount a continuous rotation servo or gear motor to roll the shade, and use little limit switch balls on the roller chain to detect full up and full down.
I want half-way detection as well as full open/closed. I'm planning on sticking a tiny magnet to the fabric and connecting three magnet sensors to detect positions. This shouldn't be a problem.
You might put a motor on one end and an encoder on the other end.
I would much rather measure it than attempt to calculate it. Rig up something that replicates the arrangement of components in the attachment. If you find that a pound of weight is required at the end of the 12" arm to turn the pulley then you then you know that a foot-pound of torque is required. Online calculators will enable you convert to other inch-pounds, kg-cm, etc. I would add another 50% to compensate for other variables that might add to the required torque.
Have you given any consideration to over current protection such as when your system jams and the motor still attempts to drive it?