Hello all
I want to try and make a camera rotator using Arduino and a stepper motor. I have minimal experience with electronics but I am slowly gathering information for this project and this is what I think I need so far...
Am I right in thinking that the Nema 17 requires 12voltsDC and that the ULN2003 breakout will control it as long as I have a separate 12VDC power source? Is the Nema 17 overkill?
I have alot of other things to consider about this project but small steps and all that.....
Your help is very much appreciated
Thanks
Jeremy
I'm totally new to all of this myself, having only completed one electronics project in my entire life, and that was motorising focusing on my Esprit.
One thing I can tell you though is that Nema 17 is the frame size of the motor, and doesn't say much about the amount of torque it delivers, though you may find there's some upper or lower bounds for motors with that size.
You need to figure out how much torque you need, and from there find a motor that delivers that. If you don't know how, or can't be bothered, you can always wing it (that's what I did), but you run the risk of buying multiple times when you find out the thing you originally bought wasn't right (also what I did).
Another thing to keep in mind is that those stepper controller boards will have limited current output, often controlled by a potentiometer. I didn't know this (probably a real "duh" for anyone that knows anything about electronics). I mention this because when I bought my first controller boards of the low-cost ebay-knockoff variety, this wasn't mentioned on the specs at all and I ended up not supplying enough current to my motor, causing it to deliver significantly less torque than it could.
You probably won't need 12 volts either, but again it's going to depend on the specifics of the motor in question.
Do you have a design in mind? How's this physically going to fit together? Any reduction steps will modify the amount of torque, in turn changing the requirements of the motor.
As to how I am going to mechanically attach the thing I am not 100% sure, it was going to be a "get it and tinker" kinda deal. A timing belt and pulley system to turn the focuser and not too sure yet about much else!
I am figuring if I can get the electronic components right (motor, driver etc) then I will just play with it to get the mechanical part right.
I played with an A4988 and also with an Easy Driver (not the "Big" version) when motorising my focuser. One thing to note is the amperage you can push through the boards without active cooling. I think that might be about 1A with the A4988. The big easy driver you've linked there says it should be able to do 1.4-1.7 without active cooling, but needs cooling when approaching 2A.
The bigger motor you've linked to is rated at 1.68A. That doesn't mean you have to run it at that, but it's where you'll get the most torque, but it's also the max recommended. Based on that I'd be inclined to get the Big Easy if you go with the larger motor, either if you go with the smaller motor. The bigger motor has about twice as much torque, and can chew up about 5x more power. Without knowing how much torque you need it's difficult to make a recommendation.
One thing to note is that the bigger motor has 0.9 deg per step, whereas the smaller one was a more typical 1.8. I don't know the sort of resolution you need, and you can increase this by microstepping, but you lose torque and I believe increase the chances of misstepping.
I'm not being all that helpful, I know, but if there's one take-away from this: pairing the A4988 with the bigger motor might not make for the simplest of solutions.
Oh and here's a tip I learned playing with this stuff: never, ever disconnect the motor while there's power going to the controller board. You'll instantly brick the board. I did this more than once due to having dodgy connections whilst prototyping. Just to be sure, I'd recommend buying a couple of controller boards.
Gday Lee
Thank you for all that, it is indeed very helpful.
I haven't worked out what torque I will need (not sure if I will ever work it out!) but I am hoping to wing it as you said. I suppose I will get something more powerful than what I think I might need and hope this works. A QHY9 and 7 pos filter wheel will be hanging off the back of the scope so I would imagine it will need a fair amount to get that all round.
So would the Big easy and the 1.68amp stepper be an ok combination? I know you said it doesnt have the step size of the smaller one but I don't think I will need to be hyper accurate with this rotator (as opposed to a focuser)
hi jwoody
when you say camera rotator do you mean to rotate the camera or rotate the lens for focus or aperture ring ? my main interest has been timelapse movies with steppers for moving the camera dolly a few mm then taking a pic.
you can get 17's with a gearbox which slows your rpm but improves the torque and most likely get the other size nema's with gearboxes as well if need be . my first driver board i bought didn't have micro stepping its a nice feature to have but i haven't played with micro stepping yet. size wise i think nemas start at 8,11,14,17,23.34.
17 is what i would call a nice hobby size.they seem to be a standard size for 3d printers as well from what i have seen on the net. one thing about some cheaper drivers is that they run smoothly in a narrower band than say your more pricey drivers which may or may not be ok for you.my 17's will run faster and gruntier on 24v but run on 12v as well. from what little i know the nemas i chose where happy at either 12v or 24v but the amps had to be right. still you might want to double check with your motors specs as to what they like. i know my geared 15 to 1 nema 17 with lift a canon 60d with a lens mounted on a dolly vertically no problems that should give you some indication of how much torque it has not sure what you want to do with yours hope that helps
you can get 17's with a gearbox which slows your rpm but improves the torque and most likely get the other size nema's with gearboxes as well if need be.
A gearbox is a good idea to improve torque. I did this for an older EQ platform but the only issue that was annoying is returning the platform back to the original setting.
If going this route then you will need to release the rod so that the camera will return to its original setting. Can be awkward but do-able.
Wired it up, amended some code and I have control in forward or reverse at three different steps (1/4 1/8 1/16). For those with some Arduino experience is there another way to run the code other than using the "serial monitor" function?
Still waiting on a couple of bits before I start to try and attaching it to a scope.
Thanks
Jeremy
Jeremy,
That's one big stepper. You won't run out of torque.
I had to make a few assumptions about your reduction gears to do the calculation..
With gearing and using 16x microstepping and a final step size of 0.5 arc sec per step, I calculate 400+Nm of torque. With 0.2 arc sec per step, I calculate almost 1200 Nm of torque.
You might find such big steppers induce a lot of vibration. Hopefully with a small step angle and microstepping, it won't be too bad. I read some of the posts when you first asked but you didn't tell us what you wanted to do. You were calling it a camera rotator. Most of us thought it was a DIY polarie. Now you are talking about hanging a scope and heavy cameras. It is a telescope mounting or a small camera platform?
Some people prefer to drive steppers from a computer, some from a stand alone pulse generator. Some have their preference and won't sway from it.
I prefer to match the drive to the application. You haven't told us if this is a portable or backyard rig. If portable, a pulse gen may be the way to go. If your camera is running off PC anyway, a PC drive may be the way to go. A pulse gen can be a simple timer circuit or a small programmable PC or similar microprocessor. Running off a PC is very clunky if it is portable but easy if it is a back yard or observatory rig.
For example, my solar eclipse mount is very light and designed to be transported on planes. My design goal was to have the whole mount inc tripod weigh <5kg but still solidly support the scope. I did that using hollow construction. I didn't need a high precision drive for a total eclipse - longest exposure is only 4s. So a simple 555 timer circuit is fine for me as a pulse gen and essential for portability. The drive electronics are built into the eq polar axis housing.
I'm not familiar with the specific driver you have and whether it can take a pulse gen drive or not but the motor is bipolar and there are many very drivers out there that can run off a pulse generator or micros. You need to have the design goals set for yourself even if you don't want to share them here, so you can make the best choice.
Hello Joe
Thanks for the information.
It is going to be a telescope mounted rotator so I can frame my shots as i like without touching the scope. I have an observatory so everything is permanently mounted.
I honestly have no idea if it will work or not, it is a bit of a suck it and see kinda project. There may be just too much weight (camera,filter wheel) to move it how I want it to.
I have a design in mind, but it may be quite laughable so I will try it out first
If I do get it to work properly I will defiantly be sharing it here in case others find it helpful. $1000 odd dollars for a ready made commercial rotator is just way too expensive for what it is, IMHO.
Thanks again
Jeremy
Some good progress made.
It works reasonably well. It rotates but because the filter wheel of my QHY9 isn't round (more oblong shaped) it will get so far and then start to slip. I think a bigger toothed timing belt will do the trick.
Once that is done a bit of a clean up of some edges and a paint job and should be finished.
Some photos below and a quick video on youtube if you are interested. https://youtu.be/zMVOT29cu-0
Cheers
Jeremy
Hello Aaron.
The scope (Sharpstar 65Q) already had manual rotator. I am now going to take it of the 65Q and put it on my Takahashi fsq85 (which also has a camera rotation feature). Just waiting on some more timing belts with bigger teeth!
When I get it totally finished I will do a summary post with all the parts I used, the Arduino code etc etc.
Cheers
Jeremy
Any update on this? I'm considering this for my moonlite. It already has bolt holes on the right side flange for the actual Moonlite rotator so is an easy attachment. I already have a DIY focuser working, based on the myascom2 sourcecode page so would be an easy addition, in theory.
How did you attach the belt toothed gear to the focuser housing?
Hello Tim
No update at all as making a driver to make it ASCOM compatible is in the too hard basket at the moment. I have no programming experience at all (BASIC on a C64 I don't think counts!)
I attached the belt to the tube by using double sided tape.
I also then put another,slightly over sized, belt loosely on the tube and that is what the belt from the motor actually binds to, but it is not really necessary and I only did it because it help with an alignment of the stepper and tube.
So some double sided tape on the part of the OTA that will rotate and stick a belt around the tube.
Has to be someone out there in the same situation regarding the drivers... I wonder if you could reverse engineer a focus motor driver for this purpose? It does essentially the same thing.
