I know that the Arduino can run 2 stepper motors but is there a way that I can run several stepper motors with one board? Can I hook mutiple motor driver boards to 1 MEGA?
Thanks,
John
The Arduino can run no stepper motors without drivers. What drivers are you talking about?
Are they shields or separate boards? (Shields have issues of pin-clashing to consider).
Are you driving bipolar or unipolar steppers - what performance do you need? The various
RepRap electronics boards run upto 5 steppers from a Mega, but they only need two
pins per driver using StepSticks or equivalent.
[ Oh, BTW, seen this guide?: Stepper Motor Basics - Motors, Mechanics, Power and CNC - Arduino Forum
I had not seen that guide. Thank you.
I am uncertain which type of steppers I will get. I am going to use them to rotate gauge needles in my A-10c flight simulator. There will be no torque load on them at all. I'm using servos for many of the gauges but need a few steppers for the flight instrumentation.
from what you've shared I will probably not be using a shield.
I'm going to go give Robins guide a read.
thank you again for your help.
John
Thick8:
I am going to use them to rotate gauge needles in my A-10c flight simulator. There will be no torque load on them at all. I'm using servos for many of the gauges but need a few steppers for the flight instrumentation.
I suspect there are some servos available with a near 360 degree span which could serve the purpose, but if you want continuous rotation, I see the point.
The problem with steppers - clearly you need only very small ones such as these - is that you must return them to a "stop" position to calibrate each time you start up the system. Mind you, that probably is realistic in many ways. You have a choice of either driving them against the end-stop of the indicator - which is quite straightforward, or providing a "zero" sensor - an opto-interrupter - as is used in ink-jet printers. You would have to do the latter for continuous-rotation situations.
Also, you require extra circuitry and control pins, where you need only one pin per servo.
Why not servos? they seem perfect for this application. Far fewer pins to worry about, far simpler to drive.
KenF:
Why not servos? they seem perfect for this application. Far fewer pins to worry about, far simpler to drive.
I think I twigged to this.
The altimeter and (potentially) the horizon can rotate multiple times.
Paul__B:
The altimeter and (potentially) the horizon can rotate multiple times.
Ah, yes. I got my PPL some years back but never did a barrel roll or looped the loop. Hence my blinkered approach, But even the gyro compass would need to be able to rotate freely so I stand corrected.
Thank you for your replies.
I did not realize that there is no position indication in stepper motors. It makes sense now thinking about the time I had to replace a limit switch in a CNC machine at work. It didn't occur to me that the switch served a dual function. There is also a touch plate to tell the controller the z-axis position. This changes things. In order to make this work I will need a small digital rotary sensor with 1 degree resolution. Do they make a continuous rotation pot where the resistive value just keeps repeating? It would have to have a small break in the resistance at the start/end point but the null value could be the stop point for centering/calibration.
Well my students are arriving so I have to go.
john
A simple switch in the home position will do the job. Basically at startup you can move the motor until the switch triggers. From then on you can keep track of where the motor is by counting the steps.
The only reason you need the switch is because you don't know where the motor shaft is at boot up. Since there's practically no load on the motor, it's very unlikely to miss any steps (assuming your code is written properly)
Thick8:
In order to make this work I will need a small digital rotary sensor with 1 degree resolution. Do they make a continuous rotation pot where the resistive value just keeps repeating? It would have to have a small break in the resistance at the start/end point but the null value could be the stop point for centring/ calibration.
No, no, no!
As I explained above - you use an opto-interrupter with a vane attached to the stepper shaft. You drive the stepper - generally backwards - until the interrupter is just broken and you have your reference position. Since the vane passes completely through the gap in the interrupter, there is no actual limitation at all in rotation.
Thick8:
I had not seen that guide. Thank you.
I am uncertain which type of steppers I will get. I am going to use them to rotate gauge needles in my A-10c flight simulator. There will be no torque load on them at all. I'm using servos for many of the gauges but need a few steppers for the flight instrumentation.
from what you've shared I will probably not be using a shield.
I'm going to go give Robins guide a read.
thank you again for your help.
John
Juken X27.589 perhaps? eBay has many deals on these, used for car dashboard instruments.
These are small geared bipolar steppers with high resistance coils, several 100 ohms,
so can be driven directly from Arduino pins (best to add two schottky freewheel
diodes per pin to prevent overloading the internal protection diodes).
I am not certain if these have a stop in them, or if they rely on your vehicle having a stop. The principle is that when you turn on your car, they are driven CCW against the stop.
If they don't have a stop, or if you can remove it, you could add some kind of sensor as a home switch.
They only take about 20mA per coil so you can drive right from an Arduino, but you MUST use diodes just as in an H bridge.
GM Stepper Motors for dashboard gauges
Sorry, I don't have quite the image I'm looking for. See the diodes here? Ignore the transistors, drive the coil right from an Arduino. It will require 4 pins per stepper, though.
Hackaday sells a motor on a PCB with diodes and header. Kind of a lot more, but ready to go.
Thank you Polymorph. Unfortunately those stepper have only a 315 degree swing per the data sheet
Many MCUs offer even high-performance DSP capabilities, often used for more complex tasks such as imaging systems coque htc one m9 etui htc one m9.
OK, there is another type of electronic gauge that uses a magnet in the core, and two windings at 90 degrees from each other.
You PWM to each coil and the magnet follows. No position sensing is required, because when you feed it a given mix of signal, the needle points in that direction. They can go 360 degrees and turn constantly without stopping. And the best part is you can either buy them, or make them yourself.
If I could only remember what they are called....
Aha! Air Core Gauge.
http://www.mikesflightdeck.com/instruments/diy_aircore_instruments.html
To build them yourself, you need diametrically magnetized magnets.
https://www.kjmagnetics.com/products.asp?cat=16
They are harder to find for sale than the little stepper gauges. Alibaba has them cheap, but at considerable minimum quantities.
They do tend to draw more current and so require H bridge drivers. Or if you are winding your own, perhaps with enough turns of thin enough wire and a well balanced pointer and core you can get away with no more than 30mA.
I have some of the tiny 20mA stepper motors. They are geared to something like 600 steps per turn.
I opened one up - the stepper motor rotor itself is insanely tiny. The good news is that there is a pin sticking out of the top gear that pokes up into a channel that limits rotation. I should be able to cut it off with a sharp set of flush cutters, and maybe sand it down just a bit to make sure nothing is sticking up.
It will then require some method of position sending. As simple as a reflective strip on the back of the needle, perhaps, and a reflective optical sensor.
The tiny little blue thing is the rotor itself... amazingly tiny. The pin is to the right of the top gear. You can see the arc of the slot it fits into on the underside of the cover on the left.
Is that the same stepper you referenced in your earlier post? I would be interested in your results after the modification. I did find a sensor that may work http://www.usdigital.com/products/ma3#description
I'd like to find a through hole model.
Who are you responding to? Me?
A rotary encoder isn't necessary with either of the gauges I posted about.
For the air core gauges, position is what you set it at.
For the tiny stepper motors, with the pin cut off some method of finding a "Home" position is needed. I'm thinking of drilling a small hole under the output gear and just putting a black mark on the back of the gear, and using an optical reflective sensor.
The issue is that most optical reflective sensors use IR, and I don't know if there will be a big difference in reflectivity between white nylon and a black marker at IR. I will just try it. I've already snipped the pin off of one. They are simple to disassemble and reassemble without damage.
In these gauges, the tiny rotor actually only has 4 steps per rotation. The gearing takes that to 600 steps per revolution.