Working follow focus test setup!

Yes! It works!

It works a little better than the video shows, but it's a little too noisy right now, and still has some kinks to be ironed out.

Video with the Canon M500

Stepper motor coming soon...

O.K. so the first stepper motor I got from MPJA worked, but didn't have enough torque for what I needed. I measured the coil resistance, and found it to be about (I forget now, I think it was about 70 Ohms). I ordered a new motor, and it should get here in two days (Wednesday).

There are no particular torque specs I found on it, but comparing it to similar motors, it looks like it has about 4 times the power that the old motor had. This is the new motor:

http://www.mpja.com/Stepper-Motor-NEMA-17-12V/productinfo/18734%20MS/

It has a specified holding torque of 3.2 kg/cm, which I think is still rather on the low side, but we'll see.

Also, that's holding torque, which is usually somewhat more than rotational torque.

I also ordered a driver IC (actually a few, I'll probably burn out at least one...) so I'll have a nice neat driver circuit instead of the big mess of transistors I had on the breadboard before.

http://www.mpja.com/ULN2003A-Darlington-Driver-IC/productinfo/19604%20IC/

This does have a nice data sheet, very helpful!

New post about LED lights coming soon.

Follow focus update

Some more parts for the follow focus came today, and things are starting to fall into place, so here's what I've got right now:

Here are all the parts, just laid out.

Here the lens is on the frame (rod system) in approximately the position it will be when mounted on the camera.

 Here are two phoctos of the gear used. The pitch is 0.08" (MXL)

Detail of the handle mount, press fit. (Also surprisingly strong!)

Close up of the drive belt on the lens focus ring

More of the same

This is how the whole thing will work, I will just slide that white mounting plate in, and mount the stepper motor on it (when it gets here), and mount the gear on the motor. The calipers are just to show size and to hold the gear in place.

Here it is from a different angle.

 That's where things stand right now, and so far it's working nicely. The new stepper motor should come soon. I ordered one from MPJA.com, only to be told that that model was not in stock, and the listing was a mistake. :( Oh well, they offered a different model that I think will work, for the same price, so I'll give that a try, and see how it works. The main thing is that I want it to run on 12 VDC, and have enough torque. The motor runs on 12 V, adequacy of torque awaiting testing.

 I can't really use it with the stepper motor I have right now because (1) I haven't figured out a good way to get enough torque out of it without blowing the driver transistors, and (2) it has a gear permanently affixed to its shaft, (of the wrong size) so I would have to cut it off to get it to work with the gear and drive belt.

 Just for reference, here are the parts used for the follow focus:

Gear: https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=58730&GroupID=217

(Or similar, exact specs not important unless you are trying to get a ratio right)

Belt: https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=51264&GroupID=213

(Or similar, length may be changed to suit application)

I didn't calculate the reduction ratio for the focus, because for now I don't need to, and it would add a lot of complications. I'm just going to get the whole thing working before I worry about that. After I have it working I can calibrate a dial, and tweak the ratios in the software. If at some point I try to make a commercial version, I may start thinking about things like that.

Hopefully I'll have the 3rd version of the .blend file ready to be posted soon, but that's all for now, until next time! 

stepper motor position control

The stepper motor now has a position control! It wasn't easy either, and it has a ways to go yet, but here's an update:

As you can see, it needs some more work yet, but it is really coming together nicely now. A few of the problems that I will try to fix are:

Jitter. It's not too bad anymore, but it's too much. I may have to use a digital potentiometer.

• Current draw. The motor is rated for 6 Amps @ 3 volts. I'm not sure that rating is right, but that was what it was specified as. The problem with that is that the transistors can't handle more than about an amp, so they are getting really hot. The other problem with the current draw is that the whole thing is running off of USB, so while this is great for testing, because it's current limited, to get the full torque out of this motor I'll need a good 3V supply and some higher current transistors. (I'm also not sure if the transistors are saturating all the way, so it might be that I just need lower voltage transistors)

• What to use for a proper enclosure.

• How to mount it to the rail system ( this is the easy one!)

Anyway, that's where I am currently. Here's the code I'm using:

---------------------------------------------------------------------------------------------------------------------
/*
 * MotorKnob
 *
 * A stepper motor follows the turns of a potentiometer
 * (or other sensor) on analog input 0.
 *
 * http://www.arduino.cc/en/Reference/Stepper
 * This example code is in the public domain.
 */

#include

// change this to the number of steps on your motor
#define STEPS 200

// create an instance of the stepper class, specifying
// the number of steps of the motor and the pins it's
// attached to
Stepper stepper(STEPS, 8, 9, 10, 11);

// the previous reading from the analog input
int previous = 0;

void setup()
{
  // set the speed of the motor to 15 RPMs
  stepper.setSpeed(15);
}

void loop()
{
  delay(100);
  // get the sensor value
  int val = analogRead(0);

  // move a number of steps equal to the change in the
  // sensor reading
  stepper.step(val - previous);

  // remember the previous value of the sensor
  previous = val;
}

---------------------------------------------------------------------------------------------------------------------

(I know that's probably not relevant to anyone else here, but I want a backup of the code online, and this is a good place to put it)

Stepper motor success at long last!

Finally!
 I now have my Arduino driving the stepper motor!
This is the motor:

Here is the driver circuit:

And here's the whole test setup:

(As you may know, I'm not especially known for neatness, as long as it works I'm happy!)

Here's the oscilloscope I'm using:

And finally, proof that it really does work:

(apologies for the poor quality)

That's it! I'll keep working on it, and hopefully add a position control soon!