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 Motorizing a focus rail 
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Post Motorizing a focus rail
I'm trying to find a cheap (and ideally elegant) way to do dolly/truck macro shots. Most of my shots are done as extreme close up's, sometimes up to 5x magnification (using canon mp-e 65 mm), so I only need to move the camera few inches in my shots. I also can't do a traditional pan because I shoot through aquarium glass at high magnification (I have to keep the camera perpendicular to avoid distortion). Ideally, any solution would allow me to ramp up/ramp down, but I can live without that just to get something basic up and working.

Basically, I need a motorized version of this (or any of the other focusing rails out there):

http://www.adorama.com/VNSSM.html

Any thoughts on how I could accomplish this?

Thanks.

DELRIOUS

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Tue Mar 10, 2009 3:29 pm
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Post Re: Motorizing a focus rail
A short distance seems like it would be 'relitively' easy. If you did a two rail system with linear bearings like this. Then rotate a threaded rod with a motor. It would take some engineerin' but for a few inches.. not much trouble.


Tue Mar 10, 2009 5:43 pm
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Post Re: Motorizing a focus rail
I think MiLapse's suggestion is probably as elegant as it can get.

Consider, for example,
[url]http://cgi.ebay.com/Screw-Drive-Stepper-Motor-Linear-Thruster-Guide-Slide_W0QQitemZ130288369277QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item130288369277&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50
[/url]
If you're not into microcontrollers I believe you can easily find a driver (EasyDriver?) that will move the stepper motor in increments [shutterdrone's cue] when prompted by an intervalometer. A simple little intermediary circuit may be needed.

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Tue Mar 10, 2009 6:42 pm
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Post Re: Motorizing a focus rail
Thanks for the suggestions! Retrofitting something like that thruster seems like it would be perfect for what I am doing, if I'm able to muster up the courage to tackle the electrical/computer connections.

DELRIOUS

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Tue Mar 10, 2009 7:14 pm
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Post Re: Motorizing a focus rail
milapse wrote:
A short distance seems like it would be 'relitively' easy. If you did a two rail system with linear bearings like this. Then rotate a threaded rod with a motor. It would take some engineerin' but for a few inches.. not much trouble.


not to be a contrarian but I would imagine that moving a few inches with a macro lens is going to be more complicated than moving a ten feet with a wide angle lens. the required level of accuracy is going to be much higher - any sloppiness (in the gearing or motor) is going to be magnified. if a motorized method doesn't work you might also try shooting a little wider and doing a synthetic move.

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Tue Mar 10, 2009 9:56 pm
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Post Re: Motorizing a focus rail
Tonight, I tried a sub $10 solution and it looks promising:

Image
Image

Test Video at high magnification:

http://www.vimeo.com/3569915

DELRIOUS

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Tue Mar 10, 2009 10:48 pm
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Post Re: Motorizing a focus rail
pixelbot wrote:
I would imagine that moving a few inches with a macro lens is going to be more complicated than moving a ten feet with a wide angle lens. the required level of accuracy is going to be much higher - any sloppiness (in the gearing or motor) is going to be magnified.


on second thought.. you have a good point there! I'm so used to my wides...


Wed Mar 11, 2009 5:37 am
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Post Re: Motorizing a focus rail
Hello,

1st post. Fantastic site. I'm astounded at the quality of work here. Absolutely fabulous!

I think the suggestions of a linear bearing is right on, but your real challenge will be pulling focus. For this type of table-top macro we often use a adjustable tilt wedge to get the framing just right when shooting with a film or HD camera (motion picture). Macro moves are usually a killer to operate in terms of holding focus, unless your subject remains plain parallel during the move. However depending on the speed of your move you may be able to set up a separate motor that would articulate with the lens via an external gear or even a tight fitting rubber band - I've used motorcycle inner tube cuttings in the past, they will often give you traction for an outside gear to bite into. Or you could use a small belt off your motor. The post Jay of Milapse shared for his f-stop pull rig is exactly what would be required but in this case used to pull and hold focus. The tricky bit will be the very slight movement required to hold focus and syncing this to your move. You may find a small stepper motor with the right reduction gearing I'm not sure where you might get such a set-up but this site appears to the source.

Very tricky and fiddly business this but once you get it right should be alot of fun.

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Wed Mar 11, 2009 8:57 am
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Post Re: Motorizing a focus rail
Yay! Linear Motion! =)

Ok, so having built, and completely failed, a home-built linear motion (truck/dolly, not pan/tilt) using off-the-shelf hardware from home-depot, (A standard worm-drive [lead screw] setup driven by a stepper.), and having a fully functional 3-axis CNC setup at home now, I can give you a few hints that may help.

If you don't already have a focus rail, I wouldn't spend the money on one for this project, unless you intend to use it for other purposes. The total cost of buying one and retro fitting it _correctly_ may exceed the cost of a new linear motion rail. (Although a moot point, as it seems from the pics below you already have one..)

If you're going to fabricate a screw-driven one, skip the threaded rod down at your local hardware store, get good Acme lead screw (threaded rod) from a place like McMaster-Carr, or good Ball Screw (better than lead screw, but more $$$) and a real anti-backlash nut. This will be a large part of your cost. Of course, there's a guy in Thailand who sells a lot of gently used stuff out of factories (never bought from him myself, so caveat emptor and all that jazz) -- big names brands at good prices, like this one: http://cgi.ebay.com/THK-Actuator-Ballsc ... 3|294%3A50 -- ready to have a stepper attached to it. The hardest part of building something like this is getting all of your parts perfectly parallel. If everything isn't perfectly parallel, it will fail on your in all sorts of bad ways =) Remember, unless you specifically buy a linear bearing with no rotational possibility (such as the ones made by 8020 that are designed to mount into two sides of their rails), you must always have two.

Looking at your setup below, it looks like you're on the right path to an inexpensive DIY rig with an existing setup, I would recommend replacing the chemical fastener with a good (in this case, inexpensive) anti-backlash or clamp-on coupler, that can be easily replaced when it breaks (although most likely won't). You can get inexpensive, and even custom-sized couplers here: http://www.dumpstercnc.com/

It looks like you have a standard DC geared motor setup. This will work, but when you want more control, the ability to have real control over speed, or to move to a shoot-move-shoot setup, you'll want to go a stepper or a very fine-grained servo.

Regarding stepper drivers, indeed, the easydriver is about as easy and inexpensive as it gets, and it doesn't suffer terribly from missed steps vs. any other, non-feedback driver. Mostly, the difference in cost between the non-feedback drivers (like the easydrivers I use in my pan/tilt setup, and the probotix drivers I use for my CNC, and the Gecko drivers I'd like to use for my CNC) is how much power you can put through them, and how long you can expect to run them at high power and in hostile environments before they start to crap out on you. Not to mention, the pulse rate and ramp capabilities, most of which will be irrelevant for your needs.

At any rate, if you want to move to a stepper-based system, or take control over that DC motor and intervalometer functions, and are comfortable with entry-level electronics and the C language, I'd be more than happy to give you some code and designs. (Or heck, if you just want to modify that setup you have to incorporate feedback and emulate a servo, I can help you do that as well.)

!c


Wed Mar 11, 2009 9:02 am
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Post Re: Motorizing a focus rail
I do have a focus rail, that works similar to the solution that Milapse was suggesting (see the photo's above, my telescope motor is coupled to the focus rail in those photos).

In my test video that I posted above, I am at 4x magnification, which is extremely high, and such it should show any flaws in the motor/drive. The video looks a bit jumpy, but I think I can fix that with a little bit of grease and some frame culling (the jump is actually the gears slipping, which I can fix, or just delete the skipping frames). At less magnification (most of my shots are 1:1 or 1:2 as opposed to 1:4), the jumpiness would be less obvious.

I'm mostly interested in doing truck shots right now, I can sort out zooms/dolly's later. With truck shots, I can easily line up my subjects to stay mostly perpendicular to the camera for most of the pan. I did a ton of tests that came out quite well last night after figuring out that it "works".

DELRIOUS

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Wed Mar 11, 2009 9:28 am
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Post Re: Motorizing a focus rail
I do think I will need to move to a shoot-move setup. Right now I'm doing shots at a very high ISO so I get some grain. I do notice that the grain is not nearly as noticeable as soon as my scenes start moving...

Thanks for the information everyone. I'm going to see if I can get my current Jerry rigged setup into a workable state and then move from there depending on how it goes. I'm going to build a permanent bracket for that motor and get some better coupling (thanks for the tips shutterdrone). I also need to build some sort of clutch with a spring to hold the motor against the gears and a clip to hold it back when the clutch is engaged (so I can manually adjust the rail).

DELRIOUS

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Wed Mar 11, 2009 9:51 am
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Post Re: Motorizing a focus rail
Quote:
Looking at your setup below, it looks like you're on the right path to an inexpensive DIY rig with an existing setup, I would recommend replacing the chemical fastener with a good (in this case, inexpensive) anti-backlash or clamp-on coupler, that can be easily replaced when it breaks (although most likely won't). You can get inexpensive, and even custom-sized couplers here: http://www.dumpstercnc.com/


The problem with using a coupler in my existing setup is it won't let me have some built in mechanism to disengage the gears. I need some way pull the motor off and adjust the knob manually (to rewind and setup shots). I was thinking if I had a geared solution, it would allow me to swap out different gears to get different speeds (until I get get a more advanced solution using a thruster or rail driven by a stepper motor that I can ramp) as well has having a spring/clip to engage/disengage the motor from the rail.

DELRIOUS

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Wed Mar 11, 2009 2:19 pm
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Post Re: Motorizing a focus rail
Ok I'm lazy and I like shooting stuff way more than I like building stuff, so I am trying to find as "off-the-shelf" as I can get. My current thought is:

http://www.sherline.com/8400pg.htm

1. Get the lathe mount and the driver box (depending the cost, I can handle wiring in my own driver box and they are very cheap elsewhere).
2. Build a mount to get this onto my tripod.
3. Make great truck/dolly shots.

I could probably save some money buy piecing together the above solution, which I may do depending on what I can find on ebay etc...

What do you guys think?

DELRIOUS

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Fri Mar 13, 2009 12:36 pm
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Post Re: Motorizing a focus rail
Or this:

http://cgi.ebay.com/1x-mini-Linear-X-Y- ... 1|294%3A50

DELRIOUS

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Fri Mar 13, 2009 12:53 pm
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Post Re: Motorizing a focus rail


As long as it goes slow... Realllllly slow. Looks ideal! Like shutterdrone is saying the backlash factor is key as well.


Fri Mar 13, 2009 5:55 pm
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Post Re: Motorizing a focus rail
If anyone is in the bay area, I just found a great place called "Action Systems" in Redwood City. They sell used factory stuff, like linear motion stages, on ebay, but they also have a walk in store. This place is a gold mine if you want to dig around for motion control parts. A large number of used linear motion stages, XYZ/rotary systems, drivers, everything.

I just got this for a good price (going to construct it as my first axis of my motorized focus rail):

http://www.danahermotion.com/website/co ... ies_TB.pdf

DELRIOUS

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Mon Mar 16, 2009 12:46 pm
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Post Re: Motorizing a focus rail
More thinking out loud:

I found this nice easy tutorial for hooking up the easydriver that shutterdrone mentioned (this looks like the easiest/cheapest driver solution by a long shot). I ordered an easydriver + an arduino USB board and I plan on building a similar setup:

http://danthompsonsblog.blogspot.com/20 ... orial.html

DELRIOUS

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Mon Mar 16, 2009 3:48 pm
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Post Re: Motorizing a focus rail
Interesting, how slow will that setup run?

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Mon Mar 16, 2009 4:26 pm
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Post Re: Motorizing a focus rail
The motor is 0.9 degrees per step (and I assume it could be microstepped?). Just spinning the screw manually, it appears to be ~10 rotations per inch. So that gives me a max of ~4000 frames per inch, which is more than enough for everything that I want to do.

DELRIOUS

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Mon Mar 16, 2009 4:43 pm
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Post Re: Motorizing a focus rail
Thinking out loud yet more:

The last part of the solution that I need will be the marrying of the intervalometer and the stepper motor control. So I am thinking of doing the following to try and solve it:

1. Get the remote camera SDK from Canon (I just applied for the license)

I assume there is a an easy to use API there that will let me call a couple functions to do stuff like trigger the shutter or stop/start exposures.

2. Write a simple application, similar to the C program in the tutorial I linked above, that let's me specify a few parameters to ramp up/ramp down, and then it will alternate between stepping the motor and calling the take picture API function.

Shutterdrone, is it safe to assume that this is along the lines of what you had to do? Are there any off the shelf solutions for alternating the stepper motor with the shutter?

DELRIOUS

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Mon Mar 16, 2009 7:54 pm
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Post Re: Motorizing a focus rail
Delrious - hey, just got back into town. Weather was crappy, so no t/l for me, alas.

Funny you mention Dan Thompson, him and I comment on each other's blog every now and then. (You probably saw a comment from me on that easy driver tutorial =)

Generally speaking, all steppers can be microstepped. Now, you need to know if the stepper on that machine is a unipolar or bipolar stepper. Generally speaking, any motors with a count of wires != 5 will work (some motors work as both unipolar and bipolar [hybrid]) with the easy driver. If yours is a five wire unipolar, don't fret, you can get a bi-polar motor on the cheap and swap it out. Of course, you won't likely find a 400 step motor for cheap, as most are 200 step. You need to figure out the pitch of your lead screw, but it looks like you handled that already by counting out the revolutions for one inch (.10 pitch). So, with the easydriver, you'll get 400 * 8 * 10 steps per inch ( steps * microsteps * pitch/threads per inch), that makes life easy enough later when coding.

I don't know anything about the Canon SDK, but I'm pretty sure you'll need your PC for that one. You could use the PC to send a serial command to the arduino whenever a shot is completed, and then have the arduino move the stepper. I mainly work with remote cable connections, and I think a lot of the Canons use the same three-pin connector as Pentax (what I use), you'll just need to connect two of these together for a period of time to fire a shot.

An important part about driving the motor, is that you don't want to start out at your maximum speed (minimal time between pulses), as this will be rough and can cause the motor to skip steps, make noise, and bounce the camera around a bit. Similarly, you don't want to stop at full-speed either, but that's less of a problem. You can either use a simple, linear speed ramp or a more complex ramp.* We'll start with no ramp to make it easy to follow at this stage, a linear ramp is pretty easy to create.

So, let's start with just controlling the motor. You'll start with this in the arduino IDE.

Code:

  // motor direction pin on digital I/O 6
  // and motor step pin on digital I/O 7

#define MOTOR_DIR   6
#define MOTOR_STP  7

// minimum # of uSec between step pulses
// we'll pick a safe, slow rate since we're not going
// to be ramping

#define MOTOR_MIN_WAIT  150



void setup() {

pinMode(MOTOR_DIR, OUTPUT);
pinMode(MOTOR_STP, OUTPUT);

Serial.begin(19200);

}

void loop() {

char input;

while( Serial.available() ) {
   input = Serial.read();
}

   // if we got S via serial input, move motor
   // right 200 steps
if( input == 'S' )
     run_motor_fixed(1, 200);
   

}

void run_motor_fixed(boolean dir, byte steps) {
  // run motor in a direction, up to 254 steps

  digitalWrite(MOTOR_DIR, dir); // set direction

  for( byte i = 0; i < steps; i++ ) {
   
    digitalWrite(MOTOR_STP, HIGH); // bring pin high
    delayMicroseconds(10); // give it long enough to recognize the
                                     // change in pin status
    digitalWrite(MOTOR_STP, LOW); // bring pin low

    delayMicroseconds(MOTOR_MIN_WAIT); // wait between steps
  }
}



(Note, the above code compiles, but that's all the testing I've done - I just wrote it up here in the browser =)

So, that's pretty simple, when you send the string 'S' to the arduino, it will move the stepper right 200 steps, at a fixed speed.

If you want to intersperse shots and movement, assuming you use the arduino to control the camera via a remote cable instead of the computer... Let's change the above code up a bit...

Code:

  // opto-isolated output pin for camera remote
#define CAMERA_PIN 3

// time between shots, in milliseconds
#define SHOT_CYCLE 1000

// how long to trigger camera for, in milliseconds
#define EXP_TIME  70


... // the other defines from above

// how much time has passed since the last shot?
unsigned long camera_elapsed = 0;

void setup() {
pinMode(MOTOR_DIR, OUTPUT);
pinMode(MOTOR_STP, OUTPUT);
pinMode(CAMERA_PIN, OUTPUT);

}

void loop() {

  if( millis() - camera_elapsed > SHOT_CYCLE ) {
     // enough time has passed, fire the camera
     digitalWrite(CAMERA_PIN, HIGH); // saturate base on opto-coupler, connecting collector and emitter
     delay(EXP_TM); // wait for exposure time
     digitalWrite(CAMERA_PIN, LOW); // disconnect opto-coupler
   
     camera_elapsed = millis(); // re-set counter
     
     run_motor_fixed(1, 200); // move motor right 200 steps
   }
     
}



In this case, it just starts running - firing the camera every second, and then moving the motor 200 steps right. You could then adapt all sorts of control from this point, but it should get you started. Let me know if you have any questions!

!c

* - I have adapted the Smoothstep technique Dan Thompson talks about to direct stepper control for both acceleration and deceleration, but I'm waiting on some hardware for testing to come in, before I share code that probably doesn't work =)


Tue Mar 17, 2009 1:54 pm
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Post Re: Motorizing a focus rail
This is all great info. I will probably have more questions once I get all of my electrical components (my delivery from Sparkfun comes in tomorrow).

Do you have to worry about burning out the motors if the end of the rail is reached accidently? I notice my rail has a system to detect/signal this so that the driver can cut the power, but I don't see any obvious way to wire this stopgap into something like easydriver.

DELRIOUS

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Tue Mar 17, 2009 3:14 pm
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Post Re: Motorizing a focus rail
Delrious wrote:
This is all great info. I will probably have more questions once I get all of my electrical components (my delivery from Sparkfun comes in tomorrow).

Do you have to worry about burning out the motors if the end of the rail is reached accidently? I notice my rail has a system to detect/signal this so that the driver can cut the power, but I don't see any obvious way to wire this stopgap into something like easydriver.

DELRIOUS


Yes, attempting to move beyond your physical limits can result in damage to something - if your motor's stall torque exceeds the breaking/bending strength of the component limiting the travel - it will bend or break, otherwise you risk eventual damage to your motor if left to run at stall rate, or even worse, feedback into your control circuitry - causing frying of your components. Many motor drivers use diodes to prevent current flow back into your circuit board - the easy driver does not!

Remember that DC motors also act as DC generators when you spin them by hand =) To speak simply on matters, it can back-flow a large amount of current when you attempt to exceed the stall torque rating of the motor. Also, always make sure the motor has stopped moving before disconnecting the power. This can cause current to flow backwards, it's helpful to put a diode on both your step and direction pins to prevent back-flow of current.

The "hall effect sensor" they speak of is a magnetic switch, either normally-open or normally-closed, the former being the general standard for motion-control systems. You can test this using the continuity tester or ohm-meter function of your multi-meter. If the two leads have continuity when it's not at the limit (or very little resistance), then it's a normally-closed switch. Take one lead from the switch to the GND on your arduino, and the other to one of the digital I/O lines. Do this:

Code:

// rail limit switch pin

#define RAIL_LIMIT_SWITCH   5

...

void setup() {

...

pinMode(RAIL_LIMIT_SWITCH, INPUT); // set as input
digitalWrite(RAIL_LIMIT_SWITCH, HIGH); // enable internal pull-up
}


Now, you can digitalRead() the limit switch input, and when it is LOW, or 0, that means you've reached your limit and you'd better stop moving! (Once you get past the basics, you can use an interrupt to cause it to stop automatically.)

What the above code does is sets it so that the pin the switch is connected to is treated as an input, and enables an internal pull-up resistor (built in to the atmega chip on the arduino) so that the pin will always read as HIGH until the switch is connected.

!c

Edit:

Also, your device came with feedback capabilities (you got all sorts of goodies *grin*), that rotary encoder attached to it can be used to verify that it took a step you asked it to, meaning no missed steps! It has a resolution even greater than your current number of steps (designed for 10x or greater micro-stepping, whereas the easydriver is 8x), so that you can be very sure that you made every step you intended to. This is a very useful feature, especially in your close-up photography where slight variations can be seen easily. Mind you, it's also a lot of work. But, you can read the encoder with your arduino as well, and make sure you're where you intend to be. Once you're past the basics, you can start using some of the techniques described here: http://www.arduino.cc/playground/Main/RotaryEncoders


Tue Mar 17, 2009 4:35 pm
Post Re: Motorizing a focus rail
edit: whoops, mis-read the spec.

!c


Tue Mar 17, 2009 4:50 pm
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Post Re: Motorizing a focus rail
This is too easy!

I've got the board hooked up and happily controlling my stage. It appears extremely smooth and should be able to do what I want.

I've never used an arduino board before, and I gotta say, this thing is slick. The C style interface makes building in controls a breeze. I'm currently writing code (based on Shutterdrone stuff above, thanks!) to do linear/exponential ramps and rewind etc...I'll post it here once I've got everything working and cleaned up.

I don't see continuity on any of the leads on stage outputs. I made sure to test continuity on every position of the rail to make sure the limit switches don't get triggered a bit before the end of the extension. So, I think these limit switches may work differently? Going to do some digging.

DELRIOUS

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Thu Mar 19, 2009 9:58 am
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Post Re: Motorizing a focus rail
Very cool guys!
Unfortunately I was terribly busy lately writing my phd thesis (I have to hand it in next week), but I guess I'll soon have time to do some tinkering again!

By the way, I will just now start with the easydriver and the arduino, thanks for inspiring me again :)
What is actually the limit on the current the easydriver can provide? I bought a rather big stepper motor...

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Thu Mar 19, 2009 10:16 am
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Post Re: Motorizing a focus rail
Michael wrote:
By the way, I will just now start with the easydriver and the arduino, thanks for inspiring me again :)
What is actually the limit on the current the easydriver can provide? I bought a rather big stepper motor...


30V, 750mA.

Have no fear though -- it's a chopping driver, which essentially means that it increases the voltage on each step until it gets feedback from the motor that indicates its reaching the danger zone. This means you run the motors well higher than their rated voltage, and as you increase the voltage, you decrease the amperage requirements.

My setups have mainly been using 6V steppers that were rated at 1.2A. I run them at 12V via the easy driver, and usually tune down to 450-500mA.

I'll have some good news for you guys soon. Argh - I wanna let the cat out of the bag, but I've still got some QA to do. Next week, next week =)

!c


Thu Mar 19, 2009 10:34 am
Post Re: Motorizing a focus rail
Delrious wrote:
This is too easy!

I've got the board hooked up and happily controlling my stage. It appears extremely smooth and should be able to do what I want.

I've never used an arduino board before, and I gotta say, this thing is slick. The C style interface makes building in controls a breeze. I'm currently writing code (based on Shutterdrone stuff above, thanks!) to do linear/exponential ramps and rewind etc...I'll post it here once I've got everything working and cleaned up.


Awesome! It's hard to beat the ease-of-entry with these things, and once you get the hang of programming and some basic electronics, the whole world seems ready for conquering *grin*

Delrious wrote:
I don't see continuity on any of the leads on stage outputs. I made sure to test continuity on every position of the rail to make sure the limit switches don't get triggered a bit before the end of the extension. So, I think these limit switches may work differently? Going to do some digging.

DELRIOUS


Hmm, I think I see what I stated wrong, there are different kinds of hall-effect sensors, and I mis-read and thought "reed relay" (a kind of mechanical switch using a magnet, which of course, some hall effect sensors do as well =).

Ok, so what you've likely got is either a current or voltage sensor, and it either has voltage, current, or PWM output! =)

Here's an easy thing to do - run the 5V line off your arduino (labeled '5V' on the board) to one lead on the sensor. Take the other lead, and attach it to your multimeter's red line, and the the multimeter's black line to the arduino GND. Measure first the voltage as you approach and reach the limit - if it begins to ramp up and then reaches a ceiling - good! You can measure this output using the ADC by attaching one lead to one of your analog input pins.

If it doesn't, well, you're kinda going to have to ask the manufacturer what kind of hall-effect sensor they used - a part number would be great, 'cos then you can look up the datasheet for it.

!c


Thu Mar 19, 2009 10:45 am
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Post Re: Motorizing a focus rail
shutterdrone wrote:
Michael wrote:
By the way, I will just now start with the easydriver and the arduino, thanks for inspiring me again :)
What is actually the limit on the current the easydriver can provide? I bought a rather big stepper motor...


30V, 750mA.

Have no fear though -- it's a chopping driver, which essentially means that it increases the voltage on each step until it gets feedback from the motor that indicates its reaching the danger zone. This means you run the motors well higher than their rated voltage, and as you increase the voltage, you decrease the amperage requirements.

My setups have mainly been using 6V steppers that were rated at 1.2A. I run them at 12V via the easy driver, and usually tune down to 450-500mA.

I'll have some good news for you guys soon. Argh - I wanna let the cat out of the bag, but I've still got some QA to do. Next week, next week =)

!c


Cool, I am looking forward to your surprise!


Dan, great tutorial in your blog, it works! But the IC A3967SLBT gets pretty hot, is that normal?

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Thu Mar 19, 2009 12:56 pm
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Post Re: Motorizing a focus rail
Sorry for the constant updates from me. When I start working on a problem like this, I'm like a freight train bearing down on it until it is solved. Once I got a taste of a truck shot from my jerry rigged solution, I looked at my static shots and started to yawn.

So, in parallel with the software side of things, I want to work on the coupling side of things. I want to get that going now, so that I am not bottlenecked later on waiting for hardware to arrive. I need to get two plates made to couple the linear stage to my tripod base and the ball head to the top of the linear stage. Ideally these plates would be fairly generic so that I can use the same design for adding more axis. It looks like I will need some pretty thick aluminum or stainless steel to allow 1.5 cm for the tripod screw and to add a screw/bolt to the top to connect to the ball head. I am thinking of going with one of these many online places that let you submit a cad design and they build it for you - albeit at a cost. Is there a better/cheaper solution? Could I get away with drilling through this type/thickness of metal with my dremel and just doing it myself?

DELRIOUS

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Thu Mar 19, 2009 3:53 pm
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Post Re: Motorizing a focus rail
Delrious - one way I could think of, is take two fairly thick pieces of cast acrylic (.315 or even .25" might work, depending on weight of your setup) - or some good, solid wood, and cut out the sizes you need, mark the position of the mounting screw holes on the slide unit (and maybe add/tap a few if needed). Then drill and counter-sink acrylic as needed to bolt them onto the slide unit using like 10-24 or 8-32 bolts.

Add a center hole on each, one with a T-nut (a pronged one for wood, and a propell nut for acrylic) to mount on the tripod, and the other with a small bolt (1/4-20 or 3/8-16) to mount the head on to.

!c


Thu Mar 19, 2009 8:10 pm
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Post Re: Motorizing a focus rail
I think my linear stage has some issues, and may need a new stepper motor, as should be expected when buying used stuff like this...

It makes a buzzing sound intermittently when idle. The buzzing sound also pops up intermittently when moving the rail, unfortunately this coincides with the rail doing some significant stalling that is apparent in my test shots.

I'm going to poke around with it some more this weekend, but if I can't fix the problem, I'll probably pop into action systems and see about trading it in for a different one or just replacing the stepper.

DELRIOUS

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Fri Mar 20, 2009 4:16 pm
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Post Re: Motorizing a focus rail
Delrious wrote:
I think my linear stage has some issues, and may need a new stepper motor, as should be expected when buying used stuff like this...

It makes a buzzing sound intermittently when idle. The buzzing sound also pops up intermittently when moving the rail, unfortunately this coincides with the rail doing some significant stalling that is apparent in my test shots.

I'm going to poke around with it some more this weekend, but if I can't fix the problem, I'll probably pop into action systems and see about trading it in for a different one or just replacing the stepper.

DELRIOUS


Did you adjust the current regulator on the easydriver?

Also, sometimes if you exceed the speed of the setup, it may come to a halt and make noise - my benchtop cnc does this sometimes when I exceed 90 IPM of speed. Try tuning your speed back, and see what happens.

!c


Fri Mar 20, 2009 7:41 pm
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Post Re: Motorizing a focus rail
Michael wrote:
shutterdrone wrote:
Michael wrote:
By the way, I will just now start with the easydriver and the arduino, thanks for inspiring me again :)
What is actually the limit on the current the easydriver can provide? I bought a rather big stepper motor...


30V, 750mA.

Have no fear though -- it's a chopping driver, which essentially means that it increases the voltage on each step until it gets feedback from the motor that indicates its reaching the danger zone. This means you run the motors well higher than their rated voltage, and as you increase the voltage, you decrease the amperage requirements.

My setups have mainly been using 6V steppers that were rated at 1.2A. I run them at 12V via the easy driver, and usually tune down to 450-500mA.

I'll have some good news for you guys soon. Argh - I wanna let the cat out of the bag, but I've still got some QA to do. Next week, next week =)

!c


Cool, I am looking forward to your surprise!


Dan, great tutorial in your blog, it works! But the IC A3967SLBT gets pretty hot, is that normal?



Thanks Michael,

I'm glad the tutorial was helpful. Yeah the chip does get pretty hot. Especially if the power for the motor is connected for longish periods. I've never had it hot enough to burn my finger with that setup though.

One thing I like about ladyada's Motor Shield, is that it has a release command. When you call this command, it cuts of the power the the motor. Handy for timelapse to save power between exposures and to keep the motor cool. I guess you could rig up a separate circuit to do this with the easydriver board as well if it was a requirement.

Otherwise, Cooling Fans and Heat Sinks might be the way to go. Good luck with it!

BTW, I'm planning on a similar style tutorial for ladyada's motor shield. I've recently been playing with one and it's seems to be going alright.


Sat Mar 21, 2009 12:53 am
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Post Re: Motorizing a focus rail
Daniel wrote:

One thing I like about ladyada's Motor Shield, is that it has a release command. When you call this command, it cuts of the power the the motor. Handy for timelapse to save power between exposures and to keep the motor cool. I guess you could rig up a separate circuit to do this with the easydriver board as well if it was a requirement.


Hmm, how about an optocoupler in one line from the power supply of the motors? That should do the job, no?

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Sat Mar 21, 2009 2:32 am
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Post Re: Motorizing a focus rail
Michael wrote:
Daniel wrote:

One thing I like about ladyada's Motor Shield, is that it has a release command. When you call this command, it cuts of the power the the motor. Handy for timelapse to save power between exposures and to keep the motor cool. I guess you could rig up a separate circuit to do this with the easydriver board as well if it was a requirement.


Hmm, how about an optocoupler in one line from the power supply of the motors? That should do the job, no?


Being new to electronics, I have never heard of one!? Would you mind describing how it might work with this kind of setup?


Sat Mar 21, 2009 2:46 am
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Post Re: Motorizing a focus rail
An optocoupler is like a switch:
http://upload.wikimedia.org/wikipedia/commons/0/02/Optoisolator_Pinout.svg

With a current between 1 and 2 you can close the switch between 3 and 4. From the function it is similar to a relais switch, but without the coil which might disturb your digital electronics due to induction. The advantage is that the two circles are electrically separated, for example with different gnd etc. I actually don't know if there is an optocoupler that can switch the rather large current in case of the stepper motor; but I guess shutterdrone can help us there :-)

Optocouplers are also great for DIY intervalometers!

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Sat Mar 21, 2009 3:19 am
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Post Re: Motorizing a focus rail
According to this http://www.jaycar.com.au/images_uploaded/optocoup.pdf they can withstand voltages of anywhere
between 500V and 7500V between input and output! Sounds more than ideal.

Thanks for the info Michael!


Sat Mar 21, 2009 3:46 am
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Post Re: Motorizing a focus rail
shutterdrone wrote:

Did you adjust the current regulator on the easydriver?

Also, sometimes if you exceed the speed of the setup, it may come to a halt and make noise - my benchtop cnc does this sometimes when I exceed 90 IPM of speed. Try tuning your speed back, and see what happens.

!c


You rock for helping me out so much with this (because honestly, I would be flailing my arms if you weren't). I think that was it. I adjusted via the current limit pot until it was super smooth. I won't know for sure if all the jankyness is gone until I do some more test shots (I just do a time lapse shot of the rail to verify).

Here is a good write-up for how to adjust the current limit for anyone else who may read this thread who has encountered the same issues:

http://forum.sparkfun.com/viewtopic.php ... d8508e29e7

The speed issue I had already addressed (I use a delay of 400 us, 160 us or 200 us did not work).

DELRIOUS

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Sun Mar 22, 2009 2:42 pm
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Post Re: Motorizing a focus rail
Daniel wrote:
One thing I like about ladyada's Motor Shield, is that it has a release command. When you call this command, it cuts of the power the the motor. Handy for timelapse to save power between exposures and to keep the motor cool. I guess you could rig up a separate circuit to do this with the easydriver board as well if it was a requirement.


Some caution when doing this -- if you're micro-stepping a stepper, the only thing keeping it in its current position is the continued application of voltage. Once you remove the voltage, it will likely fall into its nearest full-step position (or even further! It can move several steps based on how much torque is applied to its gearing) - so, I'd be careful about doing that in TL, when it may cause it to cycle between the same position over and over, with a little bit of randomness. Mostly this will happen when you're making less than a full step of motion. Also remember that when you first apply power, the motor will lock into its nearest stable position - meaning you could have up to two un-controlled movements. (In fact, there's no guarantee that it will remain in a micro-stepped position other than equal to a full-step with power applied, but I haven't seen a lot of impact of this.)


While you could certainly use worm-gearing to prevent the weight of the camera from driving the motor into a new position when the power is removed (the gear can't turn the worm, in theory =), you can't control how the motor responds to fluctuating power.

I'd be interested in seeing how well this actually plays out in real life. Remember to base your opto-coupler not only on voltage, but also current rating. You want up to 750mA to pass through it safely =)

Delrious wrote:
You rock for helping me out so much with this (because honestly, I would be flailing my arms if you weren't). I think that was it. I adjusted via the current limit pot until it was super smooth. I won't know for sure if all the jankyness is gone until I do some more test shots (I just do a time lapse shot of the rail to verify).


Any time! Always glad to be of assistance, now if I could get past this stupid problem _I'm_ having *lol* (Think new chipsets with spotty support, secondary touch screen displays with their own craziness and spotty support, and the miriad issues of software serial interfaces on an MCU. *sigh*)

!c


Mon Mar 23, 2009 7:19 am
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