Spanish newbie (with a couple of CNC projects for photography)

Hi all !

I'm not a machinist or electronic technician, I have some foundations on electronics but I'm a bit lost regarding stepper motors, etc

I'm an amateur photographer and I have a couple of projects in mind that deal with CNC.

1- There is a photographic technique called "timelapse", where you take an image every given amount of time and then when viewed as a video at 24/25 frames per second you accelerate motion.

Probably you have seen thousands of those videos already, this is a sample:

http://vimeo.com/4186181

My project involves a rail system for timelapse where you mount the camera and move it from side to side, at discrete steps or really slowly (about 1 or 2 hours per meter). (1-axis)

At a later date maybe I'll add aditional movements for tilt and pan the camera (2-axis)

I need the system to be lightweight and battery operated, as this kind of images are of course taken in the field, far from any electrical outlet.

2- In macrophotography, when you are really close to the subject and working at great magnification rates (5:1 or greater), you obtain a very swallow depth of field (the area of the image that is focused), so there is a technique called "focus stacking". You take several images (tens or hundreds) of the same subject, but moving the camera from back to front on each image (fractions of tenths of milimeter each time). Then with software you can combine those images into a neatly focused one.

For this macrophotography precision slider project what I need is a 1-axis linear movement in really small increments, 0,01 to 0,001 mms

In this case the weight isn't important, as those photographs are allways made in a closed environment, but I need extreme precision on the movements, as I will make a step, wait (to stabilize the camera), take a photo, move, wait, and so on. I will always have an electrical outlet at hand :tup:

Surely I'll start asking questions, as I have many and varied, specially with the selection of stepper motors and controller, bat also about the precision moving mechanism (I don't think usual ballscrews will have enough resolution)

I'll start a new threat (as soon as I find the appropiate place :heehee:), thanks in advance

for the tracking shots i would use a simple RC servo with a servo tester to drive it and add a step down gearbox of some description... should be easy to build and cost £30/£40 ish for the drive side of things... im sure youll work out a rail system or even a simple skater type dolly without to much trouble

you want the camera tracking during shots to maintain the motion blur that you would get if shooting 24/25 FPS (no need to stop the tracking during the open shutter... makes a build like this pretty simple)

if you can keep to the 180 degree shutter rule (very dense ND filter or two polerizers stacked... one cuircular and one standard) you will maintain the natural motion film motion blur

Attachment 4253

this is a pan tilt head i made a few of years ago for stopmotion animation so hand cranking them was the way to go (motion blur has to be done in post production with stopmotion)

the gearboxes are 3000/1 i think i paid £18 each for them at maplin

for focus stacking i would just concentrait on camera stability and hand crank a gearbox attached to a 1mm pitch screw to drive it (backlash wont be an issue as you will only be driving in one direction at a time)
if your using CS5 i dont think you need overly consistant steps as long as your steps dont over reach your depth of field... if your taking a pictures of insects the slide only needs to be short

selecting the right ratio gearbox will take a little bit of maths (you dont want to be cranking it 30 times between each frame)

let say your typical DOF is 0.1 mm then your probably safe to crank 0.05mm at a time.
ergo, 1mm pitch screw 20/1 gearbox would give you 0.05mm per revolution
if you were going to play it safe a 40/1 gearbox would give you 0.025mm and a bumble bee would need aprox 680 frames.... OWCH!!!! i hpoe you can get a wider DOF than 0.1mm :)

a single linear bearing and short piece of rail would be ideal, pre-loaded if you can, they do come up cheap on ebay now and again as most people will only buy them in sets of four

i forgot to say that you need to remove the mechanical link to the feedback pot in the RC servo to get it to run endlessly in which ever direction (and speed) you dail into the servo tester

I still have the bells ringing in my head, and haven't sit for a moment to put things in order. I'll try to make a common solution to both projects, as the differences are only in the mechanical part of the slider.

Mechanical part:

For the slider, I will use a couple of 1m rails with bearing blocks. On top of the bearing blocks I will attach a plate and a tripod head (later, the pan&tilt mechanism). To move the dolly I'm thinking of a pulley and belt system like those you may find on desktop scanners.

Motorisation:

I have three alternatives: a stepper motor, a regular DC motor (conveniently geared), a modified servo

I was thinking of a stepper controller connected to the parallel port, but if I want to be it an autonomous system I cannot depend on a computer, and laptops usually don't have a parallel port (and to make a microcontroller to drive the parallel port may be well beyond my capacity).

Manual Control:

A DC motor may be easily controlled with a PWM regulator. I may control a servo with a servo tester, but not much contro,l over the speed, etc. To control a stepper motor I will need aditional hardware.

Automated Control:

I am thinking of build a controller with the help of an Arduino board (they are dirty cheap!). I can control DC motors (or servos) with its PWM outputs, shoot the camera when needed and have limit switches. Also I can make it configurable, controlling for how long and how fast I want the motor spinning, number or frequency of shots, etc... and probably attach a LCD panel to make the configuration easier. Still not decided what kind of Arduino board to use, as I think of new features (limiters, triggers, motor control, LCD, etc) probably I'm going to need an Arduino Mega board. To control an stepper motror from the arduino I will need aditional hardware, but I think there are ready-made modules for that.

Pan & Tilt option:

The pan & tilt movement maybe done with a couple of servos. There's no need for full 360º, so no need to modified the servos.

Power supply:

Arduino board don't need much, maybe even a 9V NiMh or a pack of AA batteries will be more than enough. For the motors I have a 12V 4800MAh NiMh battery pack, havent't tested how long it may drive the motors, but probably it will do the job.

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For the slider, I will use a couple of 1m rails with bearing blocks.

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bear in mind that the type of bearing blocks and rails we use in cnc are going to be pretty heavy to be lugging around in the field

it may be cheeper to buy carbon fibre rods, maybe 30mm or 40mm di and twist someones arm to make you some wheels with the 30/40mm di profile in them and use them in pairs to pinch solid onto the rod (i havnt got a radius turning attachement for my lathe,sorry)

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I may control a servo with a servo tester, but not much control over the speed, etc.

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im not sure what you mean ? a servo tester has a dail to control the speed from very slow to flat out ? unless your refuring to top speed?
if your using a 7D 5D and shooting some standard 24/25fps then id agree that you may not get the speed you need to do run a tracking shot unless you opt for a larger servo

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The pan & tilt movement maybe done with a couple of servos. There's no need for full 360º, so no need to modified the servos.

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i cant see how you would control the speed for single frames ?

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To move the dolly I'm thinking of a pulley and belt system like those you may find on desktop scanners.

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sounds good , you can buy small "endless" timing belts by the meter
you could fix a single length and attach your timing pully and drive to your sledge?

are you looking to shoot video as well as single frames ?

You can control the speed of a modified servo ... just remove the potentiometer from the casing, make the wires a bit longer and that's your speed control. The closer you move the pot. to the position the servo is moving towards the slower it will go, and vice versa. Well, I think that will work ... never actually tried it.

I think for this application you would be fine with the 'skate bearing' on aluminum angle method. Like this one:

http://cr4.globalspec.com/PostImages...DAB26920C2.jpg

It's not as strong, but will easily support a camera. I would use steel or aluminium tube for the rails. Preferably steel as aluminium will wear badly with steel bearings running on it.

Controlling a stepper motor driver from a PIC is easy enough using the step and direction inputs. Just make it so that when you press a button it sends the right number of step pulses to move the required distance?

All what matters in motion (for this project) is speed. I'm not sure what speeds I may obtain with the different options, so I will try them all. I need quite slow movement. Surely I will learn a lot! ;)

I just ordered:

• a modified servo (with high torque)
• a geared motor that runs a mere 8 RPM.
• a timing belt and pulley
• Arduino Mega
• Serial I2C LCD display
• Motor shield (It drives servo, DC motor or stepper motor)
• Relay (for shooting the camera)
• Breadboard for prototyping
• 12V lead battery 3.3Ah

For the rail system I ordered 1m rail and bearings. The rest of the structure will be aluminum. Sure it will be a bit heavy, but must be rigid and enough to support the camera + lens + the future pan & tilt head.

Also I'm looking for ways of making a pan and tilt head for the second part of the project. I think a gimbal type of mount may do the job.

http://www.youtube.com/watch?v=d0a-bEurGg0

or something more like this:
Attachment 4290

and ..... I also ordered three NEMA17 steppers, controller and 12V PSU. I surely will make a CNC table for panel making, etc. This with ballscrew drive on all axis. Not decided the size yet... but that's another story ;)

Thanks again for the answers...

oh.. I got another question for the CNC table project...

I see there are machined and not machined ballscrews, what's the difference ? I see there exist aluminum couplings to connect the ballscrew and the stepper motor, but not sure if I will need a machined ballscrew or not.