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

[ECardenal]

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.

[blackburn mark]

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

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)

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

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

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.

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

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

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 ?

[Jonathan]

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?