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Author Topic: Rail to move a camera at precise speed? (0.25 meters per second at 1mm accuracy)  (Read 1767 times)
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Hello,

This is for a scientific experiment on exact motion blur measurements.
I am trying to construct an Arduino-driven rail that can move a small camera sideways at a precise speed: 0.25 meters per second (about 10 inches per second).
(I'll be using a CHDK-modified arduino-triggerable Canon camera)

These are my requirements:
- I'm taking 1/10th second camera exposures while the camera is moving sideways
- So, I only need +/- 1mm precision for only 1/10th second.
- Inaccuracy during acceleration and deceleration is okay.
- Rail can be short, e.g. half a meter long -- just as long as I achieve precise 0.25 meters per second (controllable in approx mm increments if possible) for the 1/10th second interval I need to take the photo

How would I construct a rail?   I could take apart an inkjet printer, mount the camera on top of the cartridge holder, and use the Arduino to move the inkjet head platform (moving the camera) at a precise speed.  Any alternatives?  Ideas?
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Massachusetts, USA
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I'd use a nut on a threaded rod and turn the threaded rod with a stepper motor.  If you use a metric threaded rod the calculations will be fairly easy.  A course threaded rod (possibly double or triple start) might be necessary if you can't get the stepper spinning fast enough.
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Is there a start/stop requirement for the camera at each position along the rail, or can the camera continue to move at the specified speed? If the camera can keep moving, then a continously moving surface like a conveyor belt or the cable on a ski lift might be fairly simple to setup. 
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I don't care about start/stop details, as long as I can keep resetting it and repeating. What I need is a photograph successfully taken automatically (Arduino-controlled shutter, Canon CHDK fimware or modified shutter button) at an approximately exact horizontal position, while the camera is horizontally moving at an accurately measurable speed.  The start/stop can be as messy or continuous; but ideally, I'd like something that fits on a desk, no more than for feet long.  It also needs to be transportable to different sites, so I'll mount all of this on a portable platform.

Essentially, camera starts moving, accelerates, [BEGIN precision requirement] then takes a picture for 1/10th second [END precision requirement], then camera decelerates to a stop.  I only need one picture, but when the shutter is open, the precision requierments apply.

Here are my preferred requirements:
(1) Must fit on a desk (ideally less than 1 meter long (1 to 3 feet long) maximum 4 feet long. Less than 1 feet deep).
(2) Speed control: 1mm per second increments, up to at approx ~300mm per second.  (more is desirable -- but not needed now)
(3) Speed error: +/- 1mm per second error (@250mm per second)
(4) Positioning error: +/- 1 centimeter (Manual shutter timing fine-tuning should be manageable)
(5) Amount of time the precision is required: 1/10th second (macro mode)
(6) Moving mass required: Typical point-and-shoot camera (1/10sec allows use of lightweight camera w/manual exposure ability)

Acceptable precision degradations, if certain parameters are expensive/difficult to meet:
(2b) Speed control: 5mm per second increments (= 0.5mm per second difference during 1/10sec exposure)
(3b) Speed error: +/- 10mm per second (= 1mm error during 1/10sec exposure)
(4b) Positioning error: +/- 5 centimeter (I can do multiple attempts until subject matter is fully in the frame)

A conveyor belt?  That could work, too.  I'd put the camera on the conveyor surface, even duct tape it down, and press a button to start moving the belt (letting logic and triggers do the work for me).
I have a discarded inkjet printer too, just in case I use its ink cartridge platform as my camera platform.  However, I'm open to ideas of easier-to-build solutions that fully meets my accuracy requirements, as my spare hobby build time is limited.  
[P.S. If someone is willing to build this for me, there's some money in it for you, above and beyond parts cost.  I will give you some publicity in my blog, if you open-source the build instructions.]
« Last Edit: November 25, 2012, 02:53:27 pm by mdrejhon » Logged

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I can do this!  I can send you a picture of the slider.  The coding is easy.  After you see what I've built, you can tell me how much this setup is worth to you.
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If you take a 0.1s exposure at 0.25m/s the motion blur will be 2.5cm - I don't see what needs measuring? (image stabilization?)

Have you considered mounting an LED on a rotating wheel driven by a stepper motor at a precise rate and seeing the blur of that?
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Quote
I can do this!  I can send you a picture of the slider.  The coding is easy.  After you see what I've built, you can tell me how much this setup is worth to you.

I'm interested in what you have done. Would you post pictures please? - Scotty
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