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Topic: Barn door mount project (Read 987 times) previous topic - next topic

dtokez

Sep 25, 2013, 10:40 am Last Edit: Sep 25, 2013, 11:45 am by dtokez Reason: 1
Hi all. I'm almost ready to start my next project, which will be a barn door mount controlled by Arduino. If you are not familiar with a barn door mount, it is basically a tracker to counteract the earth's rotation for astrophotography - http://en.wikipedia.org/wiki/Barn_door_tracker

I am still in the thinking stages, and I'm not sure if direct shaft drive or some kind of gearing would be better. I have a basic stepper motor to use https://www.sparkfun.com/products/9238, but I'm wondering where I can get gears and things like that to fit the shaft? I may also use a drive belt but I'm not sure where I could buy parts like that?

I'm in the UK so I would rather buy locally than wait for oversea's postage etc.

Thanks :)

Robin2

Shucks ... I thought this was going to be interesting ... :)

...R

123Splat

A stepper is probablly going to rattle too much.
You need a 1rpm syncronous motor (like the motor in an electric alarm clock) and any 1-1 gear pair (same number of teeth and diameter).  For get 'controlling with an arduino'.  Use the arduino to conntrol the camera in bulb setting.

dtokez

I don't know, a lot of the home made mounts I have seen have used steppers, but having never used one myself I'm not sure what to expect?

I'm not to worried about triggering the camera, will be easy to do with a couple of optocouplers.

I'd like to use a arduino to allow me to fix tracking errors in sofware so I don't have to build a double arm or curved rod type, I'm just looking into the hardware side of things at the moment and would like to know where I can gears / belts / pulleys and things like that to fit the basic stepper?

jremington

#4
Sep 26, 2013, 03:37 am Last Edit: Sep 26, 2013, 03:57 am by jremington Reason: 1
A decent drive mechanism with little backlash is necessary for something like a barn door camera mount. Unfortunately, almost every geared device is custom engineered, so it is nearly impossible for an amateur to find and put together appropriate gears to make a mechanism that will function smoothly. You can buy geared steppers quite cheaply and then all you need is a shaft coupler, threaded rod and matching nut to complete the business end of the arrangement.

This motor would probably be perfect for a barn door mount (4096 steps/revolution) but you have to wait for shipping from China. http://www.ebay.com/itm/DC-5V-Stepper-Step-Motor-28BYJ-48-Driver-Test-Module-Board-ULN2003-For-Arduino-/221288885649

I and others have thought about dispensing with the fancy lever arms and using a uP with proper step timing to eliminate the tangent error, but no one seems to published such a project. Go for it!
"It seems to run on some form of electricity"

jremington

#5
Sep 26, 2013, 07:19 pm Last Edit: Sep 26, 2013, 07:24 pm by jremington Reason: 1
Indeed, someone has published a timed-step barn door camera mount. I didn't see where he explains how he arrived at his particular timing constants, but the formulas are buried in the spreadsheet on the project page: http://www.cloudbait.com/projects/barndoor.html
"It seems to run on some form of electricity"

dtokez

Hi thanks for the advice :) I now have one of those steppers you suggested on the way, I can start planning the other hardware in the meantime.

Thanks for the link also, I will have a good read of that later!

Hopefully I won't need to source and gears with the geared motor :)

thanks again

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