10. actuation

ok – – so somethings are false economies, and some things can be happy accidents and this exercise was kind of a marriage of both of those things.

it is often the case when looking back over a project like this that you think … ‘crap, i could have just paid a guy to stand there all night with a camera, or indeed have bought a ready made unit for what ive spent doing this’

still, we live n learn right :()) .. also .. it is kind of what i enjoy doing .. just NOT when i am the one getting married.

so- – id decided on getting some iris parts cut .. based on a load of different online iris designs for small scale and large scale projects of differing sorts .. it was quite hard finding one that closed as much as possible as i didnt want to be ‘indicative’ of a moving iris mechanism … however, as i later discovered, it really is down to material thickness, flexibility and a bunch of other mechanical factors that dictate whether or not the iris will close fully .. i managed to get somewhere close….


i knew id need a fair bit of force, so an RC servo or 12v solenoid was unlikely to work .. but as with everything i seem to do.. i was basically going to have to fully build this thing in order to see if the parts id ordered were fit for purpose.

luckily i had a fair amount of space in the design .. so i hunted around for something in the ‘linear actuator’ ‘industrial solenoid’ sort of ball park … found a load of really quite expensive things .. and then found this amazing little device. taken from a tractor cruise control system (which is a good sign as far as force goes) it cost me £12 pounds … yes thats right .. 12 quid (albeit second hand) and the guy selling them was unbelievably helpful, and an electronics engineer so able to supply some handy advice/basic setup guidance.

its the black box – bottom left – in the above photo, and if you look carefully, it has a lightly serrated 50-60mm stick, sticking out of its front ..

well THAT’S the actuator arm .. and the whole amount of travel this thing provided.

however, what it lacked in stroke length (innuendo apologies) it certainly made up for in sheer force and design aspects.

the way it works is this.

it has a bunch of wires coming out of it (4 i think) .. two of them, when powered will drive the motor … and two of them drive THE CLUTCH !! .. thats right, it has a clutch !! .. i thought i was going to need to get out an arduino/rasp pi and start4 all sorts of stuff to control this .. but because RIGHTBOOTH is awesome, and has the ability to turn off and on a bunch of relays throughout the photo taking process .. i just had to have the system do the following:

wait till user presses button

engage clutch (connect two of the wires using 1 x usb relay – controlled by rightbooth)

activate motor (connect another set of the wires using 1 x usb relay – controlled by rightbooth)

run that for 3-4 seconds (just a little trial and error for however long it takes the iris to open)

turn of the motor but keep the clutch engaged (disconnect the first relay with rightbooth)

TAKE PHOTO – ‘click’

wait another second (just incase)

release the second relay (disconnecting the clutch and allowing the iris to close on a spring)

NOW – – i spent a sh*t load of time getting the spring tension exactly right so that the motor could overcome IT and the mechanism and then still return nicely — and actually i quite liked its final action .. BUT, in hindsight it would have been a darn sight easier to then just use an H-bridge to drive the actuate motor in reverse and have a solid rod linkage to take the iris back to home rather than messing about with what was essentially ‘the force’.

sorry if this loads slowly – its a BIG file
Visits: 121