Bit of a puzzle....to all Heath Robinson fans

[gerrymoore]

I have an idea to build something that, to work, would need to be able to turn a 25mm x 3mm metal circle (like a washer) exactly 180 degrees in about .5 of a second. Then about 30 seconds later it needs to do the same thing - over and over again.

Whatever I use can be given say a timed voltage pulse so a small motor would do it but hard to get the exact half turn in the time available. I have thought of a model servo but not sure if they can go in a circular motion?

Some clever guys on here ...any thoughts on how I could do it??

 

[Morrisman]

Electric solenoid type servo? In a straight line but acting on a lever fastened to the washer. You could have adjustable stops to get the exact limit of rotation.

 

[gerrymoore]

Sounds good ...and easy!! I'll start looking .....

 

[Morrisman]

Just thinking, but you might find a straight action solenoid goes 'over centre' when rotating your disc 180, but maybe not.

 

[Brad93]

Servo motor

 

[chrisg3103]

Or a stepper, with all the 3d printer hardware floating about they are fairly cheap and lots of info on control

 

[Kayos]

I'd say stepper, would probably need some positional feedback though

 

[Ton-up]

Air powered rotary actuator as -

https://uk.rs-online.com/mobile/p/rotary-actuators/7967272/

 

[Dee J]

Fixed electromagnet adjacent to rotating permanent magnet. Reverse the field and the permanent magnet will quickly respond.

 

[Agroshield]

You did not say in the description if the second move is in the same direction or the opposite direction to the original move. That might influence your solution.

Look up Geneva mechanism for a mechanical solution.

 

[gerrymoore]

Thanks all. Needs to be small and light (and cheap!!) so steppers and servos are out. Air is no good either...sorry. I have an old airplane servo so may have a play with that and I'll take a look at the Geneva mech too. But so far the old solenoid idea seem the best solution.........

 

[chrisg3103]

https://www.ebay.co.uk/itm/184142062597

One of these coupled to a £4 arduino nano is hardly breaking the bank.
Could be wrong but think all you need to add is a bit of wiring, a battery pack and some research into the correct code for the nano. Easy to set up time delays and step angles for precision control.
All depends on your needs regarding load, size etc.

Just to show stepers and controls dont need to be fancy or expensive

 

[winchman]

Stepper or rotary actuator, I feel a stepper is a much better job and so cheap now, I think Servo motor would be more expensive?

 

[outofthefire]

In my opinion the sprung solenoid is the easiest, even I could work out how to make it. It just needs a really simple timer circuit hold the power on 30 seconds the solenoid pulls in, 30 seconds later power goes off and the spring pushes the solenoid back out. Just alter the length of the pivot till you get the angle of dangle right.

I've played with arduino's and while i'm interested I don't have the time to learn to program and the downloaded programs have been hit and miss and have driven me up the wall.

The solenoid adheres to the kiss principal, why over complicate something unnecessarily.

 

[gerrymoore]

Yes, I've played with Arduinos and even built my own plasma CNC so I know all about steppers .......but I agree that the simple solenoid might be the best answer ...I have got my 'EBAY eye' on a ready built 'thing' that I'm trying to make so it might all be unnecessary ...watch this space!!

 

[Ali]

Gear with half the teeth ground off then tune the speed of your motor. Or various similar mechanisms.

 

[Ali]

 

[gerrymoore]

Clever that Ali (BTW sorry I never got back re the pipe..did it another way) ...The thing is although I want it every 30 seconds this could vary each time by a small amount and that is where the voltage pulse comes in ... so an absolute timing is no good.... with a solenoid (or similar) the pulse could set the timing each time plus or minus a few milliseconds ......or at least small bits of a second

 

[chrisg3103]

Yes, I've played with Arduinos and even built my own plasma CNC so I know all about steppers .......but I agree that the simple solenoid might be the best answer ...I have got my 'EBAY eye' on a ready built 'thing' that I'm trying to make so it might all be unnecessary ...watch this space!!

I like 'things' give us a clue

Sometimes keeping it simple is boring, I developed this contraption over the space of a month to be as convoluted as possible

Powered from a single 1.5v aa battery, all it does is feed in 45mm of tube and cut it uses a version of that indexing mechanism ^

 

[Ali]

Servo motors, voltage pulse, Heath Robinson will be turning in his grave