720° rotation (servo/motor etc) with position awareness?

Using Arduino Motors, Mechanics, Power and CNC
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Hey all, I'm developing something which needs to move to items in opposite directions by approximately 10-12cm.

My plan was to make something like this mechanism. However, that requires continuous servos and I require position accuracy/awareness.

In the title of this post, I say I require 720° of rotation, that is based on having a 2cm diameter cog in a mechanism like I linked to above. 2cm diameter is probably the largest I could use.

I'm not sure if components like this really exist. Also, end stop switches aren't an option here as it'll be in an enclosed space and need the end points to be adjustable via software.

It has been suggested to me to look at sail winch servos, but not only do they seem a bit too big for my need, they also sound like they aren't as flexible as I'd like.

Could anyone make any suggestions?

Tl;Dr:
I need to make two things move away from each other or towards each other by 8-12cm, with digitally adjustable start and end points, without using end stop switches, and as compact as possible.

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How about small gear motors with integral encoders for positional feedback? Pololu has motors with encoders. >> Pololu - Micro Metal Gearmotors

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Look for sail winch servos, like this one.

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Yeah I did look at sail winch servos, but they are so much bigger than what I need and about 5 times the price.
If they were available in 1/4 of that size, that'd be perfect, but it looks like sail winch servos are a stock size.

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Each item moves 10-12 cm or the items move 10-12 cm apart from each other?
 

How much space is availabe?

Maybe a lead screw ?   For more $$ I guess you could get one with left and right hand threads meeting in the middle. One motor operates both 'items'.

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Each item moves 10-12 cm. Imagine how people use their hands to show the size of a fish, each hand needs to move 10-12cm, so if they started out touching, there would be a 20-24cm gap between them.

It'll vary. It's a device that is to be fitted into various spaces so needs to be fairly compact and adaptable.

Ooh, now a lead screw is a really good idea. I guess the only issue here is speed. Ideally I'd want that total range of movement possible in 1 second or less. I'll definitely look into it though, thanks!

Edit: Ah in hindsight I'm not sure leadscrews would work as it would require in excess of 24cm of space with the enclosure when closed and that's not going to work.

Simple explanation of the mechaism required:

  • Imagine a box, two opposing sides of the box need to be able to move away from each other by the distances discussed. The device needs to be able to fit different size boxes (within reason), especially those where the available space inside is less than 24cm, and even more so when you take into account that in addition to the length of the screws you'd need to factor in the motors etc themselves, so likely looking at >30cm there.
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So rack & pinion, then?

Couldn't you do that with a linear sensor?
Or an encoder on the pinion?

Have you considered lead screws?

Or linear actuators?

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Yeah exactly!

I feel that would pose the same size problem as a lead screw, and they also look to be really expensive?

Now this is a VERY good idea. I think this is my leading plan so far! Thank you!

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