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• # Variable speed rotary movement design help

Discussion in 'The main mechanical design forum' started by Adrian, Sep 26, 2012.

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Hi,

This is my first thread on the forum and my background is really software engineering
but I enjoy different DIY projects I do. One of the biggest problem so far I have a real
challange with is designing a mechanical transmission of movement into variable rotary speed one.
I have a bigger sort of free wheel turning in the middle and 4 additional small ones located
at every 90 degrees of the big one. What I need to achieve is this:

- all small wheels need to be stationary for the most of the time big wheel is turning
- when appriopriate moment comes, each of the small wheels turn exactly 180 degrees one by one
every 90 degrees big wheel turns

Criteria:

- when small wheels are stationary they should not allow to any movement (movements up to 1 mm are aceptable)
- when it comes for the small wheel to turn 180 dedgress it should be as fast as possible and position the wheel
exactly 180 degrees turned
- it should be frictionless as much as possible to allow smooth transitions
- the mechanism should allow for fairly fast and smooth running - the small wheels can turn - stop - turn
few dozens of times per sec

I am open to all ideas but somehow I tough a gear combination would be the smoothest one ?
Perhaps I could easely achieve it with pre-build components if there are any available ? Use of links ?

2.
3. ### Rafael_AmenNew Member

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Oct 2012
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It looks like what you need is a combination of partial gears with Geneva crosses.
To understand it completely you should post a drawing.

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Sep 2012
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Hi Rafael,

I have managed to go through various mechanisms I could get my eyes on
from books and from internet and I think the easiest to implement and also giving the best power transferring
capabilities is to use intermittent motion of spur gears. I was thinking about geneva drive as well (even
easier to achieve with DIY techniques) but I am nto sure if that would sustain high speeds with smooth
rotating action. Maybe I am wrong - not much expierience here ..... I will try to upload some frawings
when time allows. But to be more precise this time using better wording - yes, I want to have an intermittent motion
of smaller wheels - half turn of big wheel to half turn of small wheel but small wheel should "suddenly" turn full
180 degrees at the end of half turn of big wheel. So one full (360 degrees) "smooth" turn of big wheel to two rapid
180 degrees movements of smaller wheel happening around every 180 degrees of the movement of the big wheel.

I hope I have not "over-explained" it now which could make the description worse

Thanks a lot,

5. ### Jacky_khuatvnMember

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Sep 2012
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i agree Ragael. Adrian need post a drawing that is detailed more what you wrote.

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Sep 2012
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Agreed then
I will try to upload drawing in the nest few days - very busy at the moment ....

Thanks a lot for you angagement !