Advice on springs. (Not answered)

clayton_ertley

I am working on a nifty little invention for my wife but have run into a wall on deciding how to approach the application of a spring.
The only experience that I have with springs is for my twisty puzzles and even that is just compression springs used to minimize friction.

Which is better for me in this case? Torsion or flat springs?

I have attached an image in order to illustrate my needs.
NOTE: This is quick draft done in MS Paint over a screen shot taken in the early stages of design.

Thank you in advance for any advice!

-Clayton

stg434

Seems like torsion would be the way to go in terms of quick & easy availability from McMaster.  There are a variety of formats and force options.

brucebartlett

The torsional spring should give you a more constant force through the range of travel for this application where as the flat spring will rise in force much quicker. 

mahir

I second the vote for torsion spring. More control over the amount and consistency of force. Plus you won't need a custom shape to fine tune the design. 

dennis_20

Research how sprag clutches work.  Some of them use little compression springs.

Torsion spring goes are great, but as you have it shown it is not a good installation.  Usually the axis of the spring is concentric with the axis of the pivoting part.  If you can't do that in this case then you'd be better off with the leg of the spring more parallel to the face of the pawl.  Springs are long life components.  The way you have the torsion spring installed would yield wear of the spring tip or a groove in the pawl, plus the tip is usually an imprecise length so you'd have a lot of variation with your spring forces.

PeteYodis

Nested compression springs can yield a mechanism with varying stiffness - quite handy.  Also, conical compression springs can be interesting as well.  Wave springs and nested wave springs can also be part of a nice space efficient solution.  http://www.smalley.com/about-smalley-wave-springs

(sorry - couldn't resist, the design engineer in me still leaks out from time to time.)

coleman

What @pete_yodis said. 

clayton_ertley

PeteYodis said:

Nested compression springs can yield a mechanism with varying stiffness - quite handy.  Also, conical compression springs can be interesting as well.  Wave springs and nested wave springs can also be part of a nice space efficient solution.  http://www.smalley.com/about-smalley-wave-springs

(sorry - couldn't resist, the design engineer in me still leaks out from time to time.)

 The view shown is a top down view. The 'thickness' or 'height' of gear and pawl are 5 mm. This is why I came down to torsion vs flat. If I can get a compression spring at round +-8mm diameter, I may reconsider.

 brucebartlett said:

The torsional spring should give you a more constant force through the range of travel for this application where as the flat spring will rise in force much quicker. 

It is funny how obvious the rising force is for the flat spring because that did not even cross my mind before. Thanks for the insight.

I should have also mentioned that there will be a little slider meant to push the pawl against the spring and release the gear to freely rotate.

All in all I believe I will have to go with torsion springs which kind of sucks because I have to define a lot more properties and such. I find them awfully confusing but then I have only been reading on them a day or so.
Thanks for all of your advice guys! This has helped.

philip_thomas

@PeteYodis - you are a total geek, you should work for us!
Oh, wait, i see you sitting at your desk

PeteYodis

@philip_thomas  I prefer the term "Enginerd".