Sizing Driveshafts

"Michael" wrote in message news:c1U6i.27281$ snipped-for-privacy@text.news.blueyonder.co.uk...

You need to look at the specs for whatever material you're using, and then do some calculations. Try googling for Module of Elasticity (Youngs Modulus? - it's been a while since I used it), which is a measurement of how much a material will deform, before becoming permanently deformed. Then with a few calculations, decide on a safety factor, and you can then look at sizes/different materials

But I'm sure some of the more experienced posters here will probably be able to quote the relevant details better than I can.

And having just checked, Hooke's Law is the more relevant one, along with yield strength.

I'm currently trying to find the link to a website that lists the specs for near enough every metal you can think off, but can't seem to find it just now. Anybody got any ideas?

Mark Rand RTFM

Seen on a few cars ...the longest drive shaft has pillbox shaped lump of steel bolted to it about half way along ...

this means drive shafts twisting action is stopped or lessened/ damped ...and you can get away with smaller diameters.

all the best.mark

For what? A model? An implement? A truck? Possibly a car? If it's for a car, output and input flanges dictate universal sizes, span of flanges dictates diameter of tube for stiffness...

Tom

Submarine pumpjet - they're 1.8kW motors so they need some consideration.

I'm trying to work out the smallest size I can get away with as they'll have to be Stainless and so $$$ (My keyboard is set to US)

Michael

You still have to provide more information. Beyond the critical speed (depends on material, geometry) you'll get synchronous whirl, for example.

You need to give the length and the RPM (or torque).

Nick

Hi,

I'm familar with both but must admit I've never thought they could be applied to radial loads.....

I'll 'go back to school' and see if I can work it out,

Cheers,

Michael

Oh sorry - I wasn't looking for someone to give me a figure I was curious as to the formula/rule of thumb.

No load RPM: 3350

Imperial Torque: 37.6 lbft Length: 19.6"

Metric: Torque: 4.248 Nm Length 500mm

Michael

Afraid you will need to calculate again.37.6 lbft do not equal 4.248 Nm`s

4 Nm? Do you have a max OD? I mean, 4Nm is nearly nothing. In terms of "I pick this 20mm tube and it will work".

Nick

I have googled for "torsional +stress +formula" and found this:

It looks quite complete after a quick browsing through.

If you google for "critical +RMP -linux" you should be able to solve the other problem.

Nick

Sorry I meant lb in

Michael

I'm trying to find the smallest OD I can get away with.

Thanks I'll look at that page. Every search I did with Google had 'driveshaft' in it somewhere.

Michael

Weight should not be an issue in a sub, so you can use a solid (cheaper). :-)

Nick