Hi!

I am planning design of my propshaft and currently the big question is - should I used pillow-block or no? Is there any point in using it, if propshaft is only about a 1.2 m long?
My donor car (BMW e30) has it, but probably in locost it only gives extra weight, aint it so?

Thanks in advance for your ideas!

I doubt you will need the centre bearing.
If youre building a standard Locost, i bet the total length of the shaft needed is probably about as long as one of the sections either side of the middle UJ.

The additional support in the middle of the shaft is to stop it whirling at high speed. Helicopters tend to have this problem with the shaft sections which transmit torque to the tail rotors.

when a shaft is spun, it WILL vibrate, because it is UTTERLY IMPOSSIBLE to balance it PERFECTLY. There is always a tiny amount of imbalance. When the shaft's resonant frequency (hz) matches the rotational speed (rev/second), it will vibrate quite voilently.

By supporting the shaft in the middle, the speed at which the shaft will vibrate is raised by a factor of 8 IIRC (whirling speed is a function of length between bearings cubed).

Im going home now, but if anyone is interested, look up shaft critical speeds, and whirling.

ed.

My prop is only 612mm long between uv centres, you must be making a really long car?

mine is 950mm from face to face...

Thanks for your comments.
Mine propshaft actualy is 1077 (just checked out). Chasis is 7+442, custom rear end (bloody IRS).

Gives an example of how differently people place their engines. My car is about 10" longer than standard but my prop will be about 620mm (plus splined slider length).

James

I think it also kind of depends on which gearbox you are using James

Mick

Exactly!
My engine is BMW m20, Getrag gear box, wich I simply can't put further backwards.

My type 9 is placed as far back as it will go, the Capri axle does poke along way into the tranny tunnel though

I am also using BMW M20 and getrag gearbox, and my propshaft is really long. I don't know exactly, but about as long as Tigers. It has to be that way, there don't seem to be any other possibility.
By the way, I have shortned the rear half of the propshaft, and I will use the center support bearing, I think I have to. Maybe I will rebuild the propshaft, I don't really like it the way it is now.