Quote:
Originally Posted by GregWeld
I wouldn't get too hung up on the 1/32nd of an inch....
Think about what the ujoints are there for... the rear end is going up and down like a friggin yo-yo... it's moving side to side... it's got one wheel up and one wheel down with roll... and the motor is shaking around on it's rubber mounts and ditto the transmission. In other words -- there's a whole lotta moving going on...
In your case - it might be a Whole lotta Shakin'... but that's an Elvis problem.
You might never find the last harmonic going on. It could be the trans - it could be the flywheel... it could be a wheel and tire -- and it could be a whole combination of things rotational.
The thing is -- you've been able to move the harmonic around - up or down the RPM range... with your pinion movements - so you would think it's drivetrain related...
Now we'll get into something that is actually drive line related... which is the type of driveline you're using versus the actual rpms it's running at. I can't remember all the detail -- but you have to calc your rpm's that the driveline is running at -- and the diameter of the shaft needs to be matched or you get a harmonic set up.
Damned if I can remember what it's even called -- or where I've read about it -- etc but it's there somewhere on the Internet. And it may be something Ron Sutton knows about - or someone else on here.
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Thanks to Blake's mention of Mark Williams........
Critical speed is the speed at which a spinning shaft will become unstable. This is one of the single largest factors in driveshaft selection. When the whirling frequency and the natural frequency coincide, any vibrations will be multiplied. So much that the shaft may self destruct. Another way to think of this is that if a shaft naturally vibrates at 130 times a second, and one point on the shaft passes through 0 degrees 130 times a second (7800 RPM) then the shaft has hit a critical speed. There are several ways to raise the critical speed of a driveshaft. You can make it lighter, stiffer, or increase diameter without increasing weight. This is the reason carbon fiber makes a good driveshaft, it is stiff and light and can be made to any diameter or wall thickness. Aluminum, while it has a very good critical speed is not quite as strong as steel. Steel, with good strength characteristics will have a lower critical speed.
