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Mud Motor - which drive-line joint ?

Mud Motor - which drive-line joint ?

RE: Mud Motor - which drive-line joint ?

Look for a constant velocity type joint. A cross type U-joint may develop cyclic vibration if there are not two parallel joints properly aligned.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Mud Motor - which drive-line joint ?

I'm not sure what kind of elegance your looking for but if it's pretty low you could look at using an automobile driveshaft. Typically the front driveshaft on a 4wd vehicle will have a CV joint at one end that looks like your application. You can get them custom made for a fairly reasonable price from a number of vendors online or you could hack one up out of a junkyard donor depending on your standards and equipment.

Aidan McAllister
Metallurgical Engineer

RE: Mud Motor - which drive-line joint ?

You might want to check on speeds, the halfshaft of a front wheel drive car won't go much above 1200 rpm. CV joints come in two types, plunging, and normal, Rzeppa, geometry, normally the outboard one. The latter is what you want, you don't need plunging.

Cheers

Greg Locock


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RE: Mud Motor - which drive-line joint ?

Hmm, assume you're going to handle the C of G issues some how?

By which I mean, at the moment I suspect the pivot is positioned such that the 'heavy' engine acts as a counter mass to the long light prop & shaft.

If your hinge is now between the engine and the prop shaft you don't get to play that game.

Tungsten hand grip & throttle leaver anyone?

You've also got quite a bit of mass (Inertia) from the motor helping smooth out any tendency for the prop to jump around, I wonder if that'll be more of an issue with a lighter weight rig.

Sorry, off topic to your OP but just potential issues that popped into my head after I looked at your link.

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RE: Mud Motor - which drive-line joint ?

Quote (GregLocock)

You might want to check on speeds, the halfshaft of a front wheel drive car won't go much above 1200 rpm
I was envisioning the front driveshaft of a solid axled vehicle rather than the halfshaft from something with an independent front suspension. In my experience, 4wd systems are normally rated to go to fairly high speeds (~50 mph) which puts the transmission in overdrive so the driveshaft is going approximately the same speed as the engine, so I'd bet they can do 2000-3000 rpm.

You do make an excellent point though. Speed is a pretty serious consideration with that solution and needs to be examined with care.

Aidan McAllister
Metallurgical Engineer

RE: Mud Motor - which drive-line joint ?

Fair enough. I was estimating from engine RPM to the driveshaft. I did the math starting at the wheel and came in a little lower than my original estimate.

50 mph = 52,800 in/min
30" tire = 94.25" circumference
52800/94.25 ~ 560 RPM at the wheel

Assuming a 3.55:1 differential ratio that gives you ~2000 RPM at the drive shaft.

Aidan McAllister
Metallurgical Engineer

RE: Mud Motor - which drive-line joint ?

Front driveshaft generally use same technology as rear driveshaft.
Figure WOT in high gear > 100 mph >5000 rpm
- depending on vehicle and gearing, of course.

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Mud Motor - which drive-line joint ?

true - driveshaft can run at crank speed, or faster in OD. Halfshaft runs at a final drive/wheel speed.
Driveshafts generally seem to use cross-style u-joints, where halfshafts (at least in fwd vehicles) generally use CV/Rzeppa joints.
Interesting that the higher speed application uses a device that induces a torsional vibration on the driveshaft.

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Mud Motor - which drive-line joint ?

That's why I suggested a front driveshaft (prop shaft if you're so inclined). They typically use a double Cardan joint to help alleviate the vibrations due to the steeper angle than a typical rear driveshaft.

I'm sure a Rzeppa joint will indue less vibration but at least in my automotive experience, they tend to be weaker. I figure either joint type could work in this application.

Aidan McAllister
Metallurgical Engineer

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