Heim Joints

Depends on the application.

For use as a rod end, stepped washers & locked down tight.

Spinning shafts, through Heim's, press fit or spring washers & snap rings.

I can tell you get the basic idea, the shaft & bearing should move as 1.

hi speeds or large loads, use someting else or @ least lots of lube [oil bath]

Thanks for the reply!!

I'm building a recumbent tricycle and most seem to use Heim joints as the bearings for the front wheels (two wheels in front, on in the back).

Somehow I need to get my main cross tube (1.75") over to two rod-ends while maintaining the proper steering angles. So far, I can imagine my tube with a plate welded on the end, two rod-ends bolted into that, a shaft between the two rod ends and the shaft connected to the axle of the each of the trike's front wheels.

Stepped washers... I'll sit and think (in front of AutoCAD) for a while. What about locking collars?

I just read my message and it's very confusing. Let me try again...

I'd like the shaft to stay aligned with the bearing. So if the shaft moves, the bearings do to. I guess maybe that's a press fit?

You would not want to use Heim joints for the axle/wheel bearings: Their friction is far too high. They would work OK for bearings on which the wheels would pivot for steering: although even there, ball bearings would give you better steering feel. (If you replaced your head tube bearings on a good bicycle with Heim joints, the steering would feel sticky, and you'd weeve around a lot.)

Heim joints on lightly loaded control rods work very well. They also work well for higher loads where "feel" doesn't come into play: at the end of suspension A arms, for example.

Ah wait -- I'm starting to see what you are saying: You want to use the Heim joints as the upper and lower pivots for a king pin, which would rotate on an almost vertical axis, as it does on a car. That would work well, if the two joints are spread apart enough: on a HP trike, about 6" would do. I'd think. The larger the spread, the less the cantilever force, and the lower the friction. The advantage of using a Heim joint is that you could then change alignment. You will want to google for caster, camber, and kingpin inclination settings, as well as ackerman geometry used on HPV's. There are sites that mention figures to use for exactly your application.

Thanks for the reply! You folks are a great resource and you're right on the money with your answer.

Yes, I'm attempting to build the king pin assemblies for the trike, and wanted to investigate using Heim joints for the upper and lower pivots. I see this solution on commerical trikes all the time, but can't quite come to grips with how its done, or even more to the point, if I could do it in my garage.

From my research on steering of HPVs, I've decided to have:

• neutral camber
• neutral toe in/out
• about 12 degrees of positive (leading) caster
• about 15 degrees of king pin inclination (center point steering)

Unless I'm missing the point (entirely possible) I don't have to worry about Ackerman's math yet... That will come into play once I've got the my king pin and wheel geometry set. I'll weld in tubes for the best Ackerman corrections after that.

> The larger the spread, the less the cantilever force, and the lower the friction

I'm going to have to go sit in a dark room and think about this. Right now, I don't understand how the king pin friction would change as a result of the distance between the Heim joints.

Thanks again!

Re spread:

If the centerline of the wheel is 3 inches out from the king pin center, and if the Heim joints were 3" apart, then the side load on each would equal the weight supported by that wheel. If they were spread by only 1" (very extreme) they would have a side load three times as high. If they are spread by 6" then the side load would be half the weight supported by the wheel (It is just a matter of leverage.) The friction will be a percentage of that side load. Part of the friction will also come from the weight acting more or less vertically.

You'd want to be sure that the joints are rated for adequate side load (which in your application would actually be vertical load (ball pull out load is what it is called, I think). That load would depend on many variables, including stiffness of the crossbeam, road surface, tire pressure, etc., but I'd think you'd want at least ten times the weight ordinarily supported by the wheel, and probably more. If you knew at what load a wheel would fail, then you could use a figure slightly higher than that, I suppose. Alternatively, you could calculate at what load the crossbeam fails, and use something a litter greater than that.

Be aware that typical bicycle axles are much too thin to use without support at the outboard end. I haven't looked, but I would think the front wheels on trikes have larger than usual hubs to provide for larger axles and bearings.

within certain limits, Heim joints are self-aligning which means they align their axis with the axis of the shaft passing through them, eliminating unwanted bending moments in the axle shaft. There are various ways to locate the shaft in the joint, including press fit. The drawbacks to a press fit are the precision required to get a good fit and the galling of the shaft which takes place during assembly. A shrink fit would be better but neither shrink fit nor press fit lends itself to easy assembly and disassembly for experimentors. There are many ways to locate the shaft which are easy and robust such as machined shoulders in the axle shaft with threaded ends and castle nuts with cotter pins. The shaft would be a .005 inch loose fit in the Heim joint. Cotter pins and washers have been used successfully in low load applications but I would hesitate to use this method on a bicycle or tricycle.

Ahhh.....

I get it and you have a good picture of the tools I'm working with too.

> machined shoulders in the axle shaft with threaded ends and castle nuts with cotter pins.

That's the direction I'm going to go as of right now! I'm planning on getting some quality CAD time this afternoon, when I get a drawing done, I'll post it someplace and put the link in this message thread.

BINGO!

Garthh, that's right;

"Spinning shafts, through Heim's, press fit or spring washers & snap rings."

.............plus a seal to keep it lubed.

If lower friction is needed for better steering feel, tapered roller bearings could be pressed into oversized heim joints also. The heim takes care of suspension movement and the bearings handle the kingpin loads. A shouldered shaft would also be used in this case. Its somewhat redundant but smooth. You might also want to look at the ball joints used for steering/suspension in higher end radio controlled buggys and trucks. They work very well IME and at higher angles than Heim joints.

Also look at the rear axle setups used on sprint race cars. They are obviously stronger and more expensive than you need but its a good design and can be adapted to off the shelf heim joints.