I thought of something fooling around with bone constraints. Joints are much smoother with this. I call it the "smart joint". It #1 could be used for people to lazy or don't know how to do smart skin. #2 it could be used for people who can't get the right results with smart skin. Anyway, I shall explain this now.

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IMPORTANT: before you do any of this make sure you have a new model window open.
1) Make nine cps next to the green line(y axis). Make sure their strait.
2) Go to Tools>Options>Modeling and change lathe cross sections to 6.
3) Click one of the nine cps and press L or click on the lathe button.
4) Go to bones mode and add 3 bones up the tube all attatched.
5) Rename bone 1 bottom, bone 2 middle, and bone 3 top. Make sure top is under middle, and middle is under bottom in the Project Workspace.
6) Add 2 new bones where bottom and middle, and top and middle connect.
Rename the first one bottom joint and rename the second one top joint.
7)Make sure bottom joint is under bottom and top joint is under middle in the PWS (project workspace).
8)Group the bottom two spline rings to bottom bone and the top two to top bone. Group the middle three to middle bone. Group the third ring up to bottom joint and the third ring down to top joint.
9) Right click somewhere in the model window and add New>Null. Add two off these. Name the first one bottom joint aim and the top one top joint aim.
10) Position bottom joint aim directly in front of bottom joint and place top joint aim directly in front of top joint.
11) Right click on model 1 and go to New>Pose>ON/OFF. A new relationship window should open.
12)Add two new translate to constraints by right clicking on bottom joint aim and going to new constraint translate to. Make their targets middle and bottom joint by using the eyedropper to click on those bones*.
13) Add two new translate to constraints to top joint aim and make their targets top and middle.
14) If the nulls have moved, reposition them in front of bottom joint and top joint as they were before.
15) Add Aim at constraints to top joint and bottom joint, and make top joints target top joint aim and bottom joint's target bottom joint aim.
16) Test out your tube. If the joints do not bend at an average of the distances between the to bones surrounding, see where you could have gone wrong or reboot A:M.
17) If they work fine, hide the nulls and joint bones.
*If the eyedropper will not take, open properties for the constraints and set the target here by clicking and the arrow and finding the bone you want.
CONGRATULATIONS you did it! You can use this new found knowledge to rig any joint you wish, and it always works the same!

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I want to know if there's a way to put this on a sight.
Please do not steal this Tutorial, because the post date and the date at which you may have posted it will be different unless a moderator changes it.

Have you ever heard of a "fan bone" or intermediate bone?

Two bones in a kinematic chain, such as Thigh and Shin. A third bone parented to the thigh with it's base at the point where the thigh and shin connect.
The constraint is "Orient Like". Put a orient like shin 100% and an orient like thigh 100% and the that third bone (called a Fan or intermediate bone) will average between them.

Simpler and easier than assigning the splines in the joint to a fan bone is to select those splines, right-click>edit cp weights and use that dialog to weight those cps 50% like the Thigh and 50% like the shin

Never knew that... I wasted all of this time and here's this 5 second short-cut! What is this world coming to!

fan bones are the best. They work for everything. the shortcut William mentioned works for almost everything. The only place it doesnt seem to work is in the forarm or say the neck. Where a Joint can twist and flex. If you weight a forarm along the arm and twist it works great.. but when the hand bends up or down.. there goes the arm. You could fix that with 2 fan bones to seperate the wrist motion from the rest of the forarm though.

Keep thinking.. eventually you'll invent something.

C

I did and it was a complete failure! I'll think for awhile though.... I got it! No wait wait... I don't got-Wait! No.. Wait! WAIT! No nothing.

William, you only need one orient like constraint, orient like shin 50% enforcement, since it's already a child of the thigh. If there is a problem with that, please let me know.

Here's an example of the orient like 50%.

John, I was thinking the same thing.

guys.. you only need the one orient like constraint.

Wills way is usable for some different types of joints.. like wing spreads, etc. but for elbows and knees.. you just need the fan to orient like the down chain bone.

C

Here's an example of weighted cps. The only problem is that it tends to squash the spline ring.

I was doing that when I applied the orient like to the middle bone. It came twisted and messed up like this:

Did you use compensate mode when applying the constraint?

Uh what... Ummm NO. Whoops.. was I supposed to?

Make sure your fan bone is first oriented exactly like the next bone--roll handle and all. Your tree will look like this (arm example)

bicep

elbow fan

forearm (connected to bicep)

Make sure the elbow fan is oriented as closely like the forearm as you can. Otherwise when you orient like you will negatively effect your mesh (of course this is a beginners tute to fan bones--there are ways around that).

Constrain elbow fan to forearm with an orient like constraint set the percentage somewhere around 50%. You should be all set.

Hope that works.

J

edit: I don't use compensate mode all too much.