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Originally Posted by Cory
most gearboxes will use plain ball bearings, as will a bearing inside a rotating gear in certain shifting mechanisms. I would assume that if you were to construct a swerve drive properly, you wouldn't have any need for a special bearing. As I've never constructed one myself, I can't give you a definitive answer.
Cory
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I feel I can give an answer, since I have. You do need "special" bearings for swivel drive. Since the entire weight of the robot is on the drives, and they rotate like casters, you need thrust bearings in there. Or, you can just go for angular contact roller bearings, like bikes. All the bearings in bikes are angular, because all joints take side loads and radial loads. But... finding angulars can sometimes be a pain if you have size limits. MVRT's swivel had thrust bearings on every module. We didn't do it too efficiently this year, every module used 2 thrust and 2 radial on a .75" steel shaft. You need two thrust bearings, one to take the up vertical load (weight of robot) and one to take the down load (weight of swivel module when you lift it off the ground). A little excessive, since you don't really need the second one. And of course, you have to have radial bearings in there, so the shaft stays on the same rotational axis as it should.
There are a few types of bearings, I'll list off the ones that come quickly:
- Radial: these take the rotational forces of a shaft running in them, as well as take the weight that comes at 90 degrees to that shaft axis.
-Linear: these take sliding forces of a shaft sliding through the bearing, as well as the weight that comes at 90 degrees to the shaft axis.
- Thrust: these take weight. Most are in the rotational style, they are designed to take the rotation of a shaft, and the weight that comes parallel to the shaft. The shaft needs a flange on it, to ride on the bearing itself.
- Angular Contact: these are just like radial bearings, but the contact the balls roll on is at an angle, so they double up as thrust bearings.
- Bushings: these are just inserts made of oil impregnated cast bronze. They are self lubricated, and can take lower rpms and pretty good weight loads. Every bushing has its own rating, so they aren't always usable. They come in linear, radial, and thrust styles.
However, there are MANY styles of the above bearings (except bushings). Roller bearings use rollers instead of balls, angular contacts come in different angles, radial and angular contact bearings come in one, two, or 4 contacts. There are mostly different types of radial bearings. Thin section, miniature, superprecision, heavy load, etc.. the list goes on forever.
And if you're crazy enough, you can make your own bearings. That's what I'm doing this summer, since I can't find the right size for cheap ($150 each and I need 12!!!). I'm just using rollers and cutting steel inserts, hardening and grinding them. When they press into the gearbox and the gears go into them, the rollers can't go anywhere so no flanges or seals needed. Works just as good as ones you can buy.
Hope that helps!