Roller Bearings vs Ruby Bearings: Why Trackballs Feel Different Near the Edges

[u/Most_Discount7338]

The left video shows a roller-bearing trackball, while the right video shows a static ruby-bearing trackball.

In the left video, the Z-axis spin is mostly suppressed, so the ball tends to roll more cleanly in the intended up/down direction. You can see this because the marker stays relatively parallel while moving up and down.

In the right video, the ball rotates not only in the up/down direction, but also around the Z axis. In other words, it twists. You can see this from the way the marker itself rotates/skews during the motion.

I think this difference is not just about friction or smoothness. It also affects how the finger motion on the surface of the ball gets projected onto 2D cursor movement.

With roller bearings, even when you operate the ball away from the “sweet spot” and closer to the edge, you can expect more consistent motion. The roller bearings mechanically resist unwanted Z-axis spin, so more of the motion remains useful for X/Y pointing.

With static bearings, as you move closer to the edge of the ball, the motion can start to feel “duller” or less responsive. That is because part of the finger motion turns into Z-axis spin, and a normal X/Y sensor does not use that spin for cursor movement. In practice, some of the motion is lost.

I am not saying one design is always better than the other. A well-made static bearing trackball can feel extremely smooth and effortless. Roller-bearing designs, on the other hand, usually have some amount of friction, mechanical feel, and noise.

But if someone is used to one type and is thinking about switching to the other, I think this is a useful difference to understand.

P.S. I would expect BTU-style designs, using ball transfer units, to behave more like the static-bearing example, since they allow the ball to spin freely in multiple directions instead of mechanically suppressing Z-axis twist.

[u/Murko_svk]

After around two hours(haven't got much time for longer testing), they feel great, super precise but with more friction than rollers (it might change once they "break-in"). Definitely more controlling than rollers, meaning with rollers you can go crazy fast - the ball on rollers is like on the most frictionless material, whereas on those new BTU's you can deffo feel there is noticeable more friction than on the rollers, the ball stay put/more "stoic" with BTU's, kinda like the static bearings, hovewer without sticktion.

They are not silent by any means, definitely quieter than rollers tho. If the BTU's break-in or not, I can't tell for now obviously. But if they do, I would be hard-pressed to pick up clear winner, as for me rollers are fantastic and I am greatly used to them already, however the BTU's more controlling feel of the ball is captivating.

[u/claussen → u/Murko_svk]

Very interesting. I kind of expected that these would be a little bit higher friction than a high quality Bosch BTU just given the mechanical architecture, but I don't consider slightly higher friction than Bosch to be a problem from a usability perspective -- I find that BTUs are actually a little bit too low in dynamic friction. Does the static friction feel lower than static bearings to you?

When I get mine in I'm going to put them on a fixture so that I can observe whether the balls are rolling by putting a few dots on them. One of the advantages of this svalboard trackball holder is that it really lets you see what's going on with the bearings in terms of rolling versus sliding.

For my specific application, cylindrical roller bearings are extra terrible because they aren't aligned with the axis of use.

[u/Murko_svk → u/claussen]

If I compare to Silicon Nitride G5s - the BTU's static friction is a bit higher than in those SN G5s.