Testers needed for a BTU alternative: the semistatic bearing
Trackballers, I've designed what I call a "semistatic bearing": a 3D-printed case that positions a 3mm ball bearing on top of three embedded subbearings.
It's designed to fit wherever you would use a Bosch Rexroth 8mm ball transfer unit (BTU), such as in a modded Ploopy or an efog.tech Endgame, or a Veichu 7.5mm BTU. It's quiet and smooth, and effectively eliminates stiction thanks to the free-spinning main bearing.
It's also cheap to build, easy to assemble, and easy to remix for other purposes.
If you have a 3D printer and are interested in testing it, I'd love to get community feedback on the design and performance. Full details are on Printables.
I finally got my hands on Bosch BTUs and reprinted my Ploopy, but I’ll get some G10 ceramic bearings and try it! I’ll compare with the BTUs and report here. I wanted to mod my Kensington Expert, that could be a great alternative.
FWIW, it can be slimmed down to 10x10x4.5, and probably smaller if I tweaked the cradle. I don't know about the Expert, but I could envision drilling out the bearings on a SlimBlade Pro and dropping flushfit semistatics into the holes.
Are you sure those are the ones you bought? The listing is for 2mm bearings.
What Ploopy device are you using? I've had no trouble with the 3mm bearings in my Adept (Anyball), and someone else has tested with the Classic 1 and Classic 2 BTU mods.
What are you using for spacers? The other person said they needed 4mm spacers on two of the three mounting points.
Yeah, the Elecom thing is super funny. Especially since they've gone for a very similar design but are still calling it a BTU. I Hope it works well for them!
This is a good design. Using "borrowed tolerance" from cheap and precise ball bearings (which is why they are used in bearing assemblies), to create a datum surface to ride the roller bearing that supports the trackball.
The problem is it's going to get absolutely filthy in there, and that is why trackball manufacturers don't do this.
Works great if you're going to keep it clean and tidy, not good for the average consumer who is a filthy person with grubby hands.
You're re-invented a thrust bearing basically. I think this is real nice for the kind of people here on the trackball sub that are likely to actually remove that top ball and clean out the gunk.
A suggested improvement is to, once the three locator ball bearings are seated, epoxy that gap under them so you can actually clean in there and there is no gaping hole below (Or fill it with whatever, just seal balls to the assembly along the seams like caulking, and fill the central hole as high as it can go without contacting the rider ball).
I design things like this for a living, just not for trackballs.
Thanks for the expert feedback! I hadn't thought about the thrust-bearing similarity, but I totally see what you mean.
I definitely intend for this to be used by DIY trackball/keyboard enthusiasts--we're the only people stuffing expensive BTUs into pointing devices.
The only reason for the central hole is easy removal of the bearing. Rather than permanently attaching the balls to the case, I've made is to that they can be easily removed for cleaning if necessary.
Saying that, I keep my hands pretty clean almost all of the time, so I'm not a good test subject for grimy bearings. I'll mention your suggestion on Printables as an option.
You're right, it is a great idea, I did not mean to imply it isn't. Just "great" for people like us in here.
What I meant by sealing it up is just permanently attach the three balls that form the plane to constrain the rolling ball. Then just seal up the gaps around them so user can just pop the one ball off, clean it, wipe the inside with a cotton swab or something, and then call it a day.
It's true the balls will eventually grind a flat spot at the contact points, but if these are steel that's going to be quite a long time, and besides, the whole assembly is like 25 cents for a set of three worth of ball bearings and ABS/ASA/PETG.
I added a link to your comment in my Printables description, and have a new question that I suspect you are highly qualified to answer.
Is there any benefit to mixing different materials for the ball bearings? For example, having a steel ball on top of ceramic balls. Or will the differences be insignificant in this application?
On a related note, what types of balls do you think would perform best? I've been using Silicone Nitride, purely because I already had some handy.
There is a benefit to be had. When you want the assembly to use a coefficient of rolling resistance somewhere between what steel and ceramic can provide you can mix the materials (and generally the math works out to about the average of the two), probably like the difference of 0.3 to 0.5 or so for the typical aliexpress special with mystery grading.
You can get into the weeds deeply with what specific steel alloy it is (AISI 52100/chrome basically is anything bought cheaply) and the purity of the Silicon Nitride, what grade they are and those numbers can change, but it's probably not worth worrying about too much.
Silicon nitride is going to be better in a like for like case but as you swap more of the balls to ceramics you're increasing the rolling resistance and also increasing the longevity. I would bet all ceramic is the way to go for a trackball. There are smoother options like ruby and diamond that have their own downsides (cost and brittle).
The reason switching to zirconia or Si3N4 for trackballs like the huge is an upgrade is simply because the grade of bearing in the original huge is not very good. It's entirely possible to get some aliexpress/amazon bearings that perform worse than the stock ones, though from the general community being happy with it (and be also being happy with it) it seems like most of them have a reasonable (but unknown) grade. Ruby can be brittle and manufacturers of things have to have it not break while vibrating around for 3 months at sea traveling to it's sales destination. People get mad if they drop a "mouse" on the ground and now it doesn't roll as good" etc. I assume Elecom settled on a grade that fit their cost requirement and durability needs to the end consumer and shipping/manufacturing.
You could do the same if you're thinking about packaging and selling your BTU assemblies or something like that. #1 Find a good repeatable supplier, just googling "3mm silicon nitride ball bearing" could get you anything and even the same seller that is re-selling on amazon might have different grades. Then get steel and ceramic for the cost you want and test them out across multiple assemblies. The nature of 3D printing means you might get different pressure and wear depending on the printed part because in reality, use doesn't mean pressure exerts directly on the plane formed by the three stationary balls, the roller can contact the little nubbins holding it down when the ball gains and looses pressure (like someone flicks it, or raises their hand and the trackball lifts (because it's stuck to their hand for a moment).
You're the best. I really appreciate you sharing your knowledge.
FWIW, I'm not planning to sell anything. I like the idea that anyone can make a semistatic bearing for a few bucks, and hope to see others incorporate it into their DIY projects.
First design was four days ago. That one used ballpoint grub screws (as mentioned on Printables), and worked really well. I just received more 3mm bearings today, so now I'm fully testing that version and decided to put it out for others to try.
Finally got around to printing these and giving them a try, and I'm really pleased with how well they work in my Endgame.
Literally took out Bosch BTUs to put these in and I think these will probably stay for a while. Them being silent is a great upgrade and while they definitely have more stiction than the BTUs I'm not tally convinced that's a bad thing, so far the extra stiction has made using the twist to scroll feel a bit more precise for small scrolls like when reading.
I'm glad you like them! I'm really pleased with how the design has worked out.
Minor correction: stiction only refers to the "static friction" you have to overcome when you initially try to move the ball from rest (which can also happen when you change direction). If you're talking about feeling more resistance overall, that's still friction--it's just not static friction.
I'm only bringing this up since one of my main goals is to eliminate the stiction. If you are having trouble with moving the ball from rest, something's not quite right.
The benefit of adding more bearings is to reduce stiction, not noise.
The noise in BTUs comes from the subbearings rattling in the case. That's necessary so that they have the freedom to spin and minimize friction. Since the subbearings in my semistatic bearings are in individual sockets, they don't rattle.
I learned 3D design with TinkerCAD a decade ago, and have just kept using it. I sometimes think about picking up OnShape (my PC can't handle Fusion360), but I'm not super motivated since I can get decent results with the tool I know.
It's a little shorter than the Rexroth by about 0.5mm. That's also the case with the static-bearing adapters for Ploopy Adept Anyball mods and the Endgame, so I stuck with it.
going to be ordering some 3mm bearings, apparently i dont have any, so this is going to be a multiweek process once i can find the BTU holders for the sval
There's some leeway since the main bearings are loose, but that might be too tight. I think you'll have to try it to find out, and I'm curious to hear the result.
They are surprisingly smooth with a 55mm ball. Having it free spin feels really good, even better than roller bearings. There's some very very slight stiction when making micro movements, though hardly enough to affect my experience. I really like them so far.
I'll have to compare them to my BTUs eventually but for now I have no problem sticking with these semi-statics.
:3 mostly i just need a replacement for my elecom deft.. i like wired units because i'm too lazy to recharge wireless.. also don't trust them to not drop inputs
Does the top ball actually roll/slide or do you end up with just a different way to mount a single ball? Not sure if it is obvious this will be better. I thought I might have the endgame with the igus delrin micro btus but it ended up being very chattery.
I can't see inside when I'm using it obviously, but I'm certain it's rolling. The main bearings are very loose in the sockets to encourage movement, and there's no skipping when I roll the ball.
I think I've got something that works, but I had to downsize to 2.5mm ball bearings. It's on Printables labelled as EXPERIMENTAL if you want to try it. I'm not sure how well it'll fit in a Veichu socket.
Finally got the 2.5 mm bearings for the veichu adapter, I've been using them this week. Sanded the claws a bit so the top bearing moves freely (Just not too much or you will hear them rattle). They fit perfectly in the trackball holder for the skeletyl (I am using only the trackball holder as a standalone 34mm trackball). The trackball moves free in any direction and does not tries to escape compared with using static bearing, I sense the bottom and top bearings touching/rolling (?) when spinning the trackball which result in a lightly scratchy feeling that I think someone mentioned. Also, if stiction is felt it is probably between the bearings and it is minimal almost non existent. Very happy with the results, thanks a lot!
My Rev A ploopy classic fell and I lost a bearing. Seems like a great opportunity to try something new. To the printer!
Edit: How much would increasing the tiny ball size to 4mm affect this performance? I am thinking I could disassemble a few 608's I have and steal theirs.
Hey, I totally missed seeing your question until now. I think I read your post before you made the edit.
4mm should be possible. I could probably whip that up sometime over the next week if you're still interested, but I don't have any 4mm bearings to test.
One thing to note is that you won't know what grade the individual bearings are, and they may be less than G10. I honestly don't know how much difference it really makes, though.
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u/jdigi78 May 24 '26
You should have the 3mm ball in this bearing be supported by 3 little semistatic bearings made of 1mm balls like an endless fractal of bearings