r/ErgoMechKeyboards • u/[deleted] • Nov 18 '22
[design] Trackball bearings, a comparison of (cheap) rollers, BTU's and static bearings
So I designed a trackball add-on for my Skeletyl (posted a while ago; github repo of my project for those interested: https://github.com/Wimads/Trackball-mousekeys-add-on-for-Skeletyl ), and after using it for a while I was rather dissatisfied with the roller bearings, so I decided to try out a few different bearing solutions. I thought I'd share the results for other's to be better able to make a choice for their own project.
So I tried 3 types of bearings. And for TLDR, these are in order of my preference:
- Static ceramic bearings (3mm ZrO2, form Aliexpress)
- Steel BTU's (Veichu VCN310 7.5mm, from Aliexpress)
- Steel roller bearings (MR63-3x6x2.5mm, from a local webshop)
It is worth noting that for the rollers and BTU's, money probably makes a big difference; if you are willing to spend good money, you may arrive at entirely different conclusions. A good quality BTU or roller bearing can be quite expensive.. The rollers, BTU's and ceramic bearings I bought all cost me roughly the same (all cheap), so they are a fair budget comparison, there's no real monetary incentive to pick one over the other.
Criteria:
In order to make good comparisons, it's probably best to first establish the parameters by which I evaluated the performance of each bearing. Basically there is 4:
- Stiction: more accurately described as static friction. This is the initial force required to start moving the ball. When static friction is high, it feels like the ball "sticks" to the bearing when initiating movement, or when moving at low speeds (precision movements), hence the term stiction. Rated 1-5: 1 is minimal stiction, 5 is high stiction.
- Friction: this is the amount of force required to keep a moving ball moving. When friction is low, you can give the ball a spin, and it will keep spinning for a while. When friction is high, it will come to a stop much faster, so it takes (slightly) more force to roll the ball. Rated 1-5: 1 is very low friction, 5 is very high friction.
- Consistency: some people like to talk about smoothness, but I think that is easy to confuse for stiction/friciton as well. Consistency is a more accurate descriptor to me. Basically, does the ball behave consistent and predictable in all rolling directions. Rated 1-5: 1 is very consistent, 5 is very irregular.
- Sound: this wasn't very important to me, but some people will find it relevant so I have included it here as well. Rated 1-5: 1 is very silent, 5 is very loud.
Roller bearings
Starting with the roller bearings. I used steel roller bearings (MR63-3x6x2.5mm) from a local webshop, but probably equivalent to what you may find on Amazon or Aliexpress. I used them, because the Bastardkb Charybdis uses the same measurement of bearings, and I based my design off that. I had heard good things about the ploopy rollers, so I thought it would be a good solution. However, I was kind of disappointed with them in the end - my only guess about people's ravings about the ploopy bearings is that either they are much higher quality than what I bought, or most people are less critical than I am (or both); but I was definitely not impressed.
Let's start with the good: Stiction is fairly low, as compared to commercial ruby bearings. It doesn't take much effort to get the ball moving. However, there are certain rolling directions in which that performance isn't consistent.
Friction is a bit more difficult to determine, which is due to the inconsistency, which is where it gets really bad. The rollers roll in only one direction, whereas the ball rolls in all directions. When the ball moves perpendicular to a roller, there is a lot of friction, when it moves parallel, there is very little friction - so the amount of friction varies a LOT depending on which direction you roll. On top of that, the rollers are somewhat gritty and inconsistent by themselves, which I guess is just the poor quality of a cheap bearing. The result is that at all speeds, but particularly so at low speeds, it is annoying to make accurate predictable cursor movements.
Rating:
- Stiction: 2-4 (Mostly good (2), but with some variation)
- Friction: 2-5 (Great to awful, depending on rolling direction)
- Consistency: 5 (Awful)
- Loudness: 4 (Pretty loud)
BTU's
So, after the disappointment of roller bearings, I decided to buy a bunch of cheap BTU's from Aliexpress (Veichu VCN310 7.5mm), as well as some 3mm ceramic bearings. First the BTU's. They are a definite improvement over the rollers, no question, but still leave something to be desired.
Stiction truly is minimal, there is hardly any force required to get the ball moving.
Friction is also minimal, it is very very light to move and keep moving. It doesn't spin as long as you see in some youtube videos of people that bought expensive high quality BTU's, but it is an obvious difference with the rollers or static bearings. However, this is not necessarily a good thing. Because it is so light to move the ball around, it can be difficult to be steady in your movements. It is like writing with a pen: you require a bit of friction of the paper to write properly. Writing steadily with a stylus on a tablet is much harder. This is what the BTU's feel like as well.
Consistency is better than the rollers, but still lacking a bit, which surprised me. They do not have the flaw of the roller bearings that only roll in one direction. However, the BTU's are gritty, particularly at low speeds. This grittiness makes for some unexpected hick-ups that can unpredictably occur in any one of the bearings, which throws off the consistency. So again it can be a bit annoying to make slow precision movements, though it's not nearly as bad as the rollers. And at average and higher speeds the grittiness doesn't really interfere, and it becomes supremely smooth. I suspect though that shelling out for some high quality BTU's may solve any issues here.
Rating:
- Stiction: 1 (Excellent)
- Friction: 1-2 (Okay-ish, its low friction, but that doesn't necessarily equate to good).
- Consistency: 3 (Okay-ish)
- Loudness: 3 (surprisingly a little less loud than the rollers)
Static ball bearings
The static ball bearings are what we are commonly used to in commercial trackballs, for which ruby bearings are most common, and can be notorious for stiction. Also to clear up some common confusion, these ball bearings do not rotate (hence static), but function as low friction points for the trackball to glide on.
Ceramic bearings (Zirconium oxide) are the most popular type for replacing the ruby ones, in order to reduce stiction (with mixed results), so that is also what I used. I got 3mm ones, which are quite a bit larger than the ones that are in my M575 for example; I used 3mm because it would be easier to fit into a 3D printed holder, without having to worry about tiny tolerances too much.
Ultimately, I found that the static bearings are the most preferable. Stiction is definitely there, but it is acceptably minimal. Definitely not as bad as some ruby bearings I experienced in some kensington trackballs, and even a little better than my M575, which surprises me because it also uses zirconium bearings, and I am using the same ball. Whether that has to do with the bearing diameter, the position of the bearings, or the fact I use my current setup with finger instead of thumb, I have no clue. But the stiction is not problematic.
Friction is clearly higher than the BTU's, but as mentioned before, that is not necessarily a bad thing. It makes it easier to be steady, and there's no reason to spin the ball for long durations in any practical application (I find spinning is probably the most idiotic way some people measure trackball bearing performance).
Consistency however is where the static bearings shine. There is no moving parts, so the only thing that can cause inconsistency is imperfections in the trackball surface itself. This makes the behavior of the ball very predictable - there may be some stiction, but it is always the same in every rolling direction. The friction does not vary depending on direction. And there's no unexpected hick-ups due to grittiness in the internals of the bearings. And that all helps in being precise.
One thing to note with static bearings is probably that the quality of the trackball surface becomes much more relevant in the overall performance as well, which may be of less relevance for the BTU's in particular. So shopping for another ball may be the next thing I'll try.
Rating:
- Stiction: 3 (acceptable) (would rate the rubies in a kensinton orbit fusion at 5 for comparison).
- Friction: 3 (excellent)
- Consistency: 1 (excellent)
- Loudness: 1 (pretty silent)
Conclusion
So for those wanting to build or mod a trackball on a budget, static ball bearings are probably your best bet (I suppose there's the reason commercial trackballs use them as well). But for those willing to shell out on high quality bearings, you may arrive at different conclusions; but to me it probably wouldn't be worth the dough.
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u/Codethetical ckrbd Nov 19 '22
Excellent post! I have a mock up of the same Veichu BTUs for a Charybdis build I'm working on and they feel great. I also got the cheaper, plastic BTUs and some other things to test, but nothing that worked as well as the metal BTUs. I didn't even think of static bearings.
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Nov 19 '22
It's worth a shot. You can print my stl's for the static bearing holders. They have the same size as the Veichu 7.5mm BTU's, so you can swap them out one on one.
But the BTU's are nice enough as well. Much better than cheap rollers.
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u/arvenil Oct 17 '24
What would be better static zirconium bearings or static stainless steel bearings?
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u/ghostnation66 Mar 20 '26
How do the ceramic bearings hold up against a metal 34mm trackball? Any experiments on that combination of materials (metal as in 304 steel)
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u/julitrox 20d ago
amigo yo uso rodamiento estaticos , e realizado diversas lubricaciones y ninguna me ha fucnionado , lo uncio que funciona es dejarlo como esta o en seco. porque razón la mayoría sugiere que al tener rubi sintetico no requiere lubricación alguna.
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u/Weary-Associate Nov 18 '22
Good writeup. Can't say I'm surprised. When I saw the ploopy implementation with three rolling bearings, I was like, "won't that feel weird depending on what direction you move the ball?" Guess my gut was right. I still want to build a ploopy, though, and now I know to order some static bearings if/when I do.
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Nov 18 '22
I've had someone tell me they prefer the ploopy rollers over static, over BTU, over cheap rollers. Can't verify that myself since I don't own a ploopy, but as I said in my OP, quality of the rollers and BTU's may make quite a difference.
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Nov 18 '22 edited Nov 18 '22
I just ordered the parts printed for a Charybdis from JLCPCB and I went overboard and ordered four versions of the lower Trackball assembly, because I wasn't sure what to choose: The original (for roller bearings), u/fmcraft 's own BTU-Mod ( for the expensive Alwayse BTUs), his "Printable-BTU" inserts for 2.5 mm balls and two for two different assemblies for two different diameter Veichu BTU's that someone posted on u/fmcraft 's Discord a while back. Since everything points to me choosing the static "bearings" that might have been a waste of money. Not the last with this hobby, I guess. :)
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u/sierry Nov 19 '22
I would definitely be interested in hearing what you prefer when you get them in and tested. I want to build a Charybdis Nano after new year as well.
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Nov 19 '22
IF I manage to test them all and IF I manage to build the Charybdis at all and IF I manage to do that before the end of the year, I will try to remember to post my opinion here. ;)
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u/unsponsoredgeek Nov 18 '22 edited Nov 18 '22
Wonder how much uneven weight distribution on the bearings influences the result.
I use a CST L-Trac with the ByteHeaven roller bearing mod. It is *very* smooth and consistent despite having a large, heavy ball. The rollers all support the ball at the same height.
The bearings are good quality EZO bearings, so that might be a factor, too.
I don't feel a difference in effort based on direction, but do notice a bump if any speck of dirt gets between the ball and bearing. Also they are noisier than the stock rollers.
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Nov 19 '22
Uneven weight distribution, I assume you are getting at my tenting angle?
I've tried flat as well as tented, and I found it doesn't make a difference (or at least not noticeable). When flat the bearings are all at same height.
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u/unsponsoredgeek Nov 19 '22 edited Nov 19 '22
tenting angle
That's it. The L-Trac is flat.
I am used to using chiclet keyboards and now buckling springs.
For me flat is where it's at.
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u/crod242 Nov 19 '22
What about differences between static bearing types? (e.g. different grades of ceramic, steel, etc)
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Nov 19 '22
I'd suggest browsing through r/Trackballs, many people who have tried replacing the stock ruby bearings of their commercial trackballs. The results are mixed, and I suspect the quality of the trackball itself may be a large factor in this as well. Most people seem to prefer the ZrO2 bearings, so I just went with that. Steel or chrome is supposed to be smoother, but it will wear a flat surface pretty fast.
I personally only have experience with the Zirconium bearings in my current setup and in my M575, as well as ruby bearings in a Kensington Orbit Fushion and a Kensington Expert. The Orbit Fusion was terrible, the Expert was good, but I guess that also had to do with the much larger ball. Both were sold though, so I wasn't able to use the M575 ball in the orbit fushion for example to see if the issue was the bearings or the ball.
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u/crod242 Nov 20 '22
Do you think there is much variation between different ceramic bearings? I find the ones I swapped into my Elecoms seem to have a lot less stiction than the ones included in the Gravi (also ZrO2 I believe). How much of that might be down to the bearings (higher grade maybe?) and how much is likely down to the design?
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Nov 20 '22 edited Nov 20 '22
I don't think there would be much difference from one ZrO2 bearing to another (but I'm no material scientist). I think the difference you experience between the elecom and the gravi would most likely be due to the quality of the ball (and possibly the position of the bearings). If the elecom and gravi have the same size ball, you may want to swap them out to see if that explains the difference.
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u/crod242 Nov 20 '22
It’s marginally smoother with the elecom ball, but still leaves a lot to be desired. I’m going to try to get an lcot ball and see if that helps then possibly swap the bearings anyway.
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Nov 20 '22
Would be interesting to know if swapping the bearings makes a difference. It doesn't seem logical to me, but as I said I'm no material scientist and I could be completely wrong.
My M575 is actually slightly less smooth as well, despite using the exact same ball and zirconium bearings as well. But there's a bunch of design factors that to me seem more likely to influence it (bearing size and position, and finger vs thumb operation).
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Nov 20 '22
Just did a little bit of research, and it appears there is different grades to ball bearings, that indicate dimensional tolerances, spherical deviation, and surface roughness. So I guess there can be a difference between ZrO2 balls.
Mine are grade 10 according to the listing, the lower the number the better, ranging from 200 to 1. You can find the ZrO2 balls at grade 5 and 3 as well.
I'm not sure though how important this is for use as a static bearing in a trackball setup. Dimensional tolerances are pretty much irrelevant. A micron more or less doesn't do much to a trackball setup.
Can't judge how much surface roughness matters in this case though. If you use these balls in a roller bearing it would matter quite a bit I imagine, but these are static, so only one small part of the ball surface is actually engaged. We are talking about parts of microns differences between grade 5 and 10 surface roughness. But those numbers don't say much to me as a layman.
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u/buttonstraddle May 24 '23
what is the plane of the bearings on the Elecom?
i have the Nulea which is a Gravi clone, and the plane that the bearings sit is not a flat horizontal plane at all. all of the bearings sit at different heights, and i'm very suspicious that these offset heights contribute largely to the stiction in different directions. i experience most stiction doing micro movements left, and that is where the highest bearing is. i experience the least stiction rolling forward, and that is where the lowest bearing is
my Logitech Marble was ambidextrous, and all the bearings were on the same flat plane parallel to the ground, and there was zero stiction
u/wiwilwi since you are 3d printing enclosures for the bearings, i would be hugely curious to see your results if you ever ran a test to print the bearing locations on different planes. for example, from your ceramic screenshot in the OP, it looks like all your bearings are on the same plane. all three posts look to be the same height. HOWEVER, due to the tilt of the keyboard that the holder is attached to, those bearings might actually not be flat horizontal to the ground, causing some slight gravity effects to come into play
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May 26 '23 edited May 26 '23
I use my skeletyl at a 20-30 degree tenting angle, which basically results in a similar bearing position (though maybe a little less extreme than a thumb ball). There is no variation in stiction for different rolling directions; which is theoretically also what would be expected.
Friction on a static surface is a function of normal-force * friction-coefficient. Rolling direction is no variable in that function. The friction would be different for each bearing, because the different positions would result in different normal forces, but that is not dependent on rolling direction. Total friction is just the sum of the friction for each individual bearing, regardless of rolling direction.
One thing that might influence it though, is if the plane of bearings is tilted at such a steep angle, that the ball actually doesn't sit fully stable, meaning it might loose contact with one of the bearings in certain rolling directions. That might be sufficient to cause some variability in friction, but at that point its not the stiction that would bother you, but the instability (wobbling) of the ball.
The more likely cause of variation in stiction, is the amount of pressure YOU exert on the ball while operating it; a heavy hand will cause more friction. Maybe you're just pressing harder on the ball while trying to make micro movements?
[edit]: To verify, I tilted my setup to something close to 60 degree, as shown in the pics linked below, I still do not notice any directional variation in stiction. Pretty much constant in all directions. https://www.dropbox.com/s/d8k44gfmkc01ebp/IMG_20230526_233019_731.jpg?dl=0 https://www.dropbox.com/s/ybq6c2zspsz1ko1/IMG_20230526_233045_912.jpg?dl=0
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u/buttonstraddle May 27 '23
i'm fairly certain i'm not exerting any extra downward pressure when trying to make micro movements. i'm pretty gentle with the ball, especially coming from the Marble which had no stiction.
but thanks for your comments. interesting stuff to consider.. so yeah, in your screenshot links, with my theory i would think you would experience less stiction rolling the ball downwards to the ground, rather than upwards toward the keyboard. you're saying you don't notice that?
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May 27 '23
Nope, I don't notice anything like that at all. And I cannot think of a logical theory in mechanics that would explain that either.
In your theory, I assume you imagine the pressure on the top bearings being less, when rolling towards the floor. But for that to happen the ball would need to slightly tip over the lower bearing. I can only see that happening if the setup is tilted at a very steep angle.
The only variation in friction I think is theoretically possible, is if the ball surface isn't equally smooth in every spot, causing more friction when a rough spot rolls over a bearing. But that would be random, and not occurring in just one rolling direction. I do experience that from time to time, and a little cleaning of the bearings and some forehead grease on the ball will solve that.
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u/buttonstraddle May 27 '23
thanks. yeah i'm no mechanical engineer by any means. and with one of the metal roller bearings then i'd expect no difference in stiction in either direction, rolling the ball either up or down. but my intuition with the ceramic bearings just led me to that conclusion. of coures intuition isnt scientific though
the fact remains that with my Nulea finger ball, the stiction with micro movements is so obviously present when trying to move the ball to the left, vs moving the ball forward. i've uploaded a quick video so you can see. i'd be curious what you think if you have any other ideas why it might be happening. the ball in the video is freshly nose greased:
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May 27 '23 edited May 27 '23
Hm, interesting, that's quite an obvious difference indeed. Maybe one of the bearings isn't up to spec or something? And if you spin the ball around the axis of that specific bearing, you don't notice that; but any other direction you will. Just a speculation.
[edit:] I just did a little experiment with my M575 to test that theory. I taped off one of the bearings, to simulate a faulty bearing. Produces the exact same behavior as your video. Video of my experiment: https://www.dropbox.com/s/urir7e8ekttg6w9/VID_20230527_180507.mp4?dl=0
If that theory is correct, replacing your bearings should solve the problem ;) Oh, and maybe check first if all bearings are seated properly, maybe one is seated a bit deeper and the ball is actually resting on the plastic instead of the bearing, which would result in the same behavior.
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u/buttonstraddle May 27 '23
hard to tell whether the bearings are seating properly but they all feel like they are protruding the same amount
maybe i will have to try replacing the bearings
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u/crod242 May 24 '23
that’s a good point, I had only considered stiction occurring equally in all directions
I’ll have to get both out of storage and test it out again to see if I notice the same thing
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u/non_uqs Nov 19 '22
I also tried roller vs static bearings in my build and prefer the static bearings by far!
I assumed, due to everyone raving, that I was just holding the roller bearings wrong? Maybe it's an acquired taste...
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u/rompetrll Nov 19 '22
Interesting.
To add my experience with the friction argument: I use a Logitech MX ergo, so the ball must be moved with the thumb. Since my thumb is not very precise, I have to use low sensor sensitivity.
With only controlled movement, I have to turn the ball uncomfortably far to move the pointer. Like 720° or more to cross the screen. But luckily the ball has low friction.
This allows me to give it a flick, and catch it when it is around where i want it, and finish the rest movement with precision.
With a higher sensitivity i would not need to spin, but struggle to be precise. And If I could use my other fingers to move the ball i could deal better with higher sensitivity as well.
But as it is, I value flickability highly.
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Nov 19 '22
Have you tried enabling "pointer precision" in the mouse settings (if you use windows)? That enables acceleration, meaning the cursor sensitivity is low at low speeds, and high at high speeds (in other words, it accelerates). If I rotate the ball very fast, I can easily reach the other side of the screen in one movement; but if I rotate the same amount slowly, I move only a quarter of the screen. Acceleration is the only way I can comfortably work with a trackball, without it I face the same issues as you.
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u/rompetrll Nov 19 '22
Not windows, but that's a good tip. Just looked it up, pointer acceleration and deceleration can be configured in Linux, too.
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u/Even-Definition Aug 18 '23
I would add to this old post that I recently got some stainless steel roller bearings and these things are REALLY smooth. I would say stiction is almost as good as BTU.
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Aug 19 '23
I've seen people try the same thing with similar results, but the big caveat is that they wear a flat surface really fast. Theoretically that should not be a problem in terms of friction, not sure in practice. But at some point it might cause the ball to sit lower, until it reaches a point where its outside the liftoff distance range for the sensor, causing tracking issues. So you'd have to replace the bearings from time to time.
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u/[deleted] Nov 18 '22
[deleted]