A key design decision I need to make on my way to my DIY trackball is how I would mount/attach the ball. How the ball interacts with the holder through friction and wear etc falls under the study of ‘tribology‘, which originally read like tribolites to me!
There are various arrangements used by commercial trackballs ranging from fixed synthetic ruby balls (Kensington/Elecom), free rolling zirconium oxide balls (Logitech), and roller bearings (CST). Which one is best for me?
Considerations for a commercial product vs a DIY trackball may carry different weights, I have to consider ease of assembly/manufacture so I can make the thing and perhaps not so much on longevity if I can replace or maintain it quite readily.
To make my own qualitative assessments, I 3D-printed test rigs with different arrangements to evaluate the ‘feel’ and ‘noise’ of each.
In the picture above are 5 arrangements :-
- Rear (mounted on a test case) – 3 × fixed silicon nitride 3mm diameter balls.
- Left – 3 × loose/free rolling silicon nitride 3mm diameter balls.
- Second from left – 3 × 623VV (3 × 12 × 4mm) V-groove bearings.
- Second from right – 3 × MR63ZZ (3 × 6 × 2.5mm) bearings
- Right – 3 × 8mm ball transfer units.
Qualitative personal opinion wise, the silicon nitride ball setups performed best to my liking in terms of smoothness. I had expected the roller bearings to be the noisiest, but the silicon nitride balls sounded louder but much more tolerable – the metal on metal sound was much more annoying even though it is quieter.
The ball transfer unit set-up did not work well at all, and offered significant resistance. Admittedly these are cheap units, and the grease/oil lubrication that came with them just wouldn’t work as a hand held device.
Between the ‘normal’ roller and the ‘V-groove’ roller which is meant to emulate the design change in CST trackballs, the V-groove performed smoother and more consistently. Not sure if this is the grade of bearings I had, but there seems to be a consensus out there the new rollers on the CST is an improvement, so it is nice to obtain a consistent result with that.
So it is decided, silicon nitride balls it is! With the 3D printing of the test rigs, I designed an arrangement that allowed fitment/replacement of the balls directly in the 3D print without the complication of a custom ‘ball transfer unit’ I had intended to make out of Polycaprolactone (aka Polymorph in Australia).
Next step, electronics, or specifically the laser sensor. Hopefully the PCBs will arrive this week and I’ll have some time the following week to assemble to do some tests with the sensor vs different balls.