Hi guys,
let me try to answer some of your questions.
First of all it's importand to understand, that the whole design is the result of ongoing iterations of design, build, test, redesign/adjust, build test... (while I'm writing those lines I'm currently in the 24th iteration).
All design decisions are carefully taken and well ballenced in regards to the design goals/constrains.
Design goals are
- easy to build
- easy to install
- small form factor (had 3/4 size of Arcade1up-format in mind)
- low cost
This resulted in a hard constrain for the form factor where a lot of decisions are aligned to (especially selection/ type/ size/ placing of ballbearing, decision against classical encoder wheel aproach and for optical mouse sensor)
Regarding lib/bezel:I went for a bigger lib in the first place, just to found out, that it was totally overdone.
With the current version I'm still able to hold the control panel upside down just at the trackball and it does not only slip out, it doesn't even move within the tollerances betwenn threads and CP-hole.
One of the attached fotos shows the old version with the bigger lib side by side with the current version.
Regarding ball bearingsThe ball bearing need to fit inside the big barrel that holds everything together (the one shape with the lib on the top).
And in addition to that, the three ball bearing that define the postion of the ball need to be as far away from the center and as high/ close to the balls widest point as possible to place the center of gravity of the ball as low as possible. Otherwise, if the ball gets pushed hard, it would escape the three ball bearings to "crash" against the housing with immediate high friction which result in a hard stop (bad gameplay experience).
Besides of that, friction during normal operation need to be at a minimum (only the three contact points of the three ball bearings.
To make a long story short: I tried different sizes of ball bearings and it turned out, they need to as small as possible. One of the attached fotos shows a selection of ball bearings with an 1 Cent coin as size reference.
Material/ RubustnessAs allready mentioned previously, the prototype was 3d printed with an FDM printer, used material was PLA.
I used PLA because it's very easy to print and I had never a doubt that it would not be solid enough. And of course it can be printed with any other type of filament like ABS or even Nylon or PC.
Here is a linke to 3dhubs with some overview of materials and there properties:
https://www.3dhubs.com/knowledge-base/fdm-3d-printing-materials-compared/And by the way: The material most used for injection molding is also ABS. Most likely conventional trackballs (housing) are manufactured with that.
Besides of that, rubustness is also a question of the parts geometrie (thickness for example) and printing specifications (like infill, print orientation etc).
In the case of this trackball, several "layers" of housing elements are screwed into each other which adds up to signigicant strength.
Coloring...ist just a question of selected material and can be any.
Usage of optical mouse sensor/ speed of motionI attached some fotos of a conventional product. Before I come up with the idea to the actual design, I tried to fit a conventional TB to that formfactor.
But as you can see by the look of those fotos, it's just not possible because of the required space for the both encoder wheels. In my opinion, thats the main reason for the formfactor of conventional TB's.
Those conventional encoder wheel TBs also have the problem regarding center of gravity of the ball: at the one side, the contact points of their ball beiring should be as high/as for out as possible, at the other side the bearings also have the encoder wheels attached that require space inside the housing from the ball bearing center too the housing top.
To make a long story short: a Arcade-Button form-factor with encoder wheels is impossible.
It was mentioned, that the granularity of the mouse measurements is to high, which results in fast movements with minimal turning of the ball.
Thats right, but basically all mice/track ball regardless of interface transfer delty X and delt Y values. This of the optical mouse trackball a just higher due to higher resolution.
They can be scaled down by adjustments in the software. There is also a theretical possibility, to place a microcontroller (e.g. Arduino MEGA 32U4 or something similar) between mouse sensor and gaming PC to adjust the value. I've done that with some conventional TB before (see attached foto): It reads the values from the PS2 interface of that other trackball, inverts one of the axes and scales both axes before it forwards the converted values via USB to the PC. Unfortunatly that would increase complexity alot and would also have slight impact on costs.
Hope I answered some of your question.
Best regards
Stefan
PS: my pictures where refused to be uploaded for security reasons. Any idea what's behind?