So I want to design my own trackball mouse (pic more-or-less related) but I don't have any experience in making or designing hardware, so how would I get started? I know how to use Blender for 3D modeling but how should I go about developing a prototype of my mouse?
At it's core a trackball is a ball mounted on some sort of low friction bearing. CST use steel rods, Kensington use little ceramic spheres.
An easy way to get a ball for the trackball is to buy a billiard ball.
The hardest part is the actual tracking. Modern balls use optic tracking. Older models tracked the rotation of two orthogonal bearings, but that was prone to getting stuck when too much dust accumulated on those. Maybe you can find an optical mouse sensor online. IDK how much of the tracking logic needs to be provided in software for those.
Wow what toxic replies.
If you are going to diy some mouse, you are really just making a new custom case for the mouse, you can just 3d print them once you have made it in 3d in any 3d software, all the major ones can export to a format readable by 3d printing. After that it is just a matter of sanding and painting or whatever you wanna do.
If you are making it out of wood or metal, it is just a cnc machining job but it will be too expensive for a mouse.
If you want to mass produce a mouse case you just buy a 3d printer.
Google rapid prototyping.
Design it in Blender, go to a nearby hackerspace and ask them to 3d print it for you (or order it on shapeways/3dhubs/etc), if it turns out good, take apart an old trackball mouse and try to modify the design so the original hardware fits in it. If you want to sell it, you probably have to build the hardware yourself.
You won't sell anything no matter how good it is because you'll be encumbered by patents.
Study existing patents first and give up then before you start a design and give up after having invested an assload of hours into it.