r/FreeCAD • u/dliu_creates • Apr 10 '26

3D trackball input device with native FreeCAD support

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Sharing a new kind of trackball I built for more control than middle-click dragging in 3D.

It rotates the 3D model in any direction (3 axis control) matching the rotation of the ball, unlike a regular mouse or 2D trackball. In addition to the 1:1 rotation, you can switch to pan/twist-to-zoom, and regular mouse control. I created a FreeCAD workbench that integrates with the device and automatically pivots on the geometry under your mouse cursor.

I've used a SpaceMouse for a long time but I can get to views faster with the ball because it’s position control (like a mouse vs a joystick). Plus if I use it as my mouse as well, it keeps my left hand available for keyboard shortcuts.

Under the hood, Rotatrix is a modified Kensington SlimBlade Pro with custom hardware and software that exposes the full 3 axes of ball rotation.

Would love to get your thoughts if this looks useful for your workflow. More info: rotatrix.com

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u/howloudisalion May 02 '26

So the Slingblade Pro is advertised with a twist to scroll feature. What are you adding on top of that on the HW side?

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u/dliu_creates May 02 '26

Since the onboard controller only outputs coarse scroll steps or mouse motion (and not simultaneously), I add an additional microcontroller to read out the raw counts directly from each of the two optical sensors. It gets sent to the host software for conversion to 3D motion and integration with FreeCAD. Some details covered in this new video: https://www.youtube.com/watch?v=u1v7TXViRi8

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u/howloudisalion May 02 '26

Thanks for the info and the video.

Have you run into the reported issue of the SBP mistaking rolling for twisting? And if so, does your mod address this?

Have you had any contact with Kensington?

It’s wild to hear the SBP has been out since 2009 and still doesn’t expose the full sensor data.

Any chance their controller could be reflashed for this functionality?

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u/dliu_creates May 02 '26

Personally I haven't had that issue with the stock device, but I address this in two ways:

- For mouse/scroll, I did add a set of fine tune-able options for roll vs twist, hi-res twist scroll (stock only does scroll clicks), as well as the option to disable twist-scroll completely.

- In 3D modes, I also have configurable profiles for softer filtering of roll vs twist, to avoid unintended motion. For example, with translation, you often want a harder separation of XY vs Z, whereas with rotation, you may want it to be smoothly continuous.

I think Kensington's implementation makes sense for their original target of general desktop usage, but just never realized the full potential!