Open hardware » Spherical treadmill

In this design, a 3D-printed base distributes compressed air evenly to support a floating styrofoam ball, while two sensors measure the ball’s rotation speed on 2 axes. It is typically used as part of virtual reality setups for mouse behavior (e.g. Harvey et al. 2009; originally used in insect behavior, see Buchner 1976). This open-source project is modified from a design by the Technocenter, Radboud University in collaboration with the Battaglia lab.

Spherical treadmill ready to use. Printed in black PETG.

The original design was adapted to

  1. Accommodate the Logitech G502 mouse model (earlier model was discontinued).
  2. Distance control – the sensor can be moved closer or away from the styrofoam ball, simply by adding washers between sensor box wall and base.
  3. Easy access – The sensor box can be easily open/closed (it attaches with magnets), facilitating cleaning. All sensor components can be removed in that way, giving access to the screws that enable distance control.
  4. Easy anchoring on optic tables with 4 feet compatible with M6 screws.  

This project requires 3D-printed parts (FDM), 2 Logitech G502 mice, a valve and a few screws. See the Assembly Instructions document for a detailed bill of materials and step-by-step instructions.   

Note: Depending on the 3D printing technology you use, minor deformations can happen to the small air outflow holes inside the base. For FDM, circles might print slightly oval: In some cases, it results in the ball rotating around the vertical axis (for testing purposes, can be amplified with increased air flow). This could lead to decision bias in tasks where mice are trained to run toward targets in VR. If you notice this with your treadmill, simply make the holes more round with a drill bit, needle or an M1 tapper when available.    

Spherical treadmill in a mouse VR setup at the Ernst Strüngmann Institute, Frankfurt.

Literature note: The first air-supported spherical treadmill was probably invented in 1976 by Erich Buchner for experiments on movement detection by the Drosophila visual system. It is still actively used in the field (e.g. Seelig et al. 2010, Longden et al. 2014) and there are efforts to democratize these expensive systems with open hardware alternatives (Loesche and Reiser 2021). The first version for rodents showed their ability to effectively navigate in a virtual environment (Hölscher et al. 2005). The rise in popularity of air-supported spherical treadmills in rodents – primarily mice – can be tracked back to David Tank’s lab (Dombeck et al. 2007, Harvey et al. 2009).

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