Open Source SlimeVR Project Turns ESP8266 Microcontrollers Into Low-Cost Wireless Full-Body Trackers

Low-cost body tracking pucks require no cameras or base stations, and the software and firmware are both permissively licensed.

Russian startup SlimeVR has opened crowdfunding for its eponymous full-body motion tracking system for virtual reality using open-hardware wearable sensors and open source software.

"SlimeVR is a set of open hardware sensors and open source software that facilitates full-body tracking (FBT) in virtual reality," the company explains of its design. "With no base station required, SlimeVR makes wireless VR FBT affordable and comfortable."

SlimeVR has launched its full-body tracking pucks, with shipments expected in March 2022. (📹: SlimeVR)

The heart of the system is a set of five trackers, worn on elasticated straps, which is enough to track the movement of the wearer's legs and waist. Where the application in use allows for more sensors, additional units can be added to track the user's entire body.

"It makes full-body tracking comfortable and affordable by leveraging high-quality inertial measurement unit (IMU) sensors and a Wi-Fi connection to your PC rather than wires, cameras, or base stations," the company notes. "Taking the lower-body set as an example, five trackers — one on each thigh, another on each ankle, and a fifth at the waist — are enough to get the job done."

"Each tracker monitors its own rotation in space, and SlimeVR software uses your proportions and headset location to calculate joint angles and estimate limb positions. In more technical terms, SlimeVR relies on absolute-orientation sensors, a configurable skeleton model, and forward kinematics. The result is like having virtual Vive trackers at key locations on your body."

The trackers are built around an Espressif ESP12-F module, featuring an ESP8266 microcontroller. The devices have a 100Hz refresh rate and charge a 1.2Ah battery via USB Type-C — good when fully charged, the company claims, for 15 hours of use.

They're compatible with any headsets that work with SteamVR, and both the firmware and software have been released under the permissive MIT License — and the company says it expects to see a range of DIY SlimeVR trackers pop up as a result.

The project is currently funding on Crowd Supply with physical rewards starting at $165 for a five-sensor lower-body tracker set. Hardware is expected to ship in March 2022 — primarily thanks to a 28-week lead time on the CEVA BNO085 sensor, another victim of the ongoing component shortage.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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