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

How Does it Work?

SlimeVR FBT provides simple, effective tracking of your body and limbs in VR games and other applications. 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. 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.

A set of five SlimeVR Trackers

The base set of five trackers is sufficient to cover lower-body movement (legs and waist) and is widely supported by VR games and applications, including VRChat. Other platforms, such as NeosVR and LIV, can use additional SlimeVR trackers to monitor the position and rotation of your feet, knees, elbows, chest, and more!

Optimized for Accessibility & Comfort

Your comfort is our primary goal. SlimeVR trackers are lightweight, easy to wear, and entirely self-contained. Because they do not depend on cameras or base stations, they are able to track a wide range of motion without ever being occluded, or blocked from view, in a way that would cause external sensors to lose track of them.

A pair of SlimeVR Trackers

Compatible With Many Different Platforms

SlimeVR is broadly supported by popular VR software, including:

• PC games and other applications, including VRChat, NeosVR, and Blade & Sorcery, to name just a few examples
• Streaming VR applications with an avatar
• VTubing (with Tracking World for now, but we plan to support native virtual motion capture in the future)
• SteamVR games
• SteamVR games played using the Shadow platform

And much more as we grow!

What About the Oculus Quest?

The Oculus Quest itself, as a standalone system, does not currently support full-body tracking. However, you can use SlimeVR with your Oculus Quest if you connect it to a PC and use it to play SteamVR games!

Features & Specifications

• Native SteamVR support
• 100 Hz refresh rate
• Completely wireless via 2.4 Ghz Wi-Fi
• Over 15 hours of playtime with a built-in 1200 mAh battery
• USB Type-C charging and hacking
• Over-the-air (OTA) firmware updates
• Works with all SteamVR-compatible headsets
• Does not require a PC with Wi-Fi support
• Can connect to a Wi-Fi router on the same local network as your Ethernet-connected PC or directly to your PC if it does have Wi-Fi support (via the motherboard, a Wi-Fi card, or an external Wi-Fi dongle)

SlimeVR Tracker without enclosure

Interference & Drift

SlimeVR is not affected by magnetic interference or positional drift, despite its reliance on IMU sensors for tracking. Each tracker only monitors its own rotation, which is enough for our software to estimate your pose. That means your virtual legs will never do that thing where they suddenly fly away. (So embarrassing…) SlimeVR is also unaffected by magnets or metal, as it does not rely on a magnetometer. Over time, there is some horizontal-rotation (yaw) drift, so body parts can end up facing the wrong direction after a while. We’ve done a lot of work to compensate for this, however, and it typically takes between 20 minutes and two hours, depending on your activity, for any drift to become apparent. And if it does become apparent, don’t worry. Sensor recalibration is incredibly user friendly. In order to fix any drift issues that might arise, all you have to do is hold a straight pose while pressing a single button.

Comparisons

¹ The precision of SlimeVR tracking technology depends on your setup, on the plane used for measurement, and on how your back bends.
² AprilTag requires additional waist tracker with a phone or other tracking technology (has reliable 180° coverage without).

Available Tracker Sets

The base set of five trackers allows you to track your lower body, including your legs and waist. Additional trackers can increase tracking precision or add new tracking points. If you need to monitor foot rotation in addition to foot position, for example, SlimeVR can achieve that using additional trackers. Tracker Extensions are smaller, auxiliary trackers without batteries or Wi-Fi capability. They connect to a primary tracker by means of a wire and provide a simple, comfortable way to improve the tracking of particular body parts.

Protoypes of a SlimeVR Tracker and a Tracker Extension.

The table below illustrates how different sets of SlimeVR trackers can be used in software that supports six-point tracking (like VRChat) or 11-point tracking (like NeosVR or LIV).

¹ Chest tracker extension improves spine tracking, which greatly increases precision while sitting or bending, especially in extreme poses.
² Elbow tracking relies on your controller tracking as additional reference.

Committed to Open Source & DIY Electronics

SlimeVR is open hardware driven by open source software and is released under a permissive MIT license. This open design empowers the VR community to expand on the SlimeVR ecosystem, create new devices, add compatibility with new software, and improve upon all aspects of the project. For our part, we are focused on helping that community expand SlimeVR infrastructure by adding support for various devices, protocols, and features. We are part of an active DIY community, members of which build their own SlimeVR trackers, help others get into DIY electronics, contribute to our documentation, and develop hardware with different features and at different price points. All of our hardware is hacker friendly, and we encourage you to use it in new ways and adapt it to your needs!

A prototype of DIY-Kit boards and wires, which are identical to those in our standard Tracker Sets but without enclosures and other accessories. Perfect for anyone who wants to adapt our hardware, design their own enclosures, or save some money.

Support & Documentation

Our open source software and firmware is in our GitHub repository. Our hardware schematics will be available when they are finalized. We have guides and schematics for easy DIY and are working with the community to make them better, more accessible, and compatible with a wide range of hardware and tools.

More specifically, our documentation is here, and our GitHub repository contains:

• The tracker firmware
• The server software
• The SteamVR driver

Join our community on Discord to meet other VR hackers or to chat about SlimeVR. You can also find us on YouTube. And, if you have a question for our team, you can reach out using the Ask a technical question link below.

Manufacturing Plan

Production SlimeVR boards will be fabricated and assembled by LZJ PCB, a contract manufacturer with whom we have worked to produce various SlimeVR prototypes. Each board will be tested at their factory. (We will, of course, test a sample set of trackers ourselves before we greenlight the final production run.) ICOMold will handle injection molding for the tracker cases, and our kitting partner in China will assemble and test the final product. We have agreements in place with all of our partners, and they are ready to begin production as soon as the campaign comes to an close and parts become available.

Due to the global chip shortage, the main sensor we are using—BNO085 by CEVA—has a pretty long lead time of 28 weeks. While that’s not great, it’s better than what some projects are up against these days. And of course it could change, depending on the global situation. We have preliminary agreements with multiple suppliers, including CEVA, and we will place our order(s) as soon as the campaign concludes. Given that 28-week lead time, we project that SlimeVR will ship to backers by March of 2022. If that estimate changes, we will let you know right away by means of a campaign update.

Fulfillment & Logistics

After the SlimeVR hardware is manufactured, it will be sent to Crowd Supply’s fulfillment partner, Mouser Electronics, who will distribute it to backers worldwide. You can learn more about Crowd Supply’s fulfillment service under Ordering, Paying, and Shipping in their guide.

Risks & Challenges

SlimeVR Trackers went through many prototype revisions, and our current hardware design is complete and has been tested by a few YouTube reviewers. The software, firmware, and hardware were also tested by our DIY community. The current server software performs well, but we are still working to make it even more user-friendly and to expand its feature set.

It is possible that we will face additional component-availability challenges beyond those mentioned above. Because of the project’s time line, all parts will be ordered as soon as possible to reduce delays. The good news is that all of the components except that main IMU can be swapped out for alternatives without affecting the end-user experience in any way. (We know this, because we’ve done it a few times while prototyping.) Finally, our project financials are such that we have a bit of a buffer we can use to address any sudden price increases, in both critical and non-critical parts, should they occur.