SlimeVR Butterfly Trackers
Super comfortable IMU body-tracking for virtual reality, motion capture, and VTubing
Based on the success and experience of SlimeVR Full-Body Trackers, SlimeVR Butterfly Trackers push the limits of comfort and ease of use for body trackers in virtual reality, motion capture, streaming, and more.
Like the original version, these new SlimeVR Butterfly Trackers are open hardware sensors with open-source software that track the movement of your body. They do not require base stations, can’t be occluded, are completely wireless, and last for days on a single charge. Now, with the brand-new, unique, ultra-light split design inspired by butterflies, they are less than 7 mm thick and weigh less than 10 grams, making them the most comfortable solution for full-body tracking on the market today.
Each SlimeVR Tracker tracks its own absolute rotation using an IMU (Inertial Measurement Unit). It sends this data wirelessly to the SlimeVR Server running on your PC, smartphone, or headset. The SlimeVR Server combines the data from multiple trackers, and uses your body proportions to calculate the position of your body parts using your headset as a reference point. Since they don’t require base stations or cameras, they can’t be occluded, can be used under a blanket or worn under clothing, and aren’t constrained by playspace size limitations.
Our SlimeVR Server is the open-source software at the heart of it. Developed over 5 years by our passionate team, with contributions from over 50 community members and dozens of translators! Compatible with all of the most widely used ecosystems, like SteamVR, OSC, VMC, BVH, and OpenXR, it lets you use SlimeVR however you want - for gaming, streaming, motion capture, and more!
SlimeVR Butterfly Trackers are based on Smol Slime, which are SlimeVR trackers that use Nordic’s nRF chips and a custom 2.4GHz protocol to massively reduce power consumption compared to the original Slimes, which used Espressif chips and Wi-Fi. Smol Slimes have been in development by our team and community for years now, but with Butterfly Trackers we are pushing the format to its limits.
The most critical parameter for the comfort of body trackers is their thickness. By placing the PCB and battery of the tracker side by side, we achieve a thickness of less than 7 mm without compromising the enclosure’s durability.
To make it even better, the two halves of the tracker are connected by a durable yet flexible band, allowing them to bend and better contour to the body for maximum comfort. Both of these changes make the trackers almost unnoticeable when worn, even when lying on them!
Smol Slime and SlimeVR Butterfly Trackers, unlike the original SlimeVR, don’t use Wi-Fi; instead, they utilize Enhanced ShockBurst (ESB), a wireless technology similar to Bluetooth but with fewer limitations. Because of this, they require their own dedicated dongle to connect to. Many community projects based on Smol Slime suffer from poor signal strength and short range. For Butterfly Trackers, we are using a custom PCB with a professionally tuned antenna specifically designed for small wearable devices, allowing us to reliably achieve distances of over 10 meters from the dongle, no problem.
Both the microcontroller and IMU of the Butterfly Tracker are extremely low-powered and can last up to 48 hours of play time on one battery charge with a tiny 90 mAh battery! When combined with the deep sleep feature, even playing a few hours every day would only require you to charge them once a week.
When you do need to charge them, we now offer a super convenient charging station! It’s sold separately, but there is always the option of charging them with any standard USB Type-C cable if you want to save some money.
Because Butterfly Trackers don’t use Wi-Fi, fiddling with your router is no longer required! Just plug the Butterfly Dongle into your PC, phone, or headset and they are instantly recognized by the SlimeVR Server, with no drivers or settings required!
Butterfly Trackers have a hooked backing from the hook-and-loop system (commonly called Velcro), and a set of straps is included in each set. This design also allows it to be attached to any Velcro-like fabric, providing a lot of flexibility and creativity for mounting. Feel free to experiment with other ways of wearing them, such as custom clothing with loops for easy attachment of trackers, adhesive silicone backing, belt clips, and any other ideas you can think of. Don’t be afraid to get creative! They can also be transformed into a single unit if that’s what you prefer. See below for the accessories we offer for purchase.
SlimeVR is broadly supported by popular VR software, including:
And many more as we grow!
* Refresh rate specs are not finalized
| Butterfly Trackers | SlimeVR v1.2 | FluxPose | Vive | Tundra | Amethyst | HaritoraX 2 | mocopi | |
|---|---|---|---|---|---|---|---|---|
| Developer | SlimeVR | SlimeVR | FluxPose | HTC | Tundra | K2VR Team | Shiftall | Sony |
| Form factor | 6× 10 g trackers | 5× 50 g trackers | 3× 15 g trtackers + 1x 85 g beacon | 3× 75 g trackers | 3× 50 g trackers | Central camera | 6× 17g trackers | 6x 8g trackers |
| Battery Life | 48+ h | 20 h | <24h | 7.5 h | 7 h | ∞ | 50 h | 10 h |
| Base station | No (own 2.4Ghz dongle) | No (Wi-Fi) | No (own 2.4Ghz dongle) | SteamVR Lighthouse | SteamVR Lighthouse | Kinect | No (Bluetooth or own 2.4Ghz dongle) | No (Bluetooth) |
| Prone to occlusion | No | No | No | Yes | Yes | Yes | No | No |
| Coverage | 360° | 360° | 360° | 360° | 360° | 360° | 360° | 360° |
| Precision | 1-5 cm ¹ | 1-5 cm ¹ | < 5 mm | < 1 mm | < 1 mm | 1-10 cm | 1-10 cm ¹ | 1-20 cm |
| Latency | < 15 ms | ~15 ms | < 15 ms | ~15 ms | ~15 ms | ~20 ms | ~15 ms (with dongle), >15 ms (Bluetooth) | 50+ ms |
| Update rate | 100-200 Hz² | 100 Hz | 50-300 Hz | 90-144 Hz | 90-144 Hz | 30 Hz | 50-100 Hz | 50 Hz |
| Range | > 10 m | Wi-Fi coverage | Unknown | 10 m | 10 m | 2-4 m | Bluetooth / dongle coverage | Bluetooth coverage |
| Can track any object | No | No | Yes | Yes | Yes | No | No | No |
| Open Source | SW + HW | SW + HW | Drivers | No | No | SW | No | No |
| Price | $279 | $219 | ~$450 | $390 + ~$400 Lighthouse | $360 + ~$400 Lighthouse | ~$30 (used Kinect) | $299 | $450 |
¹ The precision of SlimeVR, HaritoraX & mocopi tracking technology depends on your setup, on the plane used for measurement, and on how your back bends.
² Refresh rate specs are not finalized
Since our original campaign began in 2021, a whole industry of IMU-based VR body trackers has emerged and matured, with many manufacturers offering their own solutions, as well as dozens of third-party SlimeVR-compatible trackers. Despite that, we believe that SlimeVR is still the leader in the space.
Here are a few things that we have that others don’t:
Butterfly Trackers add even more unique and important features:
For Butterfly Trackers, we decided on a more flexible sets system than we used for SlimeVR Trackers. To simplify fulfillment, we’re selling each part of the set separately: trackers, dongles, straps, chargers, and accessories (with the exception of the Special Edition Sakura Set).
For better experience, you can still purchase Butterfly Trackers in set bundles. When you add a set to your cart, all items that set is comprised of will be added to your cart. If you wish to buy spare parts or to combine Butterfly Trackers with the previous generation of SlimeVR Trackers, you can do so in the Set Upgrades section or Replacement Parts section.
We have prepared a few set bundles that include everything you need to use Butterfly Trackers. We strongly recommend that you purchase one of the sets, and not try to build your own to avoid mistakes! In the list of products below you can find the recommended bundles with their descriptions and possible uses in gaming and motion capture.
The base set of six trackers is sufficient to cover lower-body movement (legs, hip, and chest) and is widely supported by VR games and applications when used with a headset. With SlimeVR, you can customize your experience in VRChat, Resonite, and LIV. By adding extra trackers, you can finely track additional body parts such as the feet, elbows, and more! And if you plan to use SlimeVR for motion capture, you can utilize up to 20 tracking points: chest, upper chest, waist, hip, thighs, ankles, feet, shoulders, upper arms, lower arms, hands, neck, and head.
We no longer recommend a set of five trackers, as the tracking quality with six trackers is far better than with only five.
To celebrate our lead designer’s love for everything pink, we’re offering a special edition translucent pink set of Butterfly Trackers! It includes everything from Full-Body Set Bundle plus a charging station. The trackers come in translucent pink and in special packaging! This is a limited edition that will be discontinued in the future, but we don’t have timelines on this yet.
Do you already have trackers (for example, original SlimeVR trackers)? You can purchase a few Butterfly Trackers to track additional tracking points. You will need a dongle to use Butterfly Trackers! Each dongle supports up to 10 Butterfly trackers connected simultaneously!
See the Set Upgrades tab in the list of products below for the recommended upgrade bundles, their descriptions, and possible use-cases.
We offer several accessories for purchase in the Accessories & Parts tab in the list of products below. The Charging Dock allows you to conveniently charge 10 trackers at the same time without removing them from straps, Iron-On Patches let you transform your favorite VR clothing into a motion capture suit, and Belt Clips give you the option to wear your Butterfly Trackers on the belt of your pants without the use of a strap.
We will be working with the community to expand on the available accessories, both for sale and for DIY, and encourage you to experiment and make Butterflies your own! We already have a few of the designs on our Printables account for those with access to a 3D printer, and more is to come!
SlimeVR is open hardware driven by open source software, and is released under permissive MIT & Apache 2.0 licenses. 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.
You can find our open-source software and firmware in our GitHub repository. We have guides and schematics for easy DIY, and our community is constantly working 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:
Stay tuned for the official hardware design to be released after it’s finalized. In the meantime, check the community designs if you want to build a set yourself.
Join our wonderful community on Discord to meet other VR hackers or just 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.
Check our site for other links and more information.
SlimeVR includes a two-year manufacturer’s warranty. The warranty starts on the day you receive your products. For any warranty-related questions and claims, visit our Contact Page.
Production SlimeVR PCBs are fabricated and assembled by LZJ PCB, a contract manufacturer we have been working with for multiple years. Each board is tested at their factory and by us after the final assembly. ICOMold is handling injection molding for the tracker cases, and the final assembly is done by our team and Chain Assembly in the Netherlands.
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.
Having produced over 250,000 SlimeVR Trackers, establishing SlimeVR as an experienced mid-scale electronics manufacturer. Still, launching a new product is always a challenge, and involves some risks and unknowns, especially during the times of global supply chain instability.
One of the primary concerns is components supply. Entering 2026, many manufacturers face chip shortages. Even before the campaign started, we had already secured quotes and lead times with our primary chip manufacturers that we depend on - Nordic and TDK, and have identified alternative options for most other components to reduce supply risks. But we can still face longer lead times on both critical and non-critical components which can delay project’s manufacturing.
Ongoing trade wars in the world and changing tariff landscapes could also impact delivery times. We’re budgeting a good margin to be able to cover possible changes in our fulfillment costs, but the world is unpredictable right now. We’re working closely with Mouser and Crowd Supply to make sure that delivery and fulfillment is as smooth as possible.
Certification and antenna tuning is another unknown for this project. We have successfully navigated the process of certifying our previous project with FCC as a wearable RF device, and we know the process and major issues that can occur. But certifying Butterfly Trackers will be a bit more complicated, because we are not using a pre-certified RF module. For certification and tuning we need final design of both PCB and enclosure, so it needs to be started at the later stages and is a primary risk of manufacturing delays.
We will be keeping you updated though Crowd Supply updates and in our socials with any challenges we face, including the process of resolving them, and our delivery estimates if they change.
Do you want more updates? Follow us on the many platforms where we post regularly about this and our other projects development and fulfillment as well as other cool things:
SlimeVR Butterfly Trackers is part of Nordic Community Hub
nRF52833 · Microcontroller and RF IC
Produced by SlimeVR in Rotterdam, the Netherlands.
Sold and shipped by Crowd Supply.
Six Butterfly Trackers, enough to track the position and rotation of your hip, your knees, and your chest, and the position (but not rotation) of your feet.
Eight Butterfly Trackers, enough to track the position and rotation of your hips, your knees, your chest, and your feet.
Ten Butterfly Trackers, enough to track the position and rotation of your hips, your knees, your chest, your feet, and your elbows.
Special edition translucent pink set of Butterfly Trackers. This is the equivalent of getting a Full-Body Set Bundle and Butterfly Charging Dock, but in pink and in special-edition packaging! Everything you need for full-body tracking in VR. Includes ten (10) translucent pink trackers for chest, elbows, hip, knees, ankles, and feet, along with one ten-tracker charging station, ten straps, one translucent pink 2.4 GHz dongle, one USB cable (Type-C to Type-C), one USB Type-A-to-Type-C adapter for use with standalone headsets, one dongle cradle, one instruction manual, and one set of stickers.
A set for Motion Capture enthusiasts. Includes 17 Butterfly Trackers, enough to track the position and rotation of your chest, waist, knees, ankles, feet, upper arms, lower arms, shoulders, hands, and head. Comes with a set of 20 iron-on patches to make a motion capture suit.
Two more trackers for your feet or for hands! Upgrade for your Core Set. You need a Core Set to use it (or a Butterfly Dongle Kit if you want to use it with old SlimeVR sets).
Two more trackers to track your elbows or lower arms! Upgrade for your Core Set. You need a Core Set to use it (or a Butterfly Dongle Kit if you want to use it with old SlimeVR sets).
One more tracker to track your head for use in motion capture. Upgrade for your Core Set. You need a Core Set to use it (or a Butterfly Dongle Kit if you want to use it with old SlimeVR sets).
A 2.4 GHz wireless dongle for connecting up to ten Butterfly Trackers to a host PC, standalone VR headset, or Android phone. Includes one USB dongle, a USB-A-to-C cable, a USB Type-A-to-Type-C adapter, a dongle cradle, an instruction manual, and a set of stickers. One dongle can support up to 10 Butterfly Trackers at the same time!
A plushie of our mascot Nighty! It's a large huggable plush toy made in collaboration with CorgiBeans.
Convenient dock that can charge up to ten (10) Butterfly Trackers simultaneously, and has a dedicated port for the Butterfly Dongle. Includes one USB-A-to-C cable and an instruction manual. Does not include AC adapter. Can be powered from any USB charger or from a PC via USB-C input port. Can be used as a cradle for the Butterfly Dongle.
A set of 20 pre-cut iron-on patches with loops that will grab and hold the hooks on Butterfly Trackers. You can easily iron these patches on to clothing, turning your favorite wear into a VR or mocap suit. Includes instruction manual.
A set of two (2) plastic clips to wear a single Butterfly Tracker on a belt. Each Butterfly Tracker needs two clips to be worn on a belt.
Single Butterfly Tracker with two spare hook patches, and one loop patch. Doesn't include dongle or other accessories. Requires Butterfly Dongle Kit to use!
A single 38 mm × 1100 mm silicone-lined strap suitable for the waist, chest, or hips.
A two-pack of 38 mm × 600 mm silicone-lined straps suitable for thighs or head.
A two-pack of 38 mm × 350 mm silicone-lined straps suitable for ankles, upper arms, or lower arms.
A two-pack of 25 mm × 350 mm silicone-lined straps suitable for feet or hands.
A 2.4 GHz wireless dongle for connecting up to ten Butterfly Trackers to a host PC, standalone VR headset, or Android phone. Includes one USB dongle, a USB-A-to-C cable, a USB Type-A-to-Type-C adapter, a dongle cradle, an instruction manual, and a set of stickers. One dongle can support up to 10 Butterfly Trackers at the same time!
· slimevr.dev · SlimeVR@mastodon.social · officialslimevr · SlimeVR · slimevr.dev · SlimeVR
A small company enthusiastically pursuing the goal of bringing accessible VR to a wide audience.
