SlimeVR 101

What is SlimeVR?

SlimeVR is a low-cost solution to full-Body tracking in virtual reality. It uses forward kinematics to build a model of your skeleton calculated from the rotation of each individual tracker, with your headset and controllers being the only absolute known position.

Because the headset is the only required absolute data point and that the rest of the skeleton is derived from it, SlimeVR does not require lighthouses or other forms of additional tracking to model your movement. SlimeVR uses data from Inertial Measurement Units (IMU) to determine the rotation of each tracker, and the number of IMUs used determines how many tracking points are available.

How many trackers do you need?

Depending on how you plan to use FBT in VR, choose one of the following options:

• Lower-Body Set (5 IMUs) - Your spine, knees and feet are positionally tracked. Any bending of the lower spine will have issues with tracking, and the orientation of your feet will not be tracked.
• Core Set (6 IMUs) - In addition to the previous set this adds another tracker on the spine. This allows for much more accurate and stable tracking while laying down, sitting or even just bending over.
• Enhanced Core Set (8 IMUs) - In addition to the previous set, you can now also wiggle your peets! If you plan on lying or sitting down a lot this can add a lot of emotiveness to your poses.
• Full-Body Set (10 IMUs) - In addition to the previous set, this allows you to move your elbows independently from your controllers in VR. Useful for dancers or for additional immersion.
• Deluxe Tracker Set (16 IMUs) - This set can be used for motion capture without the use of any VR gear, can be split into 2 Enhanced Core Sets, or just to have extra trackers.

If you look at the GIF above, each line there represents a tracked "bone". The more points of rotation you add, the more defined the final tracking will be. As an example, the GIF above uses the "Core Set" and as such, there is no foot rotation.

For more visuals on what these tracking options look like, watch this video:

What is an extension?

An extension is a singular auxiliary IMU attached to a primary tracker and placed at another location. This allows you to build a secondary tracker without the need for an extra battery, charge board and microcontroller. These are sometimes referred to as AUX trackers (auxiliary trackers).

Extensions allows a tracker to give accurate detail between two bend points that sit close to each other, such as tracking both the lower leg and the foot without needing another tracker that needs to communicate and be charged separately.

Devkit picture by erimel

The length of the extension is dependent on the cabling used to connect them (shorter than 80cm is a safe range). For more information please check the tracker schematics page.

The suggested extension locations are:

1. A chest extension attached to the hip tracker.
2. A left foot extension attached to the left ankle tracker.
3. A right foot extension attached to the right ankle tracker.

On the Crowd Supply store page and on our discord server, you may find a notation that specifies the number of primary and auxiliary IMUs with a plus sign. For example, the Enhanced Core Set noted above would be called a 5+3 set up, which consists of 5 microcontrollers and 8 IMU. For a better visual on how this looks when on a person, please check the recommended mounting points section of the server set up.

Please note: Building extensions is not necessary, as the foot and chest trackers will work as standalone trackers if you prefer. However, these docs assume that you are building them as extensions.

Created by calliepepper. Edited by spazzwan. Video created by zrock35