What is Slime VR?
Full Slime VR set
Inside of Slime VR without auxiliary IMU
Slime VR is a set of open hardware sensors and open source software that facilitates full-body tracking (FBT). It is the most cost efficient solution for full body tracking available in the market by today, March 17th, 2023. I always wanted to get a FBT but I already have Quest 2 which is not FBT and Vive is expensive. Slime VR is aiming general public as consumer and I believe VR/AR/MR should targetting general public as the main consumer while not excluding enthusiasts. Therefore, I made Slime VR by myself to see what is it like and learn how to do solder and read schematics.
Other FBT options
This is a comparison of available FBT by Slime VR. Slime VR is cost efficient. Furthermore, because it is using IMU instead of base station, Slime VR can be mounted under clothes. A user can go under the blanket and keep the tracking alive.
Resources for Slime VR
Slime VR DIY documentation can be found here. This is an open source project. Therefore, the documentation itself might not be up to date. I highly recommend to check their discord to receive up to date information and issues. Before going into my comments, please read Slime VR Components Guide.
This is the list of components I have used
| Components | Choice | Note |
|---|---|---|
| Microcontroller | Wesmos D1 Mini | It is using ESP 8266 |
| IMU | MPU 6500 | Precision of 1-10cm |
| Batteries | 1800 mAh 804040 Li-Po | 30 - 40 hrs using time |
| Charging Board | TP4056 USB | |
| Power Switches | SS22F32 switches | |
| Diodes | 1N5817 | Enables using while charging. Recommended for safety |
| Resistors | 180K ohm | |
| Wiring for extenstions | JST connectors 5 pins | Get something at least 20 cm |
| Straps | Generic | Make sure it fits into your case |
Wesmos D1 Mini is the standard for Slime VR. It is using ESP 8266. Mind that the C-USB on Wesmos D1 Mini is not going to be used for Slime VR. The schematics on Slime VR DIY documentation was different from what I have got. If what yours are different from their schematics, please go through GPIO and its description to figure out which pin is which. MPU 6500 is notorious for being defective. Fortunately, I have got 10 pieces and they all worked fine. I advise you to check if they are working on breadboard before solder them in. Battery for 804040 Li-Po has enough capacity for Slime VR. I have not seen it being empty yet. Charging board, TP4056 USB sometimes comes with extra margins. You might have to cut it or redesign your case accordingly. Get Straps at the last step or at least after designing cases. Diodes are optional but recommended. By connecting diodes from TP4056 USB charging board to Wesmos D1 Mini microcontroller, you can use Slime VR while charging. 180K ohm resistor is optional but recommended. By connecting the resistor between the battery and the microcontroller Slime VR Server will tell you how much battery is left.
Schematics
This is the schematics based on the components I have used. Check Slime VR Schematics documentation to find schematics that matches your components. Please mind the direction of diodes matters while the direction of resistor does not matter. Also mind that the order of power(VCC) from MPU to AUX Sensor and then the pin ADD matters.
Challenges
- I did not know how to use Platform IO nor read C. Now I have some ideas.
- It took me 3 weeks to build it. It was during midterms at UVIC. I did not get enough sleep but I couldn’t wait any longer.
- I do not have many people to ask about it except Slime VR discord. Perhaps I sould build a club.
What have you learned?
Soldering Slime VR at AUVIC/UVEEC Soldering Station
John Carmack said
I sometimes wonder if younger people these days have the same relationship with books that I do where they were such a cornerstone for me in so many ways. But that sense that I always wanted to know it all. I know I can’t. And that was like one of the last things I said. You can’t know everything, but you should convince yourself that you can know anything. Any one particular thing, it was created and discovered by humans. You can learn it. You can find out what you need on there.” - John Carmack ex-CTO Oculus VR during Lex Fridman Podcast
This inspired me to learn as much as I can about Virtual Reality. Slime VR is a decent project to initiate my knowledge in firmware. Software developer can not stay on high level language. It is necessary for us to jump on anything and learn to solve problems we are facing. Currently, I have no idea how to design PCB boards or build architecture. I hope what I have learned from this project could be useful in the future for the VR industry.
Slime VR official documentation
https://docs.slimevr.dev/index.html