wheels

Two silicone wheels you can stick things between.

Demo (NSFW): https://files.catbox.moe/9yxkkc.mp4

How to build

I wouldn't recommend building it yet. This is still in its PoC stage, and there is a lot of potential for improvement. That said, it is already perfectly functional, and if you'd like to try it, here's how to make one.

Parts

ESP-32 dev board (the diagram shows the 38-pin variant, but the 30-pin variant should also work if you change the wiring accordingly)
two high-torque (> 10 kgf·cm) analog continuous rotation servos (I used Feetech FS5113R)
two servo discs compatible with your servos, with 4x M3 mounting holes and a mounting hole spacing of 14 mm (or change the screw_holes, screw_hole_r and screw_hole_offset parameters in wheel.scad to match whatever you have)
low-impedance 1000 uF capacitor
5V power adapter with enough max current to power the servos and the ESP. Multiply the stall current of your servo by two, and add 1 A. That's how many amps you will need. For my FS5113R servos, I needed a 4 A supply.
power plug for the adapter
1x frame.stl
1x vessel.stl (might need two if it breaks during unmolding)
2x ring.stl
2x wheel.stl
2x mold.stl
at least 200 ml of skin-safe silicone casting gel with a hardness of 00-20 or softer (I used Ecoflex 00-20)
duct tape
two zip ties
breadboard and M-M jumper wires

Wheels

Put a wheel.stl, two mold.stls and two ring.stls into a vessel.stl (one ring goes to the bottom, one to the top at the end, the rest will only fit one way). Make sure to grease every surface with vaseline beforehand except wheel.stl and the outside of vessel.stl.

Secure everything into vessel.stl by wrapping a strip of duct tape around it.

Prepare 100 ml of the silicone and fill vessel.stl to the brim. Pour it slowly in a thin stream to avoid bubbles. Carefully unmold when ready. You should end up with a silicone tire around wheel.stl. Repeat for the other wheel. You can reuse every part except wheel.stl.

Screw the servo discs onto the outer side of each wheel. The screws go in from the inside of the wheel.

Circuit

You might have to solder the power plug to some jumper wires. In that case, mind the polarity. Center pin is usually the live one, but definitely test with a multimeter before connecting.

Firmware

Upload firmware.ino to the ESP-32 using the Arduino IDE. You'll need to install the ESP-32 standard libraries and the ESP32Servo library.

While flashing the firmware, you might need to hold the BOOT button on the ESP-32.

Final Assembly

Put the two servos in frame.stl. Secure each with a zip tie (the grooves on the frame are for holding the zip ties).

Screw each wheel on a servo through the servo disc.

Finally, connect each servo to the circuit. Mind the wiring (usually, brown = GND, red = 5V, orange = pulse).

How to use

The device boots up when you connect it to the power supply, like the Handy. You'll need to pair it with your PC via Bluetooth to use it.

The bridge.exe program connects the device to Intiface via WSDM. Right now this only works with Intiface Engine; you'll get weird connection drops if you try it with Intiface Central.

Copy buttplug-user-device-config.json into the directory where intiface-engine.exe is, then cd into the same directory and run:

.\intiface-engine.exe --websocket-port 12345 --use-device-websocket-server --user-device-config-file .\buttplug-user-device-config.json

With both intiface-engine and bridge running, the device should now appear in Intiface clients as two Synchro devices, each corresponding to a wheel. If you're using LoveMachine, you can assign a different body part to each wheel and simulate some pretty complex movements.

Longer term we would probably want to emulate a two-rotator device like a UFO Tw and bypass WSDM entirely, but LoveMachine can't control device features independently yet, so this setup is more featureful for the time being.

Based on personal tests, I recommend a thick lube with lots of humectant so it won't dry out that fast.

You can adjust the clearance between the wheels through the spacing parameter in frame.scad. In future releases I should try to make this mechanically adjustable or spring loaded so that you won't have to waste plastic trying to find the ideal size.

How to clean

Unscrew the wheels from the servos before cleaning. Clean with warm or lukewarm water and soap. Drying should be easy since every surface is exposed to air. Do not attach them to the device until completely dry.

Sauceke/wheels