Rock

Simple 3D printed RC car with a brushless drone motor. Drive it from your phone over WiFi, or from a PS5 controller over Bluetooth.

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Demo

Demo.mp4

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Repo

• firmware/controller/ — phone controller (WiFi web UI, runs on XIAO ESP32-S3)
• firmware/controller_ps5/ — PS5 controller (Bluepad32 + ESP-NOW, runs on a classic ESP32)
• firmware/car/ — car code (same for both control modes — the car just listens for ESP-NOW packets, it doesn't care which controller sent them)
• cad/ — fixed printed parts (3mf), print as-is

Customizable printed parts (chassis, wheels, knuckles, bearing inserts, spur gear) live on MakerWorld — pick the variant that matches your bearings and shaft size: https://makerworld.com/en/models/2819296-rock-small-brushless-rc-car

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Parts

Electronics

• ReadyToSky MT2204 2300KV brushless drone motor
• EMAX Bullet 20A BLHeli-S ESC
• MG90S servo
• Car: LilyGO T-Energy S3
• Controller (phone mode): XIAO ESP32-S3
• Controller (PS5 mode): a classic ESP32 with Bluetooth Classic — e.g. DFRobot FireBeetle 2 ESP32-E, or any ESP-WROOM-32E dev board. Not an ESP32-S3 or C3 — those are BLE-only and Bluepad32 needs Bluetooth Classic.
• 2S 7.4V 1800mAh LiPo, T-plug (Reely)
• T-plug pigtail
• Wire

Pick one controller mode. You only need one transmitter ESP32, not both.

Drivetrain

• 10T pinion (store bought, fits motor shaft)
• 58T spur gear (printed)
• 1/4" (6.35 mm) square steel drive shaft
• 4x flanged ball bearings (~22 mm OD x ~7.6 mm ID x ~7 mm wide)
• 4x shaft collars for 1/4" square shaft

3D printed parts

From this repo (cad/) — print as-is:

• battery cover
• electronics cover
• steering link

From MakerWorld — pick the variant matching your hardware (bearing size, shaft size):

• chassis
• wheel (×4)
• knuckle (×2)
• bearing insert (×4)
• spur gear 58T

Hardware

• M3 heat set inserts, screws, nuts
• 4x rubber tires for the printed wheels

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Wiring

Car ESP32:

ESC signal   -> GPIO 9
Servo signal -> GPIO 10
Servo V+     -> 5V (ESC BEC)
ESP32 5V     -> 5V (ESC BEC)
GND          -> GND

GPIO numbers refer to the ESP32 GPIO scheme, not silkscreen pin numbers. If you flash on a different ESP32 variant, check the board's pinout — GPIO 9/10 may map to a different physical pin.

LiPo to ESC via T-plug. Don't run USB and BEC into the ESP32 at the same time.

Controller is on USB. No wiring.

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Assembly

Do these in order.

1. Knuckle prep

• Press bearings into each knuckle.
• Slide the square steel shaft through and fit the square inserts.
• Secure the wheels on the shaft with the shaft collars.

2. Motor

• Drop the motor into its mount area behind the chassis.
• Screw it down with the screws that match your motor's hole pattern (varies by motor).

3. Knuckle to chassis

• Orient each knuckle so the extra hole — the one for the steering link — faces inward (toward the center of the car) and up.
• Attach with one M3 screw on top and one on the bottom. Heat-set inserts live in the top mount, not the knuckle, so the screws pass through clearance holes in the knuckle and thread into the mount above.
• Snug, not gorilla. Don't over-tighten or you'll deform the print.

4. Steering link to servo

• Bolt the steering link to the horn hole ~13 mm from the servo spline center, with the servo's wire connector facing down and the horn sitting on top of the link.
• Press the horn-link assembly onto the servo spline.

5. Steering link to knuckles

• Connect each end of the link to its knuckle with an M3 screw. This is the one joint where the heat-set insert lives in the knuckle itself — A-arm / shaft link exception to the rule above.

6. Wires

• Run servo + ESC wires through the routing channel on the chassis before screwing the cover down, otherwise they stick out and snag.

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Flash

Arduino IDE, esp32 core 2.0+ from Boards Manager.

The car firmware is the same regardless of which controller you use — flash car.ino once and forget about it. Pick one controller below.

Car (firmware/car/)

Open firmware/car/car.ino, pick your LilyGO T-Energy S3, upload (LiPo unplugged).

ESC setup is a one-time thing — done with BLHeli Suite via an Arduino Nano running the BLHeli passthrough sketch.

Phone controller (firmware/controller/)

Board: XIAO ESP32-S3.

Libraries:

• ESP32Servo
• WebSockets (Markus Sattler)

Open firmware/controller/controller.ino, pick your board, upload.

Want a different WiFi name or password? Change them in controller.ino before flashing.

PS5 controller (firmware/controller_ps5/)

Board: a classic ESP32 (FireBeetle 2 ESP32-E or any ESP-WROOM-32E dev board).

One-time setup:

1. File → Preferences → Additional Boards Manager URLs, add:

   https://raw.githubusercontent.com/ricardoquesada/esp32-arduino-lib-builder/master/bluepad32_files/package_esp32_bluepad32_index.json

2. Tools → Board → Boards Manager → search bluepad32 → install esp32_bluepad32 by Ricardo Quesada.
3. Tools → Board → ESP32 + Bluepad32 Arduino → ESP32 Dev Module. Use the Bluepad32 group, not the regular esp32 group — that's what gives you DualSense support.

Open firmware/controller_ps5/controller_ps5.ino and upload.

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Drive it

Phone mode

1. Power the phone controller.
2. Phone WiFi → ROCK_RC, password 12345678.
3. Browser → http://192.168.4.1
4. Power the car. UI shows "Car: Connected".
5. Left stick throttle, right stick steering. Show Settings for trim, max speed, ramp step.

PS5 mode

1. Power the PS5 controller ESP32.
2. On the DualSense, hold the PS button + Create button until the light bar starts flashing rapidly.
3. ESP32 picks it up automatically — you'll feel a connection buzz, then 1–5 short pulses indicating the current max-speed level (1 pulse = 20%, 5 pulses = 100%).
4. Power the car. Drive.

Two drive modes — toggle with Circle:

• Stick mode (default): left stick = throttle, right stick X = steering
• Trigger mode: R2 = forward, L2 = reverse, right stick X = steering

Full mapping:

Input	Action
Left stick Y	Throttle (stick mode)
Right stick X	Steering (both modes)
R2	Forward (trigger mode)
L2	Reverse (trigger mode)
Circle	Toggle stick / trigger drive mode
D-pad up	Max speed +20% (range 20–100%)
D-pad down	Max speed −20%
D-pad left	Steering trim −1° (range ±30°)
D-pad right	Steering trim +1°
Triangle	Ramp step −1 (smoother / slower acceleration)
Cross (X)	Ramp step +1 (sharper / faster acceleration)

Vibration feedback:

• Connection: one buzz + 1–5 pulses (current max-speed level)
• Mode toggle (Circle): single stronger buzz
• Max-speed change (D-pad up/down): pulse pattern showing new level
• Trim / ramp change: short rumble

If pairing gets cursed (controller refuses to reconnect), set FORGET_BT_KEYS_ON_BOOT = true in controller_ps5.ino, flash, boot once, then set it back to false and flash again.

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Safety

LiPo batteries are fire hazards if you mistreat them. Charge with a proper LiPo balance charger, ideally in a LiPo-safe bag. Don't puncture, don't overcharge, don't leave on charge unattended.

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Tuning

If forward/reverse or left/right is swapped:

• In car.ino — swap ESC_FORWARD / ESC_REVERSE, or SERVO_LEFT / SERVO_RIGHT (90 = center).
• In controller_ps5.ino — flip the INVERT_THROTTLE or INVERT_STEERING constants near the top.

Trim, max speed, and ramp step are adjustable live — sliders in the phone UI, D-pad / Triangle / Cross on the PS5 controller (see mapping table above).

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TODO

• Wiring diagram image
• Battery voltage in UI
• Proper retention for battery / ESC / ESP32 (snap-fit or clamps instead of tape)
• Assembly photos / exploded view

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License

• Code (firmware/): MIT — see LICENSE
• CAD (cad/): CC BY-SA 4.0 — see cad/LICENSE