Four-motor RC engineering project Revision 1
A custom 1/7 scale, four-motor RC car with one independent brushless hub motor at each wheel, plus ESP32 control, wheel-speed feedback, an inertial sensor, custom suspension, and dual bell-crank steering.
01 / Project overview
Hubba Hubba is a custom hub-motor RC car with four independently driven wheels. The engineering project combines the mechanical, electrical, and embedded-control systems of a 1/7 scale RC car: each wheel uses a separate brushless hub motor and ESC, while an ESP32 processes radio inputs and sensor feedback to command the drivetrain and steering.
Driving media
public/videos/car-pov.mp4.
The radio sends throttle, steering, drive-enable, and torque-vectoring mode requests to the car.
The ESP32 interprets those requests and decides how the steering and four drive motors should respond.
Each wheel can receive its own power command while the steering servo follows the driver's requested direction.
Wheel-speed and motion sensors show how the car actually responds, allowing the controller to correct its path.
02 / CAD assemblies
The viewer contains the full vehicle assembly and an exploded wheel view. The status label identifies an imported model, captured drawing, or generated reference model.
03 / Mechanical motion
The CAD animations show the steering-linkage range and the suspension travel around the hub-motor assembly.
M01 / Steering sweep
The top view shows the two uprights moving through their steering range while the dual bell-crank mechanism and tie rods maintain coordinated wheel angles.
M02 / Suspension cycle
The suspension study cycles one corner through vertical travel and shows the upright and control-arm motion around the hub-motor package.
04 / Vehicle control
The ESP32 reads the radio receiver, wheel-speed sensors, and inertial sensor. It sends independent commands to four ESC channels and one steering servo.
The controller continuously reads throttle, steering, and mode requests from the radio system.
Forward, reverse, and steering requests are converted into PWM commands for the four ESCs and steering servo.
The controller compares requested motion with measured wheel speed and yaw, then adjusts left-versus-right power when assistance is enabled.
These limits reduce abrupt commands and define the controller's failure behavior.
05 / Feedback control
An interactive explanation of the firmware controller: yaw uses proportional-integral feedback and wheel-speed difference uses proportional feedback. Side correction is equal and opposite; full mode can separately reduce both front outputs.
correction = Kpyaw x yaw error + Kiyaw x accumulated yaw error + Kprpm x RPM-delta error
Yaw KpResponds immediately to the difference between requested and measured yaw rate.
Yaw KiBuilds correction when a smaller persistent tracking error remains over time.
RPM KpCorrects left-versus-right wheel-speed mismatch without storing error history.
Full assist active
This one-step visualization isolates equal-and-opposite side correction. The firmware also carries a bounded yaw integral and can separately reduce both front outputs in FULL mode.
06 / Hardware stack
Each wheel has a separate motor and ESC. The ESP32 receives driver input, four wheel-speed signals, and chassis acceleration and rotation data.
DOIT DevKit V1 running ESP-IDF 6.x.
550KV, 12N14P brushless hub drives.
Separate throttle and reverse inputs; exact SKU and permitted battery voltage still require confirmation.
Driver control, software drive-enable, and selectable torque-vectoring modes.
Configured for 208 Hz accelerometer and gyroscope sampling; on-car behavior remains to be validated.
Four hardware-counted RPM inputs; full four-wheel accuracy still needs optical-tachometer validation.
07 / Specifications and results
Measured and planned vehicle performance values. Each completed result includes its units and a short description.
Values without a completed test are labeled Not tested.
08 / Steering demonstration
The limiter reduces the permitted steering angle as speed rises, targeting a maximum predicted lateral acceleration of 1.0 g by default so cornering demand stays within the configured tire-grip envelope.
public/videos/feature-steering-limiter.mp4.
V01 / Steering limiter
The controller estimates vehicle speed from rear-wheel RPM and uses the measured steering geometry to reduce the permitted road-wheel angle as speed rises. With the default 1.0 g ceiling, it is designed to prevent the steering command from demanding more lateral acceleration than the configured tire-grip target.
09 / Firmware
The firmware is divided into modules for radio input, steering, motor control, sensors, torque vectoring, calibration, and monitoring. Each module has a separate hardware or control responsibility.
10 / Live telemetry
This recording shows the earlier bridge-based dashboard receiving live ESP32 telemetry. The current viewer is served directly by the car's ESP32 SoftAP.
public/videos/telemetry-viewer.mp4.
V02 / Live telemetry
The recording shows receiver inputs, wheel RPM, steering geometry, IMU, GPS, torque vectoring, ESC outputs, logging, and guarded configuration panels. The current firmware serves this viewer directly from the ESP32.
11 / Project progress
The firmware and supporting tools are implemented and covered by build, host-test, and browser/mock evidence. Current work focuses on long-duration testing and torque-vectoring gain tuning.