Concept visualization of a bodyless four-hub-motor RC car chassis on an engineering workbench

Educational engineering project Revision 1

Hubba
Hubba

A 1/7 scale electric RC car with four independent hub motors, ESP32 control, wheel-speed feedback, an inertial sensor, and custom suspension and steering systems.

System overview CAD models

Rendered view of the chassis and four-motor layout.

4Independent hub motors

550KVMotor rating

50AESC at each wheel

200 HzMotion sensing

01 / Project overview

System overview

This educational project documents the mechanical, electrical, and embedded-control systems of a 1/7 scale RC car. Each wheel uses a separate brushless hub motor and ESC. An ESP32 processes radio inputs and sensor feedback, then commands the drivetrain and steering.

DrivetrainIndependent electric drive at all four wheels

ControlCustom motor, steering, and shutdown logic

FeedbackIndividual wheel speed and chassis motion

Driving video

Onboard POV video

Camera footage from inside the car shows the four-motor system in action during a driving test.

POV driving video not added Place the MP4 file at public/videos/car-pov.mp4.

01Driver input

The radio sends throttle, steering, shutdown, and driving-mode requests to the car.

02Vehicle control

The ESP32 interprets those requests and decides how the steering and four drive motors should respond.

03Independent drive

Each wheel can receive its own power command while the steering servo follows the driver's requested direction.

04Live correction

Wheel-speed and motion sensors show how the car actually responds, allowing the controller to correct its path.

02 / CAD assemblies

CAD models

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.

Procedural preview

Drop a GLB model

03 / Mechanical motion

Motion studies

The CAD animations show the steering-linkage range and the suspension travel around the hub-motor assembly.

M01 / Steering sweep

Front steering geometry

The top view shows the two uprights moving through their steering range while the rack and tie rods maintain coordinated wheel angles.

View: Top
Duration: 5.8 seconds
Observed: Linkage travel

04 / Vehicle control

Control architecture

The ESP32 reads the radio receiver, wheel-speed sensors, and inertial sensor. It sends independent commands to four ESC channels and one steering servo.

Radio controls Driver input and mode selection

Driver requests

ESP32 controller Input processing and feedback control

Motor + steering commands

FLFRRLRR ESC + hub motor

Wheel speed + chassis motion

Driver connection

The controller continuously reads throttle, steering, and mode requests from the radio system.

Output commands

Forward, reverse, and steering requests are converted into PWM commands for the four ESCs and steering servo.

Active feedback

The controller compares requested motion with measured wheel speed and yaw, then adjusts left-versus-right power when assistance is enabled.

Electrical design

Complete wiring map

Control limits

Acceleration rampOutput increases progressively to limit sudden torque changes

Deceleration rampOutput decreases faster than it increases

Direction interlockDirection changes pass through zero output

Radio failsafeLoss of the receiver signal sets motor output to zero

Sensor fallbackInvalid sensor data returns all four motors to equal output

These limits reduce abrupt commands and define the controller's failure behavior.

05 / Feedback control

Torque-vectoring control

An interactive explanation of the firmware controller: yaw uses proportional-integral feedback, wheel-speed difference uses proportional feedback, and total requested power is preserved.

correction = Kp_yaw x yaw error + Ki_yaw x accumulated yaw error + Kp_rpm 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.

This is closed-loop PI control for yaw plus P control for side RPM difference. There is no derivative term in the current design.

Steering+24% Left Center Right Base throttle52% 5% Command 95% Measured yaw+8 deg/s Left IMU Right Left/right RPM delta+3% Right faster Feedback Left faster

Full assist active

FL52%

FR52%

Front

0.0% side correction

RL52%

RR52%

Target yaw: 0.0 deg/s
Yaw error: 0.0 deg/s
Mean power: 52.0%

One-step visualization. The firmware also carries a bounded yaw integral through time.

06 / Hardware stack

Hardware components

Each wheel has a separate motor and ESC. The ESP32 receives driver input, four wheel-speed signals, and chassis acceleration and rotation data.

Controller

ESP32-WROOM-32

DOIT DevKit V1 running ESP-IDF 6.x.

Motors / 4x

Skywalker 2820SL

550KV, 12N14P brushless hub drives.

ESCs / 4x

Skywalker 50A V2

Separate throttle and reverse signal inputs.

Radio system

RC6GS V3 + R7FG

Driver control, shutdown, and selectable driving modes.

Motion feedback

ISM330DHCX

208 Hz accelerometer and gyroscope configuration.

Speed feedback / 4x

HW86060041

Individual motor-speed measurement at every wheel.

07 / Specifications and results

Performance measurements

Measured and planned vehicle performance values. Each completed result includes its units and a short description.

Scale1/7

Drive layoutFour-motor AWD

Motor rating4 x 550KV

Motor control4 x 50A ESC

Values without a completed test are labeled Not tested.

08 / Firmware

Firmware architecture

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.

Power on System check Ready Driving

Radio inputReads and validates driver controls

SteeringRelays the requested wheel direction

Motor controlCoordinates four independent drive units

Sensor feedbackTracks wheel speed and chassis rotation

Torque vectoringBalances straight-line and cornering response

Laptop toolsCalibration, monitoring, and live configuration

USB serial / 115200 baud

09 / Project progress

Project status

The control firmware is operational. Current work covers sensor validation, repeatable full-car tests, and calibration of the torque-vectoring controller.

Completed features

Forward and reverse with a direction-change zero hold
Steering-servo pass-through with centered signal-loss fallback
Four independent throttle and reverse outputs
Saved radio calibration and adjustable driving settings
Remote shutdown and receiver-loss handling
Wheel-speed sensing, motion sensing, and torque-vectoring modes
Laptop serial calibration and monitoring tools

Next build milestones

Confirm reliable wheel-speed feedback from all four motors
Compare RPM conversion against an optical tachometer
Verify motion-sensor orientation and vibration performance
Validate every radio control with the installed receiver
Verify steering endpoints on the installed servo
Confirm reliable startup with the full electrical system connected
Tune straight and full assist at low authority

Next test phase Complete low-power system checks, then begin controlled one-motor and four-motor testing.