IMU 9-Axis Gyro Sensor

Driving straight and turning precise angles depends on the gyro. Ordinary gyros have two old problems: they must be mounted flat, and the heading slowly drifts over time.

The MBC IMU combines 6-axis inertial sensing (gyroscope + accelerometer) with a magnetometer and offers three heading algorithms:

• 3D-compensated heading (Gyro3D): detects the mounting orientation automatically, so the heading is correct at any mounting angle. Use this first.
• Compass-fused heading (GyroWithCompass): the magnetometer corrects the gyro's accumulated error — no drift over long runs.
• Single-axis gyro + magnetometer heading: classic single-axis heading, plus a heading computed from the magnetometer alone (relative: 0 at power-on or reset, not a north-referenced bearing).

• Mount at any angle: the mounting axis is captured automatically — upright, sideways or upside down
• 📉 No long-run drift: the compass-fused heading keeps correcting gyro error
• Works as the official EV3 gyro: read it with the standard gyro blocks in the EV3 software
• 🔘 Button calibration: separate buttons for accelerometer and magnetometer calibration, stored on the device
• Full 9-axis data: raw angular rate, acceleration and magnetic field on all three axes

In the official EV3 software, use the standard gyro block; each mode maps to:

EV3 gyro block mode	Function	Notes
Angle	Gyro3D 3D-compensated heading	Preferred; any mounting angle
Rate	GyroWithCompass fused heading	No drift over long runs; unreliable in distorted magnetic fields
Angle and Rate	Single-axis gyro, magnetometer heading	Classic single-axis heading and magnetometer heading (relative, not north-referenced)
Reset	Reset all angles	All three headings reset together

Warning

The magnetometer is affected by motors, steel tables, speakers and other magnetic sources. In magnetically noisy places, use Gyro3D.

Note

In EV3 Classroom the Angle and Rate blocks behave as in the table above ("Rate" returns the fused heading, not degrees per second). In Pybricks (EV3), GyroSensor.angle() returns the single-axis gyro heading and speed() returns the magnetometer heading (relative, not north-referenced); reset_angle(0) works normally; after calibrate() it takes about 3.5 s before readings come back (same as the LEGO gyro). For angular rate (degrees per second), read mode 2 with LUMPDevice (see example 7). On ev3dev, speed() returns the fused heading.

Tip

Tested on the stock EV3 firmware (2026-11-02): detected as the LEGO gyro sensor, the stock gyro reset block works, all 7 modes read correctly, and 300 mode switches plus continuous reading never dropped the connection. ev3dev: supported.

Push the plug all the way in, in one go. If the EV3 detects the wrong device (NXT I2C or Energy Meter), unplug it and plug it back in.

The same IMU board can also be shipped with a magnetometer-only "compass" firmware: the EV3 gyro block's "angle" then returns the magnetic bearing 0-359 (absolute, north-referenced, not relative to power-on), and "rate" is always 0. Use it when you only need "which way am I facing" (maze backtracking, field orientation) and do not want to reset.

• EV3 mode only for now; choose "IMU heading" or "compass" firmware when ordering, or send the unit back to be re-flashed.
• The magnetometer is still affected by motors and steel field parts; run the magnetometer calibration (button, stored on the device) before use.

Platform	How
LEGO MINDSTORMS EV3	EV3-G (EV3 Lab, standard gyro blocks) / EV3 Classroom / clev3r: tested on the stock EV3 firmware (2026-11-02); Pybricks v4: tested (2026-11-02); ev3dev / EV3 MicroPython v2: supported (same mode table as the stock firmware)
LEGO SPIKE Prime / Robot Inventor	Not available
LEGO SPIKE Essential	Not supported
Arduino / ESP32 / Raspberry Pi	Universal I2C (address 0x6A); tested on Arduino Nano (2026-11-02)
MATRIX Mini R4	I2C; tested with the stock library (2026-11-02)

See the MBC Universal I2C Protocol for shared rules and Arduino helpers. All axes are in the sensor body frame; headings are in 1° and read 0 at power-on or after a reset.

• Heading direction: seen from above, turning right (clockwise) makes the value bigger. It keeps adding up (two turns = 720) and does not wrap to 0359; to get 0359, use ((h % 360) + 360) % 360. Past ±32767 it wraps around. All three headings are relative (not north-referenced compass angles).
• Power-on: keep it still for about 0.5 s; 0x32 bit0 (ready) only turns 1 after that. The heading resets to 0 automatically at power-on.

Tip

No coding experience? No problem: see the Arduino Examples. Every example can be copied and uploaded right away, with an English note on every line.

Register	Dir	Len	Content
0x10	W	1	0x01 = reset heading (wait 30 ms after writing before reading)
0x11	R	6	Heading bundle (= 0x12 ~ 0x14)
0x12	R	2	Single-axis gyro heading int16, degrees
0x13	R	2	3D-compensated heading (Gyro3D) int16, degrees
0x14	R	2	Gyro + magnetometer fused heading int16, degrees (relative, 0 after a reset)
0x20	W	1	0x01 / 0x02 start / stop accelerometer calibration; 0x03 / 0x04 start / stop magnetometer calibration
0x21	R	18	9-axis bundle (= 0x22 ~ 0x24)
0x22	R	6	Angular rate X / Y / Z int16, 0.1 °/s (right-hand rule: counterclockwise is positive when you look from the positive end of the axis, so with Z pointing up a right turn is negative, the opposite sign of the heading)
0x23	R	6	Acceleration X / Y / Z int16, mg
0x24	R	6	Magnetic field X / Y / Z int16, mG (calibrated)
0x32	R	1	bit0 ready, bit1 stationary, bit2 mounting axis captured, bit3 mounted too tilted, bit4 accel calibrating, bit5 mag calibrating, bit6 fusion initialized, bit7 mag auto-calibration converged
0x34	R	1	Magnetometer trust 0 ~ 255
0x35	R	1	Magnetic disturbance level (unit 0.01° per update, max 255)
0x36	R	1	Face pointing up (0 = +X, 1 = +Y, 2 = +Z, 3 = -X, 4 = -Y, 5 = -Z)

// Read the three headings
uint8_t d[6];
if (iicRead(0x6A, 0x11, d, 6)) {
  int16_t gyro1D = (int16_t)(((uint16_t)d[0] << 8) | d[1]);
  int16_t gyro3D = (int16_t)(((uint16_t)d[2] << 8) | d[3]);   // recommended: grows when turning right
  int16_t fused  = (int16_t)(((uint16_t)d[4] << 8) | d[5]);   // fused heading (relative, not north)
}
iicWrite(0x6A, 0x10, 0x01);                          // reset heading
delay(30);                                           // wait for the reset to take effect before reading