CHR-6d Inertial Measurement Unit

This six-DOF IMU from CH Robotics packs three accelerometer axes, three gyroscope axes, and a STM32F103T8 ARM Cortex processor into a tiny, 0.8" x 0.7" x 0.1" board. The small size and light weight (1.5 g) make the board well suited for unmanned aerial vehicle (UAV) navigation. The integrated 32-bit MPU takes 16-bit readings of the sensors, applies a customizable filter, and reports the results via a TTL serial interface. The Cortex's programming pins are exposed, and the firmware is open-source.

Overview

The CH Robotics CHR-6d inertial measurement unit (IMU) uses a 32-bit STM32F103T8 ARM Cortex processor to take 16-bit ADC readings from an ADXL335 three-axis accelerometer, a LP510AL pitch/roll rate gyro, and a LY510ALH yaw rate gyro, providing a full six degree of freedom (6-DOF) measurement solution. The Cortex processor applies a customizable finite impulse response (FIR) digital filter to help reduce noise and makes the results available via a simple TTL-level (3.3V with 5V-tolerant pins) serial interface at baud rates up to 115,200 bps. A USB-to-serial adapter can be used to connect the IMU to a computer running the free IMUkit PC application, which can be used for data visualization and settings configuration, or you can use the CHR-6d IMU Development Kit, which provides everything needed to connect the this IMU to a PC via an RS-232 serial port, visualize data in real-time, configure IMU settings. The Development Kit also makes it easier for advanced users to develop custom firmware.

Update: Units are now being shipped with firmware version 2.0, which adds an on-board Extended Kalman Filter (EKF) for automatic pitch and roll angle estimation.

Note that the board's pins are spaced 2 mm apart, so the board will not work with standard 0.1" headers or breadboards.

Product Comparison

We offer several inertial measurement and orientation sensors made by CH Robotics. The table below compares their capabilities:

Product Name	Sensors			Estimation				Other
	Gyros (3x)	Accels (3x)	Mag (3x)	Roll	Pitch	Yaw	Quaternion	Enclosure
CHR-6d IMU
CHR-6dm AHRS
CHR-UM6 Orientation Sensor

Features

• On-board EKF for pitch and roll angle estimation (firmware version 2.0+ only)
• 3 gyro axes and 3 accelerometer axes
• ±400°/s gyro range
• ±3 g accelerometer range

• Data output rate adjustable from 20 to 300 Hz
• Weighs under 1.5 grams (0.05 oz)
• Small size: 20 x 18 x 3 mm (0.8" x 0.7" x 0.1")
• Configurable windowed Parks-McClellan FIR filter
• TTL UART communication interface (3.3V with 5V-tolerant pins) can stream data or provide data on request
• 16-bit angle outputs provide 0.01° resolution
• Cortex firmware and PC application can be customized

Open Source PC Application and Firmware

Both the PC application for communicating with the CHR-6d and the CHR-6d's firmware are open source and available for download from the Resources tab. All of the pins needed to reprogram the STM32F103T8 ARM Cortex processor are made available to the user, as are four unused digital I/O pins that can be put to use if the firmware is modified.

Application Examples

The CHR-6d can be used in applications where a compact, 6-DOF IMU is needed, including:

• UAV navigation
• Robotics
• Motion tracking
• Platform stabilization
• Image stabilization
• Supplement to GPS navigation

Dimensions

Size:	0.8" x 0.7" x 0.1"
Weight:	1.5 g

General specifications

Baud:	115200 bps
Minimum operating voltage:	2.6 V
Maximum operating voltage:	3.6 V
Axes:	pitch (x), roll (y), and yaw (z)
Measurement range:	±400 °/s gyro, ±3 g accelerometer
Supply current:	50 mA