UM7 Orientation Sensor

The UM7 orientation sensor is a third-generation Attitude and Heading Reference System (AHRS) from CH Robotics that produces attitude and heading estimates from triaxial accelerometer, rate gyro, and magnetometer data. Unlike a typical inertial measurement unit (IMU), which only provides raw sensor readings, the UM7 features an onboard microcontroller that combines sensor data using a sophisticated Extended Kalman Filter (EKF) to generate orientation estimates 500 times a second.

Two versions of the UM7 are available: the UM7 orientation sensor, which includes an enclosure, and the UM7-LT, which does not. The two versions are functionally equivalent, and both include a cable (even though it is only shown in one of the two pictures below).

The UM7 features a number of improvements over its predecessor, the UM6, including higher gyro bias stability and lower noise, a new communication architecture for improved flexibility, optional NMEA packet transmission, UTC time-synchronisation with external GPS, and support for third-order temperature compensation on all sensors. It takes advantage of newer MEMS (micro-electro-mechanical systems) technology that allows it to offer better performance at a lower price.

Connections for power and TTL serial communication can be made to the UM7 through a polarized five-pin male connector on one side, which mates with an included cable assembly. A pair of six-pin expansion headers on the other side of the board provide additional connectivity options, including an alternative SPI interface and a secondary serial interface that can be connected to an external GPS module (like Polou's LS20031 GPS receiver). Additional cable assemblies for the expansion headers are not included.

Product Comparison

Polou carry several inertial measurement and orientation sensors. The table below compares their capabilities:

Product Name	Sensors				Estimation				Other
	Gyros (3x)	Accels (3x)	Mag (3x)	Altitude	Roll	Pitch	Yaw	Quaternion	Enclosure
Pololu MinIMU-9 v3
Pololu AltIMU-10 v4
CH Robotics UM7-LT Orientation Sensor
CH Robotics UM7 Orientation Sensor

Features

Sensors and processing

• Excellent gyro bias stability over temperature
• Adjustable low-pass filter and EKF settings provide customisable performance for various applications
• States and sensor data synchronised to GPS position and velocity using optional external GPS module
• Allows for alignment calibration and third-order bias and scale factor temperature compensation for accelerometers, gyros, and magnetometer
• Magnetometer soft and hard-iron calibration can be performed through the CHR serial interface software

Communication

• Output data:
  • Attitude and heading (Euler angles)
  • Attitude quaternion
  • magnetometer, accelerometer, gyro data
  • GPS altitude, position, velocity (with optional external GPS)
• 3.3 V TTL serial interface (UART) with baud rates up to 921,600 bps can stream data or provide updates on request
  • Note: the main UART pins, TX, and RX, are 5V-tolerant and can be directly connected to 5 V systems that are guaranteed to read 3.3 V as high
• Transmits data using human-readable NMEA strings (up to 100 Hz broadcast), binary packets for higher efficiency (up to 255 Hz broadcast), or a combination of both
• Flexible communication architecture allows UM7 to transmit any combination of data at individually adjustable rates
• Connects to the CHR Serial Interface software to allow for real-time plotting of sensor data, logging, device configuration, and magnetometer calibration
• SPI interface available through expansion connector

Specifications

• Dimensions: 1.06″ × 1.02″ × 0.26″ (27 mm × 26 mm × 6.5 mm)
• Weight: 0.12 oz (3.5 g) without cable
• Operating voltage: 4 V to 5.5 V
• Polou/O logic level: 3.3 V (with 5V-tolerant main UART pins, TX and RX)

Attitude and heading

• EKF estimation rate: 500 Hz
• ±1° typical static pitch/roll accuracy
• ±3° typical dynamic pitch/roll accuracy
• ±3° typical static yaw accuracy
• ±5° typical dynamic yaw accuracy
• 0.5° angle repeatability
• 0.01° angular resolution

Videos

In this video playlist, Caleb Chamberlain from CH Robotics shows how to get started with the UM7, configure its communication settings, and calibrate its magnetometer.

Robotics shows how to get started with the UM7, configure its communication settings, and calibrate its magnetometer.

Dimensions

General specifications

Notes:

1

Excluding mounting tabs.

2

Without included cable; 10 g with cable.

3

Note: The main UART pins, TX and RX, are 5V-tolerant and can be used directly with 5 V systems that are guaranteed to read 3.3 V as high. The secondary UART and some of the SPI pins are NOT 5V-tolerant.