The IMU (Inertial Measurement Unit) detects linear acceleration using accelerometers and magnetometers as well as rotational velocity using gyroscopes.
Accelerometers are able to sense both static (gravity) and dynamic (movement) forms of acceleration.
- One of the most common and easiest uses of the accelerometer is to sense tilt. With the use of the earths gravitational acceleration and trigonometry, accelerometers can tell you orientation with respect to the Earth's surface. In the simplest end use, mobile phones use this feature to know to switch between portrait and landscape orientation. This can also be a very easy way to create a spirit level with the IMU Block.
In the IMU Block, all the sensors’ axes are oriented in the same direction. The Accelerometer and Magnetometer axes are:
Gyroscopes on the other hand measure rotational velocity (not acceleration). Unlike accelerometers, gyroscopes are not affected by gravity. They do however compliment accelerometers, in that they can provide orientation information for objects in motion.
- As much of everyday life is in linear motion, the uses for gyroscopes are more limited than accelerometers. In the past, gyroscopes have been used in space navigation as well as air and under-water guidance. Today, they are actively used alongside accelerometers in assistance with motion derived activities.
The gyro’s three axes of rotation are either referenced as x (roll), y (pitch), and z (yaw):
The IMU produces data in the following units:
| Accelerometer | Magnetometer | Gyroscope |
| mg (Milli G) | μT (Microtesla) | mdps (Milli Degrees Per Second) |
* - Note: By default (if resting on a flat surface), the Accelerometer’s Z access is negative and around -1000 mg, this is because the gravity of the planet is constantly accelerating the sensor towards its centre (downwards). If you flip the block over, this value should become positive. The 1K measurement (1000mg = 1G Earth Gravity) indicates there sensor is constantly falling at around 1G (9.8 m/s²). In ideal conditions, the Z access should display -1000mg, the difference in values you may observe are due to noise in the data, the location on the planet’s surface and calibration of the sensor.
Sampling Rates
The available sampling rates or, how often data is collected from the sensors, are 1Hz, 10Hz, 25Hz, 50Hz, 100Hz and 200Hz. Please note that values at data rates above 25Hz are automatically averaged and sent at a maximum data rate of 30Hz (30 updates per second). This means that even if you select a 200Hz data rate, the readings will be calculated and presented to you at a much lower rate.
To change the sampling rate of an IMU just open the Properties Panel by clicking on the ‘gear’ icon:
In the ‘Custom Settings’ sections choose the desire Sampling Rate from the drop-down menu and press ‘Save’ to apply the changes.
