The AS-S20 is a Bioloid compliant IMU (Intertial Moment Unit) module that incorporates 3 accelertion and 3 magnetic sensors in one chip. It is an unconventional solution to robotic IMU (we are used to gyros) but the result is impressive and surely will become a standard given its overall excellent value. The board is Bioloid Dynamixel compliant meaning that it has one MCU chip of type ATMega8 that implements the Dynamixel protocol over its UART link and talks to the sensor chip over SPI. The sensor chip AMS0805WAH from Amosense (Korean company) is composed of 3-Axis Magnetic sensor, 3-Axis Acceleration sensor, and a custom ASIC that provides sophisticated data calibration and facilitates a high-level communications protocol over SPI. It allows highly accurate motion detection with geomagnetic direction and tilting data. The biggest advantage of AMS0805WAH is the exclusive embedded calibration algorithm called iRAC(Intelligent Real Time Automatic Calibration) which eliminates the need for initial calibrations and supports precise calculation of motion data under all environments. It is widely used and applied in handheld devices such as cellular phones (orientation), navigation applications (“dead reckoning” where gps is not enough or doesn't work), 3-D pointing device, game controllers and even Calorie counters.
Some of the chip's features:
- Wide Magnetic Measurable Range: +/- 10Gauss
- Minimum Measurable Magnetic field: 10nT (0.1mGuass)
- Maximum sampling rate: 30Hz
- Azimuth & Roll/Pitch Resolution: 1 degree
- Wide Interface Voltage: 1.6Volt ∼5.0Volt
- Low power: 6.5mA in active mode
The new software that comes with the Premium Kit allows to monitor the signal coming from the sensor and it seems to be pretty stable, reactive and with almost no noise. Because it measures the magnetic field in 3 axis, it is able to precisely provide 3D rotation speed tensor as do the more expensive solid state 3-axis gyros, but in addition it can also provide the absolute angle relative to Earth's magnetic North without accumulative error. The resolution of the chip is 1 degree, which is fine for robotic applications. The sampling rate is 30Hz which is fast enough for navigation and probably also for stabilization [[ to be confirmed with Robotis ]].
