The encoders give about 30.000 pulses per rotation. Speed measurement is therefore done separately by a Tiny26 to ensure stable timing on the Mega8. The control loop needs to be run at a fixed time interval. No interrupts can be accepted. The encoders have a A and B output, which make the speed and direction measurements simple. The data is transferred serial to the Mega8. The acceleration measurement is done with a ADXL202. The connection of the IC is very simple. The digital output of the IC is used. The measurement of the angle speed is done with a gyroscope. It is a standard gyroscope used in model planes and helicopters. The angle speed measurement and the acceleration measurement are combined to determine the angle the robot makes with the floor. Both measurements are needed for a few reasons:

• The gyroscope suffers from drift. Even a small drift can cause high deviations when the signal is integrated for a longer time.
• The acceleration measurement is influenced by horizontal acceleration of the robot.