The BiPed robot V-3 was designed to get as close to the freedom of movement of the human lower body, it has 12 degrees of freedom. The frame is made of acryl-sheets and model servos are used as actuators.
For now the robot is controlled via PC, autonomous behaviour when development finished. The software allows to generate motion-patterns, replay them and view actual sensor data.
Used sensors are a two-axis accelerometer for the orientation of the hip and four force-sensing resistors at the bottom of each footplate. A kind of torque feedback of the servos is realized by measuring the driving signal of the servo motor.
Further information at www.austrobots.com.
Step 1: Framework
The framework is made of acryl sheets. The parts get cut by a CNC milling machine, the first parts for testing were cut with a fretsaw.
The actuators integrated in the framework are servos used in RC-modeling. In general one servo is responsible for one degree of freedom. For a better mechanical stability two servos (at the top) are combined for lifting each leg. The servos actuating the footplate are working parallel.
Step 2: Electronics
Two types of ATMEL AVR controllers are used in the actual version, one mega8 as master and three tiny26 for servo-controlling, force-sensing resistor measurement and TFB-feedback. The master handles the data-transfer for each AµC via I2C bus and the communication to the PC is realized as simple RS232 communication.
The "torque" feedback measurement samples the internal control signal of the servo motors and delivers information of the load to keep the desired position.
With the four FSR's on each footplate it is possible to measure if the robot is still in balance while standing on one foot. If the center of gravity is within the footplate the robot is stable.
All sensor data is visualized in the software.
Step 3: BiPed control software
With this VisualBasic program it is possible to generate motion patterns by using the slidebars to control the positio of each servo. By pressing a button the positions are stored in a file and may be replayed at different speed grades and interpolated servo positions.
The circle at the right visualizes the data of the accelerometers. If the hip is in a straight orientation the red circle is located in the center. Leaning the robot forward moves the red circle to the front.
The same principle for visualizing is used for the sensors in the footplates. Any unequally distposition of the robots weight, while standing on one foot, results in a displaced red circle.