The mobile robotic system Justin with its compliant controlled lightweight arms and its two four fingered hands is an optimal experimental platform for the study of complex manipulation tasks.
The newly developed mobile platform allows the long distance autonomous operation of the system. It pushes the system forward towards an universal service robotic platform.

Mechanical construction

Variable base:
An extendable robot base is required In order to take advantage of the large work¬space and the dynamics of the upper body Justin, while providing the stability of the overall system. Contrary, for a reliable and easy navigation in household en¬viron¬ments compact dimensions are necessary.
The individually movable legs of the mobile platform enable Justin to use its full workspace and its dynamics for manipulation tasks. Additionally, simple and reliable navigation through narrow passages, like usual household doorways, is possible. 

Variable Base

Spring mounted chassis:
In order to stand up straight with four wheels on uneven ground and to gently drive the upper body over small obstacles like doorsteps, the wheel suspensions are individually spring damped. The dampers are equipped with a locking device to provide a very high stiffness of the platform during the execution of fine manipulation tasks with the upper body.

Power supply

The whole system is powered by a Lithium-Polymer battery block with 48V nominal voltage and 40 Ah. To support the individual robotic components, sensors and computers the main power supply is divided into six separated power lines (48V, 3x 24V, 12V, 5V). 
System design

The development of the mobile platform followed three main requirements:
   1. Functional needs
   2. Compact construction
   3. Usage of off-the-shelf components

IThese demands are challenging for the system design and the real-time communication concept which must cope with different real-time protocols and bus systems. The robotic system makes use of components that communicate via Ether¬CAT, CAN, CANopen, SERCOS and Space¬Wire. These different field busses are joined using the standard software TwinCAT and mapped on a single Ether¬CAT slave. On the separate real-time computer running the control of the whole upper body and the mobile plat¬form all robot data is available through a single real-time protocol. The data is provided in a Matlab/Simulink environ¬ment to allow rapid prototyping of the control system for the whole robot platform.An additional pc running Linux is used for 3D- vision. 

Leg Mechanics

Technical Data:

Mass: ca. 120 kg 

Power supply:
    Lithium-Polymer 40Ah / 48V
    Operating time > 1h

Actuation:
    Driving:   30Nm / 1,5 m/s (5,5 km/h)
    Steering:  360 °/sec
   
Sensors:
    4 x ToF Cameras (60 x 54 Pixel)
    2 x GigE Camera (640x480, 90fps)
    4 x Force sensors
    8 x Absolut encoders (wheel position)
    8 x Bumper + 4 x emergency stop

Computers:
    4 x Mini-ITX Core2Duo M / 2.16 GHz