Experimenting with RANBOTS
by Alvaro Cassinelli, 2007
Control N degrees of freedom with a unique actuator (1DOF) introducing noise into the others DOF through mechanical coupling; then, reduce the noise intensity as it get close to the target in phase-space.
Rationale: Sensors can be directional, but there is only one (or very few) actuators that make the object move randomly. It is easier to build (many/directional) sensors than actuators.
Example using a 2DOF system (2d position of a particle and a quadratic excitation field (dictating the magnitude of the jump):
Use natural occurring noise as sources of noise (ex: brownian motion). This can be done for instance by changing the rigidity of the robot shell.
In the case of micro or macro-robots, this can be done using a shell made of a smart material that reacts to temperature or some other environmental variable.
Interestingly, if the shell can be hardened anisotropically (thanks to a polarized electrical field for instance), then we can use random termal energy in the medium to directly generate thrust in one direction (in the case of a macro-robot in the middle of a crowd, this principle will meant the use of kinetic energy from pedestrians (bumping into the robot) to drive the robot in a specific direction). But this is not the principle of the “ranbots”.
Proof or principle (hardware)
Directional thrust is verified on a small “ranbot” with a unique vibrating motor and a distance sensor. Vibration magnitude is proportional to the proximity of an obstacle (or inversely proportional), so that statistically the object then to spent more time away from the hand (or closer to it).
This is a small prototype using four motors (three vertical, and one horizontal for producing a good random vibration). At the base, the robot has a brightness detector; different gray levels on a printed pattern controls only the intensity of the vibration, but as can be seen in the videos, this is enough to steer the robot in the right direction.
- Center attractive: [wmv-3MB]
- Center repulsive: [wmv-10MB]
- Three motors detail: [wmv-5MB]
- Whole demo: [wmv-37MB]
==> CLICK HERE TO START SIMULATION (cursor sets the minimum of a quadratic excitation field)