Robots are conventionally made mobile by rolling on wheels; however, wheeled robots have limited ability to traverse large obstacles. Obstacles much taller than the robot's wheels can prevent passage, and obstacles with significant horizontal gaps, such as trenches, can also prevent passage. One solution is to use bigger wheels and a bigger wheelbase. Both of these require more drive power, so the entire robot must be larger. This can be prohibitive in applications with cost, size, space, or transportation constraints that limit the size of robot that can be used.
One alternative to wheeled mobility is hopping mobility in which the robot jumps to move. Each jump is typically a multiple of the robot's dimensions in height and width. Accordingly, the robot can hop over obstacles much larger than a similarly sized wheeled robot could traverse. Hopping mobility can allow a small robot to traverse obstacles very large in relation to the robot itself, enabling applications that cannot be addressed by wheeled robots.
Hopping robots pose many challenges unique to hopping mobility: a linear actuator suitable for long trips, low-energy steering and control, reliable low-energy righting, miniature low-energy fuel control, misfire-tolerant single-shot actuators, navigation, and control. Hopping robots generally require a fast-acting linear actuator to drive the hop. Conventional wheeled robots use rotary actuators, and therefore can rely on more mature actuation technology. Actuators for hopping robots must additionally be able to tolerate misfires without relying on inertia of motion or flywheel effects common in wheeled robots and rotary actuation. A linear actuator suitable for a hopping robot must be able to resume operation after a single mis-actuation, or the robot will stall completely on its first fault.
Hopping robots generally will require many hops to traverse a significant distance, so low-energy steering and control are important. Wheeled robots can steer by directional control of wheels or by skid steering, using the same energy source for steering as is used for mobility. Hopping mobility does not lend itself to the same dual use as readily.
Wheeled robots generally remain in a given orientation, e.g., on the wheels substantially parallel with the ground. Hopping mobility, however, can subject the robot to unpredictable forces during hopping that can result in unpredictable orientations on landing. Hopping robots therefore can require the ability to return the robot to a known orientation after each hop, preferably with minimal energy consumption.
A hopping robot was developed that includes a misfire-tolerant linear actuator suitable for long trips, low-energy steering and control, reliable low-energy righting, and miniature low-energy fuel control. The hopping robot is capable of traversing obstacles significant in size relative to the robot, and operates on unpredictable terrain over a long range. The robot also features misfire-tolerant combustion actuation, and combustion actuation suitable for use in oxygen-poor environments.
Two versions of the robot exist. One is the size of a grapefruit, and is capable of approximately 4,000 hops of about 3 feet high and 6 feet from the starting point of the jump on a single tank of fuel (less than an ounce). The other is about the size of a shoebox (see photo), and overcomes as many as 30 obstacles that are more than 20 feet high with about 100 hops per tank of fuel.
The four-wheeled version of the robot overcomes traditional barriers associated with long-range missions and terrain including management of shock forces, hop height, and efficiency. Furthermore, the robots are equipped with compasses or GPS that allow them to orient themselves once landed.