RHex: The ‘Parkour Robot’ Can Flip, Jump, and Do Pull-Ups

University of Pennsylvania graduate student Aaron Johnson and professor Daniel Koditschek have created RHex, a “parkour robot” that can navigate its way over obstacles even bigger than itself using six springy legs. The duo is currently working on X-RHex Lite, or XRL, a new version of of the robot that can perform double jumps, flips, and even pull-ups by launching itself vertically, hooking its front legs onto the ledge, and dragging its body upward.

The original design for the robot was developed around 10 years ago, but this lighter version — X-RHex Lite (RXL) — was developed by UPenn professor Daniel Koditschek and his graduate student Aaron Johnson. They are teaching it freerunning, or Parkour, with the intent that it will one day be used for applications like searching the jagged rubble of a collapsed building for survivors, or traversing the shifting sands and rocky obstacles of the desert while taking environmental readings.

X-RHex Lite (RXL) was developed by UPenn professor Daniel Koditschek and his graduate student Aaron Johnson

"What we want is a robot that can go anywhere, even over terrain that might be broken and uneven," Johnson says. "These latest jumps greatly expand the range of what this machine is capable of, as it can now jump onto or across obstacles that are bigger than it is."

XRL differs from its earlier relatives by using lighter materials and simpler fabrication methods. A complete shell of carbon fiber panels surrounds the XRL frame, and it has only a single battery compartment. The XRL is 51 cm (20 in) long, 40.5 cm (16 in) wide, and the body alone is 10 cm (four inches) in thickness. The diameter of the six flexible rotating legs is 17.5 cm (6.9 in), giving the XRL ground clearance of 11 cm (4.3 in) regardless of which end is up at the moment. It's weight including battery pack is 6.7 kg (14.7 lb).

The XRL is 51 cm (20 in) long, 40.5 cm (16 in) wide, and the body alone is 10 cm (four inches) in thickness,weighs 6.7 kg (14.7 lb) including battery pack

For motive power, the XRL depends on two 50 watt brushless pancake electric motors by Maxon (one for each leg). The actual peak power for these motors is about 380 watts, or about half a horsepower. These motors are geared down by a factor of either 18:1 or 23:1, depending on the nature of the landscape on which it is being tested. Powered derives from a ten-cell lithium polymer battery with a capacity of 83 W-hr at 37 volts. Battery weight is about 0.6 kg (1.3 lb).

For motive power, the XRL depends on two 50 watt brushless pancake electric motors with peak power of about 380 watts, or about half a horsepower

The XRL legs are equipped with force and power sensors, which allow the work of maneuvering to be analyzed in detail. Among other benefits, the research team found that the response of the legs can be used to give an indication of on what sort of surface the XRL is walking. For example, the XRL responds to vinyl and asphalt surfaces in very much the same manner, but responds very differently to pebbles or grass surfaces (which are in turn similar to each other).

Future Trends

RHex: The ‘Parkour Robot’ Can Flip, Jump, and Do Pull-Ups