X-RHex Hexapedal Robot desert News & Opinion

Is the X-RHex Hexapedal Robot the Coolest Tool Ever?

We think so. X-RHex is the latest version of the highly mobile RHex platform, designed with greater strength, longer runtime, and more mobility than previous versions, with a modular payload architecture to support a variety of research needs. With new levels of mobility and durability, and the capability for rapid behavior development with a modular payload system, X-RHex is an effective research machine both in the laboratory and in outdoor field tests. Six powerful motors actuate compliant legs, allowing X-RHex to traverse a wide variety of terrains, including asphalt, grass, sand, mud, and rocks. By using a mil-spec rail mounted interface and standard electrical connections, X-RHex can support a wide variety of payloads, making it a mobile “laboratory on legs”. Now adding an extra sensor or testing a new behavioral algorithm is as easy as on a bench in the lab.


To encourage open collaboration in the field of robotics, the Kod*lab team at the University of Pennsylvania that came up with the robot are releasing all design files and source code associated with the X-RHex.

Check it out in action:

X-RHex Hexapedal Robot Mechanical Design

The main objectives for the mechanical design of X-RHex were to improve frame durability (both in resistance to fatigue and impact) and overall robot serviceability while achieving similar or better performance to past robots. The overall dimensions (57×39×7.5 cm) were intended to maintain as much similarity to Research RHex (54×39×13.9 cm) as possible. Research RHex leg design was preserved, and since the leg mounts are nearly centered on an overall thinner body, the robot can operate with greater ground clearance even when in an inverted state. The motors were chosen after careful analysis of the performance of past RHex robots, and use a flat brushless model from Maxon Motor USA.

  • Body dimensions: 57×39×7.5 cm
  • Ground Clearance: 12.5 cm (12 cm when inverted)
  • Leg Diameter: 17.5 cm
  • Total Weight: 8.6 kg (9.5 kg with both batteries installed)
  • Motor Continuous Power: 84 W
  • Gear Ratio: 28:1
  • Maximum Robot Power Density: 240 W/kg

X-RHex Hexapedal Robot Electronics

The electronics of X-RHex can be conveniently decomposed into four major subsystems: main computer, electronics stacks, batteries, motor assemblies. The main computer handles all high level control and communications. Each electronics stack contains three layers: motor controllers; a controller interface board which distributes power and communications to the motor controllers; and a battery management board responsible for power distribution, regulation, protection and monitoring. To the outer side of each stack, there is a lithium polymer battery and an interface board. Finally, there is a motor assembly containing a brushless motor and related sensors at each of the six hips.

  • CPU Type: Intel Atom, 1.6 Ghz
  • Communications Bus: USB
  • Motor Controllers: Advanced Motion Controls DZRALTE-020L080
  • Battery Type: 10 cell Lithium Polymer, hot swappable during robot operation
  • Battery Capacity: 144 Wh
  • Runtime: 90–180 min (typical usage)


X-RHex Computation and Software

X-RHex makes use of a real-time software architecture to provide high frequency sensing and control, as well as network communication with the robot, on a near-stock Linux distribution. Our software architecture is based on a custom-developed open source package called Dynamism.

  • Operating system: Linux (Ubuntu) with a Real-Time kernel
  • Motor PD Loop speed: 20 kHz (on the motor controller)
  • Gait regulation speed: 300 Hz (on the CPU)
  • Communications: WiFi 802.11b/g (internal) or other radio payload

This is one versatile and tough robot. I think it’s much more than a tool, but believe me – if I can get my hands on one to review I’ll staple a cordless drill to its back to make it legit!

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