A small robot that travels by hopping has been built and tested. This is a prototype of hopping robots that would carry video cameras and possibly other sensory devices and that are under consideration for use in exploring cluttered, unpredictable terrain on distant planets. On Earth, robots like this one might have value for entertainment and civilian and military reconnoitering of hazardous areas.

Figure 1. The Steering Mechanism and its geometric relationship with the tilted assembly are depicted here in simplified form. The self-righting mechanism and some other components are omitted for clarity.

The design of this robot is a compromise between functionality on the one hand and simplicity, reliability, and lightness of weight on the other hand. The robot is said to be minimally actuated in that all motions are generated by use of a single motor that drives several mechanisms.

The robot (see Figure 1) includes a foot, a bearing on the foot, and a tilted assembly that contains the rest of the robot. The tilted assembly can be pivoted on the bearing to pan the camera and to steer the robot for the next hop. The tilted assembly includes an extendable leg that contains a spring and an associated linkage for extending and retracting the leg. To store energy for the next hop, the motor drives a power screw that compresses the spring and retracts the leg. At the desired moment of hopping, the motor actuates a mechanism that releases the spring, which then rapidly extends the leg to generate the hopping motion. The spring and linkage are designed together to make the extension force a nonlinear function of displacement that maximizes the proportion of spring-compression energy converted to hopping kinetic energy.

The masses of the components are distributed so as to make the robot bottom-heavy for stability when it sits upright on the foot with its main assembly tilted and the leg compressed in preparation for hopping. Because the robot can be expected to lie toppled over after most hops, a self-righting mechanism is included. The self-righting mechanism deploys flaps to push the robot to the stable upright orientation.

Figure 2. The Robot Rights Itself after hopping and landing toppled over.

To take advantage of minimal actuation, it is necessary to perform most operations sequentially rather than simultaneously. Hence, the robot must operate in cycles. To enable the single motor to effect the desired sequence of motions, the motor is coupled to the various actuator mechanisms by use of a variety of coupling mechanisms that include an overrunning clutch and timing and logic mechanisms. The sequence of motions during one cycle is the following:

  1. Assuming that the robot has just landed from the preceding hop, the self-righting mechanism is actuated in a two-phase operation.
  2. During the second phase of the self-righting operation, the spring is compressed and the leg retracted in preparation for the next hop. Because retraction of the leg restores the bottom-heavy configuration, it aids self-righting. Figure 2 depicts a sequence of events from flight through landing and self-righting.
  3. The spring is locked in compression to prevent premature hopping.
  4. The tilted assembly is rotated to steer for the next hop and to pan the camera.
  5. The spring is released to make the robot hop.

This work was done by Paolo Fiorini, Joel Burdick, Eric Hale, and Nathan Schara of Caltech for NASA’s Jet Propulsion Laboratory.

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Minimally Actuated Hopping Robot

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This article first appeared in the November, 2002 issue of NASA Tech Briefs Magazine.

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