Jessy W. Grizzle

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Special Features: [Questions by Christine Harbig on June 26, 2007 led me to write up some of the key points of this new machine.] What is the main difference of the new robot when compared to other robots like ASIMO or QRIO? Is it the ability to be able to walk on uneven terrains or mainly a more efficient way of moving? What will be the real step forward in robot technology?

There are at least three differences:

  1. MACHINE DESIGN: the robot has springs built into the powertrain so that, very roughly speaking, it effectively has the tendons of a kangaroo. This is just to give you a very rough impression. Do not use such a statement in a report! Asimo and Qrio are built of very rigid material and the motors (= power sources) are connected to the joints via rigid gears. In MABEL, the motors for the "knee angles" are connected through springs. Hence, when the robot strikes the ground, the knees flex through the springs, as your foot does when you run in a good sports shoe, as opposed to trying to run in a rigid ski boot. The "hip angles" of MABEL are connected through rigid gearing as in Asimo or Qrio. [technically, we are not using gearing, but instead, pulleys and cables. This is really a technicality to avoid something called backlash that is associated with gears. The main difference is the springs.] Going back to the springs, if you looked at the Raibert hopper, the leg is built from a pneumatic spring, so it hops very nicely. The spring acts like a tendon in an animal. Our robot has roughly the morphology of a human, with the compliance (spring-like character) of the Raibert hopper. It should be able to run very nicely.
  2. MOTION CONTROL ALGORITHMS: Asimo and Qrio use a very quasi-static criterion for achieving a stable walking motion. [here, stability refers to the ability to react to perturbations by not falling over, and asymptotically returning to a planned walking or running motion]. These robots use big feet in order to stay upright. The robot Johnnie at the Tech. Univ. of Munich uses the same quasi-static stability notion. In the French robot, RABBIT, a team of us developed a novel theory of DYNAMIC WALKING STABILITY and verified it on the robot. MABEL is more complex, due to the springs, and thus some important extensions must be made to the DYNAMIC STABILITY theory we used for RABBIT. My students, colleagues, and I are making good progress on the design of motion control algorithms for MABEL using an advanced version of dynamic stability. Like RABBIT, MABEL does not really have feet: it will walk and run as if on stilts, the ultimate proof of the dynamic character of its stability notions.
  3. SCIENCE PLATFORM: Like RABBIT, MABEL is designed for advancing the science of locomotion and forcing the discovery of more advanced feedback control notions for dynamic motion stabilization. Furthermore, we will soon post the full blueprint of the robot on the web. All of its algorithms are and will continue to be published in leading journals. Students are being trained. Students of all ages are being invited for demonstrations. In short, no aspect of the work is proprietary....everything will be in the public domain. Good luck on learning the details of how Asimo and Qrio function....they are 100% proprietary.
    1. You can download a complete set of CAD files (SolidWorks) for the robot. With these files, you can have all of the parts of the robot machined. Click here then scroll to the bottom of the page.
    2. Publications detailing the control laws implemented on the robot are available here.
    3. A ZIP file providing a symbolic mathematical model of the robot's powertrain is available here. [Right Click and Save]
    4. Tons of photographs of the robot's ``insides'' are here.

    Our project is very science oriented and very public. This is typical of work funded by the National Science Foundation (NSF) in the US. We are really challenged to push the boundaries of learning.

    Back to your question: Is it the ability to be able to walk on different uneven terrains or mainly a more efficient way of moving (smoother movement)? I tried to make out the real step forward in robot technology but Im not sure about it. The advanced feedback control algorithms and the advanced machine design using springs in the powertrain SHOULD YIELD smoother, more compliant, more energy efficient locomotion. The robot should be able to walk more easily on rough terrain. I say **should** because if we were 100% certain, why build the machine and evaluate the algorithms? There is a very real possibility that we fail.

    Noted added on May 24, 2010: It looks like the ability to walk on an uneven surface is now a certainty and not a conjecture! See [YouTube Video, First Attempt at Walking over Rough Ground]. Fast walking has been achieved (we held the speed record from October 29, 2009 through April 2010, and then lost it to PetMan). [YouTube Video, Go MABEL Go!]. High efficiency has been demonstrated; see the efficiency table in the experiment section this paper.


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