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T.J. - Toe-Jammer Biped Robot
November 2007: alas, T.J. has been disassembled in order to construct Poco the quadruped.
Namely, it occurred to us, after putting T.J. together, that T.J.'s upper joints might make
nice rotatable shoulders for quadruped turning. See Poco.

T.J. is a simple bipedal walking robot with 2-DOF in each leg, and is called "Toe-Jammer" for obvious reasons. With the initial feet shown, it turns out to be somewhat of a trick to get it to not jam-up its feet during common maneuvers.

T.J. was basically patterned after David Buckley's biped Loki, after we noticed what a great leanover it could do (more on this later). David gets to use a neat milling machine, but all we have is a drill, hack saw, and file, so our designs are necessarily simpler.


CONSTRUCTION

Physical:

  • dimensions: body = 6" (152-mm) wide x 6" (152-mm) tall x 6" (152-mm) deep; width including feet = 7.5" (190-mm).
  • weight with batteries = about 22 oz (625 gm).

    Material:

  • body + feet use single-side copper-plated, 1/16" thick pcb material.
  • servos: 44 oz-in for hip rotation, 76 oz-in for ankle rotation.
  • servos are mounted using Lynxmotion Pan+Tilt brackets, bought from the Jameco Robot Store, and which support the servos both front and back, and not just by the servo horns alone. It was necessary to slightly bend the bracket pieces that attach to the servo horns on the ankle servos, since those servos are taller than standard servos.

    Controller:

  • uses an OricomTech BOTCOP Dual-Processor Walking Machine Controller Board for gait generation and servo control.
  • general programming, logic, and and sensors controlled by a 24-pin ARMexpress module from Coridium, which is plugged into the BOTCOP carrier board.
  • batteries: 9v battery for logic, 4 NiMH AA-cells for servo power.
  • ACTION

    Toe-Jammer takes a step.
    LEARNING TO WALK

    Getting Toe-Jammer to walk involves balance, movement, and avoidance of collision between toes & feet. On each side, rotation of 2 servos (ie, polar coordinate movements) map into linear (ie, cartesian coordinate) movements of the feet. In essence, as the "downed" (grounded) side lifts and rotates the opposite side, the servos on the oposite side must produce approximately equal and opposite compensatory rotations in order to keep the feet (a) level, and (b) parallel to each other.

    After some playing around, we realized the easiest way to proceed involved getting one foot alone to take a single step forwards and backwards, and repeating this for the other foot. The best sequence involved:

  • first, produce lift and rotate using downed-side servos (2 servo movements).
  • secondly, add compensatory movements of servos on lifted leg, to keep the feet parallel (2 servo movements).
  • thirdly, rotate lifted-side back onto the floor and level feet (2 servo movements).
  • fourthly, extend sequence to complete forward and backward steps (12 servo movements total).
  • fifthly, repeat for the opposite foot.
  • sixthly, combine forward-movement sequences from the 2 sides to produce a complete left-right forward step (12 servo movements total).

    This all sounds obvious, but building the gait one bit at a time was much easier than trying to build one complete step sequence from the get-go.

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    Oricom Technologies, May 2007