Spring Flamingo is a planar bipedal walking robot. This robot was developed as an experimental platform for implementing
The goals of Spring Flamingo are the following:
Spring Flamingo was designed, built, and controlled by Jerry Pratt in 1996-1997. The actuators were based on a design and prototype by Mike Wittig done for his Undergraduate Thesis in 1995-1996. Robert Ringrose helped with the development software which was a modification of his creature library and other lab simulation software. Dave Robinson helped with design advice and machining. Dan Paluska helped with assembly. Ann Torres helped with machining and named the robot based on its appearance. However, Spring Flamingo doesn't walk like a flamingo, nor is it intended to.
The robot has an actuated hip, knee, and ankle on each leg. An unactuated boom constrains Spring Flamingo's roll, yaw, and lateral motion thereby reducing it to a planar robot. All of Spring Flamingo's motors are located in its upper body, with power being transmitted to the joints via cable drives. Series Elastic Actuation is employed at each degree of freedom, allowing for accurate application of torques and a high degree of shock tolerance. The maximum torque that can be applied to the hips and ankles is approximately 16 Nm while approximately 24 Nm can be applied to the knees. The force control bandwidth we achieve is approximately 20 Hz. Spring Flamingo weighs in at approximately 30 lbs (13.5 kg) and stands 3 ft (90 cm) tall.
Rotary potentiometers at the hips, knees, ankles, and boom measure joint angles and body pitch. Linear compression springs are located in the actuators to implement Series Elastic Actuation. Linear potentiometers measure the spring compression. In all there are six actuators and thirteen sensors on Spring Flamingo.
To date, we have implemented simple walking algorithms for walking on flat terrain. With these algorithms, we have successfully compelled the robot to reliably take consecutive un-aided laps as shown in the MPEG video below.
We are currently developing new walking algorithms which are more robust and allow the robot to walk on sloped ground and rolling hills.
Spring Flamingo was designed using Pro Engineer from Parametric Technologies for the mechanical parts and TANGO from ACCEL for the electronic schematics and circuit board layout. The robot took approximately 18 months to conceive, simulate, design, build, make corrections, program, debug and get to walk continuously. A list of time break down by month and day has been compiled.
The actuators were designed and prototyped before the rest of the robot. All six actuators are identical and can be easily swapped with spares. The body plates were designed based on the size and travel of the actuators. The boom and feet weren't designed until the rest of the robot was built. Knee caps were added later in order to make the control easier. Mechanically, we had trouble in two areas: free-wheeling ball screws and breaking cables. The ball screws were fixed by pre-loading the balls. The breaking cables were fixed by going to a more flexible cable and designing some parts which increased the radius at places were the cables were breaking.
The robot cost approximately $25,000 in parts and $75,000 in labor. A detailed list of expenses , information on suppliers and complete part list has been compiled.
Most of the designed parts were machined in the MIT AI Lab's machine shop. The body plates were cut on a water jet in MIT Building 35 machine shop. Some of the parts were sent out to REC Engineering. All of the electronics are on circuit boards which were fabricated by CFC. All parts were soldered in the lab.
Only the first paper below is specific to Spring Flamingo. The others were written before Spring Flamingo was built, yet they still apply to the robot.
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