May 14, 2013

MIT's Robot Cheetah Making Strides

At last week's International Conference on Robotics and Automation (ICRA), the MIT team designing a fast cheetah-inspired robot presented their findings.  Their cheetah-bot can now run an impressive 22 km/hour using very efficient motors and other elements inspired from the actual speedy cats.

The Cheetah robot developed at MIT's Biomimetic Robotics Lab first made headlines four years ago. In the years that followed few details emerged about its progress, until finally in July 2012 the lab posted videos of the robot walking.

Now, at the IEEE International Conference on Robotics and Automation (ICRA), the MIT team has shown its cheetah-inspired robot running at a respectable 22 km/h (13.7 mph). Moreover, the robot has an energy efficiency that rivals that of real running animals.

The MIT researchers reported their latest results in the paper, "Design Principles for Highly Efficient Quadrupeds and Implementation on the MIT Cheetah Robot," at the conference.

The work is currently being funded by DARPA's M3 program which involves improvement of production methods and processes, improvement in control of robot mobility and manipulation, and prototype demonstration.
Among cheetah robots, the MIT version is only beaten in speed by Boston Dynamics' Cheetah which can run twice as fast.

Both the MIT Cheetah and Boston Dynamics' Cheetah are attached to horizontal bars that hold them in place somewhat during the treadmill testing, but perhaps someday soon these bio-inspired robots will be set loose among us.

MIT Cheetah Robot

Although we can expect them to run even faster, speed is not the only factor to be considered in this race. While Boston Dynamics' robot, which uses hydrauclics, was tethered to an external power source when we last saw it, MIT's Cheetah is already energy efficient to the point it can run with just on-board batteries.

In the video above, it's still tethered, carrying 3-kg of dummy weights that stand in for its four 22.2-V lithium polymer batteries.

The MIT Cheetah is about the size and weight of a real cheetah and requires approximately 1 kW when running at 22 km/h, which translates to a cost of transport, or COT (defined as power consumption divided by weight times velocity), of 0.52. The team says this COT performance rivals that of running animals of the same size.

For comparison, Honda's Asimo humanoid has a COT of 2 and Boston Dynamics' BigDog has a COT of 15, which is far less efficient than their biological counterparts. So although Boston Dynamics has had great success with its hydraulic robots, at least when efficiency is considered, its robots are not the top performers.

MIT Cheetah Robot

The MIT researchers, using DARP have identified other areas of energy losses and applied various mechanical strategies to reduce them where possible. For example, they used a regenerative motor driver (which they compare to the regenerative braking system in hybrid vehicles) to save energy during each stride.

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And they also incorporated biomimetic principles. A Kevlar tendon stretches from the foot to the knee, reducing the stress on the legs during stride by close to 60 percent. The bones themselves are made primarily out of a light polyurethane foam-core which is covered in a high stiffness resin, which makes them both light and strong. The researchers also gave their robot a spine, which is actuated not by individual motors but a differential system driven by the action of the legs.

When combined, these (and other) energy saving techniques allow the robot to run at 8.3 km/h (5.2 mph) for 1.23 hours, or a distance of about 10 km (6.2 miles) with just 3 kg of batteries.


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