Pneumatic actuators propel robots towards Cheetah speeds

Apr 03, 2024

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Four-legged robots have become increasingly popular in recent years, thanks to their versatility and agility. Powered by electric motors, these quadrupedal robots can offer precise control and nimble motion, with a number of consumer-focused robot dogs coming to market in recent years.

However, there's one thing that electric motors can't quite match: the instantaneous power of biological muscles.

That's where hydraulic actuators come in, enabling robots like Boston Dynamic's Atlas to perform impressive feats like backflips. Recently however, the African Robotics Unit at the University of Cape Town in South Africa have turned to a more traditional method of movement for their robots: pneumatics.

Inspired by the lightning-fast movements of cheetahs, researchers have been exploring the potential of pneumatics as an alternative to hydraulics. Using gas as a working fluid instead of a liquid, pneumatics offer a high force-to-weight ratio in a simple and cost-effective form.

Pneumatics also provide built-in compliance, which is lacking in hydraulics. Although pneumatics are not easy to control, researchers have discovered that complicated control may not be necessary to make a robot run like a cheetah.

Cheetahs are the fastest land animals on Earth and are renowned for running speeds of 70 miles per hour (113 kilometers per hour) in short bursts. During this brief burst of acceleration, cheetahs can cover a distance of around 460 meters (1,509 feet) and take as few as 3 seconds to reach their top speed.

Amir Patel, an associate professor at the University of Cape Town, explains, "We're arguing that fine force control is maybe not needed for rapid maneuverability."

While hydraulics are more complex, expensive, and messy if they explode, pneumatics offers an overlooked yet powerful alternative. Animals that require explosive motion from their limbs, such as cheetahs, could be an inspiration for leveraging the potential of pneumatics.

Patel and his team have built a quadrapedal robot called Kemba to explore the rapid acceleration and maneuverability that pneumatics can offer.

Watch Kemba in action below:

With the support of a boom, Kemba, weighing 7 kilograms, can repeatedly jump to a height of 0.5 meters with controlled landings, and reach a maximum jump height of 1 meter.

However, the research is not solely focused on jump height or top speed. Patel emphasizes that they concentrate on the transient phase of locomotion, such as rapid acceleration from a standstill or coming to rest at a high-speed gait. This often overlooked phase of motion is crucial for understanding the full capabilities of legged robots.

While Kemba is currently tethered, and there are plans for future upgrades, such as adding a spine and a tail, the potential of the pneumatic approach is promising.

Patel envisions Kemba becoming a platform that biologists could use to study the biomechanics of animal motion. Lowering the cost of legged robots is an added benefit of the pneumatic approach, which could eventually make legged robots more accessible to a wider audience.

While there is still a long way to go before legged robots can match the capabilities of real cheetahs, the innovative combination of pneumatics and electric motors offers new possibilities for rapid acceleration and maneuverability.