While there are now dozens of full-body humanoid robots in existence, there are few based on our primate relatives. Even the robot Bonobo, named after a species of Chimpanzee, is humanoid in shape. If you’re looking for truly apish bots the Gibbon-like Brachiator robots built at Nagoya University, Japan, are perhaps the most well-known examples.
This seems like a waste given that the primate form offers researchers the chance to explore both bipedal and quadrupedal locomotion in one robot. In particular, a gorilla robot could benefit from the stability afforded by its four-legged stance but also balance on two legs to perform manipulation tasks. As luck would have it there is one, nicknamed Lucy…
Between 2002~2004 Steven Davis (with the help of Darwin Caldwell) sought to explore these possibilities with the pMA Gorilla as part of his PhD at the University of Salford. He describes the bio-mimetic approach as analyzing an animal and breaking it down to create a simplified (yet functional) artificial model. In fact, a robot doesn’t necessarily need to replicate every part of an animal for it to be useful as a research platform. Taking cues from a female gorilla’s anatomy, he did some necessary surgery and opted for pneumatic muscle actuators (pMAs) rather than electric geared motors to drive the robot’s limbs.
These actuators have a number of unique properties, not the least of which is the fact they simulate the real deal. They have a high power to weight ratio, and their natural elasticity means they won’t kill you if an arm swings at you. That’s a big plus when your robot is big enough to really hurt someone!
Actually, despite the relatively large size of the robot, which stands 175 cm (5’10”) tall, it weighs a mere 29 kg (63 lbs). That’s because the majority of its frame is a glass-reinforced plastic composite material, with aluminum and steel used only for areas of heavy load. There are hundreds of muscles and bones in a real gorilla, so they had to reduce things to the bare necessities. The pMA Gorilla has about a quarter of the bones and just 16 DOF (2 arms x4, 2 legs x3, neck x2).
Having built the robot, it was time to put it through a series of tests. They dropped it from a height of 30 cm (about one foot) in such a way that it would land on all fours. The robot was perfectly fine thanks to the pMAs’ natural shock-absorption, which caused the knees to flex. The robot was also able to support itself standing on two feet.
However, due to the under-actuated hips and ankles the pMA Gorilla was unable to walk unsupported. They were able to do some walking experiments where some of its weight was supported by a trolley, but the legs would give out when bent beyond a certain point. In the following video, you can see it is being supported by a harness.
Following this, Steven Davis went to work at the Italian Institute of Technology for four years, where he helped design the iCub’s miniature hand. He has since returned as an Assistant Professor to the University of Salford’s Autonomous Systems and Robotics Research Lab (England). Darwin Caldwell is a Research Director at the IIT Advanced Robotics Lab, where he is working on the Compliant huMANoid robot, COMAN.
Images and project details summarized from “Biomimetic Design for Bipedal/Quadrupedal Motion in a Robotic Primate” by S. Davis, and Darwin G Caldwell. Video provided by Steven Davis.
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