Design News, January 2013

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Automation & Control Everything in the design had to be thoroughly thought through, analyzed using computers, and then ordered. "We couldn't ball-park any of our figures," Ames said, "particularly for the mechanical operations of the robotic legs." The team found that they would need to use motors and gearheads that could deliver torques between eight and 12 Newton-meters and speeds down to five to six radians per second. "At such low speeds, we were specifically concerned about cogging problems getting in the way of smooth operation," Ames said. The team decided to use maxon motors for its final robot design. The AMBER 2 robot uses three motors and three right-angle gearheads per leg, one for each joint — ankle, knee, and hip. According to Ames, "We found that we needed a single, seamless package, which allowed us to maintain the tightest tolerances for the joint mechanisms." When the robotic foot hits the ground, the motors have to reverse on impact, which causes a huge amount of torque on the motor. AMBER 2's motors are electronically commutated, which enables them to offer extremely long motor life — there are no mechanical brushes to wear out. Hall effect sensors are built into each motor in order to provide feedback to the control electronics. By assembling the motor such that the coils are outside the rotor, good heat dissipation and high overload capability is attained. Each motor has a stainless-steel housing. Models vary in diameter and length dependent on the customer's needs and selection — typically from 16mm to 40mm (0.63 inch to 1.57 inch) diameters and 24mm to 88mm (0.94 inch to 3.46 inch lengths. Ambient temperature range is -40C to 100C (-40F to 212F). For a number of reasons, the right angle joints make the robot operate in a more natural state. "We found that if we put the motor on the joint directly we encountered some odd mass distribution problems, whereas by using the right-angle motor/gearhead assemblies ... we didn't see that happening. Plus, the assembly helped with the location of the proper center of gravity for the robot itself," Ames said. With the proper joint assemblies, the components acted in a very predictable manner, which was essential when creating the control interface. "You want everything to move exactly as the mathematics and control software dictates," Ames said. The assembly allowed for the high torque motor to operate smoothly at slow speeds. The team installed larger sprockets and a chain for each of the six joints. The idea was that the chain would become the weakest link — 1/3square4_5x4_62_Layout 1 10/17/12 1:50 PM Page 1 like tendons — and would be less expensive to replace. The team is working toward surpassing the ability of wheeled robots, by focusing on collected data that shows that humans display a walking behavior that • Incomparable Customer Service mirrors a mass-spring damper sys• Huge Stock of Steel, Aluminum & Stainless Products tem, which is one of the simplest • Ideal for Industrial and Medical Equipment mechanical systems. They are now • Free CAD Downloads, Product Videos, White Board on the path to replicate that system by using a combination of motors and gearheads, along with proprietary electronics, which means that the AMBER 2 robot is well on its way to being one of the first dynamically walking robots in the world. DN Deb Setters is national marketing manager for maxon precision motors. For Hinges, Gas Springs, Latches & Handles. Think GUDEN. For More Information: Experience the Guden difference. 800-344-6437 • Fax 631-737-2933 • Design News | jaNuary 2013 | www.d esign n –58– Maxon: Amber 2 Lab site: Watch videos of the Amber 2 robot at: ProfAmes

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