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NASA’s Ranger Telerobotic Shuttle Experiment Application Note

The University of Maryland’s Space Systems Laboratory needed highly customized backplanes for NASA’s Ranger Telerobotic Shuttle Experiment, a four-manipulator robot designed for operations in the Space Shuttle cargo bay. Each manipulator with multiple sensors, actuators and cameras allows operators in the shuttle or even on Earth to grab objects, make repairs, and perform other tasks. They found their backplane solution with Bustronic’s custom design services.

The Ranger uses a proprietary architecture to handle the complex array of power and signals required. Essentially, the backplanes act as a vehicle for the motors and sensors to work with the motor drivers and CPU. The robotic arm uses three, 3U-high backplane designs – one each for the shoulder, elbow, and wrist. The wrist backplane is the most complex, requiring eight slots for all the functions needed for robotic wrist’s detailed movements. The analog-to-digital converters, computer, and power conditioning cards take up three slots, and the remaining five slots hold motor drivers that control the actuators. With fewer actuators to control, the shoulder backplane is six slots wide and the elbow five slots. The elbow backplane is also used in the ankle, knee and hip of the positioning leg.

Each backplane demands heavy-duty performance. The motors in the actuators can draw heavy currents – up to 10A per motor at 48V. The wrist backplane must withstand a possible 50A power draw. Bustronic’s Ranger backplane design was also heavily space constrained, and used as few layers as possible.

The proprietary bus includes high-speed signaling, so using a controlled-impedance stripline design was important to limit reflections. The stripline design reduces crosstalk by shielding the signal lines with power layers above and below. The 2 oz. copper outer ground planes fully shield the backplane, minimize EMI/RFI emissions susceptibility, minimize crosstalk, and maximize power distribution. The robust outer ground layers also provide mechanical protection for the backplane.

Why Did Elma Bustronic Win?
The Elma Bustronic solution takes advantage of the FutureBus Plus connector, with its combined ruggedness, speed capability, and market availability. Because the connector also has power blade options, Elma Bustronic maximized the density of the backplanes with both the power and signals on the same FutureBus connector slots.

The lab chose Elma Bustronic for the job because of their expertise and reputation in complex custom backplanes. “One of our contractors used Elma Bustronic before, and had only said great things about the company” mentioned Jean-Marc Henriette, the Embedded Systems Lead for Ranger.

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