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Testbed Hardware

The K11 is a four-wheeled rover that was initially developed by the Intelligent Robotics Group (IRG) at NASA Ames to be an Antarctic heavy explorer. It had a design capacity to transport 100 kilograms of payload across ice and frozen tundra.

The rover was also previously used in experiments to test power consumption models and in a bearing optimization study. It has been tested on various types of terrain, including snow. The lightweight chassis was designed and built by BlueBotics SA. It consists of an H-structure and a joint around the roll axis to ensure that the wheels stay in contact with the ground on uneven terrain. The mass of the rover without the payload is roughly 140 kg. Its dimensions are approximately 1.4m x 1.1m x 0.63m.Each wheel on the K11 is driven by an independent 250 Watt graphite-brush motor from Maxon Motors equipped with an optical encoder. The wheels are connected to the motors through a bearing and gearhead system (gearhead ratio r = 308). Motors are controlled by Maxon Epos 70/10 single-axis digital motion controllers, capable of operating in velocity, position, homing, and current modes.

After considering various alternatives, LiFePO4 (lithium iron phosphate) batteries, commonly used in modern electric vehicles, were selected to power the rover. LiFePO4 batteries have a high charge density, perform well in high temperatures, and are not prone to combustion or explosion. Furthermore, they can withstand a high number (approximately 500) of charge/discharge cycles before needing to be replaced. There are four 12.8V 3.3 Ah LiFePO4 batteries on the K11, connected in series. Each battery contains 4 cells.

The philosophy in developing the sensor suite on the K11 was to employ only those sensors or data acquisition hardware that are commonly available on a variety of vehicles or can be added at a reasonable cost, while also providing sufficient data for a PDM system. Each component is utilized to the maximum extent possible. For instance, the motor controllers are not only used for their primary purpose of operating the motors and giving feedback on their velocity and current consumption, but are also used to support external sensors. The unused controller analog input channels are called upon to read battery voltage and current sensors and will be used for collecting temperature readings. In a similar vein, a decision was made to utilize a modern off-the-shelf smartphone for part of the instrumentation suite instead of, for example, a dedicated GPS receiver and a gyroscope. The smartphone also provides a still/video camera, a compass, and data processing and storage resources. It has a built-in wireless capability for communicating with other on-board components and directly with the ground station (as a back-up to the main communication link through the on-board computer). The current phone used on the K11 is a Google Nexus S.

The bulk of the computational resources needed to operate the rover are provided by the onboard computer (an Intel Core 2 Duo laptop). Its responsibilities include executing the motor control software, performing data acquisition, as well as running all of the reasoning algorithms. A second laptop computer currently serves as a ground control station.

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