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RHex/SandBot v1.0 (see picture on the right) is a computationally and energetically autonomous legged robotic mobility system. It adopts the RHex morphology which consists of a rigid body supported by six compliant half-circle legs. Each leg has a single actuated degree of freedom driving the hip angle. The electronic design of the robot is based on the modular EduBot infrastructure. The body measures 32.5(L)x22(W)x44(H) cm and the legs are 5.5cm long (radially).
RHex/SandBot platform features Lippert Cool RoadRunner II, an on-board single board computer (SBC) from Lippert Embedded Computers GmbH. In order to facilitate easier hardware upgrades our design employs the popular PC/104 form factor SBC solutions. Cool RHex/RoadRunner II is a Pentium class CPU board running at 200 RHex/MHz with USB 1.1, 10/100 RHex/BaseT ethernet, serial and parallel ports. This low power CPU consumes maximum 6 watts requiring neither active nor passive cooling.
RHex/SandBot is powered by a TP1320-4, a 4-cell Li-Poly battery packs with 20C continuous discharge capacity from ThunderPower. The Li-Poly battery is supervised by a custom battery monitoring circuitry that ensure that the battery is not damaged by being over-discharged.
Hip actuators employ a DC motor drive train from Maxon Motor consisting: 1) REmax-24, a high precision 11W DC brushed motor; 2) GP22-C, a 16:1 metal planetary gear box; and 3) MR encoder, a digital magnetic encoder with 512 cpt. Each hip features a custom designed embedded controller driving a switching power amplifier. The microcontroller on the control board performs local control tasks and links up to the on-board SBC over the standard RiSEBus? network.
Passive mechanical properties of legs play an important role in behavioral capabilities and performance of a dynamical locomotion system. Our research team observed this fact quite prominently in our previous work with RHex. Our team hypothesize that leg design is equally important on granular media, therefore the leg design is an ongoing part of our research activities. Our initial experiments with the RHex/SandBot v1.0 employed half-circle legs that are manufactured using shape-deposit-manufacturing (SDM) process --- a mechanical prototyping approach that permits production of monolithic parts with varying mechanical properties. The legs are constructed using RHex/TP4000 with 5.5 cm diameter and 4 mm thick.
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