RiverCleanser

Cyrus Tabrizi, 12/26/12
9 56

      The upper body is the robotic arm which, in turn, actually consists of three main parts. One is the base of the arm that connects it to the under body and supports all the weight of the arm and any objects that come into its grasp. The second is the arm itself which is supported by some liftarms attached to the base. At the end of this arm, there is a manipulator which is essentially just a functioning claw. The fourth and last part is the counterweight that reaches back in the opposite direction of the arm. Let's begin with the first piece: the base.

      In the base, there are two motors –one M and one XL. The M motor is responsible for turning the entire upper body –this requires a substantial amount of torque and a geartrain that can handle that torque. Since an M motor was used to provide this torque, it had to be geared down to a suitable speed, one that would produce enough torque and allow the arm to rotate at a maneuverable rate. The structure of the arm's base provided very little space for any gearing at all, but after countless rebuilds, a setup was finally found that, although not particularly fast or powerful, finally allowed the M motor to transfer its rotational motion to the turntable on which the upper arm sat without any teeth slipping. While the M motor is mounted vertically, the XL motor is attached horizontally behind the M motor's geartrain. It drives two linear actuators on either side of the M motor via some gearing below the M motor. These linear actuators lift and lower the liftarms that hold the rest of the arm above the base.


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      The arm is connected to the base with some liftarms in such a way that it always remains parallel to the base and the rest of the robot. The angle that these liftarms are mounted at not only moves the arm up and down but also back and forth when they are moved by the linear actuators. This gives the arm more reach. The arm itself consists of two segments. The first part houses two motors while the second part is a slim and long connection to the claw. This segment is connected to the motor housing at one end at an adjustable angle and by pins to the claw at the other end. Since the claw is expected to be submerged or close to water, it is controlled from abroad by the two motors that were mentioned previously. Another reason for keeping the motors far from the claw and towards the rear of the arm is to shift the weight of the arm back to the center. If they were kept on or near the claw, the stress on the arm and the linear actuators would be significantly higher. Since the second segment connects the motor housing to the claw at an angle, four universal joints were used –two for each motor. To give the claw some wiggle room it is left suspended from the arm by two pins set on the same axis –this axis is its pivot point and the claw is free to swing about it. There are, however, pieces that were put to prevent the claw from swinging outside the turning range of the universal joint within it –this prevents the universal joint from locking simply by swinging. The claw itself is rather simple. It is built off of a large turntable, one that is driven by the input of an 8t gear. Through the center of the turntable runs the second input, one that leads to a worm gear in the center of the claw. This worm gear drives two 24t gears on either side of it, each connected to a side of the claw. The clawing action is driven by an XL motor (this was originally an M motor, but was replaced by an XL when the M motor's cabling stopped working) while the rotation is powered by an M motor. The claw performs rather well but has trouble grabbing onto some objects. Several versions were built; some included shocks for flexibility while others had rubber tires or treads to provide grip. Because of the arm's modular characteristics, it is extremely simple to swap the claw out for another one; simply pull out four pins and switch.