Catapult Design

How it works

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BroBot’s catapult is located on top of the rotating base, enabling it to cycle between its loading position next to the retrieval system and its launch position. The catapult consists of an arm on an axle with a polycarbonate and aluminum scoop to hold a beer can. The arm is propelled forward with one or two linear extension springs, located opposite the scoop. Either two or one springs can be used, depending on the desired maximum distance. One spring yields a maximum distance of 12 feet while 2 springs can throw the can a maximum of 20 feet.

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A large motor is mounted on the base of the catapult which is responsible for winding the catapult arm down into it’s launch angle. This is done via a sprocket and chain system mounted on one of the catapult sides. An additional motor is mounted on the other catapult side. Attached to it is a cam that is responsible for actuating a brake lever that controls a set of brake calipers and a brake rotor mounted on the catapult axle. When the catapult arm is set at its launch angle, the brake system locks up, preventing the axle and arm from moving.

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During this period, the motor that winds the catapult arm is able to run in reverse, effectively disengaging the motor from the axle. The sprocket on the axle that connects to this motor is loose on the axle and only transmits power through a set of pins located to the side of the catapult. Since the catapult never rotates more than 120 degrees, the motor can disengage during launching by running the large sprocket in reverse for at least 120 degrees. At this point, the brakes are disengaged as the cam rotates, causing the beer can to be launched, in doing so, resetting the entire system.

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