Basic Gearing and Movement

The Gearbox

We used a gear ratio of 75 to construct Marvin's two powered wheels. The design here was kept fairly simple, with a very solid flat layer of Legos held together by pegs. This created a nice base, which we could brace other sections to. The left wheel of the design also contained a few extra gears to allow space for an encoder.


The casters in the front of the robot were designed with the goal of being as short and sturdy as possible. An original design featured a slightly taller one-wheel caster, but the single wheel often got stuck or tilted too often. The next design phase was a two-wheel caster with the load supported almost directly over the axel. This did not turn as well as expected during movement and a few parts were replaced to move the load slightly off the axis, as well as adding a second identical caster in the front for more balance.


The spinners used to capture territories went through two, fairly similar, phases of design. We first built a housing for a third motor within the existing gearbox. The motor was able to sit on a beam between the gears used in movement and be braced on four sides above that. A gear ratio of 45 was used for the spinner, allowing them to spin fairly quickly. The initial set of spinners was held up only on top by the pieces seen in the picture and had a different, smaller set of tires. However, these tires would often get stuck and the whole setup would bend towards the robot due to support coming only from the top. So, the final design features larger, more robust tires with bracing on top and bottom so as to keep them aligned and avoid bending.

Lever Arm

The lever arm is a semi-elastic arm driven by a single servo, geared for torque. Each segment of the lever arm contains and will hit a peg from a different lever arm allowing it to bend out away from the robot to a certain extent. The rubber bands hold these segments against the peg, giving the arm its shape. The operation is such that the arm can bend flexibly towards the robot, but is stiff being pulled away. This was designed so that, while pulling the lever, if we should pull too far and it flicks back up in front of the arm, the arm will change shape and flick back open around the lever as the servo opens it.


Another highly functional feature of the robot is the basket used to catch and deliver ping pong balls. The basket is made mostly of long Lego sticks, using other pieces for shaping and support. The basket holds up to around 35 ping pong balls and can be dumped by operating a servo, geared again for torque, seen housed in blue bricks on the front of the robot. We cut our green base plate in order to make a smoother dump for the balls, as some were previously getting caught in spaces between the sticks.


As the competition progressed we noticed the number of collisions happening on the playing field, and the number of wires being pulled and parts falling off. So, we decided to use our remaining base plate sections to add some armor to our robot. While not the most effective solution, the flat plate is enough to keep Marvin's sides from getting completely caught on another robot during competition.


What driver doesn't need a relaxing place in their vehicle? While this may not have been the most relaxing hammock during competition, our Lego man is strapped in to take in the scenery of Marvinís explorations!