Alex Kowalski, Alex Kozhemiakov, Dan Tabrizi
Our mechanism centers around a flat truss that extends through the larger hole, connected at an angle to a rectangular base. Support beams in the truss are oriented so that they’re in tension, preventing buckling. Additional diagonal supports were added through multiple iterations to reduce twisting of the main support truss.
We use a 3-inch moment arm to lift the weight, with no counterweight. An extension piece was added to the end of the moment arm to compensate for height differences between the truss and weight. Additionally, this prevents the weight from rotating away from the optimal lift position at the end of the moment arm.
Using the equation , we can calculate the required torque to be
. Since the servo produces 72 oz-in, the torque capability is satisfied. Since the moment arm is 3 inches and the arm starts 23.5degrees below horizontal, the final position will be at 66.5degrees above the horizontal. A right triangle is formed where the two legs are 3 inches. Plugging into the Pythagorean Theorem, which is greater than the necessary 2in for the project. However, this theoretically lift is not achieved because it doesn’t account for bending/deflection of the truss. Also unaccounted for is the fact that the moment arm does not begin 45 degrees below the horizontal, causing the arm to lift both vertically and horizontally.
One feature we’re most proud of is our 2-D extension truss. This truss is reasonably lightweight but extremely strong in bending. Another element we’re proud of is our moment arm extension. This piece allows us to leverage the full power of our servo given the dimensional constraints of our truss. Overall though, we’re quite proud with the level of craftsmanship exhibited by our truss.