what is a boomilver
A boomilever is model cantilever that is designed to hold 15kg. Many science and engineering competitions, such as Science Olympiad, host boomilever competitions to help teach basic physic concepts to students.
In this post, we will discuss physics concepts used when creating a boomilever.
Stresses on boomilever beams
One important concept to understand is that beams act similar to springs; when a load is placed upon a beam it bends elastically. This bending is usually able to return to its original position unless the load breaks the beam.
If you look at any structure like bridges or towers, they are constructed by a series of beams that ultimately support a given load. However the stresses placed on the beams of a boomilever or other cantilevers are much different that the beams of other structures.
If you look at the figure below, most structures have simple beams which distributes the load across the entire beam. However, cantilever beams have the load at the edge of the beam, causing most reaction forces to occur at the opposite end of the load force.
Because the distance between the reaction forces and the load force is greater on cantilever beams, it is much more likely to bend and, therefore, easier to break.
Cross-sectional area of beams
One way to increase the strength of your boomilever is to increase the cross-sectional area of its beams. By increasing the cross-sectional area of the beams, the moment of inertia on the beams decreases, increasing the beams’ strength.
Another way to reduce the moment of inertia on the beams of a boomilever is to increase the projected cross-sectional area. Similar to the previously discusses concept, using hollow tubes to make support beams allow you to reduce weight while also being able to have a greater projected cross-sectional area. This is the main reason for why tube boomilevers and tower chimney boomilevers are mores successful than standard boomilevers.
Because wood has elastic properties, a boomilever’s is likely to sag or deflect when a load is placed on it. If you know the modulus of elasticity of the wood used to make your boomilever, then you could calculate the theoretical deflection.
However, knowing the amount deflection is not necessarily important for boomilevers because the base and tension members are solidly connected. The only main effect that deflection causes is that there will be more tension strain on the main tension piece and the deflection may bend the main tension piece, cause that piece to break at either end.
Another way to increase the strength of a boomilever’s compression beams is to increase its buckling strength. There are many ways to accomplish this task but the main methods are to increase the amount of bracing on compression members, reduce the length of the compression member, or increase the cross-sectional area of the piece.
Source for all pictures: “Teaching With Midwest’s Boomilevers” from Midwest Products Co, Inc.