Mechanical Design
At first it appears that most of the mechanical components
on our project our project were over designed—many were made of metal, and most
were machined. This was not done
just to make the project heavy!
Instead, was the result of a trial and error process. We found that components that were
designed using less accurate methods did not provide enough accuracy for us to
hit our target with the laser reliably.
One of the most critical components for our project was the
laser stand. This component was
designed to move the laser through its full range of motion very
accurately. If it was not accurate,
the errors in the servo motors, connecting wires, and laser stand would combine
to a very large amount of error.
The stand is able to rotate around a vertical axis because
of a pin that is press fit into the plywood base, and has a clearance fit to the
laser stand. The stand, which is
rotationally symmetric, was created in a lathe and then a mill was used to
drill locating holes in it. One of
these locating holes is for the pin just described, the other is for a second
pin that extends above the stand and connects to the laser. This second pin is where the angle iron
is connected, and the angle iron is what actually holds the laser.
Another major consideration was the motors. Selecting the motors was not very
difficult since they were not required to operate at high rpms, high torque, or
low power. Selecting them was
simply a matter of visiting a local hobby shop and choosing motors that were
within our price range. We choose
to use servo motors because they best suited our need—turning to a specific
angle and staying there.
The motors were attached to the laser stand using a stiff
wire that was threaded through a hole on the laser stand and a hole on the
shaft of the servo motor. They
were positioned so that the wire was parallel to the plane it was rotating the
laser in. The wire length was
determined by turning the servo shaft to its clockwise extreme, and the laser
to its clockwise extreme, and measuring the distance between the holes on each
of them.
Additional Drawings and Pictures of the Design:
