Homopolar Motor Design Challenge
Mission Statement: The objective of this design project was to design a homopolar motor with provided simple materials while maximizing angular velocity.
Design Theory & Constraints: The team sought out to design a motor from their knowledge of electromagnetic fields and forces.The project had minimal constraints. The motor must contain only the materials provided: a single AA Energizer battery, copper wire, and a significantly strong magnet. In order to optimize rotational velocity, the team desired to minimize angular momentum and friction while maximizing the Lorentz force necessary for the rotation.
The amount of force exerted by the magnetic field on the current carrying wire is expressed by F=q x B =I x B. Therefore the force on the wire will be maximized when the design maximizes the amount of wire that is perpendicular to the magnetic field. Magnetic field lines leave through one end of a magnet, before wrapping around and entering the magnet on the other side. Thus the team’s design will attempt to intersect the magnetic field as the field lines go out away from the battery.
Implementation of Motor: One of the issues involved with the implementation of our design was the ability of the wires to stay in contact with the battery. On the top of the battery, the point of contact was continually slipping, causing the wire to move and potentially fall off the battery entirely. To minimize this slipping the team tried to maintain a good balance of the wires. By shortening the wire length of the pinch that culminated to the point of contact, the wire was able to balance better on the metal and therefore maintain balance and therefore motion for a greater amount of time.
On the other end of the circuit, the wires had to maintain constant contact with the magnet. However, too close contact would result in excessive friction, thus slowing the motor or inhibiting motion all together. In an attempt to maintain contact, the team formed the wire around the circular base of the magnet, however, did so loosely in order to minimize the friction involved.
The team designed the shape of the wires so as to maximize the amount of magnetic field intersecting the current carrying wire. The wire therefore hugged close to the battery in an attempt to intersect with the field lines circling out from the center of the battery. The narrow shape also minimizes the rotational inertia of the motor.