A series array of power resistors arranged in a circular pattern form the resistor track. These resistors have surface mount packages, which are cheap, easy to assemble and have a low profile. These packages usually include a pad that can be connected to a heatsink, but these pads can be soldered down directly onto the resistive plate PCB instead, to prioritize minimizing PCB size over thermal capability. To ensure the largest possible resistance range, the resistors are placed in ascending order according to their resistance values. Different resistance values can be selected to increase the total resistance range, but this adds complexity to the feedback implementation. For this design, three different resistor values were selected: 0.05 Ω, 0.10 Ω, and 1.5 Ω and are distributed around the circumference of the resistor plate. The resistors for this design are placed clockwise in ascending order around the circumference of the board. The initial third of the circumference contains 0.05-Ω resistors, and so the resistance increases in steps of 0.05 Ω for a total of 1.5 Ω. The second section of the resistor track contains 0.1-Ω resistors and the series resistance increases in steps of 0.1 Ω for a total of 3 Ω. The remaining section contains 1.5-Ω resistors to achieve a total resistance of 36 Ω. With all of the resistors in series, the total available resistance can vary from 0.05 Ω to 40.5 Ω. Mounting holes can be included on the resistor plate to allow for a heatsink, enabling higher continuous power dissipation through the apparatus. The resistance from the positive terminal to the negative terminal is the sum of the series resistors between the positive terminal and the mechanical copper arm (GND). The remaining resistors on the resistor track form the RDiv which is used to apply feedback control to the apparatus. It is critical to expose the PCB copper and remove the silkscreen along the path of the mechanical arm assembly to ensure that electrical contact can be made between the track and the arm.

One important consideration when designing the resistor track is the size-to-accuracy trade off. By using larger resistors, their radial arrangement will likely require a plate with a larger radius which is generally undesirable. The maximum number of resistors are limited by the step size of the chosen motor. For instance, if the motor is capable of rotating 1.8 degrees per step for a total of 200 steps per rotation, then at most, the load can contain 200 discrete resistance values, if they are arranged such that each resistor is 1.8 degrees away from the next resistor. However, this is a very small step size and would push out the resistor track farther away from the center. This particular design favors a small solution size and so the number of resistors used is less than 200 and they are placed at angles larger than 1.8 degrees from each other. Figure 3-4 shows a section of the track.