The VEX Potentiometer V2 is a sensor that measures the rotational position of a shaft by providing a variable voltage signal. It offers higher durability, reliability, and precision compared to previous potentiometer model.
How the Potentiometer V2 Works
A potentiometer is an analog variable resistor. It produces a voltage output that varies based on the position of an internal wiper arm moving across a resistive material. As the shaft rotates, the wiper arm sweeps across the resistive track, changing the resistance and therefore the voltage output.
The Potentiometer V2 uses a conductive plastic resistive track rather than a traditional mechanical resistive material. This provides smoother operation, reduces wear, and extends the sensor’s life. The sensor produces an analog voltage that is read by a V5 Brain 3-Wire Port and converted into a digital value between 0 and 4095.
A potentiometer also contains a region called the deadband, where no resistive material is present. If the wiper arm moves into this area, the circuit becomes open, and the sensor outputs 0 volts. The Potentiometer V2 is designed to minimize deadband effects, allowing for more consistent readings.
Many common potentiometers, such as those used for volume knobs or light dimmers, use a fixed shaft to adjust resistance as it turns. These designs often rely on frictional contact with resistive materials that can wear down over time.
In fixed-shaft potentiometers, the rotation of the shaft directly moves the wiper across the resistive track. Over time, mechanical wear can lead to inconsistent readings or sensor failure.
The VEX Potentiometer V2 uses a through-hole design rather than a fixed shaft. A square shaft passes through the center hole, allowing rotation to be measured without restricting mounting options. This design provides flexible integration into a variety of mechanisms while maintaining durability and accuracy.
Common Uses for the V2 Potentiometer
The two applications Potentiometer V2s are commonly used for are controlling the position of an assembly or providing varying feedback to the V5 Brain to select a function or change a variable value. Some classroom examples of these would be:
Controlling position: The shaft for the 84T gear (step 32 V5 Clawbot build) found on the V5 Clawbot’s arm could be replaced with a longer shaft so a Potentiometer V2 can be inserted on the shaft and mounted to the tower of the Clawbot (steps 35,36). Once the sensor is in place, the students can be challenged to use the feedback from the sensor to move, stop, and hold the V5 Clawbot’s arm at 3 different heights when buttons are pressed on the V5 controller, as shown in the animation below.
Adjusting variables/functions: A short shaft can be inserted through a Potentiometer V2 and fixed to the sensor’s hub with Rubber Shaft Collars, then a small component (such as a Driver Shaft Lock Bar) can be added to the shaft to serve as a knob.
Once this assembly is mounted to a robot drivetrain, the students can be challenged to use the feedback from the sensor to change the degrees the robot turns. In this case, each time the program is run, if the knob on the Potentiometer is turned to a different location, the robot will turn a different amount.
Another fun activity using this assembly would be to divide the values returned from the Potentiometer into seven ranges. Challenge the students to create a user program so as the knob is turned from one range of values to the next on the Potentiometer V2, a different day of the week (or other cute message) is displayed on the Color Touch Screen of the V5 Brain.
Uses of a V2 Potentiometer on a Competition Robot
Shaft control verification: The V5 Smart Motor’s encoders are excellent when used for control of the rotation of a shaft during a competition. However, there may be cases where a Potentiometer V2 may be useful to verify a secondary shaft is rotating to the correct angle. For example, a Potentiometer V2 could be added to the wrist shaft (step 43, Flip build) of the “Hero” Robot - Flip.
In this example, the sensor will provide feedback for an autonomous program to assure the chain drive for the wrist has not skipped a tooth on the wrist’s sprocket and is in sync with the V5 Smart Motor’s encoder. This is shown in the animation below.
Program Function Selection: The V5 Brain with its ability to hold 8 different programs can provide many programmed routines. These programs can be selected by the Brain’s Touch Screen prior to the start of a match. However, a Potentiometer V2 with a knob could be used to select functions within a program or adjust variables in the last moment prior to setting the robot on the field without having to remove the Touch Screen’s protective shield.
For example, the knob on the Potentiometer V2 could be rotated from one side (low range) to the other side (high range) to switch the robot’s autonomous routine from a Blue Alliance routine and a Red Alliance routine.