Potentiometer

Potentiometer Kit

The potentiometer kit comes with two potentiometer assemblies (pictured below).

Functions

A potentiometer is an electrical device whose resistance is adjustable. The user can therefore adjust the degree to which the potentiometer opposes electric current through it, simply by turning a shaft that is attached to the center of the potentiometer. As the resistance of the potentiometer changes, so does the voltage, which thus causes the potentiometer to act as a variable voltage divider. This varying voltage can be measured by the VEX Controller and is directly proportional to the angular position of the shaft connected to the center of the potentiometer. This allows you to obtain an analog measurement of an angular position. The VEX potentiometer is designed with a “D-hole” in the center, which should slide easily over the VEX square shafts. The potentiometer includes two arcs, each ½in from the center hole; these arcs exist to assist with mounting the potentiometer to the robot structure.

Benefits

Incorporating the VEX potentiometer kit into your project can make it easier for your robot to perform autonomous behaviors. A robot equipped with a potentiometer becomes aware of the position angles and motion of different components, thus making it more aware of its actions.

Applications

The VEX potentiometer can be used to measure variations in angular position of different robot components. It can be very useful when implementing robot manipulators or shooters. For example, if you are designing a shooting robot, it is possible to estimate the angle at which the robot should shoot a ball in order to get the ball into the goal from a known distance.

Range Limits

The mounting arcs allow for up 90º of adjustment to the potentiometer’s position. Since the potentiometer has limited angular travel, it is important to ensure that the shaft that is being measured by the potentiometer does not travel more than 260º (the potentiometer can only move approximately 265º ±5º and can only electrically measure 250º ±20º). The adjustment arcs allow the potentiometer’s range of motion to be repositioned to match the shaft’s range of motion. To measure the motion of something that rotates more than 230º, try gearing down the shaft’s motion such that the gear attached to this “primary” shaft turns a larger gear attached to a “secondary” shaft. This secondary shaft will therefore rotate less distance than the primary shaft. Once the gear sizes are adjusted such that the range of motion of the secondary shaft is within that of the potentiometer, attach the secondary shaft to the potentiometer. This way, you should be able to indirectly measure the rotation of the primary shaft by directly measuring the rotation of the secondary shaft.

Technical Information

• Sensor Type
  • Potentiometer
• Size
  • 1¾in x 1½in
• Weight
  • 0.04lb per sensor
• Wiring
  • Black - ground; Red – (+) power; White- control signal

Before Using

Before you can use the potentiometer, you must reprogram your VEX Controller to read the varying voltage of the sensor on the corresponding port you are planning to connect to.

easyC Sample Code

CMU Robotics Academy Resources

• Programming with Sensors in ROBOTC (Teaching ROBOTC for VEX)
• Potentiometer Printout (Teaching ROBOTC for VEX)