Energy Consumption Rate in a Robot/Motor

We made several measurements of current through the motor and voltage across it using a different current sensor, INA219. Our objective was to compare the results to those from the Hall effect current sensor measurements. Current increases as we slow down the motor by applying a mechanical force. We learned how to use CoolTerm to save data to file (http://www.instructables.com/id/Visualize-data-from-sensors-using-Arduino-coolte/). We worked on our lesson plan: Lenz’s Law and Back EMF. Yancey built a DC motor circuit with the electronic snap circuit kit and videotaped the measurement of voltage across the motor and the current through it. Results are consistent with our expectations. We may use this video to present our lesson plan at the end of the RET program. We also tweaked the Arduino program to print out only the voltage and current to an Excel-readable file. Below is a sample of analysis of data with Excel.

We took data for different cases: motor spinning in air with no mechanical load, with a brief mechanical load, and the motor completely stalled with a mechanical force. We collected data for motor spinning in both directions.

We double- checked the values of voltage across the motor using a digital multimeter (DMM). As a next step, we wanted to use the INA219 along with the Adafruit Motor Shield v2.0 so that we could control the speed and direction of the motor using code. Although we were able to connect everything correctly and got to control the motor’s speed and direction, the voltage and current values made no sense.The output of INA219 is digital, and perhaps our issue has to do with our inability to convert that digital output to an analog readout. We decided that coupling the INA219 with the shield is not central to our work.

Professor Kim emailed us and said it was important to collect data for the cases in which we do positive work, negative work, and no work on the motor as it spins. How can we do that reliably? We are thinking of using a drill press and force the motor to spin in the direction we want. We made a wooden mount for our clamp that grabs the motor and we will use the following set up (on the right) to do our experiments next week.