This week was the last lab for The Hot Shocks. After realizing we hadn’t collected force and temperature data without the heater and with the updated LabVIEW VI, we ran tests at 30 and 90 RPM with no heat addition. Afterwards, we tested out Eric’s PID controller. The controller works, but the gains need to be tuned in order to optimize its respontse. The PID controller is currently not as effective as the hysteresis controller, for several reasons. First, the proportional gain on the controller was too low and it was not ramping up quickly enough. Second, the integral term was contributing significantly to the input during the ramp-up phase, which means it was including terms that were not actually error but merely part of the transient response. We eventually tuned the gains to work well, but this implementation was still not as effective as the hysteresis controller, both because it took longer and because it had greater temperature ripple in steady-state. We believe that a hybrid controller incorporating both hysteresis and PID modes would be the ideal controller for this system - the hysteresis controller would keep system response fast, while the PID would help it maintain a better steady-state temperature, reducing over- and undershoot.
At the end of lab, we received thoughtful and valuable advice from our GSI, Spencer, about the transition from undergraduate studies into industry or graduate school. As we move on to bigger, and hopefully better, things, we will always have Spencer’s tips to refer back on. In the coming days, we will work to improve the controller’s user interface, write our final report, and prepare for our presentations to the GSI’s and our classmates next week.
Thanks for reading!
-The Hot Shocks
This week in lab, we focused on data collection and testing the various controllers we have designed. In the coming days, I plan to design a new piece of hardware to act as a dial for the temperature setpoint. We purchased a small LCD screen from Jacob’s hall, and we plan on laser cutting a small piece of wood to hold the LCD screen and the potentiometer to make the Hot Shocks Hot Box look more visually appealing. I also plan on working on data analysis with some others in our group on Sunday or Monday so that we can use the data to officially verify the functionality of our controller.
This lab has been a great experience this semester. I think the Shock Dyno lab offered something for everyone in our group. Personally, I enjoyed considering the fluid dynamics aspect of the shock dyno, while others spent more time focusing on the control system and data analysis. I appreciate that this lab allowed all of us to explore different aspects of mechanical engineering in which we were most interested.
After working a little more on the final report last week, I realized that we didn’t quite have all the data we needed to confirm the improvements from our heaters. Because of this, we started the lab by taking data for force and temperature vs. time with no heat addition with the updated LabVIEW VI. Once again, I manned the workstation while tests were being run to ensure that data was collected and exported correctly. I’m a little sad that my time with the Hot Shocks’ is coming to an end, but I’m very proud of what we accomplished this semester and I’m happy to have forged closer friendships with all my teammates. I’m looking forward to reports and presentations next week so we can show our GSI’s and classmates what we’ve done!
This week I worked with Eric on tuning the PID controller. We found that it is not as effective as the hysteresis controller in stabilizing temperature - I would hypothesize this is because the integral term accumulates too much error during the ramp-up phase and causes the system to overshoot. We were able to compensate for this by reducing the integral gain, but this renders the system less effective at reducing steady-state error and effectively makes the integral term a moot point. An ideal controller for this would be a nonlinear hybrid controller that operates in hysteresis mode when outside of a small range about the reference temperature, and switches to PID mode when it gets close to the reference temperature. This would speed up system response in both the ramp-up region and the steady-state region, and I believe it would improve our controller’s effectiveness by reducing temperature ripple. This weekend I will be working on an LCD and analog interface that allows the user to see the current temperature, the reference temperature, and the PID gain values. This system will also have dials that allow the user to adjust reference temperature and PID gains without having to reprogram the Arduino. By next Wednesday, the system will be able to run independently. It will also incorporate a switch that allows us to turn the heater on and off while leaving the power supply plugged in - currently we have to unplug the power supply to turn the heater off, which is very inconvenient for normal operation. Lastly, I had originally hoped to remove the microcontroller from the system and make it a PID controller, but implementing an LCD requires the use of a microcontroller. If I have time, I may still attempt to transfer some parts of control to hardware, where the signals (especially integral and derivative terms) will be less noisy and more reliable than in the Arduino.
This week in lab I helped gather data with the rest of my group. In order to make sure that we have enough data to compare, we took a couple more tests without the controller so that we can analyze the difference that the controller makes on the force output. We also tested Eric’s PID controller which is a good reference for future adjustments of this project. I have worked on both the presentation and the final report in this past week and will continue to do so. It is also time for more cupcakes.
This week we ran some of the PID tunings and custom PID controller that we had written. Unfortunately we had some software issues with the custom PWM signal. Additional controller tuning and system modeling would be required.
Before lab, I lasercut an acrylic flame logo to finish the hot box. This allows the indicator light to stay inside the box and the light can be viewed through the acrylic. During lab I helped collect data that I plan on analyzing during the next couple days for the final report and presentation. I also plan on helping Les integrate an LCD screen for the box to display the temperature setpoint without the need for a computer.