Day 5 began in high spirits and we were ready for more testing on all fronts. Some brainstorming the previous night had resulted in ideas on how to fix the issues with the fuel-cell system and the motor. For some reason, the fuel-cell controller was turning off during operation and stopping the flow of electricity to the car. We were also ready to install our new motor controller, the Vedder, which had just started working the previous night. We were expecting this to increase the speed of the car with more precise control over the motor.
Testing revealed that the issue with the fuel-cell controller was triggering immediately after a hydrogen purge. Our fuel-cell stack purges hydrogen gas on a regular basis. In order for this to happen, the purge valve needs to open for 2 milliseconds and then close again. When the purge valve closed, the pressure regulator registered a fluctuation in the system pressure. Reegan, Alex and I realized that the pressure was fluctuating enough to trigger an over-pressure/under-pressure alarm which was turning off the system! Once we realized what was going on, we changed the pressure alarm values in the controller code, pressed the start button, and voila! Perfect operation.
Simultaneously, some other members of the electrical team were working on installing the Vedder motor controller into the car. After connecting the correct wires and some tinkering with the code to set the right current limits and pedal settings, the Vedder was ready to go. We crossed our fingers, held our breaths and pressed the accelerator pedal a little bit. VROOOOOOOOOOOOOOOM!! The motor roared to life. “Give it more gas!!” came the command from behind the car and the pedal was pushed all the way. This time, Alice was loud enough to drown out the loud music playing on the Paddock speakers. Lots of cheering ensued. Our motor was clearly going faster than before – a necessary part of moving from a dead stop and completing a run. Things were looking good.
The next step was to take the car out to the small practice track at the back of the paddocks area and give Alice a quick trial run before the actual attempt. We lined up, waited for the teams in front of us to finish testing, and rolled out onto the track. The newly fixed fuel-cell system was started up, the GoPro’s recording button was pushed and our project manager feathered the pedal a tiny bit...*Wobble* *Wobble* *Wobble*... and the car was off! She was going much faster with distinct improvements in speed and throttle response! Nik’s face under the helmet visor was filled with joy as he did round after round of the practice track with our Canadian flag taillights flashing in victory. After more celebration, we brought the car back into the paddocks to prepare for the dynamic brake testing component of the competition where we would also have an opportunity to attempt a run on the actual track at 6 pm.
We decide to take a quick break and take a Canada Day selfie at this point. As it so happened, Shell's media team was nearby and took a picture of us taking a picture!
Time went by fast and we lined up at the start of the track. Some waiting later, we pushed the car to the starting line. The track marshal gave his go-ahead, Nik pressed the gas pedal……*Wobble* *Wobble* *Wobble*.... and the car was off again! Happiness was writ large on our faces as we headed back to the paddocks. The biggest challenge at the London track is a very steep hill towards the end of the course. Almost all the teams at competition were having issues with climbing it and so were we. In fact, the hill was one of the biggest reasons we put the Vedder in. Nik approached the hill and started climbing, the car’s speed started dropping. If the motor slows down too much, the controller is unable to track its position with respect to the coils. This results in a decrease in performance. The speed was getting dangerously low. Nik made it halfway up the hill aaaaaand…. the car came to a dead stop. The motor controller was unable to spin the motor anymore. Oh no. The car was brought back to the paddocks and we set about trying to fix this issue. At competitions like this, giving up is never an option. Thankfully, we had two more tricks up our sleeve. Here's a video of our first attempt:
The motor’s configuration used something called back EMF to track its position. This system breaks down when the motor slows down. However, there was another way to track its position – a hall-effect sensor. This sensor allowed the controller to track the motor even when the motor was near a dead stop which is what we were facing on the hill. Our second trick was air-starving the fuel-cell stack in order to increase its performance. This involves limiting the amount of oxygen available to the stack and running it for some time which burns off built-up platinum oxides. Our Electrical Co-lead, Mike Bardwell set about soldering the hall-effect sensor and by the end of the night, we were able to get it to work with our motor. Alex and I used this time to air-starv the fuel-cell. But it was almost 11 pm and the paddocks were going to close. So, we cleaned up and prepared to set everything up the next morning. Tomorrow we try again!