SunSpec 4 Motor & Drive
Testing Sunspec 4
Motor Testing in Singapore
In Singapore, the only car testing we had was at the stadium and at Clean Tech Park. The car moving maximum speed was about 50 km/h. The test was to test the brake distance for SunSPEC 4. The brake test unfortunately failed as the mechanical brakes cannot stop the car in time. The Bbattery we used was from SunSPEC, a total voltage of 115V.
The test speed was at 50 km/h and the stopping distance was 20m. Regenerative was not very effective in such low speed as battery was full. We failed the test for the first few rounds. Then, our team came into a discussion of how to bring in the regen braking more obvious with a low speed. Using our knowledge from Mobility module, the “E” at the motor must be greater than the “V” from the battery side.
Hence, we open up the program to further analyze how to bring up the regen braking. Mitsuba has many safety factors to protect the motor. The program has parameter such as battery voltage, position of potentiometer for regen braking to take place. We seek the battery group to confirm the current battery voltage. The battery voltage measured was 115 V. Program parameter for battery voltage we key in was 115 V. Therefore, there will be no regen braking to take place.
If the battery is at its maximum, if we would over charge it, the battery would be damage. Hence, we feel that maybe Mitsuba controller is smart to prevent such event to take place hence the regen brake does not take place. This was just a prediction at first. Over at clean tech park, battery voltage was at about 115 V and program in Mitsuba controller set at 115 V. There was no regen while driving, until after many laps and bring the battery voltage down to about 110 V, the driver reported regen brake started to kick in but very little and was not able to stop the car in time.
Then, we fail the test over at clean tech park. The next test came, Mechanical team try to put their best brakes while our team plan to trick the program to make regen braking kick in even obvious. For example, the battery voltage measured is 110 V, we key in 130V into the program which is 20 V higher.
After that, we test on free wheeling and then it works. Then we put it on track for the driver to test and it basically work and lastly we earn the PE certificate for brakes. Finally, our team learn how to solve such scenarios and happy about it.
Motor Testing in Hidden Valley
Conclusion on Motor Testing
Regenerative braking is used to slow down the car without using any mechanical brakes. This will reduce the friction of the brake pads and by regen braking, power is pump back into the battery hence gaining extra energy.
Mitsuba controllers are easily setup with a bit of trail and error. The controller has many safety feature such as preventing regen braking while battery is full. Hence due to passing the brake test during dynamic scrutineering, we trick the program but then we set back to normal setting during the actual race as safety is concern as when the battery is full during the start of the race, we don’t want extra energy to be pump into the battery as the battery might be overcharged.
Proper isolation of every device on the car must be properly isolated as the car body is made from carbon fiber which is a conductor of electricity. Using isolation tapes, plastic screw or isolation materials. This can prevent leakage current into the car body. But even with proper isolation, we must to a resistance test to check weather there is enough resistance in the car body.
Testing at hidden valley racing track, motor plays a big role. One major issue that our team was worried was the performance of the motor in a long run such as did our program set in the controller correct for the car. We did many test over at hidden valley and tune up to its best performance. Driver reports that the motor is behaving very well and the motor are very quite during high speed.
During dynamic scrutineering, the car couldn't brake in time as the regen did not work then we realize that the same thing happens in Singapore. Regen kicks in at speed above 50 km/h to slow down the car but then, driver report that regen brake has a bit of delay and hope we could solve this issue so that once the driver release the accelerator, regen kicks in straight and not delayed to pass the last test.
Our team explore further more in the program and realize there is a sensitivity for the regen brake to kick in. It works by when the accelerator is released to a percentage, the controller then brings in the regen. Hence, this is how the program works, when the potentiometer(accelerator) resistance is 0 ohms, the accelerator is at 100%. When the accelerator is released fully is 0%. The program gave us regen take places at 10% 20% or etc. It means when the controller sense the accelerator was release at 10% mark, regen kicks in rather than the accelerator position at 0% which delay the regen. However, everything set and we solve another issue and learn from it.
While we were doing the Motor testing in Hidden Valley, we discovered that there was some electricity passing through the Carbon Fiber Body of the SunSPEC 4. We had some suspicion of where the electricity is coming from.
Firstly, it might be the static charges building up in Carbon Fiber Body as the only contact point to the ground is the rubber tires which is insulator thus the static charges is unable to discharge
Secondly, we suspected that the screws that were on the high voltage box is somehow transmitting some electricity to the body of the car. But that suspicion was clear when we isolated all contact from the High Voltage Box from the car.
Lastly, we did a resistance test and found out that when the Miniature Circuit Breaker for the right motor was turned on, there was a drop in resistance however there was nothing with the wires. After some discussion with the lecturers, we deemed it was safe to operate the car as the resistance was in Mega-Ohms..
In conclusion, it is important to isolate every device to the body and by doing mega or resistance test before anyone getting in the car as we are dealing with High Voltage and High Current.