Rotary Racer Car Data

Rotary Racer - Car Performance

National Final Goodwood 2009-10-18

Results

This was the Greenpower National Final race at Goodwood with Rotary Racer RR8. We had an excellent race, despite some minor difficulties, and managed to win the race and hence the Greenpower National Champianship !

Car Computer Log

This shows the main items measured by the Rotary Racers car computer. They are:

Item Description
Throttle The position of the twist grip throttle from 0 to 100%
MotorCtl The motor power output setting. The Car computer sets the motor power based on the drivers throttle position, the speed of the car and the current being used. There is a software algorithm to implement this "drive by wire" system. The Car computer drives the PWM (Pulse Width Modulation) Motor Speed controller with a duty cycle proportional to this value. 0 - 100%
Speed The speed of the car in Km/H calculated from the magnetic read switch pulse generator by the Car Computer.
Voltage The batteries voltage under load.
Current The current being taken from the batteries.
Charge0 The charge left in the battery pack 0. This is calculated by the car computer using an algorithm that has been honed to match the battery discharge curves for the Yuasa batteries. It currently bases its results on the current being used from the battery.
Charge1 The charge left in the battery pack 1. This is calculated by the car computer using an algorithm that has been honed to match the battery discharge curves for the Yuasa batteries. It currently bases its results on the current being used from the battery.
BatPack The battery pack in use (0 or 1), the turbo button (2) and the Pitstop warning (4) . We generally change the battery pack with each driver change.
Temp The Temperature of the motors casing in degrees C.


The graphs show the overall data, the actual ASCII data log files are also available, from the links below, for detailed analysis.

Car Data Log

Practice Laps Data

Car Data

Battery Voltages

These are the battery voltages measured with a multimeter at the end of each change. The readings were taken as soon as possible after the batteries were taken out of the car and placed back in the battery area. We were a bit to high to remember to take the last set of readings :)

Battery Pack BatA BatB
0 (RR11,RR12) 12.4 12.4
1 (RR13, RR14) 12.2 12.2
0 12.1 12.0
1 11.7 11.7
0 11.8 11.9
1 ? ?

Notes

  • The Car was RR8c. This was the cars fourth race. Some minor aerodynamics changes had been made following ideas and VWT simulations. The area behind the front wheels was sloped, foam slopes were added over the drivers sholders and the rear section behind the driver was extended to a point. We used the Schwalbe Durano tyres on the rear and our old continentals tyres on the front due to the new Schwalbe Durano tyres being shreaded during braking in practice. The batteries were kept in new insulated and warmed (about 32 degrees C) battery boxes that were finished just in time for this race.
  • After practice with a 19:49 ratio, in the race we used a 18:49 (2.72) ratio on the chain drive.
  • There was a problem at practice where we got a puncture in the front left tyre. This was caused by the front left brake locking up nunder heavy braking. On inspection the right hand brake was way out of adjustment and the automatic brake balancer had probably reached the end of its travel. We need to look at what happend here. I suspect that when the wheels were taken off to do the aerodynamics changes and the brakes re-adjusted, the brake outer cable may have ridden up onto the outside edge of the adjuster on the inside brake balencer adjuster, where it cannot be seen. During the practice it probably slipped back into place leading to incorrect adjustment. The brakes are also now too powerfull for the wheels now that they have bedded in. We will probably need to fit a new brake lever with less leverage to reduce the brake preasure and/or taper the leading and trailing edges of the pads.
  • The Goodwood circuit is 3.862Km long and is fairly flat with sweeping corners. There was very little wind on the day (8 Km/H ?).
  • The Car Computers "Average Current" setting was at first 25.00 Amps, the Control Speed was 38 Km/Hour, this was tweaked during the race to obtain an average current of 24.5 Amps. From battery tests this looked like a safe current to use for the race leaving a reasonable amount of reserve. It was lowered near the end of the race to make sure we finished ok when one battery pack failer earlier than expected. Again we used a touch to much current in the early stages. The current averaging algorithm on the car computer reports to low a value in the early stages of the race. We need to improve this. The software was car15.
  • Drivers were: Ben Millar, James Allington, Tom Alington, Gareth Barnaby and Dan Dando.
  • The drivers drove excellently, the drivers performance was well matched. They addeared strictly to the yellow flag, chicane and pit lane rules and had no black flags throughout the race. The pit stops were smooth and excellent. Even after being rear ended in the pits, the team carried on and got the car out quickly after checking it over. Battery pack RR13/RR14 was hit in this incident and needs to be checked. Above all they were not to serious and had fun :)
  • The car ran very well, there were only a few problems during practice and the race. The small aerodynamics improvements certainly improved the cars performance and helped us to the win. The motors temperature was generally below 41 degrees.
  • The CarComputer and MotorSpeed controller worked well, however there were times where it would not accept changes to the average current and current turnover parameters over the telemetry. Reseting the computer during pitstops fixed this. We need to look at why this happened and fix it. The new Voltage/Current based battery charge indicator algorithm worked well.
  • The batteries were RR11/RR12 (new at last years final and had been used in just that race) RR13/RR14 (new this year). From battery testing we had determined that we could use about 24.5 Amps from these batteries on average (at about 18 degrees) and that the older ones had about 15% more capacity than the new ones. In actual fact, for this race, the older battery pack had about  20% less capacity than the new batteries .... The current average over the race ended up being 23.7 Amps (42 Amp/Hours fromRR11/RR12 and 52 Amp/Hours from RR13/RR14). The main reason for this lower than expected average current is that when we put in the RR11/RR12 batteries for the last stint, although the computers reported capacity from both average current and voltage/current sensing and battery open circuit terminal measurments led us to believe we had plenty of capacity to finish the race, within a few laps the batteries dropped off to 20V. We had to do a quick change back to the RR13/RR14 battery pack. We turned down the current level substantialy to make sure that we did not stop out on the track and lose our first place. This battery set (RR13/RR14) still had about 10% capacity remaining at the end of the race. We need to find out what happened to the RR11/RR12 battery pack, perhaps a cell failed or perhaps the main switch had problems ? After taking the batteries out they still reported 11.8/11.9 Volts open circuit suggesting that they were ok ... The RR11/RR12 pack only ran for 105 minutes and produced 42 Amp/Houres while the RR13/RR14 battery pack ran for 135 minutes, produced 52 Amp/Hours and still had about 10% capacity left, the warming certainly helped here. It was seen that the brake light stayed on even when the main switch was off, so maybe the main switch has a fault ? Looking at the logs the battery voltage dropped by almost 2.5 volts going from 0 to 23 Amps. Normally the voltage drop is about 1V at this state of charge.
  • The average speed was about 47.6Km/H and the peak about 60Km/H. The fastest drivers (where the power level was at full) were lapping at about 4:20 (53 Km/H (33 MPH)).
  • We managed 120.00 miles the furthest we had ever done, but it would have been more without the duff battery. There was also quite a few yellow flag incidents to contend with and hence quite a lot of throttle and probably brake work.
  • What a year, a podium at every race with the new car, three firsts and a second. An excellent result for the team and its new car.