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Welding the rear axle
Rotary Racer - Car Performance
Dunsfold Park 2008-09-28
Results
We won !
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 Yuassa 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 Yuassa batteries. It currently bases its results on the current being used from the battery. |
| BatPack | The battery pack in use (0 or 1). We have changed the driver with each battery pack 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.
Practice Laps 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 we placed back in the battery area.
| Battery Pack | BatA | BatB |
|---|---|---|
| 0 | 12.45 | 12.26 |
| 1 | 12.42 | 12.43 |
| 0 | 12.22 | 12.13 |
| 1 | 12.17 | 12.17 |
| 0 | 11.78 | 11.76 |
| 1 | 12.04 | 12.04 |
| 0 |
Notes
- The Car Computers "Average Current" setting was 22.50 Amps. The current setting was lowered to 21 Amps in Ben Millars stints due to concerns over battery charge. The software was car11.
- We had moved motor was inside the car, with cooling fans and we were using a 19:57 (3.0) ratio on the chain drive.
- The Dunsfold Park circuit was on an old aerodrome. The circuit was about 1.28Km long and fairly flat. There was little wind on the day. The corners were quite tight and there was quite a lot of traffic to contend with.
- Drivers were: Dan Isles, James Alington, Tom Alington, Gareth Barnaby, Dan Dando, Ben Millar.
- The CarComputer and MotorSpeed controller worked well although there was a little issue in downloading the data to the laptop that needs to be fixed. The viewing of the lap data during practice laps and on driver change needs to be improved. First the data needs to be saved so that it is not lost when the power is switched off and second the average current measuring system needs to be looked at at it was giving higher values that actually borne out when reading the data logs. The Motor Power Control algortithm could do with some more work as well.
- There was a glitch in the Charge for battery pack 0 at 2008-09-28 14:36:35 for 12 secs near the end of James's run. Could the power have been switched off ?
- The Motor cooling system worked fine. The temperature graph shows the motor slowly heating up through the race and reaching a top temperature of 44 degrees C. The Car computer would have been running the fans between 50% and 75%. (The fans go up from 50% to 75% at 42 degrees). We could run the motor slightly cooler by modifying the Car Computers fan control algorithm. We should be able to estimate the internal thermal resistance of the motor (how well the motor can get heat away from the armature) using the voltage/average current for the race and the rate of rise of the motor case temperature with this data.
- The drivers drove excellently again. They had a lot more experience of over taking in this race especially on the tight corners. Tom in his first drive of the car did exceptionally well. He started off cautiously and slowly speeded up through his stint getting respectable times near the end.
- We had a concern during the last drive that battery pack 1 was failing quickly as the lap speed had dropped significantly. Looking at the data this was due to the throttle no being fully opened :) . The battery set (1) was actually well up on charge as the voltage readings taken in the pits suggested. We might need to do something with the throttle control.
- We actually were only averaging 20.8 Amps during this race (about the same as Castle Combe). The batteries terminal voltage under load were: 21.83 (10.91) and 22.97 (11.48). The Car Computers charge levels were: 13.5% and 25%. Looking at the battery data we had 6 mins left in battery pack 0 (5%) and 32 mins left in battery pack 1 (25%). Overall charge left was about 15%. We could, at a push, have used 10% more power. The computers charge calculations seem about spot on for a good set of batteries. Battery pack 0 has noticeably lower capacity as we know.
- The race log clearly shows the CarComputer limiting the current once the car was up to speed. Generally is was restricting the motor to about 93%.
- The average speed was 40.97Km/H and the peak 55Km/H. The slower average was due to the amount of slowing down to pass cars on the tight corners. You can see from the throttle graph the amount of throttle control that was used.
- No real answer as to if the performance was better or worse with the motor inside the car. We might be able to look at these and the Castle Combe figures in detail to see this.
- There were no issues with the motor speed controller doing the power limiting. It might be worth checking the actual efficiency we got during the race though.