Race Strategy

1. Race Strategy What do we need to do to make the car as fast as possible? Greenpower schools education event, Castle Bromwich 1st May 2013 Dan Lloyd & Robin Boyd

2. Introduction • Race Strategy is made up of our Powertrain and Electrical teams • Our aim is to make the car go as fast and as far as possible during a race • What can affect the car’s performance during a race? • Batteries • Gearing • Aerodynamics • Driver • Other cars • Pit stop? • How do we know what needs improving? • The experimental method

3. Experimental Process

4. Data… Lots of data

5. Data… Lots of data • Before a Race: • Test the batteries • Look at data from other races • Use simulation to help select gear ratio • During Practice: • Check whether gear ratio is correct • Make sure everything on the car works properly • During the Race • Monitor car data • Decide when to pit • Simulation & Strategy • Analysis • Practice & Race • Afterwards • Use data to improve simulation, design or processes (such as pit stops)

6. Today’s Activities Simulation & Strategy: Driven vehicle simulation – Vicente Analysis: Motor dyno and losses – Dan Understanding Batteries – Robin • Simulation& Strategy • Analysis • Practice & Race

7. Race Strategy – Simulation & Strategy Working out how fast and far we can go before we get there

8. Simulation & Strategy • Target of the Race: • Do as many laps as possible in 90 minutes… • … using only 2 sets of batteries. Go faster!! Go slower!!

9. Simulation & Strategy Gear Ratio

10. Simulation & Strategy Gear Ratio

11. Simulation & Strategy Gear Ratio

12. Simulation & Strategy Gear Ratio

13. Simulation & Strategy ↑↑ Gear Ratio -- Speed ++ Force ↓↓ Gear Ratio ++ Speed -- Force Which Gear Ratio? ? • Every car is different: • Different aerodynamics • Different wheels • Different losses Test and simulation will help you decide

14. Simulation & Strategy Motor calculations Battery model Vehicle losses Track Data Aerodynamic equations

15. Simulation & Strategy

16. Race Strategy – Motor and Losses A quick guide on how to prevent your motor from melting

17. Motor Fields and Forces • How does the Greenpower motor work? Example of a 2 pole motor Example of a (broken) Fracmo motor

18. Motor Fields and Forces • There are 2 important fields at work: • Electric field from windings • Magnetic field from the magnets • A current flowing through a wire in a magnetic field creates a force which makes the shaft spin. BUT moving a charged wire through a magnetic field induces a voltage that opposes the supply. These reach an equilibrium and a maximum speed is reached

19. Motor Power and Efficiency • How do we calculate how much power the motor uses? Power = Current x Voltage (Watts) (Amps) (Volts) For example: For a 24V motor running at 20A the power used is 480W This is higher than the motors rated power! We can do the same to measure power out from the generator and calculate the efficiency. Now it’s your turn!

20. Where’d the power go? So the power in was more than the power out… The energy must have gone somewhere • You can’t create or destroy energy, only change it from one form to another.

21. Motor Losses • Noise • Heat • From friction in bearings • Electrical resistance in windings • What about other losses on the car? • Friction in the chain • Friction in axle bearings • Aero resistance • Tyre friction (rolling resistance) • Voltage drop across wiring

22. Motor Losses All these losses mean that the motor draws more current to run at the same speed… And more current means more heat! How do we reduce current? • Reduce losses and external loads • Change gear ratio

23. Learning our lessons • What do we do with this information? • Try to minimise vehicle losses • Use better bearings • Keep chain clean and oiled • Improve aerodynamics • Make sure tyres are inflated properly • Keep motor cool • Don’t work the motor too hard • Feedback results into the simulation

24. Q&A Any Questions?

25. Thanks

26. Race Strategy – Batteries Squeezing the most from your cells

27. Batteries • What do they do? • How do they do it? How can we get more out of them?

28. Source of Energy • 32Ah - Amp Hours (what does this mean?) • Can produce 32 Amps for 1 hour, at 12 Volts • 384 Watts, for one hour (P = I x V) • 192 Watts, for 2 hours…

29. Source of Energy • For Comparison… ?  11.2kg, 12V, 32AH

30. Source of Energy

31. How do they work? • Chemical Reaction. http://members.kos.net/sdgagnon/te33.jpg http://hilaroad.com/camp/projects/lemon/1lemon_meter.jpg

32. How to get more? • Change things about the battery • Nature of the reactants • Physical state • Concentration • Temperature • Catalysts • Pressure • (source: Wikipedia)

33. How to get more? • Temperature • BUT • Limited to 25 degrees by regulations…

34. How to get more? • So we did some tests. • Remember… 384 Wh • Actual number measured? ~300Wh

35. Where has the power gone? • Peukert'slaw • The faster you discharge a Lead Acid battery, • the less usable capacity you get (http://en.wikipedia.org/wiki/Peukert's_law)

36. Understanding the discharge Fixed current at 28 Amps Volts Time

37. Can they Recover? • Removing the load can cause the battery voltage to recover • This doesn’t give you more energy, but it does change how the battery provides that energy • Doesn’t last long…

38. What do we do with this? • Combine the information with: • Motor Info (Dyno) • Track Info (Simulation) • Car Info (Aero, drag) • Race info (Competitors) • And then use this to tune our choices and decisions

39. Thanks!