The Greenpower Masterclass
How to Engineer a Race Winning Electric Car in the
Greenpower Challenge
The Greenpower Challenge has been described as“the best technology competition for schools in theUK”. The unique hands on engineering challenge isfor children and young people from 9-25 to design,build and race a single seat electric powered race car.
The challenge is divided into three age categories:
The Greenpower Challenge
For 9-11 Year olds the challenge is to build a GoblinKit Car, design and build sustainable bodywork andcompete in a series of challenges; drag, slalom andsprint.
IET Formula Goblin
IET Formula 24
The IET F24 Greenpower Challenge is to build thesingle seat electric car that travels furthest over afour hour endurance race on 3 pairs of 12 voltbatteries.
For 6th Form students, universities and apprentices,the F24+ challenge is a shorter, faster race than F24with a “constructor’s championship running throughthe season. This challenge has attracted teams fromJaguar Land Rover, Bentley , Peugeot Citroen, EtonCollege, and of course, Chipping Sodbury School!
IET Formula 24+
The F24 Challenge
With all teams using the same power supply andmotor and stringent design/safety regulations inplace the challenge faced by teams is how toengineer a 4 hour endurance race winning car withinthese restrictions.
Making The Difference
We have with us today some of our top competitorsincluding past and present National Champions whoare willing to share some of their knowledge inbuilding a race winning car.
Science and building a car
First of all KISS (keep it simple stupid). The carhas to last the race to win.
It takes a lot of time to build and develop a car.
Understand the Science:
Forces and Drag
Rolling and friction resistances
Aerodynamic drag
Electric motor operation
Gearing
Science: Aerodynamics
•Air resistance takes most energy from the batteries
•Air resistance = 0.5 pv2ACd
•Power required to overcome drag = 0.5 pv3ACd
p is the density of fluid i.e Air
v is speed
A is area
Cd is coefficient of drag
Basic Aerodynamics
•Frontal Area – How big the cross section is
•Coefficient of Drag – How aerodynamic the shapeis.
•Some Shapes are better.
•Nature Provides some good examples
Frontal Area vs Coefficient of Drag
•Decision: Inside or out side wheels
Panel Gaps
Helmet Fairing
Rolling resistance, drive andgearing
5 x slides Rolling resistance, drive and gearing
Wheel geometry & steering
Matthew
Aerodynamics:
Aerodynamics:
To build a successful racing car, one aspect youhave to consider is the aerodynamic drag. This isthe force needed to push an object through theair.
The aerodynamic drag (or wind resistance isequal to the frontal area of the object multiplied bythe air Drag Coefficient (this Is calculated usingthe shape of the object) and the speed squared.
The wind resistance
increases as the
square of the
Speed.
Aerodynamics:
This is a model similar to that of the standard greenpower kitcar. The red areas represent a high air pressure, and the blueareas represent a low pressure area. There is both a large airpressure on the front, and a low air pressurebehind it, however the high pressure on the front has a smaller affect than thelow pressurearea on the back
Aerodynamics:
Rotary Racer has a long tail sloping, this largely reduces thelow pressure area on the back of the car bringing the air backtogether cleanly.
Aerodynamics:
We use a web based, Virtual Wind Tunnel, to carry out testswith different car designs.
We use 3D CAD programs to draw different car designs.
This provides us with the overall drag information as well aslines of air flow and colours showing pressure.
Once the car is built, we continue to refine the designs.
Aerodynamics:
We have designed and built a Wind Tunnel for the cars.
Aerodynamics:
Tips to reduce wind resistance:
Taper the back of your car down close to a point, but make sure you don't makethe taper to steep, otherwise it will still create a vacuum behind the car due tothe air separating from the body
Reduce the frontal area of your car as much as possible,
Put a tail on any parts that stick into the airflow (like the roll bar)
Try to keep the wheels in-line with the
sides when designing a new car
but make sure you retain a wide-
enough wheel base.
Try different shapes of wind shield, in front of the
Driver's cockpit, and try to keep mirrors and
Other items out of the airflow
Electronics
not essentialElectronics are not essential for a winning car.
However,However, using Electronics can add an edge andmake racing performance consistent
Gathering data, energy management, problemhandling and driver or pit crew information are justa few uses for such systems.
Electronics: Data Logging
Data logginganalysedData logging allows car performance to beanalysed after and perhaps during a race.
With it we can record information such as motorcurrent, battery voltage, speed and motortemperature.
We can also calculate average current per lap,average speed amongst other things.
After a race, the data is put into graph form on acomputer for analysis and feedback back atheadquarters (or school, as it’s better known).
Electronics: Data Logging
Electronics: Telemetry
Telemetry allows us to monitor car performanceduring a race.
reliableThe data recorded in the car is relayed to a laptopin the pit area, where it can be interpreted by thereliable pit crew.
We can then make decisions based on the datareceived, including adjusting the power levelparameters and calling the drivers in in for abattery change.
Electronics: Telemetry
Electronics: Energy Management
fixedamount of energyIn a Greenpower race the car has a fixedamount of energy in the batteries. This needs tobe distributed so that after 4 hours you have justabout used all of the energy.
Without electronic energy management this isquite tricky. Gear ratios need to be rigorouslytested, and in different conditions a ratio thatnormally works perfectly may leave you with nopower.
Electronic speed control allows the motors poweroutput to be finely tuned.
Electronics: Energy Management
Electronics: Rotary Racer
Computer
Speed Controller
Telemetry
GPS
Driver Display
Pit laptop
Team work and Race Tactics
Its not all about the design of the car !
The car has to be well prepared.
The team have to work as a team.
Team meetings, post race meetings
Continuous development
The race day has to be planned as much aspossible !
A race is a race,
anything can happen !
Race Tactics: Car Preparation
Essential to do before a race.
Fix the problems from the last race.
Check the car over.
Check the tracking.
Tyre wear and pressure
Check the tracking again !
Race Tactics: Pit Stops
Have to pitstop at least 4 times for driverchanges. What driver order ?
Can use more than 5 drivers, driver training, fun.
Need to change batteries at two of these at least.
When are batteries running out ? Lap timingand/or electronics with telemetry.
Battery change times, driver time (20mins min).
Pit stop practice
Who are in charge of batteries, pit stop board etc
Conclusions:
This presentation covered the main aspects indesigning, developing and racing a winningGreenpower car
KISS: Its got to finish the race to win !
Remember: The challenge is to involve studentsin engineering to promote this career path.
Students need as much involvement in the cardevelopment as possible.
The rules define the challenge.
Conclusions: Some cars
Conclusions: What can beacheived
A Greenpower car can use an average of 400Watts of electrical energy during a 4 hour race.
An efficient Greenpower car can average about30 MPH with this level of power and thus travel120 miles or more.
In electrical terms travelling 120 miles would costabout 20p in electricity.
In terms of MPG of petrol this would be about3000 MPG !
Conclusions: At the races
Conclusions: Getting involved
Greenpower teams are made up of students withteachers, parents and other helpers.
As well as engineering, there is team work,funding, presentations etc.
Engineers from industry can be a great help,providing an engineering background.
But engineers, try and keep your hands behindyour back !
Any questions ?
Greenpower is a unique engineering challenge forthe engineers of tomorrow
Any questions to any of the presenters ?