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 the UK”. The unique hands on engineering challenge is for 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 Goblin Kit Car, design and build sustainable bodywork and compete in a series of challenges; drag, slalom and sprint. IET Formula Goblin

IET Formula 24 The IET F24 Greenpower Challenge is to build the single seat electric car that travels furthest over a four hour endurance race on 3 pairs of 12 volt batteries.

For 6th Form students, universities and apprentices, the F24+ challenge is a shorter, faster race than F24 with a “constructor’s championship running through the season. This challenge has attracted teams from Jaguar Land Rover, Bentley, Peugeot Citroen, Eton College, and of course, Chipping Sodbury School! IET Formula 24+

The F24 Challenge With all teams using the same power supply and motor and stringent design/safety regulations in place the challenge faced by teams is how to engineer a 4 hour endurance race winning car within these restrictions.

Making The Difference We have with us today some of our top competitors including past and present National Champions who are willing to share some of their knowledge in building a race winning car.

Science and building a car First of all KISS (keep it simple stupid). The car has 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 shape is. 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 and gearing 5 x slides Rolling resistance, drive and gearing Wheel geometry & steering Matthew

Aerodynamics:

To build a successful racing car, one aspect you have to consider is the aerodynamic drag. This is the force needed to push an object through the air. The aerodynamic drag (or wind resistance is equal to the frontal area of the object multiplied by the air Drag Coefficient (this Is calculated using the 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 kit car. The red areas represent a high air pressure, and the blue areas represent a low pressure area. There is both a large air pressure on the front, and a low air pressure behind it, however the high pressure on the front has a smaller affect than the low pressure area on the back

Aerodynamics: Rotary Racer has a long tail sloping, this largely reduces the low pressure area on the back of the car bringing the air back together cleanly.

Aerodynamics: We use a web based, Virtual Wind Tunnel, to carry out tests with different car designs. We use 3D CAD programs to draw different car designs. This provides us with the overall drag information as well as lines 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 make the taper to steep, otherwise it will still create a vacuum behind the car due to the 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 essential Electronics are not essential for a winning car. However, However, using Electronics can add an edge and make racing performance consistent Gathering data, energy management, problem handling and driver or pit crew information are just a few uses for such systems.

Electronics: Data Logging Data logging analysed Data logging allows car performance to be analysed after and perhaps during a race. With it we can record information such as motor current, battery voltage, speed and motor temperature. We can also calculate average current per lap, average speed amongst other things. After a race, the data is put into graph form on a computer for analysis and feedback back at headquarters (or school, as it’s better known).

Electronics: Data Logging

Electronics: Telemetry Telemetry allows us to monitor car performance during a race. reliable The data recorded in the car is relayed to a laptop in the pit area, where it can be interpreted by the reliable pit crew. We can then make decisions based on the data received, including adjusting the power level parameters and calling the drivers in in for a battery change.

Electronics: Telemetry

Electronics: Energy Management fixed amount of energy In a Greenpower race the car has a fixed amount of energy in the batteries. This needs to be distributed so that after 4 hours you have just about used all of the energy. Without electronic energy management this is quite tricky. Gear ratios need to be rigorously tested, and in different conditions a ratio that normally works perfectly may leave you with no power. Electronic speed control allows the motors power output 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 as possible ! 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 driver changes. 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 timing and/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 in designing, developing and racing a winning Greenpower car KISS: Its got to finish the race to win ! Remember: The challenge is to involve students in engineering to promote this career path. Students need as much involvement in the car development as possible. The rules define the challenge.

Conclusions: Some cars

Conclusions: What can be acheived A Greenpower car can use an average of 400 Watts of electrical energy during a 4 hour race. An efficient Greenpower car can average about 30 MPH with this level of power and thus travel 120 miles or more. In electrical terms travelling 120 miles would cost about 20p in electricity. In terms of MPG of petrol this would be about 3000 MPG !

Conclusions: At the races

Conclusions: Getting involved Greenpower teams are made up of students with teachers, 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 behind your back !

Any questions ? Greenpower is a unique engineering challenge for the engineers of tomorrow Any questions to any of the presenters ?