We investigate what it takes to build a competitive formula racer by visiting a group of industrious local tertiary students doing just that…
Chances are that, at some point, you attempted to build a soapbox car or even a go-kart. Did what seemed like a simple task at the time quickly become a major headache? Spare a thought for the group of Cape Peninsula University of Technology (CPUT) engineering students who have designed and built a racecar to compete in the Formula Student (FS) challenge at Silverstone Race-way in the UK (which would make it their third visit), as well as other similar events. CPUT is the sole South African tertiary institution engaged in developing and building such a vehicle for the FS competition.
The competition
Formula Student (FS) is an annual competition that attracts engineering-student teams from all over the world. They enter formula-style racecars that they built according to strict competition rules. FS is based on Formula SAE in the United States, but with supplementary conditions. There is a strong focus on design, innovation, efficiency and teaching the students about manufacturing techniques.
At this year’s event, for example, 230 cars and 3 000 students are expected. There are three types of powertrains that compete in class one: internal-combustion; alternative-fuel; and electric power. Cars are judged on static and dynamic criteria as follows:
Static events: Presentation 75; Engineering design 150; Cost analysis 100
Dynamic events: Acceleration 75; Skid pad 50; Autocross 150; Efficiency 100; Endurance 300
In most events, the points are allocated according to the relative performance of the specific racecar compared with the field of entries. Therefore, the vehicle that fares best is allocated maximum points; the last-placed vehicle doesn’t receive points.
The rules
Students are expected to familiarise themselves with the rules in an SAE document spanning an exhaustive 182 pages, as well as a secondary piece with supplementary conditions for the Formula Student competition that adds a further 45 pages. It’s hugely important that the rules be studied to the nth degree; not only will the entered vehicle be legal, but there is always the chance to spot a gap in the regulations that will allow teams to gain a competitive advantage. Remember Ross Brawn of Brawn GP winning the drivers’ and constructors’ titles in 2009 with the help of a double-diffuser that was declared legal by Formula One’s governing body, the FIA?
The team
The Cape Speed team from CPUT consists of 16 members (11 engineers) and the responsibilities of building the car are divided into three sections: chassis, suspension and propulsion. The team also includes non-technical members who focus on the business case, public relations and photography. Three faculty advisors oversee the project.
It’s extremely important for the team to work closely together, as each decision influences the next. As early as the concept phase, a computer-aided design model of the complete vehicle was created because this allowed all designs to be evaluated from regulatory, mass and performance perspectives before a single component was manufactured.
Chassis
This forms the backbone of the vehicle by providing mounting points for the suspension and drivetrain, and, most importantly, a driver safety cell.
Goals: Maximum torsional rigidity; pass all safety criteria; light weight.
Main regulations: There are strict safety regulations regarding roll-over, side-impact and frontal-collision protection. Furthermore, there are material properties relating to the strength of the chassis and spatial constraints, including a minimum wheelbase of 1 525 mm and a template governing the opening area of the cockpit.
Concepts evaluated: Tubular space frame; full composite-monocoque structure; hybrid chassis combining the mentioned concepts.
Final decision: The chassis team decided on a hybrid solution with a carbon-fibre monocoque for the passenger cell and front-suspension mounting points, but a tubular space frame for the rear to mount the powertrain and rear suspension. The composite monocoque was chosen for its excellent mass-to-strength properties and the tubular section for better cooling of powertrain components. It also helps with access to the latter items.
Challenge faced: The gel coat used on the mould of the monocoque for easy removal after curing was not suitable for the application and led to damage on both the mould and the monocoque structure when removed. A more appropriate gel coat was then sourced.
Suspension
The suspension team was tasked to not only choose the most appropriate tyres, suspension setup and spring and damper settings, but also spec the braking and steering systems.
Goals: Optimum contact of tyres on the road surface; maximum mechanical grip from the tyres; quick steering while limiting the steering force to the driver; a braking system that is progressive but powerful enough to lock all four wheels on dry tarmac; all systems needed to be lightweight.
Main regulations: The minimum wheel travel is stipulated as two inches (50,8 mm); minimum wheel-rim diameter of eight inches (203,2 mm); steering free play limited to seven degrees; braking system capable of locking all four wheels.
Concepts evaluated: All types of suspension; direct and rack-and-pinion steering; different tyre sizes and rubber compounds; disc-brake options.
Final decision: The team chose the proven double-wishbone suspension setup, with optimised wishbone lengths bottom and top. At the rear, pushrod suspension is used to make space for the driveshafts. A 13-inch wheel was chosen for the disc brake and callipers to fit inside. The softest compound Hoosier tyre was chosen to provide the best grip possible and, as the vehicle weighs a mere 250 kg with the driver, the relatively narrow tyre width nevertheless guarantees a good contact force between the road and tyre to allow the rubber area to heat up and provide expected grip. A rack-and-pinion steering system with less than one turn lock to lock was chosen, and that means the driver does not need to let go of the wheel during cornering.
Challenge faced: Rod ends on the suspension components tend to break, so it was decided to cast the ends of the A-arms of the suspension and use carbon-fibre tubes instead of metal to save mass.
Propulsion
The propulsion team had to provide the maximum motive force in the most efficient way.
Goals: Powerful with good torque characteristics; fuel efficiency; light weight.
Main regulations: Internal-combustion engines are limited to 610 cm3 and an air restrictor of 20 mm applies to 95-octane unleaded and a 19 mm restrictor if the engine runs on E85.
Concepts evaluated: A 600 cm3 superbike engine; 600 cm3 single-cylinder unit; 450 cm3 single-cylinder unit. Transmission and limited-slip differential options were also assessed.
Final decision: Owing to the course layouts of the dynamic event, it was calculated that the theoretical maximum of 80 kW that is allowed with the air restrictor in place might go unused. Torque and efficiency were deemed more important than absolute power, which favoured the 450 cm3 single-cylinder unit. The KTM race engine weighs only 32 kg (30 kg less than a 600 cm3 inline-four) and delivers the close-to-perfect torque spread needed for the event. It should also use considerably less fuel. It was decided to run on E85 fuel, as this ethanol blend has a higher octane rating and better combustion-chamber-cooling properties to compensate for the smaller air-restrictor size. The final drive ratio was chosen to use only the first four gears of the standard KTM gearbox (the maximum speed during the event is around 110 km/h), with a power-shift actuator that allows gearshift paddles behind the steering wheel. A limited-slip diff was bought in to reliably stop the spinning of the inside wheel and provide traction during extreme dynamic events.
Challenge faced: There was no space at the rear to legally fit the exhaust silencer, which is now located within one of the side pods of the vehicle.
Specs
CAR No: 35
Engine:0,45-litre, 1-cyl, four stroke, petrol
Power: 46 kW @ 9 750 r/min
Torque: 52 N.m @ 7 250 r/min
Trans: 6-spd manual with power shifter
Differential: Drexler limited slip
Brakes f/r: 254/203 mm ventilated
Tyre size: 152/63 R13 (racing slicks)
Fuel tank: 5,0 L
Length: 2 730 mm
Width: 1 400 mm
Height: 1 405 mm
Wheelbase: 1 605 mm
Tracks: 1 200 mm
Mass: (sans driver) 180 kg
Top speed: 110 km/h (geared speed in 4th gear)
Project budget:
Front monocoque & front Roll hoop: R190 328,66
Pattern, moUlds and body paintwork: R41 472,88
Rear chassis: R1 052,02
Steering system and seat: R42 942,18
Electronic sensors and management system: R87 704,97
Fuel system: R14 176,27
Engine intake system: R16 910,08
Engine and drivetrain: R126 833,34
Rims, uprights and hubs: R26 459,59
Tyres, dampers and anti-roll bars: R51 199,66
Suspension system: R55 414,99
Braking system: R40 077,38
Pedal box: R5 639,70
Safety: R3 187,60
Cost to build: R747 246,68 +
Logistics: R1 678 408,86
TOTAL: R2 425 655,54
For more info or sponsorship opportunities, contact Dr Oscar Philander, associate professor, department of mechanical engineering. Call 021 953 8435 or email [email protected]
