Revving it Up with Powertrain

30 03 2011

Axle Design

This is the first year that Ravens Racing will be designing an All-Wheel Drive car.  The rear axle is driven by a gas-powered motor and each front wheel will be driven by a separate electric motor.  With an electric motor driving each wheel in the front, the need for a differential is eliminated.  A chain drive system will increase the torque from the electric motors.  The front gear ratio is 3.38:1, which when combined with performance curves of our electric motors, puts us alongside the top teams at competition for electrical power.  The front axle is unique in that it must supply power to driven front wheels that turn.  In order to do this there must be two types of CV joints; a plunging joint that allows the half-shafts to move longitudinally and vertically, as well as a high-angle joint that allows the wheels to turn while still transferring power.  For the RR11 we will be using a tripod style joint as our inboard plunging joint, and an Rzeppa high angle CV Joint as the outboard joint.   The rear axle will use a cam and pawl type locking differential.  The gas powered motor also uses a chain drive system to increase the torque applied to the wheels.  The rear gear ratio is 3.07.

Internal combustion Engine Integration

This being the first year entering a hybrid race car in competition, a lot of changes have been made to the car. This year we chose to go with an all wheel drive race car that has a gas powered engine to drive the rear wheels and a pair of electric motors to power the front wheels.  However competition rules regulate the engine to have a maximum displacement of 250cc. A 2008 yamaha WR250x supermoto motorcycle was purchased as a donor for the engine and electrical system.

Since the engine was removed from a motorcycle, various components have to be modified and retrofitted to fit the race cars frame and driver controls. The shifter in the engine has been modified from the standard foot pedal to a cable and hand shifter system. The throttle and clutch cables are changed from a hand throttle and  lever, both to foot pedals.

The engine was taken to a local motorcycle dealer for a dynamometer test to see what kind of performance the engine was capable of. It was found that it has 25hp and 16 lbs/ft of torque. In comparison to last years race car with a 510cc engine, this years 250cc engine produces about the same performance values.

Hybrid Electric Drive

The hybrid design of the vehicle utilizes a parallel configuration where the power plants work independently from each other. This allows for us to take advantage of the benefits of both the internal combustion, which provides maximum torque at high speeds, and the electric motors which operates better at lower speeds. The electric portion of the vehicle is powered by two permanent-magnet DC Agni 95R motors capable of producing up to 26kW of power and 53Nm of torque. The motors are powered from six Odyssey Extreme Racing AGM batteries configured in series and capable of producing  72V and up to 800A of current.

The electric control system of the vehicle receives all inputs from the driver and sensors, calculates the desired response, and outputs the signal to the appropriate device. The brain of this system is a self-programmed based Arduino microcontroller. The control algorithm is programmed in C and monitors the temperature of the electric devices and outputs the desired response of electric motor torque output.




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