The West Philadelphia High School Electric Vehicle Team
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The West Philadelphia High School Electric Vehicle Team |
We followed the following steps in making our hybrid go-kart:
1. Define the Need
We need to build a hybrid go-kart to serve as a demonstration for our hybrid Jeep. For the past two years, a team of students has built and raced a hybrid vehicle in the Tour de Sol competition. We need a working model to demonstrate how hybrid technology works, especially as an educational tool for the Tour de Sol competition.
2. Design Criteria
Hybrid vehicles are a compromise between gas and electric powered vehicles. The advantages of electric powered vehicles are that they are pollution free and very efficient. The disadvantages are charging (refueling) takes a long time and they have limited range (100 - 150 miles). So hybrids use a smaller gas engine (more efficient and less pollution) and use an electric motor to help propel the vehicle when its needed.
1) Smaller than usual go-kart gas motor (5hp to 8hp is usual size)
2) Electric motor
3) Both motors can drive the vehicle
4) Battery pack to store electric energy
5) Increase strength to carry extra components
6) Safe vehicle construction
3. Search Literature for Background Information
Hybrids have been around for a long time. A hybrid vehicle is a vehicle that uses two power sources. Examples are cars that uses gas and electric, boats that use wind and gas, locomotives that use electric and diesel, and mopeds that use pedals and gas. For cars there are two basic categories: parallel and series. A series hybrid uses the gas engine to generate electricity and charge the batteries. The electric motor then drives the wheels. A parallel hybrid uses the gas and/or electric to drive the wheels and can also recharge the batteries using the same electric motor. The Hybrid Jeep that our team built and raced is a series hybrid. It is easier to build and control. The go-kart is an example of a parallel hybrid. Toyota and Honda both build parallel hybrids because they are more efficient. After a very extensive search, we found gas powered, electric powered, and pedal powered go-karts but there are no hybrid go-karts. We are building the first one.
4. Preliminary Design (Addressing Existing Problems)
Our preliminary design was based on an electric go-kart we built in a summer program at University of Pennsylvania’s School of Engineering. The go-kart from the summer had a two major problems. First it was too short, so we had a difficult time fitting in the vehicle. To fix the problem of it being too short, we cut the frame and lengthened the go-kart using steel bars. This also created extra room for the batteries. Second, it had a solid axle so that is could not turn very well. To fix the second problem, we had many ideas. We thought of cutting the axle in half and supporting it in the middle with bearings and having the separate motors driving each axle. The easiest idea we came up with was to allow one of the tires to free-wheel.
5. Preliminary Design for New Systems
There were two major systems that needed to be added to the go-kart. The first was the hybrid drive system. We needed to create a way to fit both the electric and gas motors on the vehicle. We also had to figure out how to make them both drive the vehicle. We decided to try to mount both of them in the back and run the chain around both of them. The second system that needed to be added was the batteries. We decided to create a battery box that would fit between the back of the driver’s seat and the motors. This would keep the center of gravity low and keep the weight well balanced.
6. Build and Test a Prototype
To carry out the design we did the following:
1) We cut the frame and welded extensions to make the go-kart longer. This solved the problem of being too short and made room for the batteries.
2) We removed the key from the right rear wheel so that the wheel spins freely. We tested it and now the go-kart turns very easily.
3) We fitted a roll cage on the go-kart for safety. We also made a front bumper to attach the roll cage to.
4) We cleaned up an old 3HP gas engine one of the teachers donated to us. We cleaned and adjusted the carburetor to get it running.
5) We designed a metal motor mount for the electric motor. We used wood in the summer for our electric go-kart which would flex and cause the chain to pop off. Therefore, we decided to make this one using aluminum plate. It was more difficult to work with but it we made a very strong mount. One of the shop teachers welded it up after we cut all the holes for mounting the motor.
6) We attached the electric motor to the mount and then mounted it on the go-kart.
7) We mounted the gas motor. We had to use angle iron to raise the gas motor so that the chain would go around both the gas and electric motor gears. We used slotted holes for mounting the gas motor so that we could add tension to the chain.
8) We built a battery box out of angle iron and our teacher welded it in the go-kart for us. We also did some of the welding.
9) We installed the batteries, measured and cut battery cable, put lugs on, and wired them in series.
10) We mounted and wired in the controller.
11) Because the frame was extended, we had to modify the brake cable and gas cable. We reattached the brakes and connected the throttle cable to the electric motor control box. Then we added a hand throttle cable for the gas motor.
12) We tested it. It worked great.
7. Testing and Redesign
The go-kart performed just as it was designed to do. It drove faster than when it was just an electric. The small gas motor gets better gas mileage than a typical 5 or 6 HP go-kart motor and it creates less pollution. The gas motor needs the help of the electric motor to accelerate just like a Toyota or Honda hybrid. It is really a perfect example of a hybrid vehicle. The only thing that needed to be redesigned were the brakes. One day while testing it, the brake cable broke and our teacher wrecked. We created a better attachment for the brake cable and fixed the bent tie-rod.
8. Conclusion
Our hybrid go-kart is a huge success. It met all the original design goals and is an excellent demonstration of a hybrid vehicle. We are looking forward to taking it to the Tour de Sol this year!
9.Next Steps
For next year’s project there are several improvements we plan to make. We would like to add shocks to the go-kart, add a controller that has reverse and regenerating braking, and add a seat-belt. We also would like to do extensive testing so we can calculate the fuel efficiency and pollution the hybrid makes and compare it to a pure electric go-kart and a pure gas go-kart.
