Trans-Options Junior Solar Sprint Cars

Concepts in Systems Design

Sub-systems

A number of subsystems can impact the performance of your car.

- Gears and Power Transmission

- Chasis and materials selection

- Wheels and Bearings

- Solar panel and electrical systems

Gearing and Transmission

Gear - A toothed machine part, such as a wheel or cylinder, that meshes with another toothed part to transmit motion or to change speed or direction.

Trade offs when using gears

Speed vs. Power

- Big powering little = FAST

- Little powering big = POWERFUL

Gears for speed

- In this simple gearbox, there is a large gear wheel with 40 teeth, a medium wheel with 20 teeth, and a small wheel with 10 teeth.

- When I turn the large wheel round once, the medium wheel has to turn twice to keep up.

- When the medium wheel turns once, the small wheel has to turn twice to keep up.

Gears for power

- Same gears, different direction- Little gear turns one time- Medium Gear turns one half- Large gear turns ¼- This gear box can lift 4 times the weight!!!

Examples

Questions for brainstorming

What happens if the gear on the motor does not fit perfectly with the gear on the axle?

How can I mount the motor so that the gears mesh? What is friction and how might slow down or steal

energy from your gear system? What happens if you build a very fast gear box with

almost no power to the wheels (the system can not do much work)?

Chassis Design and Materials

Chassis – The frame of the car, it holds together all of the other components of the system

Trade offs in chassis and materials selection

Stiffness vs. weight- A light weight chassis will require less energy to get and keep moving

- Many light weight materials lack stiffness (resistance to bending and deforming shape)

- A chassis that is not stiff will waste energy by bending

- A chassis that is not light will not move fast (rolling resistance)

- A chassis that is TOO light may blow backwards with wind

Materials Choices

The material you choose to use impacts weight and stiffness

EXAMPLES: (YOU MAY CHOOSE OTHER MATERIALS!!)

- Foam Core- Light, Stiff, Inexpensive

- Balsa Wood- Lighter, Stiffer, More expensive

- Paper- Light, Not stiff unless modified

- Cardboard- Light, more stiff than paper

- Styrofoam- Light weight -Some Plastics

Enhancing material properties

Add Re-enforcements– You can add pieces to you chassis such as strips

of wood or cardboard. Just be sure they are in the right direction for proper stiffness.

Possible Materials

– Stiff insulating foam– Foam Core– Balsa Wood– Masonite– Brass Tubing– Cardboard Tube– Shoe Box– Ridged Plastic– Corrugated Cardboard

Guiding the Chassis

The car must be attached to a thin fishing line (30 lb monofilament) in less that one minute prior to the race, your chassis should include some feature that allows this.

Wheels and Bearings

Purpose - Wheels support the chassis and allow the car to roll forward. Bearings support the wheel while allowing them to rotate.

Wheels can be large, small, narrow, wide…

Trade Offs – Dealing with Friction

Friction is a force that appears whenever two objects rub against each other. Although two objects might look smooth, microscopically, they're very rough and jagged, as this picture shows

ARGGGG!!!! Friction…

Friction is the "evil" of all motion. No matter which direction something moves in, friction pulls it the other way. Move something left, friction pulls right. Move something up, friction pulls down. It appears as if nature has given us friction to stop us from moving anything

But….

Friction also make sure our shoes, our bike tires, and everything that sits still is able to work.

Without Friction our cars wheels could not grip the ground to move (traction)

So… Friction is good???

NOT ALWAYS – If your axles do not move freely in a bearing, energy is lost in the form of heat by materials rubbing together

Try it: hold your hands together tightly and rub fast. What happens?

Misaligned Axles

Wheel and Bearing Ideas

For Traction, Things that may work are:

– Rubber O-Rings (hardware store)– Rubber Bands– Rubber Sheet – Cloth Tape– Silicone or other caulking (hardware store)

For the Axle: The axle must be stiff, narrow, and round, some ideas are:

– Nails– Brass Rod– Brass Tubing– Coat Hanger wire– Welding sticks

For bearings, some ideas that would support

the axle:

– Screw Eyes/ Eyebolts (hardware store)– Brass Tubing– Hard Material (wood, aluminum, etc.) with a hole

drilled in it.– Brackets with screw holes pre-drilled– Holes drilled directly into the chassis

For wheels, you may choose to use the standard wheels available to you or find or create your own. Any round object which you can put an axle in will work, but each design choice you make may have both positive and negative aspects

Wheels and bearings – The Good the, the Bad, and the Friction

Brainstorming concepts:

- Wheels should have good traction to make sure energy goes into rolling your car forward

- Wheels should have bearings to let the axles slide freely

- Bearings must be perfectly lined up and SYMETRICAL to prevent friction

- Cars weight should be spread out so that wheels maintain contact throughout the trial runs

Essential Features – Solar Panel and Cargo

Your car must capture and use the radiated energy from the suns rays to provide energy to move.

This is done with a Photovoltaic (solar) cell

The sun… ITS MOVING!?!?!?!?!?!?

Not really, we are.

The sun does move, but all motion is relative to another object, and the fact that the sun is moving acoss the sky, and its location is actually dependent on the motion of the earth, not the sun. SCIENCE!!!!!

Solar Panel

Your mounting for your solar panel should account for this fact (adjustable!!!)

Cargo

Transportation systems are created to move People and Goods. This is the Cargo.

- Your car must be capable of carrying an unaltered, empty, 12 ounce soda or seltzer can

- The can must not support any part of the car

GOOD LUCK!!

The tips and concepts presented in this presentation represent just a few of the challenges you will encounter when building your car. Remember to be open to new ideas, and to always document the changes you make to your design. As you build there will be plenty of ups and downs, but remember as students of technology you are problem solvers and even though it seems tough, by using creativity, research, and scientific data, you can solve even the toughest of problems with your solar car!