Mini Solar Car

Objective:

1. To learn about renewable energy vs fossil fuels
2. To learn the basic mechanics and physics of building a mini solar car from a kit
3. Hack the mini solar car kit and make your own solar car
4. Race!

These are the prototypes that I made for facilitating a group of 7-8 years old kids in building a simple mini solar car.

I found these tutorial videos, and I adopted some of the skills or get inspiration for the design of my car

I thought it would be easy to make. Basically it's only connecting a solar cell to a motor and put these circuit on a chassis, easy right? But it was more challenging than I thought. So I would like to share my experience (some common challenges) here and show you how I do the troubleshooting.

Materials:

• Mini Solar Car Kit (RMB 8)
  
  • solar cell
  • mini motor (small amp)
  • Spur gear
• Soldering iron
• Solder

Assemble:

This is an individual work. Each kids are given one kit with assembly instruction. They would need to read and follow the instruction sheets to finish the assembly. There are 2 major challenges for them. #1 Since the nuts and bolts are pretty tiny, kids may find it challenging to tighten the bolts. #2 Soldering to connect the solar cell to motor need a steady hand and coordination of left and right hand to feed the solder. Here facilitators can show them once how to use a soldering iron, then let the kids to finish the remaining by themselves. But if you see they have a difficult time to manage both hands, you can have the kids hold the tool and you help kids to feed the solder.

My experience is this assembled car need several fine adjustments such as the wheels comes to close together and tight, the teeth gears are not touching each other very well, nuts and bolts are too loose (which may make the motor not catching the gears so well) etc.

Test:

This mini solar car runs pretty fast under strong sunlight. If you want to test the car indoor, ambient light just doesn't work. You need to use a strong light source such as construction lamp or studio lamp.

Learning Debrief:

Facilitators can ask students the following questions.

- How the solar panel make the motor spin?

- What difficulties did you encounter? And how did you solve it?

- How the motor push the car in motion? (the teeth of spur gears on motor and the wheel axiel must be touching each other)

- How can you improve this car design?

Materials:

• foam board
• cardboard
• straws
• bamboo skewers
• Plastic bottles
• Plastic bottle cap
• Aluminum foil
• Hot glue gun
• cutter
• soldering iron

We posed 4 Challenges:

1. The Fastest
2. The Biggest
3. The Most creative
4. Best presentation

Students work in group of 3 to 4 to design and build their own solar car. To facilitate the hacking session, we asked the kids to decide which challenges do they want to focus on (can be more than one), then have them draw the design on paper. This helps them to have a more concrete idea and were able to list out the materials needed. Even though you know the design won't work, do not tell the kids at this point. Just let them make prototype and test it. Let them fail fast and then help them to iterate. Now you can suggests some ways that are works and leave them to decide how to make their own car.

For instance, if the group want to build a fastest car we can suggest them to use light materials to make the chassis, or increase the power of the motor by connect more solar cells in parallel.

Chassis

The lighter the body, the better.

Foam board is a better material for chassis because it is stiffer and lighter than cardboard.

Wheels and axle

When drilling a hole on the wheel, it needs to be exactly centred. Otherwise, the car will be wiggle and harder to move.

Second, the wheels must spin smoothly. So it's essential to have a low friction and rotational part to attach the wheel and axle to the chassis. One easy way to make a wheel and axle is to use straw and bamboo skewers like this:

The engine - Solar cell & Motor

If you intend to do this activity indoors you will need strong lights, room lighting is never enoughUnfortunately I have not had much success with fluorescent or LED lightsThis is one possible reason I got from online: The absorption spectrum for silicon better matches the output from the incandescent bulbs and their infrared output. (from University of Washington Clean Energy Institute)

Ways to raise the power efficiency:

• sunlight concentrator (E.g. magnifying lens, aluminium foil, mirror etc.)
• Connect solar cells in parallel (in series also increase the voltage, but the current stay the same, also it would need to overcome a higher threshold to start the motor) -- why?
• Use a motor with lower starting current (E.g. 3V, 30mA, 19000rpm)

Energy transmission

1. Spur gear set

2. Pulley and belt (by friction)

3. Fan (by action and reaction force)