Have you ever used a portable fan to cool you down on a hot day? Well, have you ever noticed that the fan runs continuously at the same speed no matter how warm or cool the room gets? This project aims to make portable fans more effective! All you need is an old box fan, an EV3, and some Legos.

Supplies

Box Fan
Lego EV3 Brick
Lego EV3 Motor
NXT Temperature Sensor
1 Lego wire
Lego gears
Lego axles
Lego technic bricks
Caliper
Access to a 3d printer
Velcro

Step 1: Get Measurements From Your Box Fan

Most box fans have a cap which you turn to control the speed of the fan. Take off this cap to reveal the inside part that latches on to the cap. Using the caliper get measurements of the knob part underneath the cap because soon we will make a custom cap in CAD that we will fit on the fan which will allow the EV3 to control the speed of the fan.

Step 2: Get Measurements of the Lego Axle

Using the caliper, measure the face of the Lego Axle. You will need this for creating the custom Cap in CAD for the fan.

Step 3: Create Custom Cap in CAD

For this step I am going to use tinkercad, however you could use any 3d modeling software. First, start off by making a cylinder. The diameter of the face of the cylinder should be big enough to fit the cutout that that can house the inside knob of the fan. Next, make a hole at the bottom of the cylinder that matches the shape of the knob sticking out of the fan. Then, make an axle cutout at the top of the cylinder that will house an axle connected to an EV3 motor. Remember to add some wiggle room because the printer won't print 100% accurate to the dimensions you give it.

Step 4: Print Out the Custom Cap

For this step you will need to have access to a 3d printer. If you don't have one, check your local library because they may have one available. Also, print the cap out in a material that allows for some flexibility such as ABS or PET-G. Make sure to test if the cap fits on the box fan and what the the lego axle fits through before proceeding.

Step 5: Create Lego Gearbox to House on Fan

Since the knob on a box fan is meant to be turned by humans, it takes quite a bit of force to turn it. Because of this we have to add a gearbox to the motor since the motor is not strong enough by itself. I have attached some pictures as to how I put together my gearbox. As every fan is different you may need to tweak the gearbox to make it more or less strong. Make the gearbox by adding cascades of bevel gears to a frame. Add velcro to the geared down facing side so that we can later stick the gearbox to the fan.

Step 6: Program the EV3

To bring the project to life, you will have to program the EV3 brick. You can do this in many different ways, but the easiest way to make this program would been EV3-lab. This is because this is the only Lego produced software that both supports the EV3 and the NXT temperature sensor. The basic idea for the code is that you turn the motor when the temperature changes which in turn spins the knob on the fan thus changing the speed of the fan. I have attached a sample code created in EV3 Classroom just because it is easier to understand but it would be quite easy to replicate the sample code in EV3-lab. Download your working code to the EV3 when you are done.

Step 7: Put It All Together

Attach the 3D-printed cap onto geared down end of the gearbox.
Velcro the gearbox onto the fan so that the 3D-printed cap attaches to the fan.
Connect your EV3 motor to the other end of the gearbox. Secure the motor to the fan with Lego pieces and velcro.
Plug the motor and the temperature sensor into your EV3 brick.
Connect power to your fan and to your EV3 brick
Start the code and make sure everything works fine
Voila! You know have a more effective and efficient fan to help keep you cool!