Eddy Current in a Model Car

We (Pijke, Jilles and Jasmyn) built a model car equipped with a damping system based on eddy currents for our first-year undergraduate Applied Physics course DEF (Design Engineering by Physici).

In our design, a small container is suspended by elastic bands above a set of aluminum tubes. Magnets are attached to the underside of the container. When the car drives over a bump, the container starts to vibrate up and down. As a result, the magnets move through the aluminum tubes.

This movement induces eddy currents in the conductive tubes. These eddy currents generate a counteracting force that slows down the vibration of the container. In this way, the up-and-down motion of the car is damped!

Materials

1. 4x wheels (around 7.5cm diameter)
2. 1x wooden plank (20cm x 30cm)
3. 2x aluminium cilinders (11cm length, 8cm diameter)
4. 8x ITEM poles
5. 4 x 21cm length
6. 2 x 30cm
7. 2 x 20cm
8. 4x simple elastics ( we used 150 x 1.5 mm)
9. 2x wood plank (6cm x 15.5cm)
10. 1x wood plank (15.5cm x 20.5cm)
11. 2x wood plank (6cm x 20.5cm)
12. Cilindrical magnets (we used small neodymium disc magnets and mixed and matched them up for our required damping. We used around 18cm total length of magnets - so 9cm length per cilinder - with 1cm diameter)
13. Glue sticks
14. Duct tape
15. Paper

We used the following materials so we could show a difference of the damping with-and without magnets, these can be skipped if you only want to build the modelcar with magnetic damping.

1. Arduino Uno
2. 2x breadboard
3. 2x z-axis speedmeter (eg. ADXL345 Digital Triple Axis Sensor)
4. Breadboard wires (1m)
5. Cable to connect Arduino to laptop (USBC-USBC)

Tools

1. Laser cutter
2. Hot glue gun
3. Metal drill
4. Saw
5. Wood drill

First, we used a laser cutter to cut out the cmxcm box. See attached file (25-autodemping-4.svg) for inspiration or to use. We hot glued the box together to make it more sturdy.

We then sawed a plank 30cmx20cm.

(See only the plank and the box, ignore the rest - the pictures were made after complete assembly)

Secondly, we drilled a hole slightly larger than the diameter of the magnets into the aluminium cilinders. We then hot glued the aluminium poles to the middle of the plank (make sure the middel of the box can be suspended above these).

We assembled the ITEM poles (cm) to the edges of the plank using hot glue again and added the (cm and cm) poles between standing ITEM poles using duct tape.

Disclaimer: you can also use a sturdier way to assemble these parts. We had to do this project for a course and went through a lot of iterations which made the hot glue and duct tape easy to use. If you are building something to last we recommend assembling it in a more durable manner.

Then, we drilled holes into the wood so we could attach screws. We did this because the magnets can attach to the screw and we can easily pull them off. We also added a bit of hot glue to the screws and the bolts on the wood so it would not get loose.

This has to be levelled with the holes in the aluminium. so the magnets can perfectly go through without friction.

Disclaimer: If you want it permanent you can simply just hot glue the magnets to the box.

We then attached screws on top of the ITEM poles so we could easily montage the box. We also hot glued small screws on the edges of the box for the elastics. The elastics ca be stretched between these screws as shown in the picture. The magnets should be half inside the aluminium cilinders, there should be room for the box to go up and down.

We lastly connect two breadboards and two accelerometers using the above circuit (see picture). One breadboard was put in the box while the other was put on the plank to measure the difference in damping. The code used is attached in the file below (rmsScopeForTwoAccelerometers.pde).

To test our project we pushed our modelcar over a 'hill'. This was constructed with duct tape. If you used the Arduino, you can run the code on your laptop and check out the graphs of the damping!