Home Design Concepts Demonstration Other

Materials and Build of the Demonstration

Materials:

· A bike and its rear wheel (front wheel is optional)

· A way to stabilize the bike while the rear wheel is spinning

o Two chairs and a piece of wood did the trick as seen in the photos below

· A sheet of aluminum to be cut

· Nuts and bolts

· Electromagnet

· Power supply

· Speed sensor for the wheel in order to analyze the time it takes for it to slow in detail

o Here a Garmin speed sensor was used along with a Garmin head unit to record the speed

o A speed sensor and corresponding head unit can be foregone if you are not looking to quantify the braking effect

Design:

The bulk of the design is in retrofitting a rear bicycle wheel in order to be used as an eddy current brake. The approach taken here was to cut a sheet of aluminum into four separate pieces (shaped as quarter arcs of a circle) using a water jet cutter such that when these four pieces are put together they will form a circle with an inner radius equal to that of the radius of the rear bicycle wheel being used (from the center of the wheel out to the lower profile of the rim). The goal here is that this circle created with the aluminum fits snuggly around the wheel in the location where an inner tube would normally sit on a bicycle wheel. The outer radius of this aluminum circle will depend on the dimensions of the bicycle being used. This means that the outer radius needs to be large enough so that it sticks out from the rim and can pass through the field produced by the electromagnet, but small enough so that it does not interfere with the frame of the bicycle. Moreover, the thickness of the sheet can be altered depending on the gap of the electromagnet that it has to pass through. In this case the thickness of the sheet used was 1cm, but a greater thickness if possible is better for creating a greater braking force. To connect these four pieces together, slots were cut into each piece near each of its ends and then nuts, bolts and small aluminum pieces (with holes also cut into them) were used to fasten adjacent pieces together.

Once this rear wheel has been created, it is inserted into the bicycle just as a rear wheel usually would be. Next the bicycle must be positioned such that the rear wheel is off the ground and will be able to spin so that the aluminum passes through the gap of the electromagnet. Finally, the wheel can be spun by turning the crank of the bicycle and then once it is up to the desired speed, the power supplying the electromagnet can be switched on so that the magnetic field is setup. The time taken for the wheel to come to a stop from a particular speed when the magnetic field is present should be noticeably shorter than when the magnetic field is switched off. When the magnetic field is not present, the wheel would spin forever if it were not for frictional forces in the hub of the wheel and air resistance. If the two stopping times with and without a magnetic field are not noticeably different, this is because the magnetic field is not strong enough and so it should be replaced with a stronger electromagnet until the affect is observed.

Pictures:

The images below will hopefully provide a better visualization of the design and materials used.