2023-05-11 08:41:00
All bicycles, whether muscular or electric, need a transmission to carry the torque that the cyclist makes on the pedals to the rear gear system. Whether or not there is an electrical assistance system, this process entails a series of phardworking energy caused by friction between the different components, which has a direct impact on performance. Minimizing these losses is part of the job of design engineers, who try to locate materials and geometries that reduce friction to a minimum.
Tom Stanton, engineer and youtuber at the same time, set out to find a way to eliminate all the gears that are part of a bicycle transmission. These transmissions can be made up of a classic cassette made up of several sprockets, a single sprocket, which is usually the solution used on urban and cheap electric bicycles, or gears hidden in the hub of the internal gear systems.
Stanton resorted to magnetism to make your purpose come true. The gearless magnetic bicycle is an experimental project that replaces the traditional gear system with a magnetic one. This clutch is made up of two discsone of copper and one of aluminium. The latter is where the powerful magnets that generate the magnetic field are located.
Eddy currents
The physical principle that governs what happens between these two discs is related to the Lenz’s Law. When a conductive material moves within a time-varying magnetic field, an electric current is induced in it, known as eddy current (in honor of the French physicist Léon Foucault, who discovered them in 1851) also known as parasitic currents or eddy currents. The direction of this electric current is determined by Lenz’s Law, which states that the magnetic field generated by the eddy current opposes the change in the original magnetic field that produced it. This generates a force contrary to the movement of the conductor which is known as electromagnetic braking. They are used in various applications, such as non-destructive inspection of materials, metal separation, and electromagnetic braking in motors and generators.
In this case, the copper disk it remains stationary and is responsible for turning the wheel jointly with it. For his part, he aluminum disc it is connected by a classic chain to the pedals and rotates when the rider pushes them. The magnets located in the aluminum disc are what generate the eddy currents in the copper disc, creating a resistance that can be used to control the speed of the bike.
The result of the homemade experiment is described by Stanton in his video where he shows the entire process of designing and building the magnetic clutch. It includes the prior selection of the best materials for the discs, the calculation of the necessary number of magnets and the study of the best orientation, to later proceed to the design and 3D printing of the components.
After several tests, the final version of the prototype has 200 magnets mounted on the aluminum disc and required increasing the diameter of the front disc to increase the gear ratio and generate more torque. Finally, the previous hypotheses are fulfilled in the real world and the rear wheel of the bicycle moves when pedaling according to the demands of the cyclist.
As Stanton explains, the magnetic clutch offers some advantages over traditional gear systems. As there is no type of contact between the discs, friction is eliminated, which reduces friction losses and also helps in the braking process, so that discs can be dispensed with.
On the other hand, it also has some limitations caused by the complexity of controlling the wasted thermal energy which makes it more difficult to manage. In addition, it does not provide advantages over a direct chain transmission when climbing slopes. In his conclusion, Stanton says that the gearless magnetic bicycle is an interesting experiment in the use of magnetic technology in bicycles and may be a source of inspiration for other innovations in this area.
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