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  • Thesis Project - Flywheel, Main spring, or pressurized air? Need help deciding

    Discussion in 'The main mechanical design forum' started by JGab, Oct 10, 2013.

    1. JGab

      JGab New Member

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      Hello guys!

      I've been pondering in which thesis project to tackle for my last year of college. I decided to get some suggestions from the engineering department at my school but they seem to be quite busy.

      I finally narrowed down my thesis on the area of bicycle transportation in the category of helping in the fight for a "greener" future: What Im to develop is a method that will decrease the amount of endurance (pedaling effort) it takes to get from point A to B by using energy more efficiently, in return, making commuting via bicycle more practical to commuters looking to try cycling.

      Basically a bicycle that will store down hill energy (staying away from electrochemical methods) and later using it while tackling up the same hill to get back home.

      I need help knowing that the methods listed below are practical or at least aren't filled with bullet holes and are able to hold water. And if so, deciding on the most practical method. Also, if it isn't too much to ask for, I would appreciate some guidance in forms of ideas that could come up while reading this post. My professors aren't mechanically savvy per say :S

      I've looked at KERS (Kinetic Energy Recovery System) systems that use a flywheel to store energy as it spins. Then later as needed, decelerating it to use the stored energy. (please correct me if I'm wrong).


      • My concerns with using a flywheel to store down hill energy would be the practicality of the system for use on a bicycle. For one, those things need to be spinning at a great speed. Im not sure a mass of 200lbs (bike with rider) tops, going down a hill at 15mph would create enough energy to spin the flywheel to its performing velocity.--My other concern is the amount of energy lost for every minute it is spinning -- And my last concern is will it be able to discharge its energy with enough force (torque?) to assist the rider back up the hill when needed?


      • I've ran into KERS systems that use a mainspring rather than a flywheel. My concern with this method is the amount of torsion force the spring would be under. Although this method could possibly store a greater amount of torque, it is limited to a certain amount of charge until the spring is all the way wound up; and adding multiple springs wouldn't be practical.


      • My last possible method is pressurized air. Down hill energy could be translated into pressurized air using an air pump (attached to the hub). Then released back into the pump when needing pedaling assistance. I haven't completely research this method yet. But I could only assume that energy could escape in the form of heat while running the air pump.

      I have considered using both the mainspring and flywheel. Using the flywheel as a ride-n-use storage device, while the mainspring will store energy while the bicycle is not in use (pressurized air could be used as a long storage method too). So basically winding up the flywheel on the way to point B from A, then translating the energy stored in the flywheel into winding up the mainspring when the bike is not in use. Then after work, unwinding the mainspring to turn the flywheel, in return assisting the user up a monstrous hill.

      Why mechanical storage rather than electrochemical? because im here to save the earth (lol?). But i did have a slight thought of reusing batteries from all the older model iphones that were turned in to be replaced by the newer model to power an E-Bike.

      Thank you guys so much, I hope this isn't too much to read :(
       
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    3. Erich

      Erich Well-Known Member

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      Two issues with using a flywheel.

      1. Extra weight on a bicycle is BAAAAAAAAAAAAAAAAAAAAAD.

      2. The flywheel will act like a gyroscope. Might make turning interesting.
       
    4. JGab

      JGab New Member

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      Thanks Erich,

      I know there are guys out there making flywheels out of lighter polymers that have the same performance as those made out of metal.

      I thought that if i try to place the flywheel as closest to center i would reduce the chances of a gyro effect. But this might just make the bike more stable.
       
    5. Dana

      Dana Well-Known Member

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      Compressed air is a very inefficient method of storing energy; you lose a lot of energy via heat loss when compressing the air. Flywheels are heavy, or need to spin really really fast, which means they have to be strong, which usually means heavy. Springs are efficient, but there's a limit on how much energy they can store. Batteries are probably your best bet, but as you say there are environmental issues in their manufacture and disposal.

      You need to consider the consequences if your device fails, i.e. the spring breaks, the flywheel bearings fail, the air tank ruptures. All this energy being released suddenly between the rider's legs is a recipe for disaster.

      Your first step is to calculate just how much energy you want to store (vehicle weight times vertical distance), and compare that to the capabilities of the various storage techniques.
       

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