h a l f b a k e r yRecalculations place it at 0.4999.
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As struck upon by [bungston], flywheels that are used for energy storage are typically heavy. In a bicycle, the heaviest component is the human rider - we don't want to be adding further weight for the cyclist to have to shift about. Therefore, [bungston] suggestsusing the rider as a flywheel... [lurch]
immediately latched onto the halfbaked aspect that includes the rider's dizziness and nausea.
Rather than make the rider into a flywheel, make them into a counter weight: as a rider presses the brakes a set of gears contact the drive wheel and transfer the momentum into vertical motion through teeth on the saddle column, pushing up the rider.
When the rider wants to proceed they release the brake (which will operate some kind of latch system so they don't have to hold the brake the whole time). Their own weight will add an extra boost as they set off again.
An issue that complicates the matter is that cyclists tend to place weight on the pedals, rather than be seated the whole time. This would mean that the whole pedal system would have to move. The principle is the same though.
{Note: I have not bothered to do the relatively simple calculation to discover the momentum of an average cyclist and the height required to store the gravitational energy... It could end up being impractically and comically high}
[bungston] prior art
Be_20the_20Flywheel
'Be the Flywheel', is regenrative braking that involves using the cyclist as a flywheel. [Jinbish, May 15 2009]
[link]
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This idea has been proposed for motor vehicles. |
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A brief calculation illustrates it's lack of faesibility: |
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A mass trvelling at 5 m/s (a reasonable 11mph) has enough energy to lift itself through a height of 1.27 m (4' 2") so unless the cyclist has good stationary balance and a head for heights, it's not going to be practical. |
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Well, I wouldn't call 2 days later "immediately", even if I did get there first. |
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For motor vehicles? Really!? I can't imagine the weight of a person being significant enough to give a boost to a car. |
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1.27m? That's ok - we'll just add stabilisers. (Or maybe even a tensioned spring?) |
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[lurch], but I imagine that your thoughts occured as soon as you read the idea...? That's immediate enough for me. |
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//release the break// sp. brake |
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//tensioned spring//
I second this. For low mass / high energy density storage of mechanical energy, it's hard to beat a rubber band. Maybe try bungee cords for a prototype? |
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//break//
I must have been desperate for my cup of tea at work when I wrote that! (fixed, thanks [csea]!) |
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Of course the moment of inertia calculations are also within your grasp, given the increased height of the rider against the wheelbase...... |
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/the halfbaked aspect that includes the rider's dizziness and nausea./ |
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I suppose my flywheel concept would not be a good fit for wusses. I love that Twizz did math. It is so cool when that happens. The PPCC High Lifting concept might be applicable to a circus-type extra-long unicycle with a telescoping stem. |
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If you're proposing using the rubber band ~instead~ of gravitational potential, then we're back on already halfbaked ground. |
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If a 5m/s stop raises the rider by 1.27m, surely we can divide that using a clever arrangement of pulleys, levers, or inclined planes, as you would raising a weight with a block and tackle. Multiple passes of the rope over top and bottom pulleys lower the force required, at the expense of pulling more length of rope through in direct proportion. |
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Or do I have that backwards? If the goal is to lessen the amount that the rider rises for a given amount of brake energy, then we need a mechanism to multiply their weight, rather than dividing it. |
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Using a pneumatic or hydraulic cylinder inside the seat stem, one could apply the braking force with a tiny piston, while having the seat mounted to a larger piston. If the seat piston is 4x the surface area of the braking piston, the length of travel would be 1/4th, and so forth. |
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The rider has to rise. Ideally they would rise just short of a level where they won't bang their head on lamp post. |
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Love it!
/If I've understood correctly: This idea's superb because the more you weigh, the more braking force is required to stop you; but that's OK, because you weigh more, you'll have it!
{BIG FAT JUICY BUN for you - and that'll mean you stop better, and have all that pent-up potential energy for when you'll need it to pull away} |
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Bunsen, no matter how large, or no matter how fractionally small, the mechanical advantage between wheel and rider's seat, the height he needs to rise (to absorb the his forward kinetic energy) remains the same. |
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The rider's initial forward kinetic energy is described as |
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His gravitational potential energy (due to rising) is equal to |
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If we pretend that the dynamic brake system causes the whole bicycle to rise, then we can factor out the mass, producing |
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Since the height we need to rise is proportional to the velocity squared, I forsee riders being shot up off their bicycles when braking. |
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Moment of Inertia has been mentioned a couple of times: It's worth considering how much less you'll be able to brake once your weight is up in the air without making a sudden close inspection of the tarmac. |
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The motor vehicle incarnation of this idea had the whole vehicle lifted on it's suspension. |
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Well, raising the bicycle's centre of gravity in this way would certainly make maneuvering more difficult but I'm not sure that that is necessarily a bad thing.
Also, you would probably need to raise the whole bike frame rather than just the saddle, otherwise the rider will lose contact with the pedals & handlebars and they wouldn't be able to reach their drinks bottle either. |
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I love this. The moment of inertia problem could be simply solved by also moving the rider backward to create an opposing moment. |
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" A brief calculation illustrates it's lack of faesibility: " |
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Faesibilty: A measurement unit describing the possibility that the act in question could be performed by faeries. |
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[goldbb] Quite right you are. Jiggering about with pneumatics and such can only alter the force required/produced, not the energy. Such a basic error, I feel half-ashamed. |
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