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- Thread starter Nicodemus Rex
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- #26

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- #27

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1200lb total vehicle weight

800lb total flywheel mass [4x200ea]

Diameter 18.75"

Flywheel RPM 3500 [120v electric motor plugged into wall]

Pulley to drive wheel at 1:1 [6"pulley] or to 12' pulley

Please help write the end of this story before I start. This is a "rev up" car built for big kids, in that it's plugged into the wall to spin up the flyweels [x4] to 3500 RPM. These RPM are transferred to the ground using kevlar belts and pulleys to the tire.

I pull the lawnmower style belt clutch and dump the stored kinetic energy to the back tires directly onto the spines of my enemies. How many nemesis can I smear on a charge?

Less useful answers might be -

How would you rate the potential power to compare it to a 1/4 mile car? Newtons and spinning and procession mathubations aside, I want to know if the power is delivered to the tires how fast will I get in 1/4 or a mile based on the stored power and weight of the vehicle.

I have done the calculations on every link in this forum, and used every calculator available that can translate from meters per second to dangles per minute. I realize aerodynamics and tire limitations are there, that's a real world penalty I don't need addressed either. What I have not been able to come to grips with is whether I'm working with enough stored energy or not. The force calculators all say that with the newtons available the vehicle should do over 3000mph. That's horsedirt. I'm off and totally wrong. Before I build framing I have to know how much of a bomb I'm driving.

I have searched a month for the answer, even asked my NASA guy before growing the stones to ask here. Please think in the context of a flywheel toy that a grown up sits in, trying only to go super fast for 8 to 10 seconds or less.

Forgive me if the answer is posted somewhere, I promise no answers I've seen help me so far. Thank you in advance for any help or suggestions you have.

- #28

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$$v_{v\ max} = \sqrt{\frac{m_f}{m_v}} \omega_{f\ max} r_f$$

For ##\omega_{f\ max}## = 366.5 rad/s (3500 rpm), ##r_f## = 0.238 m (9.375"), ##m_v## = 1200 lb and ##m_f## = 800 lb then ##v_{v\ max}## = 71 m/s (160 mph).

Sorry everyone, I don't really know how to reply, format a reply, etc. My main point is that the interaction of a spinning flywheel geared to a drive wheel, and dropped to the ground with a speed mismatch, is correctly and easily handled with Impulse methods. The unknown impulse applied to the wheels will cause a drop of flywheel speed, and an increase in vehicle speed. You can find that impulse by requiring that the final state is one of rolling without slip. Then you can optimize the gearing for any given flywheel I and vehicle m, to get the best possible final speed; it works out to initial angular velocity (rad/s) times a 'radius' defined as half the square root of (I/m). The gearing should be chosen to provide a speed of SQRT(I/m)*omega This speed is less than that achieved by perfect energy conversion.

You can get closer to the ideal by changing the gear ratio, either in steps or continuously. For continuous, look at a Zero-Max variable transmission or, less reliably, a Kelvin Wheel (which I have heard was used on a garden tractor) A cheapskate version would be a 'fusee', a drive cord wound around a conical sheave, so it starts at large radius and ends up at low radius. That could be tuned to never skid the tire and otherwise provide the fastest acceleration with minimal loss. Otherwise, you could use a 2 speed or other arrangement, in which you want to switch fast (or drop some additional wheels to the ground) to get a better top speed with reduced slip.

Anyone who is going to take bumps and corners with a fast flywheel, I would suggest both disks counter rotating on the same shaft, very close together (with rollers between in case flex causes contact -- reduces shaft bending. Just a concentric V groove on each, with a bunch of balls that mostly sit in one place. The disks can counter rotate due to a simple reversing gear at periphery,)

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