Torsion Powered Vehicle

[kandrathe]

Hi,

You piqued my interest, so I Googled some. First thing I found was not exactly on topic, but of some interest.
Next thing was a little more on topic. At 0.0003 MJ/Kg, it would take around 7000 metric tons to store that amount of energy. Yeah, not optimized. But that's more than three orders of magnitude more than is reasonable (a one ton storage is already some twenty times more than a gas tank). I don't think a little bit of development and improvement will get you there, even with fancy materials and design.

I am concerned about the source for the Energy Density calculation you referenced, as they refer to the energy in clock springs, then cited a site for calculating the size of spring needed for a garage door. I'm not sure I trust the .0003 MJ/Kg for spring energy density, or use the design of garage door springs to power the vehicle. The design of the garage door spring is optimal for its purpose, but an alternative design with say a lighter weight material in a more compact design might pack more power/kg. It's definitely a balance of materials cost with other factors such as its potential for energy storage, but also its ability to last a long time.

I found some materials (also need more research) that fit these characteristics, a bulk metallic glass called Vitelroy-1 (Zr 41.25 Ti 13.75 Cu 12.5 Ni 10 Be 22.5) and ultra high molecular weight polyethylene. Also, we only need to translate the mechanical force into an electrical force so we can bleed the mechanical power as needed to spin a small flywheel driving our generator. This means the winding force of our multiple springs only needs to be sufficient to overcome the moment of our flywheel and not assist lifting a 300 lb garage door 10 feet in 30 seconds. What I'm concerned about is the longevity of the torsion energy stored, and the efficiency of transfer from the springs into the generator. Some limited amount of batteries or capacitors would help with starts and stops, or if large enough, the flywheel might aid the solution.

So, thinking of Hooke's law and converting it to potential energy we have PEs = 1/2 kx^2 where k is the spring constant, and x is the compression distance. Assuming the PE needed is the 2500 MJ and that k is a limited constant which will not vary enough by material property to get us what we need, the the only movable variables are the number of rotations on the torsion spring and the number of springs connected to the array.

In my mind I'm thinking for winding purposes charging the springs would be easier if they were partially decoupled from each other, but for driving they could combine for more available force. One side of the device could be designed for winding(charging), and the other side for delivering the force.

This might be hard to picture, but I envision a torsion spring wound around a 2cm axle housed in bearings, the lever arm of the outer torsion spring is mounted in a sleeve which is also attached to the axle via bearings but in series the outer sleeve would drive the winding of the next axle in the array. Both the axle and the sleeve would need to be free to rotate within some housing. Figure about a 20 cm diameter and a 15cm length for each spring assembly and figuring about the same space as the engine and transmission for total area (~1.2 to 2 m^3). We might fit 8 devices in each linked group, with 6 rows per layer and 6 layers high for a distribution of the 2500MJ across 288 torsion spring devices, but lets go with 250 for simplicity. Then each 20cm x 15cm spring device would need to deliver a mere 10 MJ or 7375.62 ft-lbs.:) I found the weight of Titanium can be calculated from lbs. per linear inch = .1631 x thickness x width. So I figure 30" x 5" x .25" is a little more than 6 lbs plus add at least 4 lbs more for axle, gears and housings. The 250 units would weigh 2500 lbs (ie. much heavier than I would want!).

Using the torsion spring calculator from one of my prior links, and working backwards from 7400 ft-lbs, 3600 degrees of rotation (10 windings), and a 6" spring moment, the spring constant would need to be 12.33 lb-in/deg which I need to figure out if it is possible on a 15cm x 75cm x 6 - 10mm(??) sheet of rolled titanium. 12.33 lb-in/deg seems rather too stiff to me. Then, I'm not sure if my guess of 10 revolutions is right either. Is it possible to get 20, or 100? If so, that reduces the spring constant by an equal proportional factor meaning I might use a thinner material. Again, I only need to overcome the inertia of the flywheel at rest.

I guess another way to figure it would be to calculate backwards from the desired result. If we choose an acceptable MPG, like 25, typical vehicle weight and calculate what distance the 15 gallon tanks would take that vehicle, or 375 miles between fills. Some other considerations would be the maximum speed, and the acceleration rate needed. I was thinking about this more today, and it might to acceptable to wind up the car every evening. So a smaller linear distance of say 100 miles might work, although I still think it still might be possible to come up with enough power to approximate our expected vehicle performance.

I guess I'll start building some spring driven generators. When in doubt, test your hypothesis. :)

Oh, and here is another interesting site with wind up devices.