Torsion Powered Vehicle

[kandrathe]

So, considering the most common fuels yield around 40-45 MJ/Kg, and an average fuel tank being around 55 liters. Or, a gallon of gas is equivalent to about 132 MJ.

Would it be possible to store around 2000-2500 MJ of energy in a lightweight serial sequence of torsion springs to replace the chemical fuel? I say serial, since it wouldn't need to be a single torsion spring that contains the energy, just an interlinked sequence of springs that would release their energy over time. So far my GoogleFu has not revealed any torsion spring capable of doing what I'm asking. In order for me to calculate the possibilities I would need to research more about materials properties to understand maximum potential spring constants.

For the less physics minded reader, to put the 2500 MJ or 2,500,000,000 joules in perspective;
joules = newtons * meters
power = work / time or in electrical terms, watts = joules / seconds
and, power = work/time = (force * distance) / time

I would envision the release of the spring energy into a generator that would power the wheels, and regenerative braking into high energy capacitors as is standard on today's hybrids. Rewinding the car would be accomplished via an electrical motor in the home garage, or even someday the "winding station".

If one could design such a series of springs, wouldn't this be a better option than batteries which are heavy, present their own chemical/electrical hazards and wear out rather quickly?

Here are some interesting sites I came across in my research, Mechanical, Industrial and Technical Calculations, Spring Makers Resource, Spring Engineers and Engineers Edge.

[--Pete]

Hi,

. . . most common fuels yield around 40-45 MJ/Kg, . . .

Should be pretty easy to calculate a rough number for spring energy density. Pick a spring for which you have the constant, the max deflection and the weight. To a first approximation, the energy is simply 1/2 * constant * deflection^2. If this gives an energy density close (i.e., within an order of magnitude or so) to that 40-45 MJ/Kg (or whatever it is for state of the art batteries) then it is doable. If it is down by two orders of magnitude or more, it's probably pretty hopeless. In between would need more investigation. My guess, based on experience with mechanical systems, is that springs will fall far short of what you need.

Would it be possible to store around 2000-2500 MJ of energy in a lightweight serial sequence of torsion springs to replace the chemical fuel?

I wouldn't worry about the details (i.e., 'serial', 'torsion') until the overall concept pans out. If the energy density isn't there just considering material properties, then the details won't help you.

In order for me to calculate the possibilities I would need to research more about materials properties to understand maximum potential spring constants.

Give the spring engineers the benefit of the doubt. Assume they get close to ideal performance from the materials and designs they use. So just look at a few commercially available items to get a rough idea. And remember, exotic materials usually have exotic prices:)

If one could design such a series of springs, wouldn't this be a better option than batteries which are heavy, present their own chemical/electrical hazards and wear out rather quickly?

Yep. Which adds to my doubt of the viability. In a world where things like high speed rotors have been considered, I find it difficult to believe that no one has considered springs. That no one seems to be pursuing it makes me think that the potential is not there. But happy hunting;)

--Pete

[TaMeOlta]

Oh yeeesh ... I'm just trying to picture what cleaning up after the first car accident would look like .... picking up springs everywhere ..... :blink:

Now , I barely remember the GEO Metro , I know it was tiny , could almost pick up the front end (engine and all ) by myself ( :lol: ) , fantastic gas mileage and super cheap , and then they seemingly vanished .

[Kevin]

Now , I barely remember the GEO Metro , I know it was tiny , could almost pick up the front end (engine and all ) by myself ( :lol: ) , fantastic gas mileage and super cheap , and then they seemingly vanished .

I had a 1989 Geo Metro that I got in 96, it had 77,000 miles on it when I got it. Due to some of the conditions it had to live in it finally died in 2003, frame cracked. I had put I think another 80,000 mies on it. Towards the end of it's life the MPG had falled to 35 or. But some of that was because I hadn't given it the best care either. But from 96 to 2001 it would regularly make the 450 mile trip from where I lived to where my parents lived (and the 28 additional miles to where my wife's parents lived) 1 to 6 times a year. Most of that driving was done on interstates, much of it at 70-80 miles per hour (oh yes I would speed, I even got a speeding ticket for going 89 in a 70 zone one year). The little bugger would be carrying 800 pounds between me my wife and the stuff we were hauling. I would frequently see 50 miles to the gallon when I filled up the little 10 gallon tank. Several of those trips were made with no stops at all. We would eat stuff from the little cooler and could go 7 hours without needing the restroom.

The tanks of gas that got burned all on driving in town were still often over 40 MPG.

Did it have it's drawbacks? Yeah, it wasn't exactly a power house. A 5 speed transmission (it was a manual not an automatic) on a 998 CC (that was embossed on the engine block) 3 cylinder engine isn't exactly super powerful. It was basically an in line instead of cylindrical motorcycle engine in a car. It was a light vehicle. I could lose speed going up a hill. I drove it a bit like a semi with trailer. I would let it overspeed at the bottom of the hill so that I would have a bit more momentum for the next hill. But it wasn't too bad. I did actually pick up a side to get a block under it to change a tire once, that was when I was in better shape than I am now. And while it was small, it was bigger than it looked. I'm 6 foot tall. Many of the cars sold today are awful for me to sit in the back seat. My head hits the roof and my legs are cramped. I had no issues in that little 5 door Metro in the back seat.

For a poor college student, it was a fantastic vehicle. Insurance was like $100 a year. Gas was like $100 a year. :) It got me from A to B with stops at C and D in the middle sometimes just fine. I ended up replacing it with a 1988 Honda Civic, of course the engine in that Civic was made in 2003. I was so disappointed when I calculated my first tanks gas mileage at 32 MPG. It felt like such a low number and then there was a tank that was in the 20's since it was all in town driving. Sure it was the upper 20's but it was in the 20's.

I can understand why the Metro didn't last. People didn't feel safe in them. It's not a lot of car around you and the fact that yes you could lose speed going up some of the steeper hills and you needed to "wind-up" a bit sometimes to pass folks would put people off. But I liked the little guy. Of course I was in my 20's and quite poor too. :)

[Bun-Bun]

Oh yeeesh ... I'm just trying to picture what cleaning up after the first car accident would look like .... picking up springs everywhere ..... :blink:

Playing with torsion power always leads to a twist ending.

[--Pete]

Hi,

I had a 1989 Geo Metro . . .

You know, it sounds a lot like my '61 bug. I never got that kind of mileage, but other than that there are a lot of similarities. When it finally died, at 250 thousand plus miles and on its second engine, I calculated that it cost me three cents a mile for everything including the original purchase. Of course, the 'safety' gear on a new car probably weighs more than that old beetle did in total;)

--Pete

[Kevin]

I can't find my old notes, but back when I was studying to be an electrical engineer (before I took 4 years off from school while being 2 semesters from my degree and starting up my own business, which I then let fail and going back to school for 3 years to get my Management Systems degree) in our electrical machines class my professor did some discussion of creating electrical power from torsion devices. His aim was more along the lines of the stuff you are seeing talked about and experimented on in some of the gyms out there. Tracks and walkways that convert the energy of the human heel strike into electrical power. I know that isn't the same thing as storing the energy isn't the same thing as you are discussing but it was kind of one of the intermediate steps. Getting that type of mechanical energy converted to electrical.

But in the lab we actually would up springs and then controlled the release of them and worked on various ways of getting that to produce current and store that electrical power and use that power. It wasn't exactly great returns. But then he was only looking for returns that were good enough so that you could get something else out of other work that was being done anyway. The bench press machine is being used to generate some power, ect.

We looked at some stuff with fly wheels too as I recall. They generally looked more promising but a lot less safe when practical application came to mind.

The topic of mechanical storage for electrical power was brought up it never seemed better than batteries for long term or capacitors for short term. But I do recall that toy cars were brought up and some of the calculations showed that you might be able to get something where the kid could wind the springs and get 5 minutes or so of RC run out of the car. I wish I could find those notes. But I don't see them in the trunk with all my other stuff from that time.

I don't know it's a bit fuzzy. It was 12+ years ago and it's knowledge that generally never gets out and gets exercised to stay fit. :)

[eppie]

So, considering the most common fuels yield around 40-45 MJ/Kg, and an average fuel tank being around 55 liters. Or, a gallon of gas is equivalent to about 132 MJ.

Would it be possible to store around 2000-2500 MJ of energy in a lightweight serial sequence of torsion springs to replace the chemical fuel?

My instinct tells me that your problem will be the light weight part. I can't imagine a light spring being able to give enough power to drive a car.

[--Pete]

Hi,

You piqued my interest, so I Googled some. First thing I found was not exactly on topic, but of some interest.

Would it be possible to store around 2000-2500 MJ of energy in a lightweight serial sequence of torsion springs to replace the chemical fuel?

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.

--Pete

[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.

[Zippyy]

Playing with torsion power always leads to a twist ending.

You're right Bun, let's bounce.

[Concillian]

Oh yeeesh ... I'm just trying to picture what cleaning up after the first car accident would look like .... picking up springs everywhere ..... :blink:

I think I'd be less inclined to worry about picking up springs so much as fishing them out of the various bodies they'd impale.

Springs with the energy necessary to emulate the amount of chemical energy in a gas tank would have huge potential for massive carnage.

After figuring how much mass of springs you'd need, figure out how much additional mass you need to properly keep the springs from killing peoplee in the event of an accident. My guess is you'll have to factor an additional 30% mass just for the safety aspect.

My off-the cuff inclination (as someone with a degree in Materials Engineering, but someone who doesn't really use the "large metals" part of it) is that the weight of springs necessary to emulate the amount of chemical energy in a gas tank is going to rival the weight of an entire car.

[the Langolier]

I think I'd be less inclined to worry about picking up springs so much as fishing them out of the various bodies they'd impale.

Springs with the energy necessary to emulate the amount of chemical energy in a gas tank would have huge potential for massive carnage.

Agreed. Considering fatigue, springs are virtually guaranteed to fail in the lifetime of the car. Fatigue is a decrease in the yield strength of a material under a load over a given period of time. As the springs are held in torsion or twisted the metal will just keep getting weaker until the thing will eventually explode into twisted shrapnel. Of course increasing the number of springs will decrease the amount of energy stored in each one so failure won't be so catastrophic and replacing broken springs would be more practical.

Also keep in mind that the spring constant is not constant with deflection so this system is non-linear. A simple power calculation from 1/2*k*d^2 is not likely to be very accurate.

[kandrathe]

Agreed. Considering fatigue, springs are virtually guaranteed to fail in the lifetime of the car. Fatigue is a decrease in the yield strength of a material under a load over a given period of time. As the springs are held in torsion or twisted the metal will just keep getting weaker until the thing will eventually explode into twisted shrapnel. Of course increasing the number of springs will decrease the amount of energy stored in each one so failure won't be so catastrophic and replacing broken springs would be more practical.

Also keep in mind that the spring constant is not constant with deflection so this system is non-linear. A simple power calculation from 1/2*k*d^2 is not likely to be very accurate.

I was reading in one of the articles I came across that for some springs the concept of tired springs was a myth.Contrary to popular belief, springs do not appreciably "creep" or get "tired" with age. Spring steel has a very high resistance to creep under normal loads. Say, in a car engine valve spring typically undergoes about a quarter billion cycles of compression-decompression over engine's life time without noticeable change in length or loss of strength. The sag observed in some older automobiles suspension is usually due to the springs being occasionally compressed beyond their yield point, causing plastic deformation. This can happen when the vehicle hits a large bump or pothole, especially when heavily loaded. Most vehicles will accumulate a number of such impacts over their working life, leading to a lower ride height and eventual bottoming-out of the suspension.

I would think that fatigue would only be a factor in plastic deformation, not from operating within its modulus of elasticity. I imagine that the quality of the spring material itself also might be a factor though, where I could see that metals with larger granularity would fatigue faster than ones specifically crafted to be high tension springs. The design I'm thinking of would most likely fail by sheering the lever arm on either side of the spring coil resulting in the unwinding of the stored energy within a confined sleeve. It would be doubtful to result in any explosive effect other than a bang.

[--Pete]

Hi,

Just a quick post for now, more later. I've got some ideas that I want to check out, but my vision is too blurry right now.

I would think that fatigue would only be a factor in plastic deformation, not from operating within its modulus of elasticity.

Strictly speaking, fatigue is only a factor in the elastic regime. Once you get out of the elastic regime, you're talking permanent deformation leading to ductile fracture. Fatigue is caused by the migration and pinning of dislocations caused by elastic deformation which eventually leads to brittle fracture.

--Pete

[Concillian]

Agreed. Considering fatigue, springs are virtually guaranteed to fail in the lifetime of the car. Fatigue is a decrease in the yield strength of a material under a load over a given period of time. As the springs are held in torsion or twisted the metal will just keep getting weaker until the thing will eventually explode into twisted shrapnel.

Springs are generally made of materials that have a high fatigue limit and their operating window is generally chosen so that they are within their fatigue limit. What this means is that under normal operating conditions, a spring will not continually weaken until it fails... unless there was a poor materials selection process.

it's part of why you don't see aluminum springs. Most aluminum alloys have a fatigue limit that is essentially zero, so they degrade with time. Steel and nickel alloys that springs are usually made from have relatively high fatigue limits.

[RTM]

Was going to post about springs and the safety thereof, but was beaten to that.:)

I've often thought about spring-powered vehicles myself, usually while playing with my kids' little pull-back-and-let-go cars. My conclusion was that, aside from safety issues (and aside from any math, it should be noted), the energy expended to "charge" the spring would probably not be efficient enough to warrant making the technology work in a full-sized vehicle. In the case of my kids' cars, you pull the car backwards a few feet to charge it up, and it will go maybe 20 feet. That seems pretty good but then you consider that the car accelerates very slowly and has little to no ability to overcome obstacles or go up any sort of incline.

I'm sure there is a workable solution to those problems, but the ultimate question is: "Do I really want to drive backwards for a mile or two just to make my commute to work?":)