Unlimited Rotational Kinetic Energy Storage?

I see no limitation on the amount of rotational kinetic energy that can be stored in a flywheel that is not used as a weapon in the FRA rules.

Anyone care to comment on this?

Thanks!
Mack

Yes, as some people are researching the potential of magneticaly in vacume suspened flywheels for energystorage this seems a potential energysource for a fighting robot.Just crank up the RPM to store more enegery without increasing the weight.

But all experiments up to now are on a too small scale or/and cant handle any mechanical shocks.

So, if you can build a flywheel energystorage, that can power a robot, any weightclass, with satisfying result, we have a new rich man in RW.As that would be a moneymaker.


Now, I had, years ago now, an idea to use a small disks that runs at very high RPM counterclockwise to the weapondisk, to counter the disadvantage of a horizontal disk, the trouble with steering.

It was meant to be an 25 cm diameter 2 kg disk, that would be running at 25000 rpm to counter the 1000 rpm rotating disk.
But after starting to build the basic parts of the robot I noticed that the building of a heavy was so timeconsumong that it wouldnt be fun to see my machine splattered all over the arena.And it goes against my first liferule -dont do anything to anyone what I dont want to happen to me- so I started to look into the non smaching robot technology of flippers.

Greetings Mack,
Welcome to the FRA forum, always glad to see our friends from across the pond here!
You are quite right, there is no limit to the KE that can be stored in a flywheel, used as a weapon or not. (rule 11.2 & 11.3 applies) What kind of application for a flywheel do you have in mind? If I knew this, maybe I may be able to offer you some more detailed advice.
Regards,
Geoff.

Well, my comment is: Test it to destruction in a nice, safe, deep hole in the ground. :)

whilst there is no limit, you need a dam well balanced disc to spin at high speeds, jst remember that! and make sure that anything supporting it is as strong as u can possibly make it

Do you think you would be allowed to spin up a flywheel before entering the arena? Obviously you cant do so with an exposed flywheel - it would be worth checking with the powers that be about encased flywheels before spending too much time on a design.

I see several rules regarding spinning weapons, but nothing other than two fail-safe rules for rotational kinetic energy storage devices (flywheels). I like to demonstrate my point by going to ends of the spectrum, so in this case, consider a flywheel running at 100000rad/s with 1GJ of kinetic energy that has a failsafe that causes it to spin down within 60 seconds to meet the safety rule; is that safe?!

My guess is that there is or *should be* some additional rules governing flywheels. If there is, I want to know what they are. If there arent, then I urge the safety folks to consider adding some.

Mario - Id be more likely to consider existing ball bearings rather than frictionless magnetic/vacuum-packed bearings; theyre alot cheaper! I think that the energy losses in conventional bearings would be tolerable. As for the problem with gyroscopic effects in spinning disks, there shouldnt be any problem with a horizontal disk (here, I mean a vertical disc axis). The problems arise when you have a horizontal disc axis/shaft but vertical disc (maybe thats what you were talking about). Id mount my flywheel with a vertical shaft. I have to disagree with your first liferule - I *want* my bot to beat the other bot, but I *dont want* my opponent to beat me :-). However, I have to agree that I dont want them to dessimate my bot.

Geoff - Thanks for the welcome! I have no specific design in mind yet, only possibilities. Im just trying to find out which of my ideas are good *and* legal.

Do any of you guys know of any bots-of-the-past that used flywheels to power their weapons (not spinners where the flywheel *is* the weapon)? If so, how did they do?

Regards,
Mack

Theres always Tip-Top (dont have the URL though).

Tip Top has a spinning disc, but its a weapon. Im talking about a bot that uses rotational kinetic energy to power a *different* weapon. Know of any like that?

Thanks,
Mack

Yes, but that weapon also powers the robot itself.

Right, and the name is just as clever as the design! But because it is a spinning weapon, it is limited by the rules of a spinning weapon.

Regards,
Mack

There was a time when someone was talking about having a vertical flywheel which would hook onto an axe, thus providing the axe with a lot of kinetic energy. Did this ever get built? Another related idea which Ive not seen implemented is to spin up an internal flywheel and hook onto an external disk/bar once up to speed - which means youre not quite so constrained when shoved against a wall (see Hypno-disk vs Tornado). You could do a CO2-less flipper the same way, possibly with a Cassius III-style (when it was still going to have it) vertical flywheel at the back as an exposed weapon as well, although the engineering would be... challenging.

Ive often wondered about the idea of two counterrotating flywheels mounted above each other on a common axis, thus avoiding torque steer. The effect would be to chew into a relatively limited area on the opponent rather than to throw panels off, but it would stop the robot with the disks being thrown around the arena so much (although of course it puts more pressure on the axle). Is this a bad idea? Not that, for the same philosophical reasons as Mario, Im ever likely to build a spinner...

If youre talking about maintaining the KE in the flywheel for the whole fight (not powering it from batteries or similar) then I think thats more of a challenge; the buffering needed to survive the various forces to which the robot would be subjected would make it very difficult to do anything useful, and youd need a *lot* of energy to be up there with the amount stored in CO2, petrol or even batteries.

Just my tuppence.

--
Fluppet

we did toy with the idea of having a second flywheel inside the shell to give a boost to the spin up but it would have taken too much weight away from the actual weapon and it would have been difficult to effectively transfer the energy.

I also thought about the axe idea however the forces involved would require very well mounted components etc and prob in the end wouldnt be any easier than CO2.

I think I wrote something on the last forum about an axe like that. However, it was just an idea and never anything I had planned to build.

If all of the kinetic energy stored in a flywheel could be transferred into the opponent in one shot, Im sure that this would be more effective than a gas system. I agree that it may be difficult to design an energy transfer linkage that would be able to withstand the material stresses involved, but Im curious how much energy could be transferred with reasonable linkages (materials and geometry) without them yielding or quickly fatiguing. Transferring some fraction of the energy would simply mean that the unused kinetic energy of the flywheel would be left over for another shot or that it would take less time to spin the flywheel back up to speed.

In theory, you could hook any weapon to the flywheel and could even link the drivetrain as well for bursts of speed for ramming or evasion. Perhaps a flipper *and* an axe/hammer could go into the same design (simultaneously, not as interchangeables), but space would surely get cramped.

Fun to think, about, though! I think itd be fantastic to have a tossbot rather than a flipper that heaves the opponent vertically several meters. Getting under their center of gravity would be the challenge there, but seems possible.

I think that gas systems are a bit of a cheat because they enter the ring with huge quantities of energy that was stored prior to the match. Non-gas systems must convert chemical energy into kinetic energy no sooner than the start of the match. But given that those are the rules, it does seem quite wise to take advantage of this inconsistency.

Mack

thats a good point Mack, never thought about it like that with the stored energy arguement........ hehe, fully spinning typhoon 2 entering the arena....... o the possibilities! :proud:

The stored gas and therefor stored energy,has its own disadvantages.But enough advantages to kept in use.
And cheating..... I wouldnt call it that. You can do just the same with batteries, springs and a motor. Or like some feather already do, with a compressor.
It is just a little less convenient. CO2 converts heat from the suroundings to pressure, and it needs time top do that, or the system around it has to be able to cope with the pressureloss.

And, stored energy to weight, .5L of gasoil has lots more calories in it than CO2 bottles or batteries.It is just to find the right trick to get those calories out.

Sorry for the above post.. it was posted before I realized that it was gone.Normaly the draft of the later part of this message.

All experiments concerning energy storage in flywheels are done at ridiculous rpm like 100000 +. Even faster than turbos on cars.It is also the only way to put in enough energy in a limited weight. Using a 30 kg energy storage flywheel beats the purpose, as you can do that a lot easier with batteries. And before you say thats limited, look how hard Beta can hit.

And for beating the other robot. Most flipperfights are over quickly but spectacular, even in arenas without moat around between inner and outher screen. How many times I have seen champions stacked against the sidewall of the RR arena, its about uncountable.
You dont have to disassemble the opponent.It looks like fun, until you see your own machine scattered around the arena.-This is something you say yourself Mike.

Now the mechanical systems to couple a flywheel to an axe, weapondisk or even flipper. The simplest,most weightefficient system I can imagine is the dry plate coupling from a Ducati.

Forget anything with interlocking teeth or gears.The moment is way to big to distribute in a reasonable weight.

And CO2, or other compressed gas feels like cheating?0.5L Gasoline is more calorierich than any CO2 bottle useable in RW.So thats also unfair.
No the rules allow both, and it is up to the builders to use those unfair tricks as best as possible. Storm II (and 1) or Tornado neither use CO2 or gasoline, and still they are very competitive.Is the use of batteries then unfair?

Actually, the compressed gas in a CO2 bottle takes a fraction of a second to activate a weapon (for all intents and purposes, immediately after the match starts, the weapon can be used). The pressure drop of the escaping CO2 in the process will cause it to cool, but the energy is immediately available regardless of this cooling. To prove my point, consider that you vented all of your pressure in one strike/flip/etc. This could be done immediately.

A gasoline engine cannot burn up all of the chemical energy stored in its fuel tanks all at once and transfer that energy into the opponent. A battery cannot drain all of its power through a motor in a single, quick burst either.

The gasoline and battery powered systems are limited by their horsepower or voltage/current limitations, respectively.

The appropriate analogy between a CO2 system and a gas or electric motor system would be entering the match with the chemical (gasoline or battery) energy pre-transformed into immediately usable energy such as kinetic energy (spinning disk) or potential energy (compress a huge spring such that it stores kJ-order energy).

As for the amount of energy that can be stored in a flywheel, if you get a dense enough material positioned at the maximum radius your design wants to armor (tungsten is a very dense possibility), and you connect this with a lightweight set of spokes or slotted disk, you can store a tremendous quantity of kinetic energy at a few thousand rpm. You dont need 100000 rpm.

Did some scavanging to collect the info, and if you had a tungsten ring that was 3cm thick, had an inner radius of 37.5cm and an outer radius of 40cm, it would have a mass of 35.1kg. If you then spun this ring up to 1000rpm, youd have 29kJ of energy. If you dumped all of this into a 100kg bot straight up, itd go 29.5 meters straight up!! And what goes up...

This is a bit unrealistic, because it would take quite a long time to spin this disk up to 1000rpm, but you get the point; this would fit in a bot.

I have an idea of how to get the energy out of the disk into whatever needs it, but I have to do a bit of research to determine if my approach would work...and then there is the minor detail of actually building it ;-)

Mack

Mack, I do not know you have seen Tough As Nails in action.If not, get yourself an ICQ account, and add me maddox10@hotmail.com

Originaly that machine was intended to have 20 horsepower of ICE engine on board.Completely hydraulic driven.Speed about 50%(25mph-accelerationin .8 sec) faster, and 6.3 tons of squize on the ends of the claw.With the Dual Maddox system they can grab the opponent inside 0.2 seconds.
That power would be available from the momentactivate was called.

So dont say CO2 is cheating.Using things outside the rules is cheating.


Now, a 35.1 kg disk @1000rpm= 29kilojoules. Now ;let us say another 15 kgto get this energy into a flipper or disk.=50.1 kg.
The coupling ,and the weaponsystem capable to withstand this energytransfer cant be light.

And you seem to be able to calculate how much energy is storaged in something-what I cant-how much Kilojoules are there in 1.7 liter gas on 55bar?If you can answer that- I can tell you a little secret....

First of all, I didnt say it was cheating. Obviously, because the rules permit CO2 systems, its legal. I said that I think they are a bit of a cheat, and I think Ive sufficiently conveyed what I wanted to (CO2 systems enter the arena with immediately usable energy that needs no chemical conversion, and ICE and electric motors dont have that luxury). Its inconsistent. And nowhere did I say that non-CO2 bots *couldnt* create usable energy. Obviously, there are plenty of excellent non-CO2 bots.

I dont know where you were going with the 15 kg linkage stuff. I was just demonstrating that you dont need 100000rpm to have a useful flywheel.

As for the energy storage in a gas system, Id have to look into my thermodynamics texts and refresh my memory a bit...or alot.

Regards,
Mack

Im only guessing about this, but doesnt the energy involved in a CO2 bottle depend on how fast you can get your ram to expand?

If youd have a buffertank a hundred times larger than than your ram, it would still use up the same amount of gas, yet it would expand a lot faster than a ram without buffertanks.

The same goes for the valves and the pipes, larger bore would equal much higher energy, yet use the same amount of gas.

Any thoughts about this?

The gas has a fixed amount of energy (give or take). High Flow rate is simply taking advantage of all that energy as best you can. Its about efficiently converting the potential energy into power- higher flowrate = more efficient conversion.

@ Mack Oh, an electric motor cant give all the power in an instant?Since when has electricity a slower than lightspeed reaction..If you want more electrical power you just use a bigger motor, bigger wires,better and/or bigger batteries.
All for lower resistance.
Fueldriven things, just thesame, if you want more power you burn more fuel in the same time, how you do that, more RPM, bigger motor etc.
With 0.5L fuel mixed in the right amounts with air and BOEM, the arena has a new pit.
It is all in the idea behind it.Not in the stored energy
Compressed gas is just an easier and in most cases cheaper way to get fast useable energy.

How I got to the 15 kg disklinkage.Easy. Total setup to use the very light and strong enough dry plate coupling from a high power motorbike like a Ducati. You need something to pull that.And no, 4 servos acting together dont sound to reliable.So you need or an electrical system based around a large solenoid or a strong and fast enough motor.Or a Pneumatical system.Even hydraulic are possible(with the system Kos is building even one of the lighter options)
The original housing is not that handy to use in a robot, so a custom build part is needed.As this cant be cast in hi strength alloy(it can but would cost a little much), you will have to make that in a milled version, and that is always heavier than a Hi tech cast version. The axles from and to the energy storage and weapon must be strong and stiff-so weight is adding.
To make a long story short. I did work on the idea.

@ Christian, bigger buffertanks, bigger pipes and bigger rams are a way to use more gas in a faster way, again it is all in the construction.And everything needs to be in thesame league, you can use a 200*200 ram, and dont have a weapon.Try to fill that with a 1/8 bsp hose.

Christian, as Eddy mentioned, the energy in a compressed bottle is fixed. Power is the rate at which you use the energy (or provide it), so if you consider a fixed amount of energy in a single dose of expanding gas, the faster you can deliver it into your opponent, the more power. If you deliver your dose over 1 hour, its pretty useless. 1/10 of a second is MUCH more effective. However, I think that larger plumbing increases the efficiency of the dose; viscosity and turbulence eat up energy, so if you have more efficient plumbing, you decrease these losses and get more of the energy into your linkage (and into your opponent).

Mario, your motor is limited to 36V, and I dont know what kind of battery out there that can deliver the amperage required at 36V to give the same energy output as is contained in an entire gas bottle. Heavy duty 12V car batteries can only crank out 500 or so amps, but their illegal (wet cell), and weigh 30kg or so. Sure, electricity travels fast, but its circuitry has resistance which causes heat which melts said circuitry if you try to flow too much current through it. Even then, youd need one helluva motor that could handle that current. For an ICE, youd need to burn the whole tank of gas at once which would probably require an above average car motor. Both the electrical and ICE options therefore require a motor that would eat up most of if not all or more of the allowable bot mass of 100kg. You need no motor for a gas system. You need the linkage, but you also need that for the ICE and electric motors. The bottom line is that in one case, you have to convert the chemical energy to another form which requires an electric or ICE motor, and in the other case, you dont. That basic difference is why I think the rules are inconsistent. But as I mentioned before, its legal, so its probably wise to take advantage of it.

Again, as for the 15kg linkage stuff, I agree that you must connect the flywheel to the weapon. My point was that you could store enough energy in a flywheel of 1/3 your bots total mass and easily within typical bot dimensions to toss a 100 kg bot twice the length of an average house straight up in the air. It was purely demonstrational. A more practical scenario would be to toss it 1.5 meters in the air 20 separate times. The linkages required to achieve this would be much more practical.

As for cast vs machined bit, Im almost positive that if the shape of the part can be machined (some shapes cannot be machined but can be cast), then the machined part will be the stronger of the two. Therefore, the machined part could be designed to be even lighter than the cast counterpart. The strongest cast aluminum in my materials book is less than half the strength of 7075 T6 aluminum billet. It might be that if you can get a steel mold of the part vs a lost foam sand casting, you could get the part cast in 7075 T6, but usually, you have to either have TONS of cash to make a one-off in this manner or plan on manufacturing numerous parts that can be sold to offset the cost of making the mold. I had a fun time in college making some styrafoam molds of some pillow blocks for a race car that could be used to sand cast some aluminum parts (you bury the foam part in sand, then pour the molten Al into the foam, the foam evaporates holding the sand in place, and the Al fills the void), but we got lazy (err strapped for time) and ended up machining them instead. Made a cool hot wire styrafoam cutter and everything! But thats a bit off topic ;-)

Regards,
Mack

Mark, your arguments are still valid. I never disagread on them, but I still am from the opinion that a good build ICE, kinetic energy, or hydraulic powered system can be as effective as any pneumaticaly powered weapon. It is all in the construction and the ideas behind them.

Batteries, according to my info, the Hawker Cyclon 8Ah battery, allowed in RW as they are Gelcells, can crank out over 600A.The 25Ah version reaches the 2000A mark.The motors to handle this current.Any motor can, if it doesnt take seconds.But my bet would be the pancake style motors, or a 6V carstarter from an old volkswagen beetle.
I wonder how much amps Betas axe draws, that needs an Albright 280 relay, a brand know to be capable of withstand 500Amps and more(the biggest they have can switch 1500A).The example how electrical power beats pneumatical.Beta is the only hammerbot up to now that dented Tough As Nails hard enough to make a real impression.

Hydraulics.
For excample, how does a hydraulic set up sounds. Inside 6 kg, flowrate 40l/min and a peak pressure of 3000 psi.And the electrical motor doesnt drop lower than 75% efficiency.Oh, and the 6 kg include the safetyvalve.With 5 kg more you have a ram and valves to operate a Razer powerlevel like weapon.A smaller version is being build by Kos, to be used in a featherweight.

Now pneumatical systems. It takes more than big tubing and large valves and rams to use the complete content of a bottle in 1 go.Especialy when using CO2. So I repeat the question. How much energy is there in a bottle with a volume of 3L and 55 bar pressure?It is normaly 165L on 1 bar.
For example Gravitys ram, an 100 bore 180 stroke uses 77.75L in a fill action.How do we get more than 10 very usefull actions out of that system?Oh, that robot uses 2 bottles that size, so theoreticaly 330L on board.
Just a question, and maybe your answer is also a reason to know that pneumatical systems have own problems and enginering behind them.
Other excample Tough As Nails, using a 100 bore 354 stroke ram, with only 1 bottle , can have 3 or 4 useable damaging actions, and at least 6 good grabbing actions.How do we do it?

The cast vs machined bit.The machined parts will be stronger, but heavier, as you will leave metal on spaces it isnt needed.Mountings to put the piece in the mill or lathe,ridges to prevent big deformations. I know this from years of practical machining.Including hi pressure aluminium casting.Also, consider the total amount of time needed to replicate a cast piece with machining,and even using handtools as a Dremel.

The evaporating foam idea sounds fun, but dangerous, the vapours will try to escape the mold.And not very quality oriented, as gasbubbles will be cought in the solidifying ali.And Off topic, it is nice to hear alternative ideas.

Mario, any chance of the hydraulic TAN setup being built?

If anyone wants to donate a custom build crankshaft and about £3000 for the valves, Yes.
Thats the reason why the Hydraulic setup didnt happen.Time, and lack of money to buy the valves and crankshaft.I must admit that Plan B isnt that bad, as been proven in Series 7.

Mario, the problem with the energy of the gas cylinder is that you need to also factor in the temperature. We know the gas temperature in the bottle is roughly room temperature in the beginning, but the vented gas cools as does the remaining gas in the tank after the first use. If you know the density, temperature, and pressure of the gas, you know its internal energy per unit mass. So we know the initial energy, but not the final. I think that some assumptions can be made about the expansion process (perhaps adiabatic) that might give a good ballpark estimate of the new gas temperature both in the vented gas and the remaining gas (ignore conduction of heat into/out of the gas), but my thermo skills are completely shrouded in cob webs. Ill try to ask some workmates whose thremo is fresh in mind. Im almost positive that a fairly accurate calculation of the work done on the piston by the gas can be made.

I agree that if you cant machine the same geometry, you dont have an option but to make the part another way. Thats why I said if the shape of the part can be machined. There are plenty of shapes that can be machined, but Im not sure what the part looks like in the Ducati clutch. I was leaning toward an alternative design using some off-the-shelf or slightly modified components (not a clutch).

The lost foam sand casting bit is not something I invented. Many auto motor blocks are cast this way. If you look at a Saturn block, it looks like silver styrafoam (you can see the individual beads from the styrafoam in the actual block surface texture). The styrafoam vapor escapes through the sand, not through the metal. Its pretty easy to do if you have the ability to do green sand casting and dont need optimal material properties. Agreed, all of the problems with sand casting still exist.

Mack

Mario: using PV=nRT gives you 0.556m^3 of CO2 at 1 bar from 1.1kg, which is equivalent to 56kJ of work done on the atmosphere. The most energy you can actually extract from the gas is 28kJ as a ram with only 1 bar absolute pressure will do no useful work, you need 1 bar gauge pressure which leaves you with only 0.278m^3. This is if the gas is expanded slowly and is allowed to reach ambient temperature. If large buffer tanks are used I think this is approximately correct. [a 30C drop in temp only drops the energy by 10%]
1.1kg of NiCads would give you 286kJ. 500ml of petrol could give 7600kJ!

Mack:I dont think you could use up your whole CO2 supply in 1/10second. I reckon it would take more than 3s to completely vent a fire extinguisher and even then you would loose a lot of energy to friction/heating effects. This leaves you with about 8.5kW/kg. [or about 2kW/kg taking into account mass of the entire system]
Probably the ultimate electrical system would be 3 packs of Nicads and a LEM200 weighing about 6kg, giving out 6kW. obviously this is 1kW/kg
A RC plane engine can put out about 2HP peak and weighs about 1kg. giving around 1.8kW/kg.
Now the above engine/motor needs a transmission, but belt drive to a disc weapon doesnt weigh much.
A steel disc can store about 180kJ/kg before it explodes; a CFRP one can do better at 720kJ/kg, but these are both very high tech, scientifically designed discs with expensive bearings run in a vacuum. I cant find figures for the sort of power you can extract from them but ultimately as Mario suggests it isnt going to be a light solution.
So all in all I dont think its right to say CO2 systems have an unfair advantage.
Personally I think ICE is the way to go for weapon power but they all have their advantages and disadvantages.
Mark

Thanks Mark,

Is that 7600kJ the chemical energy in 500ml of fuel? If so, do you have a good sense of how efficient a small motor is? I recall something like 30-40%. 2.2MJ still makes an ICE pretty attractive.

The whole flywheel idea is to be able to buffer your ICE or electric motor energy output so that you can run the motor at 100% until the flywheel is at its max design speed (Im thinking more like hundreds of RPM). Then you can extract energy from the flywheel as needed by a weapon or whatever and have the motors continue to pump restoring energy into it. Then you arent limited by the peak power output of the motor for each weapon use.

So now I must think on the ICE powerplant instead of the electric motor. As a mechanical engineer, that suits me just fine :)

Mack

Thanks Mark.Your answer has done what I hoped for. Proving that CO2 power isnt everything, and that to build a good system, you need to take everything in account.

Oh, and it will take longer than 3 seconds to vent a 2 kg CO2 bottle.The let trough is rather small.
And expanding slowly? Not for a flipper or axe Im afraid, we want explosive reaction, to have as much force in the action as possible.The bottles that come out of a robot used in combat, those are frozen all over, and sometimes solidified CO2 is heard to rattle in the bottle.

Some small methanol RC motors do about 40000RPM and peak at over 2000W (but only weighing about 300 grams each).

Youll need some monster gearing to bring that down to a sensible speed, but for a spinning disc?

Mack: I read somewhere the actual energy content of petrol was 50MJ/kg but most engines are only 15% efficient. This is immaterial though becasue its the weight and performance of the whole package that counts.
I think you idea for using an internal flywheel to store energy from an ICE is interesting. It could work really well on a crusher to allow you to quickly get a nip on your opponent, using all the energy youve stored while manouvering for position. Given the way hybrid car designers are going though, I think it would probably be easier and more efficent to use the engine to drive a motor/generator to charge your batteries, then when you want max power out use the engine and motor in parallel.
Mario:You know much better than me about the realities of CO2. I was thinking that to get the most power out you would charge multiple buffer tanks, allowing the phase change to allow over a relatively long time, then empty them quickly into a ram. Am I correct in thinking that CO2 freezes at -50C? If all the gas cooled to this level I think you would still get about 20kJ out. Does this sound reasonable to you? I heard that Gravity can get about 100 flips. 100 flips of 1m high is 98kJ! Does Gravity have 2 2kg tanks as by my calculations that would be just over 100kJ stored on board.
Chrisitan:Can you give me some more information on those engines (Supplier, price etc). The gearing in RC cars handles that power with a gear ratio of about 8:1 and doesnt weigh too much. The belt drive to the disc can handle the rest of the reduction.
The bit that appeals to me the most about using a setup similar to this is that many RC cars use an automatic transmission, meaning that you could have low gear ratio for a fast spin up time, but then the high gear would kick in and still give you high maximum energy storage. The only problem with this is I dont know how much heavier the system would be after you had reinforced it enough to survive in the arena. Have any uk featherweights used nitro engines succesfully?

Mark

Mark, Gravity uses 2 2kg bottles,and 2 buffertanks.Newer versions of this set up use more but smaller buffertanks, to get more surface to exchange heat.
Now, WJ never tested Gravity on the amount of flips he has, but 50 good ones reasonable reasonable.As demonstraded in the wars, After about 30 weaponactions enough force was applied to get Dead metal turtle.
CO2 solidifies on -79°C.And has something like 15 bar at -10°C-this is a guestimate.The ram of Gravity was 100 bore 180 stroke with a leverage of 4 to 1. On 15 bar that still gives you a 295 kg shove for a lifting hight of 720mm.This is more than some other FP using heavies have with warm bottles.(Hard for example).

Oh, and by the way, my grasp of the porperties of CO2 are all based on practical tests, not a lot of calculations.Only the safetyfactor on the used materials and mechanical parts are calculated toroughly.

Mark, the one I was thinking about is manufactured by OS Engines.

http://www.osengines.com/engines/osmg2071.htmlhttp://www.osengines.com/engines/osmg2071.html

The price should be about £200 (but as a foreigner, Im not 100% certain about this).

thanks Christian. I too found it for about £200 on the net.
http://www.centrehobbies.co.uk/acatalog/engines_car_os.htmlhttp://www.centrehobbies.co.uk/acata...es_car_os.html
Is more expensive but shows a range of engines. Its interesting to compare them in price and performance to a Magmotor:
._______________|___Mag______|__OS .21 V-R__|
cost____________|___£269_____|___£210_______ |
peak power______|___2234W____|___1875W_____|
weight__________|___1.7kg_____|___0.315kg____|
max revs________|___6000RPM__|___42000RPM__|
peak torque._____|___14Nm_____|___~0.5Nm____|

If the nitro were geared to the same max RPM as the electric it would still only produce a peak torque of 3.5Nm. I think this must be why such light drive-trains can handle such relatively high power in RC cars. It also shows why they have multistage gearboxes.
Mario:I based all my figures on calculations using basic formulas so wouldnt expect them to be too accurate. Ive found a phase diagram for CO2 that basically agrees with what youve said.
Do you have any experience of CO2 being use to power rotary actuaters? Given pnuematic systems high max power to weight ratio they should be good for accelerating a disc.
Mark

But for a small spinning disc (with one of those three stage gearboxes), theyll probably great!