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Thread: Unlimited Rotational Kinetic Energy Storage?

  1. #31
    Guest
    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

  2. #32

  3. #33
    Guest
    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?

  4. #34
    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

  5. #35

  6. #36
    Guest
    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).

  7. #37
    thanks Christian. I too found it for about £200 on the net.
    http://www.centrehobbies.co.uk/acatalog/engines_car_os.html
    http://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

  8. #38
    Guest
    But for a small spinning disc (with one of those three stage gearboxes), theyll probably great!

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