10 ms·

Students break acceleration world record...for electric vehicles. This isn't close to the record for dragsters; if they can increase the energy density per uni

Students break acceleration world record...for electric vehicles. This isn't close to the record for dragsters; if they can increase the energy density per unit mass there are traction and downforce improvements that can be used to improve this. It's very hard to beat chemical energy like detonating gasoline or nitromethane - you're looking at roughly a factor of 100, with ~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery - especially if you're racing through a 15 PSI gas that you can use in your chemical reaction without having to accelerate it onboard. I suspect that traction control for an electric motor may someday allow electric vehicles to exceed the records held by internal (well, mostly internal) combustion engines. You could keep the tire at exactly the right amount of slip for maximum acceleration, rather than trying to balance centrifugal clutches to get just the right amount of power at the right time. I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire...though cables that can carry megawatts of energy are probably pretty heavy. Edit: I think the most interesting category here is the typical friction-propelled, human-carrying vehicle of either chemical or electric power sources. Railguns, rockets, fan cars (using active downforce), and vehicles which engage the ground by rack and pinion are qualitatively different. When the question is accelerating your own mass forwards using the friction developed by your own mass being pulled down by gravity, there's an interesting optimization problem trading off weight and power.

MontyCarloHall 4y ago
>cables that can carry megawatts of energy are probably pretty heavy Required cable thickness (and thus weight) is proportional to current, not voltage. Conductors to carry megawatts of electricity could be fairly light as long as the voltage is extremely high and the amperage relatively low.
- deleted 4y ago
  [deleted]
- jvanderbot 4y ago
  And magnetic force is a function of current, and magnetic force is what drives wheels. Technically you are correct, but thick cables are actually needed to do lots of translation from electricity to movement.
  - willmadden 4y ago
    I don't think there's a problem with cable weight with electric motors. Production EV's today have ridiculous amounts of torque and don't require prohibitively heavy cables. The issue with acceleration using wheels is gravity. You are limited to 1g, the downforce on the wheels, which you use for traction to push the vehicle forward. Spoilers increase the downforce on the vehicle beyond 1g, but the energy required to do that is proportional to the drag on the spoiler. Short of a rocket engine, the way to accelerate beyond 1g with a wheeled vehicle is to have a downforce fan. That can be powered by combustion or by electricity. I don't know which would offer the highest power to weight ratio.
    - deleted 4y ago
      [deleted]
    - lazide 4y ago
      I’m not sure having a ‘reverse Helicopter’ on the back of your vehicle really qualifies as ‘ground vehicle’ at that point. Especially if it’s providing enough force to literally drive upside down on a ceiling somewhere.
      - stefs 4y ago
        it's as ground as can be, short of a tunneling machine maybe.
      - sacrosancty 4y ago
      - et2o 4y ago
        This was the basis of a very famous F1 car in the 1970s. It was ultimately banned.
- omegalulw 4y ago
  This seems...wrong? Let's say you can control voltage, cross section area A. Now, you want a constant power across a load P = V * I. Your net resistance R is C + D * L / A where C and D are constants and L is your cable length. I is proportional go V * A / (C * A + E) where E is also a constant. So your load power is proportional V^2* C * A / (C * A + E) which is proportional to V^2 * A / (A + F) where F is also a constant. With a large "enough" A, this is effectively V^2. With a small A, this is V^2 * g where g is A / F. So the smaller the area you have the more power you are wasting (roughly equal to V^2 * (1-g) which is heat in the wires). So the smaller area you have, the less efficient your power delivery. And juicing up your source power is a lot more expensive than juicing up your source voltage.
dheera 4y ago
> though cables that can carry megawatts of energy Not really, high speed train lines do it all the time. They usually operate at 25 kV or 50 kV and often consume a few megawatts per train. (At 50 kV, one megawatt is only 20 amps, which you can deliver on 12 AWG wire, theoretically.)
- titzer 4y ago
  Uh no, do not put 50,000 volts through 12 AWG wire.
  - jefftk 4y ago
    What goes wrong?
    - WJW 4y ago
      Most store-bought wires won't have sufficient covering to prevent arcing, so you might get a short circuit somewhere. If you insulate the wires sufficiently however, any wire will take almost any voltage. It's the current you should worry about, as other commenters have already mentioned.
  - cesaref 4y ago
    As has been stated, voltage isn't a limitation, its the current that. Go and look at the HT wiring used in a cathode ray tube display, and you'll see it's a lot less that 12 AWG, and happily carries 10-20kV.
  - the_third_wave 4y ago
    When I went to high school the teacher told about a science fair where someone had put a sign next to his project reading: WARNING 2 million Ohms (or something like that, I don't remember the actual number of Ohms for this specific project) A remarkable number of people kept their distance from this obviously dangerous experiment. The chemistry-equivalent of this joke is to warn everyone around you of the presence of dangerous di-Hydrogen Oxide which kills hundreds of thousands of people every year.
whartung 4y ago
As a visceral experience, there are few things that top a Top Fuel drag race. They're really something worth experiencing at least once personally. You really just have to be there.
- naikrovek 4y ago
  yeah the real "all I hear is ringing" experience can't be beaten. I've been to two Top Fuel drag races and I left feeling like I was surrounded by people who have just enough sophistication to know that they like to play with fire whenever possible. they are not like that, of course, but they were definitely caught up in the visceral feeling of watching a race and I was caught up in the idea that I'd never be able to hear again. I do not recommend races, myself.
  - karamanolev 4y ago
    Earmuffs? Isn't it worth seeing (maybe just once) even if you do wear hearing protection?
    - yamazakiwi 4y ago
      Worth seeing to whom? I'm not trying to be contrarian but none of that seems enjoyable or a Top 3 visceral experience when I'm not actually involved with the action. It's weird to hear someone say something is in general a Top Experience.
      - whartung 4y ago
        Even in todays world of crazy sound systems and 8K video, some things are simply worth experiencing live. "You have to be there." Like live music, like going to a playoff game, watching a rocket launch. Even if you don't care about the race, the game, or the music. The energy of being in these places, experiencing it, feeling it, the spontaneous giggles, the sense of awe being caught in the middle of it, has a value all its own. You can watch the race on TV, catch the game in a pub, listen to the live recording over, and over, and over again. But it's not the same as being there.
Someone 4y ago
> I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire...though cables that can carry megawatts of energy are probably pretty heavy. For a one-off design, those cables could be very short. You could even have a very small pantograph (https://en.wikipedia.org/wiki/Pantograph_(transport) https://en.wikipedia.org/wiki/Pantograph_(transport)) I am not sure the end result would be faster, though. You’ll need grip to get up to speed, and starting from a standstill, you won’t get that from aerodynamics. you’ll need mass. Take away the batteries, and you may have to add a similar mass in dead weight (could be used to add a good Faraday cage to protect the driver from mishaps with the electricity supply)
- karamanolev 4y ago
  I think what you care about is to have enough power to be at the limit of the grip of (all) your tires. If you are heavier, you need more power to reach at point. If you do have enough power, then it's all about maximizing grip - tires, surface, downforce and so on. More mass and more power are roughly equivalent to less mass and less power, if the above holds. Maybe even with less mass it's easier, since you can produce significant downforce with smaller wings.
MichaelZuo 4y ago
It does seem like a clickbait title.
jvanderbot 4y ago
Does the engine weight count in that MJ/kg?
- LeifCarrotson 4y ago
  No, I suppose not, but neither does the electric motor count towards battery density. In top fuel events, they're burning roughly 20 kg of fuel per second, so a 200kg engine still doesn't equalize the density of that chemical fuel.
tim333 4y ago
I think probably the fastest accelerating ever car with a driver was the Vanishing Point drag racer which did 0-60 in about 0.25 secs using a peroxide rocket. Not very practical for everyday transport though https://youtu.be/7QC6tymIvKA?t=209 https://youtu.be/7QC6tymIvKA?t=209
- karamanolev 4y ago
  The differences are massive between road-going (on an asphalt surface, ~1 friction coefficient), drag racing type (on a drag strip, which has massively more grip, ~4) and rocket driven (no friction at all, just the thrust/mass ratio) vehicles. It should be clear they are in totally different classes and advances in any of those classes are exciting and worth mentioning, I feel.
- Gravityloss 4y ago
  Elon Musk at some point tweeted about the idea of an "air rocket" for the cars. But air is too light to give a lot of momentum. What would really work well for acceleration is a water rocket with an electric pump. Water mist is harmless beyond a short distance, as long as it's properly dispersed. To make a 1000 kg car accelerate at 4 gee or 40 m/s^2, you need 40000 N of force. A water rocket engine with 200 m/s exhaust velocity can deliver that with 200 kg/s of mass flow. Since your target velocity is only 28 m/s, you only need reaction mass for 0.7 seconds, or 140 kg or 140 L of water. That's one feed barrel. The back of the envelope kinetic energy of the water jet is only 3 million joules or less than a kilowatt hour. But the power is 4 megawatts. Pumps also have startup acceleration cavitation issues, so it'd need to start gradually etc. One could maybe do it with a lot of small independent systems in parallel: a ultra high C rate lithium iron battery connected via a transistor to a pump. Each has its own water pouch and nozzle. If you can achieve 400 N of thrust with one pumping 2 kg/s, then having 100 of them in a 10x10 grid would work. The transistors would be controlled centrally. A more boring alternative is, like in a real bottle rocket, also here, a compressed air tank half filled with water, a much more straightforward source of pressure energy.
WalterBright 4y ago
Top fuel drag racers already have traction control. The slip is adjustable and getting it right is a big factor in winning.
- jcims 4y ago
  I just saw a breakdown of a crash where the engine shut down, allowing the clutch to stop slipping. That final clamp dumped a huge impulse into the drivetrain and ripped the tires off the wheels. (At least that's the way I understood it). Clay Millican has an amazing YouTube channel that brings you behind the scenes of an NHRA top fuel team - https://www.youtube.com/channel/UClT3GT7hxLbNnypukfyxelQ/videos https://www.youtube.com/channel/UClT3GT7hxLbNnypukfyxelQ/vid...
- jcampbell1 4y ago
  The clutch slips for about 2/3 of the 1/4 mile. It is a huge factor. My college motorsports team got to meet with John Force, and someone suggested a flexible rear spoiler for variable downforce. He was quick to note it likely would be faster but would almost certainly get you killed.
- abfan1127 4y ago
  its my understanding that the clutch designers are the highest paid crew members. Choosing how the clutch performs is the critical piece to winning, based on track temperatures, weather conditions, engine performance, etc.
twobitshifter 4y ago
Think like a purpose built dragster. You only need enough energy for 1.5 seconds and that’s as long as the wiring needs to take the current for. I think a purpose built electric dragster might be lighter just because of the parts you don’t need. The motors may reverse the energy weight savings
- lazide 4y ago
  As long as the copper doesn’t vaporize until the end, we’re all good?
Sharlin 4y ago
Well, dragsters are laughably slow to accelerate if we're just talking about "acceleration world record" without qualifiers. (Assuming that "acceleration" here means "acceleration of a ground vehicle with a human driver" is just as arbitrary as "…of an electric ground vehicle…", after all. Actual acceleration world records of macroscopic objects are in the 10,000s of gs…)
- andbberger 4y ago
  i have an ultracentrifuge in lab that can do 100,000gs sustained for hours
  - colordrops 4y ago
    What is it used for?
    - throwaway4PP 4y ago
      Centrifuges are used for separation. An ultra is usually used for separating nominally-stable colloids (such as fine nanoparticle colloids), and miscible liquids where such high centrifugal force causes them to density separate.
    - thelittleone 4y ago
      I was also curious and found this youtube [1]: Summary (found in video at 10:48) 1) separation of subcellular organelle (DNA/RNA) 2) extract solutions in biological fluids from aqueous to organic solvents 3) seperate lipid components 4) pelleting of ribosomes 5) pelleting of macromolecules [1] https://www.youtube.com/watch?v=lRT_8nFc2Tk https://www.youtube.com/watch?v=lRT_8nFc2Tk
      - HeyLaughingBoy 4y ago
        Ha. On a hunch I watched that video and hunch confirmed in the first second: I used to work for those guys, but not in the Centrifugation division :-)
bumby 4y ago
Small nit: >detonating Should be deflagrating because the ICE flame is designed to be subsonic.
- slowhand09 4y ago
  Not sure this applies here Top Fuel engines are nearly burning a liquid rather than a gas. And yes I know you can't really compress a liquid. The typical ratio is 1.7 pounds of air to burn 1 pound of Nitromethane. It burns slower than gasoline tho. And normal gas engine runs in the vicinity of 14.5:1 air to fuel.
  - bumby 4y ago
    >And yes I know you can't really compress a liquid. Sure you can, it's what the bulk modulus measures. You may be right. My assumption is that, by definition, a detonation is an uncontrolled pressure wave and controlling the pressure in an ICE cylinder is a big deal that a lot of engineering goes into. As you point out, the major benefit to nitromethane is that is requires less air because it brings it's own oxygen. So the size of the combustion chamber isn't as much as a limiting factor. I don't think it's intent is to change the flame regime, though. It just crams more energy into the cylinder.
    - lazide 4y ago
      Keep in mind, there is a very common type of ICE that is really a IDE (internal detonation engine) - diesels. With strong enough engines, detonation isn’t ruled out.
      - bumby 4y ago
        I don't think that is correct. Autoignition doesn't automatically imply a supersonic flame front. Diesels should not detonate. The autoignition in a diesel occurs by the piston compressing the air/fuel mixture; in detonation, the autoignition occurs by the flame front compressing the air/fuel mixture. To the OP, the definition of detonation is a flame front that is supersonic; that is not the intended operation of a diesel cycle. Diesels do not have a "flame front" like a spark-ignition engine because combustion occurs at various parts of the cylinder as the air/fuel mix reaches autoignition temperature. So by definition, properly operating diesels cannot detonate. The rattle-y sound of diesels is from the high pressure rise and local ignition of air/fuel, but it's not the same as detonation.
isoprophlex 4y ago
> I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire... Getting dangerously close to "car launched by a railgun" territory, hehehe
- tshaddox 4y ago
  Yep, it very quickly becomes a question of what exactly you're trying to test. If you take energy and power density out of the equation by allowing unrestricted access to external fixed energy delivery infrastructure, the only thing left to test is traction management (assuming you're not allowing things like adhesive tires, cog rails, active downforce, etc.). If you do start to allow those post-traction things, you are as the stage where you might as well build a railgun.
rainbowzootsuit 4y ago
A cable that can carry 1.21GW is only about the diameter of your finger.
- 3000000001 4y ago
  Great Scott! That’s surprisingly small. In all seriousness though, that’s probably not at useable voltage, you might end up with a 5 ton transformer on the car if you delivered 33kV in such a small cable.
dreamcompiler 4y ago
> you're looking at roughly a factor of 100, with ~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery If you only care about acceleration, energy density doesn't matter very much. What matters is power: The rate at which you can move energy from the storage medium to the wheels. In that respect a capacitor-powered dragster could probably smoke a top fuel dragster, even though the energy density of capacitors is pretty lousy. No idea if anybody has tried to build a full-size capacitor-powered dragster. Or if any human would be brave enough to drive one.
- perilunar 4y ago
  Has anyone considered flywheels? Much higher energy density than capacitors, and higher power output than batteries.
  - LawTalkingGuy 4y ago
    Have you tried spinning the batteries?
- LeifCarrotson 4y ago
  Having investigated some of these questions with respect to quadcopters and micro-mouse 'bots, the power density (both in mass and volume) of capacitors is pretty terrible. Whether you're talking about aluminum electrolytic traditional capacitors or double-layer supercapacitors, they're inferior in most cases to a lipo. That's especially true if you're open to high-discharge 50C or 75C lipos, which can dump their entire energy capacity in ~60 seconds. If you only need a few milliseconds of 'zap', yeah, a capacitor bank is great. It's the only option if you need to do that more than a couple hundred times in the life of the battery; a chemical battery will wear out but a capacitor can last for millions or billions of charge/discharge cycles. But even a time as short as 1.461 seconds is probably on the far side of the inflection point where capacitors make sense. If you like, run through the options on Digikey: https://www.digikey.com/en/products/filter/electric-double-layer-capacitors-edlc-supercapacitors/61 https://www.digikey.com/en/products/filter/electric-double-l... ex: https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-xv%20supercapacitor-cylindrical-snap-in-data-sheet.pdf https://www.eaton.com/content/dam/eaton/products/electronic-... Also remember that an ultracapacitor is about as far in behavior from a physicist's ideal plate capacitor as you can get - they're not linear, they have highly significant internal series resistance...
mrb 4y ago
«~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery» That is correct. Out of curiosity, I looked it up and for the Tesla Plaid that's 0.65 MJ/kg (or 181.5 watt·hours per kilogram) But my follow-up question is: if gasoline has an energy density about 100 times higher (well, 60 times) why are dragsters not even faster? This Stuttgart EV does 0-100 km/h in 1.461 seconds (1.87g), and dragsters do it in 0.8 seconds (3.42g). It sounds like with such a phenomenal energy density, gasoline-powered dragsters should be able to accelerate at much more than 3.42g, maybe 10g, or more. Intuitively this indicates that the bottleneck isn't energy density, but mechanical factors (gears, traction, etc). Therefore if battery energy density can increase just a little more, maybe to 2 or 3 MJ/kg, this may be sufficient for EV to be able to beat dragsters. Edit: actually just thinking about it for a few minutes, I realize that energy density doesn't matter. An EV like the Tesla Plaid uses less than 1% of its entire battery capacity to do one acceleration from 0-100 km/h. So the battery could be reduced to 1% of its size and it would still perform one acceleration at the same speed. So dreamcompiler is right. It's not energy density, but power output that matters. Edit #2: The Plaid has a power output of 352 watt/kg (761 kW / curb weight of 2162 kg), while the Stuttgart EV has an output of 1241 watt/kg (180 kW / curb weight of 145 kg), so about 3.5 times more.
- dQw4w9WgXcQ 4y ago
  > why are dragsters not even faster? This is like asking if Usain Bolt can run a 9.5s 100m why is a cheetah that can run 6.1s not that much faster
  - mrb 4y ago
    Your comparison would make sense if cheetahs had 60 times more muscular mass than Usain Bolt, or were somehow 60 times more powerful. They don't. They aren't.
    - xwolfi 4y ago
      This can only be verified with a duel.
jackmott 4y ago
fnordpiglet 4y ago
This said my understanding is thermal efficiency in a typical engine is around 20%, and in an electric motor it’s in the 90% range. Holding traction aside I would have assumed the power is considerably more important than energy density, and energy density plays a bigger role in distance, no? After 500 hours of Kerbal space program I’m a bit of an expert in these things.
- voxelghost 4y ago
  Well there are two kinds of energy density measures, energy-unit/volume-unit and energy-unit/weight-unit. For distance, it can be (usually is?) the energy/volume that is the limiting factor, but for acceleration, it is the energy/weight as weight is the other balancing factor, besides power, of your acceleration equation.
  - fnordpiglet 4y ago
    Is volume due to drag?
soheil 4y ago
To get anywhere near the the down force required to avoid spinning the tires you need a vertical acceleration vector from something like the propulsion thrusters used in dragsters.
nabilhat 4y ago
> Students break acceleration world record...for electric vehicles. ...that made the effort to submit to Guinness. In racing, established racing orgs are where racing records matter. 0-60 just isn't relevant in drag racing. Any optimum 1/4 mile run under 7s doesn't spend nearly as long as these students did dawdling along under 60 mph. NEDRA record 1/4 mile runs have been under 7 seconds for at least 10 years. http://nedra.com/record_holders.html http://nedra.com/record_holders.html The current fastest run ticked off 0-60 mph in under a second. The 60 foot time was over a second. That means they ticked off 0-60 mph in significantly less than 60 feet (~18m). Submitting that 0-60 time to Guinness would require lots of work and time, and wouldn't be relevant to competing or their sponsors. https://insideevs.com/news/447378/video-custom-electric-motorcycle-breaks-world-record/ https://insideevs.com/news/447378/video-custom-electric-moto... So, this Guinness record is still easy pickings, as these things go. I'd bet nothing more than moving this run to proper sticky drag strip pavement instead of that grotty old runway would scrub off a tenth or two. Then better drag tires, drag optimized suspension, maybe all wheel drive, gearing optimization, weight reduction, weight placement optimization... and sooner or later Guinness is going to stop taking 0-60 mph submissions for safety reasons.
fho 4y ago
> especially if you're racing through a 15 PSI gas that you can use in your chemical reaction without having to accelerate it onboard. Are there any wild designs that actually use the air in an electric powered design? Cooling is obvious, but could I just convert the electric energy to heat (100% efficient) and run the air through a heated mesh, ramjet style? :-)
- fho 4y ago
  To answer my own question: this is basically the concept behind nuclear ramjets (e.g. https://en.wikipedia.org/wiki/Project_Pluto https://en.wikipedia.org/wiki/Project_Pluto). "Going nuclear" solves the energy density problem here ... the same thing with LiIon batteries would just not work (equally well). Apparently, electric ramjets for spacecraft propulsion is an active field of research: https://www.sciencedirect.com/science/article/pii/S1877705817314534 https://www.sciencedirect.com/science/article/pii/S187770581...
xxs 4y ago
>~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery - especially if you're racing through a 15 PSI Gotta love the the mix up SI and imperial units, truly effortless. 15PSI is just one bar, it'd even fit nicer too.
moss2 4y ago
Did you also know that the Cheetah runs faster than Usain Bolt?
fennecfoxy 4y ago
Of course for electric vehicles. It doesn't matter that fossil fuels are energy denser, it's much harder and less efficient to convert fossil fuel into mechanical rotation by setting it alight than it is to turn electrical power into mechanical rotation. Electric will always win out simply because it's battery->motor. That's it. Apparently the top fuel dragster can do 0-60 in 0.8 seconds and it looks like its biggest advantage is all the downforce it gets from exhaust gasses and airfoil. I'm thinking this is more a difference in the formats of the vehicles; no point making an electric dragster or f1 when the battery won't last the whole race/series. Batteries are heavy af though, you're right in the disadvantage there. Perhaps the inefficiency of exploding fuel doesn't matter in the face of just how freaking heavy batteries end up being.
flqn 4y ago
ICEs don't detonate the fuel under normal operation; that's called "knocking" and can be extremely damaging to the engine.
raxxorraxor 4y ago
Is it really the motor that is the limiting factor at this point? I would guess it is far more about getting the force onto the road. So tires, spoilers, etc.

MontyCarloHall 4y ago

>cables that can carry megawatts of energy are probably pretty heavy Required cable thickness (and thus weight) is proportional to current, not voltage. Conductors to carry megawatts of electricity could be fairly light as long as the voltage is extremely high and the amperage relatively low.

deleted 4y ago
[deleted]
jvanderbot 4y ago
And magnetic force is a function of current, and magnetic force is what drives wheels. Technically you are correct, but thick cables are actually needed to do lots of translation from electricity to movement.
- willmadden 4y ago
  I don't think there's a problem with cable weight with electric motors. Production EV's today have ridiculous amounts of torque and don't require prohibitively heavy cables. The issue with acceleration using wheels is gravity. You are limited to 1g, the downforce on the wheels, which you use for traction to push the vehicle forward. Spoilers increase the downforce on the vehicle beyond 1g, but the energy required to do that is proportional to the drag on the spoiler. Short of a rocket engine, the way to accelerate beyond 1g with a wheeled vehicle is to have a downforce fan. That can be powered by combustion or by electricity. I don't know which would offer the highest power to weight ratio.
  - deleted 4y ago
    [deleted]
  - lazide 4y ago
    I’m not sure having a ‘reverse Helicopter’ on the back of your vehicle really qualifies as ‘ground vehicle’ at that point. Especially if it’s providing enough force to literally drive upside down on a ceiling somewhere.
    - stefs 4y ago
      it's as ground as can be, short of a tunneling machine maybe.
    - sacrosancty 4y ago
    - et2o 4y ago
      This was the basis of a very famous F1 car in the 1970s. It was ultimately banned.
omegalulw 4y ago
This seems...wrong? Let's say you can control voltage, cross section area A. Now, you want a constant power across a load P = V * I. Your net resistance R is C + D * L / A where C and D are constants and L is your cable length. I is proportional go V * A / (C * A + E) where E is also a constant. So your load power is proportional V^2* C * A / (C * A + E) which is proportional to V^2 * A / (A + F) where F is also a constant. With a large "enough" A, this is effectively V^2. With a small A, this is V^2 * g where g is A / F. So the smaller the area you have the more power you are wasting (roughly equal to V^2 * (1-g) which is heat in the wires). So the smaller area you have, the less efficient your power delivery. And juicing up your source power is a lot more expensive than juicing up your source voltage.

dheera 4y ago

> though cables that can carry megawatts of energy Not really, high speed train lines do it all the time. They usually operate at 25 kV or 50 kV and often consume a few megawatts per train. (At 50 kV, one megawatt is only 20 amps, which you can deliver on 12 AWG wire, theoretically.)

titzer 4y ago
Uh no, do not put 50,000 volts through 12 AWG wire.
- jefftk 4y ago
  What goes wrong?
  - WJW 4y ago
    Most store-bought wires won't have sufficient covering to prevent arcing, so you might get a short circuit somewhere. If you insulate the wires sufficiently however, any wire will take almost any voltage. It's the current you should worry about, as other commenters have already mentioned.
- cesaref 4y ago
  As has been stated, voltage isn't a limitation, its the current that. Go and look at the HT wiring used in a cathode ray tube display, and you'll see it's a lot less that 12 AWG, and happily carries 10-20kV.
- the_third_wave 4y ago
  When I went to high school the teacher told about a science fair where someone had put a sign next to his project reading: WARNING 2 million Ohms (or something like that, I don't remember the actual number of Ohms for this specific project) A remarkable number of people kept their distance from this obviously dangerous experiment. The chemistry-equivalent of this joke is to warn everyone around you of the presence of dangerous di-Hydrogen Oxide which kills hundreds of thousands of people every year.

whartung 4y ago

As a visceral experience, there are few things that top a Top Fuel drag race. They're really something worth experiencing at least once personally. You really just have to be there.

naikrovek 4y ago
yeah the real "all I hear is ringing" experience can't be beaten. I've been to two Top Fuel drag races and I left feeling like I was surrounded by people who have just enough sophistication to know that they like to play with fire whenever possible. they are not like that, of course, but they were definitely caught up in the visceral feeling of watching a race and I was caught up in the idea that I'd never be able to hear again. I do not recommend races, myself.
- karamanolev 4y ago
  Earmuffs? Isn't it worth seeing (maybe just once) even if you do wear hearing protection?
  - yamazakiwi 4y ago
    Worth seeing to whom? I'm not trying to be contrarian but none of that seems enjoyable or a Top 3 visceral experience when I'm not actually involved with the action. It's weird to hear someone say something is in general a Top Experience.
    - whartung 4y ago
      Even in todays world of crazy sound systems and 8K video, some things are simply worth experiencing live. "You have to be there." Like live music, like going to a playoff game, watching a rocket launch. Even if you don't care about the race, the game, or the music. The energy of being in these places, experiencing it, feeling it, the spontaneous giggles, the sense of awe being caught in the middle of it, has a value all its own. You can watch the race on TV, catch the game in a pub, listen to the live recording over, and over, and over again. But it's not the same as being there.

Someone 4y ago

> I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire...though cables that can carry megawatts of energy are probably pretty heavy. For a one-off design, those cables could be very short. You could even have a very small pantograph (https://en.wikipedia.org/wiki/Pantograph_(transport) https://en.wikipedia.org/wiki/Pantograph_(transport)) I am not sure the end result would be faster, though. You’ll need grip to get up to speed, and starting from a standstill, you won’t get that from aerodynamics. you’ll need mass. Take away the batteries, and you may have to add a similar mass in dead weight (could be used to add a good Faraday cage to protect the driver from mishaps with the electricity supply)

karamanolev 4y ago
I think what you care about is to have enough power to be at the limit of the grip of (all) your tires. If you are heavier, you need more power to reach at point. If you do have enough power, then it's all about maximizing grip - tires, surface, downforce and so on. More mass and more power are roughly equivalent to less mass and less power, if the above holds. Maybe even with less mass it's easier, since you can produce significant downforce with smaller wings.

MichaelZuo 4y ago

It does seem like a clickbait title.

jvanderbot 4y ago

Does the engine weight count in that MJ/kg?

LeifCarrotson 4y ago
No, I suppose not, but neither does the electric motor count towards battery density. In top fuel events, they're burning roughly 20 kg of fuel per second, so a 200kg engine still doesn't equalize the density of that chemical fuel.

tim333 4y ago

I think probably the fastest accelerating ever car with a driver was the Vanishing Point drag racer which did 0-60 in about 0.25 secs using a peroxide rocket. Not very practical for everyday transport though https://youtu.be/7QC6tymIvKA?t=209 https://youtu.be/7QC6tymIvKA?t=209

karamanolev 4y ago
The differences are massive between road-going (on an asphalt surface, ~1 friction coefficient), drag racing type (on a drag strip, which has massively more grip, ~4) and rocket driven (no friction at all, just the thrust/mass ratio) vehicles. It should be clear they are in totally different classes and advances in any of those classes are exciting and worth mentioning, I feel.
Gravityloss 4y ago
Elon Musk at some point tweeted about the idea of an "air rocket" for the cars. But air is too light to give a lot of momentum. What would really work well for acceleration is a water rocket with an electric pump. Water mist is harmless beyond a short distance, as long as it's properly dispersed. To make a 1000 kg car accelerate at 4 gee or 40 m/s^2, you need 40000 N of force. A water rocket engine with 200 m/s exhaust velocity can deliver that with 200 kg/s of mass flow. Since your target velocity is only 28 m/s, you only need reaction mass for 0.7 seconds, or 140 kg or 140 L of water. That's one feed barrel. The back of the envelope kinetic energy of the water jet is only 3 million joules or less than a kilowatt hour. But the power is 4 megawatts. Pumps also have startup acceleration cavitation issues, so it'd need to start gradually etc. One could maybe do it with a lot of small independent systems in parallel: a ultra high C rate lithium iron battery connected via a transistor to a pump. Each has its own water pouch and nozzle. If you can achieve 400 N of thrust with one pumping 2 kg/s, then having 100 of them in a 10x10 grid would work. The transistors would be controlled centrally. A more boring alternative is, like in a real bottle rocket, also here, a compressed air tank half filled with water, a much more straightforward source of pressure energy.

WalterBright 4y ago

Top fuel drag racers already have traction control. The slip is adjustable and getting it right is a big factor in winning.

jcims 4y ago
I just saw a breakdown of a crash where the engine shut down, allowing the clutch to stop slipping. That final clamp dumped a huge impulse into the drivetrain and ripped the tires off the wheels. (At least that's the way I understood it). Clay Millican has an amazing YouTube channel that brings you behind the scenes of an NHRA top fuel team - https://www.youtube.com/channel/UClT3GT7hxLbNnypukfyxelQ/videos https://www.youtube.com/channel/UClT3GT7hxLbNnypukfyxelQ/vid...
jcampbell1 4y ago
The clutch slips for about 2/3 of the 1/4 mile. It is a huge factor. My college motorsports team got to meet with John Force, and someone suggested a flexible rear spoiler for variable downforce. He was quick to note it likely would be faster but would almost certainly get you killed.
abfan1127 4y ago
its my understanding that the clutch designers are the highest paid crew members. Choosing how the clutch performs is the critical piece to winning, based on track temperatures, weather conditions, engine performance, etc.

twobitshifter 4y ago

Think like a purpose built dragster. You only need enough energy for 1.5 seconds and that’s as long as the wiring needs to take the current for. I think a purpose built electric dragster might be lighter just because of the parts you don’t need. The motors may reverse the energy weight savings

lazide 4y ago
As long as the copper doesn’t vaporize until the end, we’re all good?

Sharlin 4y ago

Well, dragsters are laughably slow to accelerate if we're just talking about "acceleration world record" without qualifiers. (Assuming that "acceleration" here means "acceleration of a ground vehicle with a human driver" is just as arbitrary as "…of an electric ground vehicle…", after all. Actual acceleration world records of macroscopic objects are in the 10,000s of gs…)

andbberger 4y ago
i have an ultracentrifuge in lab that can do 100,000gs sustained for hours
- colordrops 4y ago
  What is it used for?
  - throwaway4PP 4y ago
    Centrifuges are used for separation. An ultra is usually used for separating nominally-stable colloids (such as fine nanoparticle colloids), and miscible liquids where such high centrifugal force causes them to density separate.
  - thelittleone 4y ago
    I was also curious and found this youtube [1]: Summary (found in video at 10:48) 1) separation of subcellular organelle (DNA/RNA) 2) extract solutions in biological fluids from aqueous to organic solvents 3) seperate lipid components 4) pelleting of ribosomes 5) pelleting of macromolecules [1] https://www.youtube.com/watch?v=lRT_8nFc2Tk https://www.youtube.com/watch?v=lRT_8nFc2Tk
    - HeyLaughingBoy 4y ago
      Ha. On a hunch I watched that video and hunch confirmed in the first second: I used to work for those guys, but not in the Centrifugation division :-)

bumby 4y ago

Small nit: >detonating Should be deflagrating because the ICE flame is designed to be subsonic.

slowhand09 4y ago
Not sure this applies here Top Fuel engines are nearly burning a liquid rather than a gas. And yes I know you can't really compress a liquid. The typical ratio is 1.7 pounds of air to burn 1 pound of Nitromethane. It burns slower than gasoline tho. And normal gas engine runs in the vicinity of 14.5:1 air to fuel.
- bumby 4y ago
  >And yes I know you can't really compress a liquid. Sure you can, it's what the bulk modulus measures. You may be right. My assumption is that, by definition, a detonation is an uncontrolled pressure wave and controlling the pressure in an ICE cylinder is a big deal that a lot of engineering goes into. As you point out, the major benefit to nitromethane is that is requires less air because it brings it's own oxygen. So the size of the combustion chamber isn't as much as a limiting factor. I don't think it's intent is to change the flame regime, though. It just crams more energy into the cylinder.
  - lazide 4y ago
    Keep in mind, there is a very common type of ICE that is really a IDE (internal detonation engine) - diesels. With strong enough engines, detonation isn’t ruled out.
    - bumby 4y ago
      I don't think that is correct. Autoignition doesn't automatically imply a supersonic flame front. Diesels should not detonate. The autoignition in a diesel occurs by the piston compressing the air/fuel mixture; in detonation, the autoignition occurs by the flame front compressing the air/fuel mixture. To the OP, the definition of detonation is a flame front that is supersonic; that is not the intended operation of a diesel cycle. Diesels do not have a "flame front" like a spark-ignition engine because combustion occurs at various parts of the cylinder as the air/fuel mix reaches autoignition temperature. So by definition, properly operating diesels cannot detonate. The rattle-y sound of diesels is from the high pressure rise and local ignition of air/fuel, but it's not the same as detonation.

isoprophlex 4y ago

> I wonder what the record is for a vehicle that can pick up electric energy from a tether/rail/overhead wire... Getting dangerously close to "car launched by a railgun" territory, hehehe

tshaddox 4y ago
Yep, it very quickly becomes a question of what exactly you're trying to test. If you take energy and power density out of the equation by allowing unrestricted access to external fixed energy delivery infrastructure, the only thing left to test is traction management (assuming you're not allowing things like adhesive tires, cog rails, active downforce, etc.). If you do start to allow those post-traction things, you are as the stage where you might as well build a railgun.

rainbowzootsuit 4y ago

A cable that can carry 1.21GW is only about the diameter of your finger.

3000000001 4y ago
Great Scott! That’s surprisingly small. In all seriousness though, that’s probably not at useable voltage, you might end up with a 5 ton transformer on the car if you delivered 33kV in such a small cable.

dreamcompiler 4y ago

> you're looking at roughly a factor of 100, with ~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery If you only care about acceleration, energy density doesn't matter very much. What matters is power: The rate at which you can move energy from the storage medium to the wheels. In that respect a capacitor-powered dragster could probably smoke a top fuel dragster, even though the energy density of capacitors is pretty lousy. No idea if anybody has tried to build a full-size capacitor-powered dragster. Or if any human would be brave enough to drive one.

perilunar 4y ago
Has anyone considered flywheels? Much higher energy density than capacitors, and higher power output than batteries.
- LawTalkingGuy 4y ago
  Have you tried spinning the batteries?
LeifCarrotson 4y ago
Having investigated some of these questions with respect to quadcopters and micro-mouse 'bots, the power density (both in mass and volume) of capacitors is pretty terrible. Whether you're talking about aluminum electrolytic traditional capacitors or double-layer supercapacitors, they're inferior in most cases to a lipo. That's especially true if you're open to high-discharge 50C or 75C lipos, which can dump their entire energy capacity in ~60 seconds. If you only need a few milliseconds of 'zap', yeah, a capacitor bank is great. It's the only option if you need to do that more than a couple hundred times in the life of the battery; a chemical battery will wear out but a capacitor can last for millions or billions of charge/discharge cycles. But even a time as short as 1.461 seconds is probably on the far side of the inflection point where capacitors make sense. If you like, run through the options on Digikey: https://www.digikey.com/en/products/filter/electric-double-layer-capacitors-edlc-supercapacitors/61 https://www.digikey.com/en/products/filter/electric-double-l... ex: https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-xv%20supercapacitor-cylindrical-snap-in-data-sheet.pdf https://www.eaton.com/content/dam/eaton/products/electronic-... Also remember that an ultracapacitor is about as far in behavior from a physicist's ideal plate capacitor as you can get - they're not linear, they have highly significant internal series resistance...

mrb 4y ago

«~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery» That is correct. Out of curiosity, I looked it up and for the Tesla Plaid that's 0.65 MJ/kg (or 181.5 watt·hours per kilogram) But my follow-up question is: if gasoline has an energy density about 100 times higher (well, 60 times) why are dragsters not even faster? This Stuttgart EV does 0-100 km/h in 1.461 seconds (1.87g), and dragsters do it in 0.8 seconds (3.42g). It sounds like with such a phenomenal energy density, gasoline-powered dragsters should be able to accelerate at much more than 3.42g, maybe 10g, or more. Intuitively this indicates that the bottleneck isn't energy density, but mechanical factors (gears, traction, etc). Therefore if battery energy density can increase just a little more, maybe to 2 or 3 MJ/kg, this may be sufficient for EV to be able to beat dragsters. Edit: actually just thinking about it for a few minutes, I realize that energy density doesn't matter. An EV like the Tesla Plaid uses less than 1% of its entire battery capacity to do one acceleration from 0-100 km/h. So the battery could be reduced to 1% of its size and it would still perform one acceleration at the same speed. So dreamcompiler is right. It's not energy density, but power output that matters. Edit #2: The Plaid has a power output of 352 watt/kg (761 kW / curb weight of 2162 kg), while the Stuttgart EV has an output of 1241 watt/kg (180 kW / curb weight of 145 kg), so about 3.5 times more.

dQw4w9WgXcQ 4y ago
> why are dragsters not even faster? This is like asking if Usain Bolt can run a 9.5s 100m why is a cheetah that can run 6.1s not that much faster
- mrb 4y ago
  Your comparison would make sense if cheetahs had 60 times more muscular mass than Usain Bolt, or were somehow 60 times more powerful. They don't. They aren't.
  - xwolfi 4y ago
    This can only be verified with a duel.

jackmott 4y ago

fnordpiglet 4y ago

This said my understanding is thermal efficiency in a typical engine is around 20%, and in an electric motor it’s in the 90% range. Holding traction aside I would have assumed the power is considerably more important than energy density, and energy density plays a bigger role in distance, no? After 500 hours of Kerbal space program I’m a bit of an expert in these things.

voxelghost 4y ago
Well there are two kinds of energy density measures, energy-unit/volume-unit and energy-unit/weight-unit. For distance, it can be (usually is?) the energy/volume that is the limiting factor, but for acceleration, it is the energy/weight as weight is the other balancing factor, besides power, of your acceleration equation.
- fnordpiglet 4y ago
  Is volume due to drag?

soheil 4y ago

To get anywhere near the the down force required to avoid spinning the tires you need a vertical acceleration vector from something like the propulsion thrusters used in dragsters.

nabilhat 4y ago

> Students break acceleration world record...for electric vehicles. ...that made the effort to submit to Guinness. In racing, established racing orgs are where racing records matter. 0-60 just isn't relevant in drag racing. Any optimum 1/4 mile run under 7s doesn't spend nearly as long as these students did dawdling along under 60 mph. NEDRA record 1/4 mile runs have been under 7 seconds for at least 10 years. http://nedra.com/record_holders.html http://nedra.com/record_holders.html The current fastest run ticked off 0-60 mph in under a second. The 60 foot time was over a second. That means they ticked off 0-60 mph in significantly less than 60 feet (~18m). Submitting that 0-60 time to Guinness would require lots of work and time, and wouldn't be relevant to competing or their sponsors. https://insideevs.com/news/447378/video-custom-electric-motorcycle-breaks-world-record/ https://insideevs.com/news/447378/video-custom-electric-moto... So, this Guinness record is still easy pickings, as these things go. I'd bet nothing more than moving this run to proper sticky drag strip pavement instead of that grotty old runway would scrub off a tenth or two. Then better drag tires, drag optimized suspension, maybe all wheel drive, gearing optimization, weight reduction, weight placement optimization... and sooner or later Guinness is going to stop taking 0-60 mph submissions for safety reasons.

fho 4y ago

> especially if you're racing through a 15 PSI gas that you can use in your chemical reaction without having to accelerate it onboard. Are there any wild designs that actually use the air in an electric powered design? Cooling is obvious, but could I just convert the electric energy to heat (100% efficient) and run the air through a heated mesh, ramjet style? :-)

fho 4y ago
To answer my own question: this is basically the concept behind nuclear ramjets (e.g. https://en.wikipedia.org/wiki/Project_Pluto https://en.wikipedia.org/wiki/Project_Pluto). "Going nuclear" solves the energy density problem here ... the same thing with LiIon batteries would just not work (equally well). Apparently, electric ramjets for spacecraft propulsion is an active field of research: https://www.sciencedirect.com/science/article/pii/S1877705817314534 https://www.sciencedirect.com/science/article/pii/S187770581...

xxs 4y ago

>~40 MJ/kg for gasoline and 0.4 MJ/kg for a lithium ion battery - especially if you're racing through a 15 PSI Gotta love the the mix up SI and imperial units, truly effortless. 15PSI is just one bar, it'd even fit nicer too.

moss2 4y ago

Did you also know that the Cheetah runs faster than Usain Bolt?

fennecfoxy 4y ago

Of course for electric vehicles. It doesn't matter that fossil fuels are energy denser, it's much harder and less efficient to convert fossil fuel into mechanical rotation by setting it alight than it is to turn electrical power into mechanical rotation. Electric will always win out simply because it's battery->motor. That's it. Apparently the top fuel dragster can do 0-60 in 0.8 seconds and it looks like its biggest advantage is all the downforce it gets from exhaust gasses and airfoil. I'm thinking this is more a difference in the formats of the vehicles; no point making an electric dragster or f1 when the battery won't last the whole race/series. Batteries are heavy af though, you're right in the disadvantage there. Perhaps the inefficiency of exploding fuel doesn't matter in the face of just how freaking heavy batteries end up being.

flqn 4y ago

ICEs don't detonate the fuel under normal operation; that's called "knocking" and can be extremely damaging to the engine.

raxxorraxor 4y ago

Is it really the motor that is the limiting factor at this point? I would guess it is far more about getting the force onto the road. So tires, spoilers, etc.