Why did the flywheel hybrid system never catch on for road cars? (2021)
arstechnica.com
arstechnica.com
I was talking to one of their engineers a long time ago, so the details may be fuzzy, but I think they're able to start supplying power in a single 60hz cycle. The idea is that the flywheels cover the start time of your diesel generators.
They were not considered a battery replacement though, what they did was for areas of the world that take frequent and quick power loss events they allow the UPS system to ride through a small power loss without hitting the batteries (prolonging life) or generators (saving wear/fuel). The flywheel only lasts a couple minutes under full load. Any power loss longer than that transfers to battery and triggers a generator run to prepare to take the load long term.
In that case why have batteries at all? Because generators and transfer switches aren't perfect. On typical data centers the batteries are sized for a fifteen minute full load capacity. That's fifteen minutes where the on site people can potentially fix something. That's one reason, the other is with flywheel you must start the genset earlier so it can take power before the flywheel dies, leading to more wear and fuel usage. Starting motors creates a lot of wear, drastically increase that and your gensets don't last long at all.
Why not have a lot more batteries than fifteen minutes? The batteries are sized for the computer load only, not the full facility HVAC load. In general in a server room that's at capacity you have fifteen minutes run time without HVAC before you start shutting servers down on high temperature.
So as you can see flywheels are an expensive addition that only make sense in certain isolated areas with bad power.
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See also:
https://hackaday.com/2021/05/30/bicycle-flywheel-stores-a-bi...
A few years ago supercaps were predicted to be in every car for storing shorterm energy from breaking, since then Tesla sold Maxwell Technology [1].
Have any car makers deployed a different technology than Lithium?
1: https://passive-components.eu/tesla-sells-maxwell-technology...
A flywheeel is basically a bomb in all but name.
A flywheel on the other hand is intentionally unbalanced, an offset weight, kind of like a clock pendulum spinning really fast, making it incredibly dangerous when something does go wrong. It basically becomes a centrifugal slingshot.
T = w cross aEDIT: Oh, I see what you're saying. I thought you were talking about the oppsite direction: hit brakes, and car turns. You're instead talking about putting a caliper on each disk, and snapping the car left/right. Oh man, that would be fun ^^
To be clear I’m agreeing with you.
Added weight and complexity.
Another option is a gimbal mount, though that makes any mechanical coupling more difficult, and requires more space. For electrically driven / driving flywheels, it's an option however.
One of the gyros seized and the whole thing flipped and slammed into the ground with tremendous force.
Which are often tangential.
Having a fifteen pound weight spinning at 30,000 RPM being maintained as well as your average vehicle sounds utterly terrifying.
Obviously there’s energy from batteries or gasoline or whatever in regular cars
Of course you can do the same with chemical energy, but we have good intuition around things that will detonate.
With everyday substances, both a stick of butter and an SUV traveling at 100 mph contain about a kilowatt-hour of energy, but the latter would generally be more destructive if something goes wrong.
Alternatively, it's humbling how bad and inefficient we are at manipulating the physical materials in our environment, because we can't so much as replicate a stick of butter without making it noisy and dangerous.
A butter stick sized piece of C4 is similarly stable but contains more stored energy.
1 kg of TNT has roughly 4.6 MG.
1 kg of petroleum has roughly 45 MG, ten times as much.
The difference is that the trinitrotoluene combusts rather more rapidly than the oil. But if, say, you simply want thermal energy and have a mass budget, you'll go with the oil.
C4 has an energy density of about 5.1 MG/kg, slightly greater than TNT, but only 1/8th that of petroleum.
From a practical perspective, at least within Earth's atmosphere, that oxygen is "free". There's not need to carry it with you, though some combustion applications may require feeding it at high rates (turbochargers, compressors, gas turbines, and the like). Most automobiles functions strictly under natural aspiration, and even industrial combustion typically utilises relatively low-power bellows or air introduction.
Rockets, of course, carry their own oxidizer, so we can compare energy densities based on net yield.
The Saturn S-IC (first stage of the Saturn V stack) is powered by the combustion of RP-1 (a highly-refined grade of kerosene) and LOX, liquid oxygen.
The tank sizes were 730,000 L fuel, for which I'm assuming an average density of 0.9g/mL (0.81--1.02 given by Wikipedia), and 1,204,000 L oxidizer, at 1.41 g/mL.
That works out to 657 tonnes of RP-1, 1,374 tonnes of LOX, or a total of 1,511 tonnes.
The fuel alone is 43.5% of the total mass, which means total specific energy is reduced to 17.63 MJ/L, which is still about 3.5--4 times greater than TNT or C4, by comparison.
There's one further question as to whether or not the rocket is tuned to run rich, stoichometric (balanced fuel and oxidizer), or lean. Most LOX rockets burn somewhat rich, based on recollection and Wikipedia, so the LOX quantity is slightly short of what might support complete combustion, though not enough to affect the overall outcome here.
<https://en.wikipedia.org/wiki/S-IC>
<https://en.wikipedia.org/wiki/RP-1>
<https://en.wikipedia.org/wiki/Liquid_oxygen>
<https://en.wikipedia.org/wiki/Rocket_propellant#Mixture_rati...>
I noticed something similar when I'd go skiing. Loading up with eggs and butter for breakfast meant I'd never feel cold.
Talking of old-school, I am reminded of Robert Wood's The 2oz Backpacker from 1980-something that advised hikers to take a swig of cooking oil before going to bed, for calorie-burning warmth.
How's that?
This can be converted to 0.94 kWh: (calories)(joules per calorie)(watts = joules/second)(kw = 1000w)
Kinetic energy is 1/2(v*v^2)
The average SUV weighs about 2000 Kg. That yields about 0.55 KWh. Perhaps the parent used a larger SUV.
If your turboimpeller is doubling as kinetic energy storage, you're doing it wrong.
Not that I think this is a good counter argument...
A flywheel would typically be spinning not only far more often but at great speed and load.
Also this is a problem enough at <10,000 RPM with just normal metal flywheels and clutches that many drag racing and Motorsport rules require extra “scatter shields” to protect both drivers and spectators from them exploding or exiting from the normal bell housing.
Regenerative braking converts mechanical energy to electrical energy to send into a battery. This energy is then extracted, reconverted into mechanical energy, and then transmitted to the wheels.
A compact and efficient flywheel should remove the energy conversion and could improve the efficiency of EVs. We'll obviously hit a density limit at one point, but we're currently far off.
Williams proved it works, but because F1 cars have to use an ICE in a tight package, they had to pick between batteries or flywheels. We should hopefully start seeing EV race cars implement this soon.
The downside is size and weight, which makes me believe miniaturization is the key.
1. Increasing RPM
2. Increasing the mean radius of the mass
3. Increasing the weight
Two of these directly impact either size or weight (#2 and #3 respectively) and the first one is limited by the tensile strength of the materials in use. I'm going to go out on a limb and suggest that the F1 teams were already using exotic materials, so there may not be a lot of ground to gain here.
What makes you think there is unexplored potential at spinning even faster? What material or process do you think is unexplored in specific?
1: e.g. https://www.researchgate.net/publication/261388468_Optimal_d...
Breakthroughs have been found recently. People use busses and watch cars win 24h endurance races using this technology, partly thanks to the research on composite materials.
https://www.lanemotormuseum.org/collection/cars/item/gyro-x-...
The benefits are mixed. Amongst other problems, the Earth's own rotation actually puts a lot of stress on the rotational axis. free-floating flywheels aren't generally highly practical, so compensations (I believe magnetic bearings are common) are used.
The apparently obvious storage mechanism ... turns out to be rather difficult to operationalise.
It'd be fun in a scifi movie to see large disc shaped buildings sticking half way out at an angle all over.
Most grid-support gyros are in fact cylindrical rather than disk-shaped, as this optimises for mass at the outer radius of rotation. To gimbal-mount a large cylinder you'd have to have a proportionately large spherical enclosure.
I'm only somewhat generally and vaguely aware of the issues here and I don't know what R&D or theory are specifically ongoing here.
As noted, polar and equatorial locations would require the least adjustment, as polar flywheels could be aligned perpendicular to the ground, equatorial ones parallel (along the north-south axis), which would minimise any movements, as others have noted.
(I don't think that Earth's axial inclination would matter, and am presuming that precession of Earth's own axis is Too Small to Matter.)
Such gearboxes aren't really a thing (at least not without massive caveats).
The best you can do is fixed gear ratios and a clutch, or a CVT and a clutch to handle the ends of the range.
Both are mechanically complex and not very efficient (a typical shift under load with a clutch wastes half the energy into heat in the clutch material).
Compare to electric, where a 'gearbox' consists of software/inductors/capacitors/switches, and you can effectively have an infinite ratio (software) gearbox.
Edit: okay, that's probably going to need a little more explanation.
You've got a car travelling (frictionlessly in a vacuum, as per all good physics experiments) with a flywheel that can be connected to the driveshaft with a clutch. When you engage the flywheel it disengages the driveshaft from the engine.
Your car is travelling at 50mph, so it has some amount of energy that you can calculate from its mass. The flywheel is at rest. When you engage the flywheel clutch, the car will slow down and the flywheel will speed up until both have (neglecting losses, remember) an equal amount of energy, and the car will be doing 25mph.
Bring the car to a stop, with the clutch disengaged again. The car has no energy but the flywheel is still spinning.
Now engage the clutch to move off. The car will accelerate to 12.5MPH, because it gets half the energy in the flywheel and once they have an equal amount no more energy can be transferred.
You can get around this with clever gearboxes, a bit, and if you're building a multimillion pound racing car that's definitely the way forward.