[Stunt Driver]

Originally Posted by Overlander23

In the case of the flywheel... it acts like a battery, storing energy within its mass. As the flywheel spins down it releases that energy

I guess you never-ever use brakes on your car? Others go long ways to invent Regenerative Braking and such Just wonder why


ps

Everyone is worried about how much energy it takes to spin the flywheel, but no one is considering that the energy has to go somewhere.

You are right, It goes right back to heating your disk brakes.
I wish I was living in a city where i can take off from my house and nEveR touch brakes till I reach my work. And during last mile, while I am waiting for the speed to come down to zero, I would not have angry people behind be, wondering, what's up with speed? Or at 90 degree turns - i would have to coast in a way, so I slow down from my 40mph to 10mph, so I can make the turn. Oh people behind me would be happy

So, Overlander23, if all you are saying is that if you don't use brakes ever - flywheel doesn't affect your range - I would 100% agree. But if we get back to real world - that doesn't fly.
Some one did calculation for average distance between red light - numbers were real, allthou not killing.


For my car being a low cost convertion - I can't go above 40mph, and do not have to shift out of 2nd gear, but every time red light pops up - I transfer energy from flwheel and pressure plate to my front brake pads. That is why i'd remove it, if I can find time. My tranny never grinds upshifting, and on downshift I have to give a small kick to gas pedal to shift smooth. But again, I rarely need this. Only if on a long straight I want to get higher than 40Mph speed, but it comes at higher AMPs, and probably only hurts my range.

Now, if my convertion would be higher voltage - I would actually need the clutch.

Clutch or No Clutch debate - does not have a universal answer.

[Overlander23]

Sorry, I just realized this is responding to a couple of other responses, not just Green Caveman's.

I don't disagree that using the brakes will kill the energy in the flywheel leading to total system efficiency losses. I'm right there with you on that. But how much energy is that?

I don't know how you think you're using the figure 700+W. And where do you get the idea that the flywheel stores over a mile of energy every time it spins up? There seems to be a lot of confusion over power/energy/units. Do you really think that people with clutches and flywheels are losing over a mile of range each time they come to a stop? You can test it yourself, spin the flywheel to 4000 rpm with the clutch depressed, then dump it and see how far you get. That's pretty much how much range you'll save by removing it if everything survives. <note: this last sentence is hyperbole>

(Yes, I know that accelerating a vehicle consumes far more energy than just maintaining its speed. The point was to give you an idea that there isn't much energy stored in a conventional car flywheel.)

Here are the numbers.

Firstly, watts is a unit of how much power is flowing at any given time. You need to have a time component for it to be an amount of energy. In the case of O'Zeeke's conversion, he calculated 46274 Joules of energy to spin his 33kg flywheel/clutch combination to 4000rpm. That comes out to (http://www.unitconversion.org/energy...onversion.html): 46274 Joules = 12.854 watt-hours (700+ watt-mins, actually more like 770 watt-mins.)

Luckily, we gauge EV efficiency in watt-hours. An efficient EV may consume 200 watt-hours/mile (a very efficient EV, I might add). That's 1/15th of mile in flywheel energy consumption (5%), but only if 100% of the energy in the flywheel were bled off uselessly.

Unless you're in the habit of braking hard enough to stop the vehicle instantly, therefore insuring that 100% of the stored energy in the flywheel was converted to heat, then the larger 5% figure starts to go down to 0% (a non-braked coast to a stop).

As KiwiEV points out, there are so many other variable involved, such as a sudden braking maneuvers. Obviously, if your EV is more inefficient the effects of the flywheel will be even less. The effects of vehicle speed will play a factor since the EV will not use 200 watt-hours/mile all the time. The flywheel will be spinning at different speeds so will not always be storing the same amount of energy... etc. You stand more of chance of getting back the 0-5% energy loss by changing your driving behavior.

So yes, I agree with you, the clutch/flywheel combination will technically be more inefficient, but practically it won't be very significant, IMO.

I even machined the ring gear and a raised portion off of my flywheel, but knowing it was to save overall vehicle weight. Even then it didn't amount to much, but I had it piggybacked onto some other machine shop work I was having done.

I'd be curious to know just how much more range Craig Vinton got due to the 12lb flywheel shave (not even something like a 33kg loss), as opposed to his aerodynamic aids... or merely different driving behavior.

Of course, what do people mean when they say significant?

Edit: I realize now, that Green Caveman's use of 700+W was probably from F16bmathis' report of 771 watts in converting 46274 Joules to Watts (correct me if I'm wrong). What's confusing is that while watt usage is typically assumed to be usage for an hour, sometimes it isn't. If he then claimed that he could "generate the 771 watts in a minute or two (not verbatim)" then he'd be generating 771 watt-minutes of energy (or 700 watt-"two mins" for the latter, to be esoteric), or divided by 60 mins, about 12 watt-hours. This only works if the 771 watt figure was quoted for a minute, though.

In a later post, his real-world experience of being able to maintain 75 watts of power on his bike generator is probably accurate. If he were able to cycle at that rate for an hour he would produce 75 watt-hours of energy, or 4500 watt/mins (75w*60mins). Assuming F16bmathis' abilities on the bike generator, the equivalent amount of energy in the flywheel could be generated by him in around 10 seconds. Now that does seem small, doesn't it?

Hmmm, that was supposed to clarify things...

OK, one more analogy. Remember that 46000 Joules? That's equivalent to about 11 nutritional calories. Now that really seems small.

Originally Posted by green caveman

Craig Vinton with his Chevy Tracker claims that machining 12lbs off the flywheel improved his range. If the stored energy is really 700+W, then that's more than a mile of range every time you stop that without recoverying the energy. For a 3000lb car moving at 30mph that's about 25% of the kinetic energy of the car stored in the flywheel - a significant chunk, but as you say, that only comes into play when you stop it with the brakes.

Since we have a Sepex/Regen system, it should be possible to recover energy from the 5000 RPM hunk of very heavy steel even on a quick stop - so long as you remember to push out the clutch.

I still tend to think that some amount of material can reasonably, and cost effectively, be removed from the flywheel without any danger to the structure and that it would be an advantage to do that.

[O'Zeeke]

Originally Posted by Overlander23

OK, you've calculated it takes 46274 joules to spin your 33kg flywheel to 4000 rpm. Where does that energy go then?

As stunt driver correctly pointed out it is converted to heat when the brakes are applied. There are a lot of hear say and subjective comments about this as "I doubt if it would make much difference" or "it's probably insignificant" but if we stay objective and stick with the math the numbers tell the story. There is an energy savings because it does take energy to spin that flywheel but it is up to the individual as to how "significant" it would be for them. For me It's all about range. I have a lot of stop and go on my commute and although my ev shifts easily, I almost always just leave it in 2nd, so for my circumstances, clutchless makes sense

[Jan]

Originally Posted by Overlander23

OK, you've calculated it takes 46274 joules to spin your 33kg flywheel to 4000 rpm. Where does that energy go then?

Originally Posted by F16bmathis

If this is all correct, I used an online calculator and came up with 771 watts, which I can produce on my bike generator in a minute or two, so not really much of a drag on my truck?

If the 46274 joules is correct. That eqauals 46274 Watt seconds.

(c) http://en.wikipedia.org/wiki/Joule

If you accelerate upto that speed in lets say 10 seconds. It will cost you an extra 4.6kW those 10 seconds, you'll never get back. The faster you want to accelerate, the more it will cost. And visa versa.

I personaly find 4.6kW significant. But I haven't checked if those 46274 joules are correct. I wouldn't know how.

[O'Zeeke]

Originally Posted by Jan

I personaly find 4.6kW significant. But I haven't checked if those 46274 joules are correct. I wouldn't know how.

Here's the formula
Wikipedia http://en.wikipedia.org/wiki/Rotational_energy

[Overlander23]

46274 joules is "close enough". I say that because the inertial moment is hard to determine exactly from a flywheel/clutch/clutch plate combo. It should be in the ballpark.

Give me an idea of how significant you find 4.6kw-s to be? 46274 watt-seconds is equivalent to 4627.4 watt-ten seconds, not 46274 watts of energy for each second of 10 seconds. You're mixing terms. Power vs energy.

Using your example, what if you wanted to accelerate to the same speed but over a period of 100 seconds? Have you used 100s x 4.6kw? No. You've used 4.6kw-s of energy stretched out over 100 seconds.

By your figuring, the harder you accelerate the less energy you use.

If that's not what you mean, then I apologize. One thing is for sure, though... you will use 4.6kw-s of energy to spin the flywheel.

EDIT: Turns out that's not what Jan meant. I believe Jan was talking about the loss of power incurred by the flywheel.

Originally Posted by Jan

If the 46274 joules is correct. That eqauals 46274 Watt seconds.

(c) http://en.wikipedia.org/wiki/Joule

If you accelerate upto that speed in lets say 10 seconds. It will cost you an extra 4.6kW those 10 seconds, you'll never get back. The faster you want to accelerate, the more it will cost. And visa versa.

I personaly find 4.6kW significant. But I haven't checked if those 46274 joules are correct. I wouldn't know how.

[Jan]

Originally Posted by Overlander23

Give me an idea of how significant you find 4.6kw/s to be?

It's not 4.6kW/s. During those 10 seconds you have e.g. 40kW of power available from your motor and controler system. power is timeless.

Of these 40kW you'll loose besides all other resistance an extra 4.6kW to the flywheel.

46274 watt/seconds is equivalent to 4624.5 watts per ten seconds, not 46274 watts of energy for each second of 10 seconds. You're mixing terms. Power vs energy.

1 joule is 1 Ws, not 1 W/s. I really don't think I'm the one who confuses them now.

[Overlander23]

You are correct, that's my nomenclature mistake. A joule is indeed one watt-second.

But a joule is a unit of energy. A watt is a unit of power. You are correct, you will lose power to the flywheel, but you will not lose much energy, and the discussion thus far has been about the effects of the flywheel on range... which is about energy consumption, not power.

No one has claimed that the flywheel would not absorb power.

Originally Posted by Jan

It's not 4.6kW/s. During those 10 seconds you have e.g. 40kW of power available from your motor and controler system. power is timeless.

Of these 40kW you'll loose besides all other resistance an extra 4.6kW to the flywheel.



1 joule is 1 Ws, not 1 W/s. I really don't think I'm the one who confuses them now.

[Jan]

Originally Posted by Overlander23

You are correct, that's my nomenclature mistake. A joule is indeed one watt-second.

But a joule is a unit of energy. A watt is a unit of power. You are correct, you will lose power to the flywheel, but you will not lose much energy, and the discussion thus far has been about the effects of the flywheel on range... which is about energy consumption, not power.

No one has claimed that the flywheel would not absorb power.

That's true. It will have an insignificant effect on range if you accelerate once or twice during a long trip. But more than 10% loss during acceleration, I find significant.

[DC Braveheart]

Originally Posted by Overlander23

Everyone is worried about how much energy it takes to spin the flywheel, but no one is considering that the energy has to go somewhere. It goes back into moving the vehicle.

Actually I think you'll find that all that stored energy goes into heating up your brakes when you stop.

Now if you put your clutch in before you brake, the flywheel (and motor rotor) will continue spinning for a while until the stored energy is again transferred to heat in the various bearings due to friction. If, after stopping, you try to move off again then you'll need to slip the clutch a bit as you pull off, as the motor/flywheel is still spinning faster than the transmission and you'll transfer some of the stored rotational energy to heat in the clutch, again due to friction. I doubt much of the energy stored up in the flywheel ever actually makes it to the wheels.

In any case, I doubt anyone with a MT EV uses the clutch that way - I'm pretty sure that the clutch only get used when changing gears NOT to keep the motor spinning when stopped.