Commando Crankshaft Porn

I disagree that a crank doesn't draw energy. I agree it stores it but anything set in motion requires force and a heavier object requires more force to turn and keep in motion.

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Once an object is at a steady state speed it only needs the energy lost to friction to be replaced to maintain that speed. Friction is not related to weight in low friction bearings or spinning weights.

http://en.wikipedia.org/wiki/Conservation_of_energy

Hi , should'nt we take in account: the shape of the flywheel, and the balance factor ? it seems that a circular flywheel is different from a triangular (bell shape )one. the weight at a certain distance from the bearing shell is somewhere pre-determined by the weight of the rod/pistons and thus the BF (sorry if my english is a bit pidgin)....!

Generally speaking the flywheel shape determines the inertia . A porkchop flywheel provides mass only where needed to offset the weight of the
pin rod and piston. A full circle adds metal at 90 and 270 degrees which doesn't affect the balance factor but adds inertia.

A heavier crankshaft requires no more power to keep in motion than a light one. It simply stores more power on the powerstroke and makes it available on the next three strokes. With the sixty tooth reluctor wheel on the crank of my fuel injected bike I can actually watch the crank change speed through the cycles of the engine. You would be amazed at how much the crank speed changes between the power sroke and the compression stroke. That is where you see the most difference between a light crank and a heavy crank. The actual acceleration rate change is small and once the bike is in gear and the clutch is released the difference is negligible in comparison to the inertia of the bike and drivetrain.
Of coarse I am just considering the relatively small changes in crank mass in a Norton motor and not the out of the realm mass of an old Motoguzzi or BMW flywheel. They generally benefit from loosing some flywheel inertia.

The lightweight crank and flywheel idea originated with dragracing cars and was a way of matching the engines stored momentum at launch to the available traction from the tires. It paid big dividends in the first 100 ft. From there it spread - good or bad. Jim

Hi Jim , many thanks for your explanations, though we are may be not going to a 19 pages topic, it appears to be very instructive and i am sure lot of people appreciate your knowledge..............

marinatlas said:

Hi Jim , many thanks for your explanations, though we are may be not going to a 19 pages topic, it appears to be very instructive and i am sure lot of people appreciate your knowledge..............

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Thanks, a lot of my thinking may be somewhat 'out of the box" but then the guy who taught me the most tended to follow his own path and did very well with it. I probably drove him nuts. Jim.

Crankshaft inertia along with hi CR and hi rpm-low gearing is the bane of modern sports bikes when they Need to cut power going into leans, the poor things, the engine can drag too much for fat tires to take so engineers have come up with both slipper clutches and extra fuel maps to inject over idle to keep engine tire drag from further upsetting the corner cripples. As much as fast throttle speed up is desirable I find the power cut behavior way more vital to get around in my case. When I'm aggressive into turns I don't use engine drag to slow up, its so hard on drive train and not that much slow up even if rear is almost chirping/hopping. But I also don't want to feel engine-torque-over-run to keep thrusting forward on closed throttle with clutch still engaged.

There is also crank gyroscope resistance to lean changes, Just saw ad, 1st production bike with crank rotating opposite the tire spin - brags its to help handling. No reports seen yet on how its working out. Bruce MacGregor on Drouin/850 mailed me this week he'd finally tried a chicane area with other cycles and could feel the impeller resistance annoyance. I've held and seen photos of webbing cut out between the impeller vanes, Compromising decision of strength for some relief. If I put on a longer belt and extra idler pulley might could get Peels impeller to spin 'backwards' and still have on/off lever. Impeller still freewheels undriven but likely not as fast as driven. Mystery is if I can notice annoyance/compensation/effort on Peel or not. I tease thee not Peel catches air sideways as times, first thrown at me hitting stones/holes just wrong on THE Gravel to lift &/or twist sideways before planting again, in less than a heart beat. Both linked Peel and un-linked Trixie give slower more delayed less scary reactions than my SV650 with off road set suspension.
Do not know if tires, chassis or engine/crank gives most the difference felt but I like the Cdo's better as less effort to keep on track and more time to react after the fact. Twice as good? 1/2 heart beat vs a whole beat time range.

Reading about power pulse Big Bang vs tire hook up harmonics was a revelation to me a few years ago. Crank mass and BF may be key to why I like Cdo traction hook up better than anything else. Both plain Trixie and special Peel could hook up loose hill climbs on any tire better than my 4 wd PU made and set up for it. Here power is not part of the equation as all my craft can easy spin tires going all the way up, so its a matter of which can plant more power. Going up a loose climb with rear skipping drifting is very very similar to the control I need in loose turns too. I have the G's forces and hook up of various tires imprinted in my joint and tendon nerves and bone magnetic flux domains.
I get a sense of dragging a latex covered finger over smooth still glass plate vs the vibrating release by the glove membrane or the plate itself or both.

Ken is making Peels crank to allow up to 90's BF, which also adds spun mass.
I've seen on report of 94% isolastic racer and also a Harely friend loving 94% BF as smoothest Shovehead he's experienced. No report on 94% iso, just that its was done. What would rear tire and pilot feel with extra HI BF vs regular Lo?
HI oscillates more in line with drive thrust while Lo more 90* to line of drive.

ludwig said:

kommando said:

..Once an object is at a steady state speed it only needs the energy lost to friction to be replaced to maintain that speed..

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Well said .
And that heavy spinning crank doesn't like to be slowed down .
I used to tinker on stationary engines ( one cyl. diesel ) .
These things have MASSIVE flywheels .
It's the energy that is stored in these spinning flyweels that allows them to do their job..
An article about modern aplications :
http://en.wikipedia.org/wiki/Flywheel_energy_storage
"..Advanced flywheels, such as the 133 kW·h pack of the University of Texas at Austin, can take a train from a standing start up to cruising speed."(quote )

RennieK :
about your exemple with the 2 bikes : I 'm pretty shure the one with the heavier crank will be more fuel efficient ..

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Gee, "it only needs energy lost to fiction to maintain it's speed" isn't that called perpetual motion? I can't get my head around the fact that more mass/weight requires more energy to move it. Even in the example of the heavy flywheel moving the train sufficient energy had to be applied to the flywheel in the first place to move that amount of mass. If someone made a 40 lb Norton crank you would see where I was going when I asked " At what point is the heavier crank drawing more energy on it's own than is necessary" It sounds like Jim's formula addresses this issue although it sounds quite complex.

As we've seen just from this thread there have been successful cranks in Nortons weighing between 18 -28 lbs. Thanks everybody so far, I'm gaining a better understanding of cranks and their workings. I thought I had a good grasp of them before but now my level of understanding is somewhere between 180' and offset. : (

If it were not for the energy lost to friction in the bearing and the air around the crank then a spinning crank would spin perpetually, no matter how heavy it was. Jim

ludwig said:

"..Advanced flywheels, such as the 133 kW·h pack of the University of Texas at Austin, can take a train from a standing start up to cruising speed."(quote )...

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That reminds me of a very nice story years ago when the flywheel which accelerates the cars in my old uni's crash test facility was installed and subsequently approved by the authorities. The TUeV engineer who had to rubber stamp the whole thing went through the papers, had a good look at the whole thing, did some calcs and his usual full act just to pull out a compass in the end. That raised some eye brows and nobody knew what he was doing. He went outside the building, had a look at his compass again and at the orientation of the building and finally told everybody around that "the cathedral is reasonably safe" - which happens to be Aachen Cathedral and this is about 8-10km away from said institute .... :wink:


Tim

That reminds me of a very nice story years ago when the flywheel which accelerates the cars in my old uni's crash test facility was installed and subsequently approved by the authorities. The TUeV engineer who had to rubber stamp the whole thing went through the papers, had a good look at the whole thing, did some calcs and his usual full act just to pull out a compass in the end. That raised some eye brows and nobody knew what he was doing. He went outside the building, had a look at his compass again and at the orientation of the building and finally told everybody around that "the cathedral is reasonably safe" - which happens to be Aachen Cathedral and this is about 8-10km away from said institute .... :wink:


Tim[/quote]

I was at the Superflow facility a few years back and they were showing me the flywheels they were accelerating to some incredible speed to do inertia testing on top fuel motors. He said "no problem, we ex-ray the flywheel after every run". Made me glad I live 50 miles away. Jim

Regarding crank weights, whether or not you believe the heavy one requires more energy to spin, I know which one I would rather try to stop! Can a rider feel the difference of 4 pounds in crank weight going into corners or braking? I would think this would represent a considerable amount of energy.

I would have to say a difference of four pounds was apparent when the engine was free revved but it was not really noticeable once the bike was moving. I have not had the opportunity to ride two bikes that were identical except for crank weight back to back however so that would be a hard call to make. Jim

ludwig said:

rvich said:

..Can a rider feel the difference of 4 pounds in crank weight going into corners or braking? ..

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I would think so !.
It's in uphill turns like these that you learn to appreciate the inertia of a heavy crankshaft :

( Splügen pass , Italy )

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You got that right.
That looks like a beautiful and fun ride by the way. Reminds me a of a road near me called the Coronado trail. A whole afternoons worth of 1st and 2nd gear switchbacks that will have you looking forward to the motel at the end of the ride. Jim

It's in uphill turns like these that you learn to appreciate the inertia of a heavy crankshaft :

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Many years ago we built and fitted a 1293 sprint engine into a well modifed Cooper S Rally Mini. The flywheel was a special lightweight alloy affair and the crank lightened. Great for sprints but a real handful rallying, the motor would stall with 4000 on the tacho. Fitting a Leyland Special Tune steel flywheel got it off the line easier, reduced engine braking a tad and made it a nicer package to rally.

Cash

ps It was still a handful for me.

I do up and down hill turns routinely and have noticed that if engine enough power to spin tire at will [not that you are spinning it though just really pushing it]- powering up a turn tends to lift bike from low siding and powering down tends to increase low sides toss downs. Someday I may have a feel for how much a few lbs of crank mass either adds to or subtracts from these base line handling effects.
Spin tire out much going up or down a turn can lead to instant falling of course. Its stinking in by the feedback that more crank mass means more stored energy to smooth power delivery to not just spin tire uselessly unintended. Rule of thumb is it takes about 10% difference in power or handling to be plainly sensed by pilots.
If 22 lb taken as factory base line then 2.2 lb either way would be noticed if using engine and bike to the max- I think.

OH yeah I came across spinning mass reference on cycles that showed wheels spin inertia is generally 5+ x's more effect than crank gyro inertial effects. For handling change and speed acceleration/deceleration I assume.

A bit of a sidestep maybe...
Suzuki's had a go at pros and cons of light/heavy flywheels in their GR650 twin, early eighties, bore/stroke 77/70 mm.
The manual quotes:
-high mass at low speed: easy to ride, smooth idling, fewer gear changes needed
-low mass at high speed: quick acceleration, better engine braking, improved fuel economy.
The GR has a flywheel in 2 parts.
A centrifigal clutch takes care of letting go the auxilliary mass at above 3000 rpm.

A guy over here did the same to the big external flywheel (7 kg) of a Guzzi Nuove Falcone single.
Now 2 lumps of 4 kg each, separating at over 1000 rpm.
Apparently big improvement on gear changing and engine breaking.
do not know if all is sorted out yet.
Some vids on youtube:

http://www.youtube.com/watch?v=FkLftKo3_JI
http://www.youtube.com/watch?v=qC-aPcth ... re=related
http://www.youtube.com/watch?v=qC-aPcth ... re=related

The guy holding the flywheel with the alternator V-belt running behind is full of trust...

Custom crank for 1960 Manx racer on ebay this week.

Small dim light flickering in skull, pressed up 360* crank, central flywheel with large dia pin pressed right through, main cheeks pressed on to the out side, would it work :?: :?:

splatt said:

Small dim light flickering in skull, pressed up 360* crank, central flywheel with large dia pin pressed right through, main cheeks pressed on to the out side, would it work :?: :?:

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Don't know why it wouldn't. Jim