MotoGP 2013

[Crasherfromwayback]

Sorry Crasher but you heard wrong,the original idea was about maneuverability/change of direction.
Yamaha have had reverse crank rotation since it's (and 2 strokes)very first 500cc Championship with Agostini in 75.
Honda adopted it from 87 onwards and then subsequently dropped it in the current 4 $troke era.

Or maybe not...

This OW61, the first YZR500 to mount a V4 engine was unveiled at Saltzburg in May of 1982. Then, two years later the OW76 appeared with a crankcase reed valve. Eddie Lawson rode this machine to win his first world title in 1984, after which the V4 engine continued to dominate the GP scene.

The biggest turning point for the two-crank-axis V4 probably came with the OW81 in 1985, '86. This was the machine that Lawson won back his title on after losing it to Freddie Spencer on the Honda NSR500 in '85. "On the OW76, the first YZR500 to adopt a crankcase reed valve, there were things we still had to work out concerning the effect of the engine characteristics on the machine handling. We needed to improve the gyro moment of the crank shafts, find measures to improve torque reaction and reduce vibration," says Mr. Shiohara. These things caused the development team to turn its attention to the revolving direction of the crankshafts.

With the existing two-crank V4, both crankshafts revolved in the direction of forward motion, but the question was raised that that might be affecting the handling stability of the machine. A prototype was created to test this possibility. "In fact, we had created the OW77 prototype and were already running tests on it since the previous spring. It had a two-crank V4 engine on which both crankshafts could be revolved in either direction and it was set up to enable actual running tests as well. Based on those running tests it was decided to have the two cranks revolve in opposite directions, and we built that into the layout." Mr. Shiohara adds.

[DidJit]

Amended calendar for 2013. Argentinian round postponed until 2014.

[merv]

Interesting the early Yamaha V4 had both cranks turning the same way which meant it needed another gear between them, presumably the gearbox drive gear anyway and that would have taken a slight redesign to run them opposite. The NSR Honda was a proper V4 and therefore had only a single crank. This is what prototype racing should be about, people trying stuff to find an edge.

[Drew]

Don't the Yamaha twin crank motors have the clutch and input shaft between them?

Making them not a great deal bigger than a single crank.

No two stroke is a conventional 'true V twin', since they don't share a crank pin. Only reason they are a V that I can see, is heat dispersion.

[Mental Trousers]

For a single one yes, but when you add a second spinning mass going the opposite way in the same frame, it'll reduce the reaction force, therefore, the resistance to change also reduces.

EDIT Nevermind it's covered up above by others

[denill]

I have a theory that finesse riders like Rossi and Lorenzo are naturally suited to the Yamaha, while riders like Stoner are comfortable manhandling the harder to turn Honda or Ducati and then using the power to get out of the corner hard and charge the straights. I don't think Rossi was ever going to have the goods to throw the Ducati around quite how it needs to be.

Thanks for a very good sumation - specially the quoted comments. Right on the money, without the emotion that so often clouds comments.

[pritch]

OK so I had to look rather further afield than I had initially thought to find comment by Mr Cameron on engine rotation and steering.
CFWB's comments lead me to what I was looking for.


"... after 1985 Spencer's fantastic time of brilliance in GP racing was over.

Now began a long running argument over engine architecture. Yamaha's twin cranks canceled each other's gyro effect, leaving only the gyro effect of the wheels to oppose a rider's attempts to change direction. Yet in its immediate previous design era, Yamaha had rotated the in-line cranks of the TZ750 and architecturaly similar 500GP engines opposite to the wheels. Even with this feature the TZ750 had never been a swift direction-changer."

"In 1987 Honda, too, reversed their engine rotation."



"The Grand Prix Motorcycle - The Official Technical History" by Kevin Cameron, 2008

Although errors and spelling mistakes will be mine.

[BMWST?]

rotating mass is rotating mass,i canr see that i"cancels out the other.Contra rotating cranks may cancel out tourque reaction but i cant see that it cancels out the gyro effect

[bogan]

rotating mass is rotating mass,i canr see that i"cancels out the other.Contra rotating cranks may cancel out tourque reaction but i cant see that it cancels out the gyro effect

If you have gyros spinning in the opposite direct, the reaction force (think countersteering) will also be in the opposite direction, so the application of force to one gyro (you'd apply it to both but it might make sense to think of one first, then the other) causes the other gyro to apply a force in the same direction as you've put in, cancelling out the countersteering force.

That probably needs an example, the reaction force trails the applied force by 90 degrees, so when you push on the left bar and apply a clockwise rotation (looking top down), you then go around 90 degrees (now you're looking front in, and upside down) and clockwise causes the bike to lean over to the left (or right when looking from the front).
So now you have the engine spinning backwards, and have just applied a clockwise (front on force), trailing that by 90 degrees and we are back to a top down view, with the reaction force being applied clockwise.
Notice the reaction force of the reversed gyro is the same as the force applied initially, so it subtracts from the force the rider must apply for the same result.

So all the gyro forces etc are still present when dissected, but by being bound together they cancel out. Clear? If not, go bolt two angle grinders back to back.

[Badjelly]

rotating mass is rotating mass

But angular momentum (which is what we're talking about here) is a vector pointing along the axis of rotation. Bolt together two gyroscopes with equal and opposite angular momentum and the overall angular momentum of the body is zero. Ie. it's no longer a gyroscope.

[tbs]

But angular momentum (which is what we're talking about here) is a vector pointing along the axis of rotation. Bolt together two gyroscopes with equal and opposite angular momentum and the overall angular momentum of the body is zero. Ie. it's no longer a gyroscope.

Correct.

I had to go and do a bit of reading after my last post, and while I had understood it mostly correctly, I think I should clarify something.
There are two effects coming into play with the direction of crankshaft spin. Gyroscopic stability, and torque reaction.

As Crasher pointed out, manufacturers started experimenting with crank direction back in the 2 stroke days as a means of countering torque reaction.
Imagine you have your bike up on a paddock stand, rear wheel only. The engine is running and you twist the throttle. The front of the bike will lift as the inertia of the crankshaft speeding up pushes against the rest of the bike. The crank uses the rest of the bike as a lever, pivoting off the back wheel. Now if you have a reverse spinning crank, it will push the front down, so by spinning it backwards, you can help keep the front down on hard acceleration. This will also have the effect of pushing the front down and loading up the front tire when downshifting into a corner, because as you downshift and the revs come up, the torque reaction increases.

According to a comment I read by Jerry Burgess, the torque reaction is more pronounced in 2 strokes. Why this might be I have no clue, but it does mean that in the modern GP bikes, torque reaction is very much a secondary consideration.

The main aspect for consideration here is the gyroscopic stability. Basically the faster something spins, the more effort required to change it's direction, and then once it is changing, more effort is required to make it stop changing direction. This is why the faster you go the more stable your bike becomes.
It gets even weirder. If you hold the front fork of a mountain bike with a wheel mounted up and give the wheel a spin, you will see a very strange effect. If you try to turn the wheel to the left, it react at 90 degrees to the direction of twist. Confused much? Basically this means as you hold the steerer tube with the wheel hanging straight down, spin the wheel and then turn it to the left, the wheel will end up horizontal to the ground.
What this means for a motorbike, as that as you push the left clip-on to initiate a turn, it resists change, but then as it starts to change, it will keep going and lay the bike on it's side. The pressure from the front contact patch is one of the things that stops the bike from falling right over. This helps explain why when I enter a corner on the road marked say, 80, at about 120 I end up having to push the outside bar to stop the bike from turning in too far. The pressure from the front tire is not enough to stop the bike flopping right over.

So, The more gyroscopic stability, the more difficult it is to initiate a turn, and then the more difficult it is to stop the lean and stand the bike back up. And you can reduce that gyroscopic stability and make the bike correspondingly easier to change direction on by reversing the direction of the crankshaft. With me so far?
So why then does it make such a difference with an inline 4 as opposed to a V configuration?

Well, now imagine you are holding a 2kg ball in your hand, arm out in front of you, palm down. Now roll your hand over side to side. The mass of the ball is completely centered inside your hand, so it will be very easy to roll it over. Now try the same thing with a 2kg dumbell. It is going to be far more difficult to roll it over with all that mass so far out, and once you do get it moving, it is also going to be more difficult to stop. Now try with a 2kg barbell... (theoretically of course). It is going to be virtually impossible to roll that barbell over. Well it is the same with a longer crankshaft. This is called the dumbell effect, and it means that all other things being equal, a V4 engined bike is going to be easier to lay on it's side than an IL4.

So, by using a reverse rotating crank, manufacturers using IL4 engines, can reduce the gyroscopic stability in order to offset the dumbell effect of the longer, heavier crankshaft.

I hope this makes sense.

b.

[Crasherfromwayback]

According to a comment I read by Jerry Burgess, the torque reaction is more pronounced in 2 strokes. Why this might be I have no clue, but it does mean that in the modern GP bikes, torque reaction is very much a secondary consideration.
.

Maybe as it's making power every rotation? I first hand discovered this by product while trying to do wheelies on a GPZ500. Their cranks rotate backwards.

[McWild]

b.

Bro. That post was amazing. Cheers.

[tbs]

Bro. That post was amazing. Cheers.

Thanks. I failed physics in high school.

Maybe as it's making power every rotation? I first hand discovered this by product while trying to do wheelies on a GPZ500. Their cranks rotate backwards.

Ah, of course, that'll be it.

[Crasherfromwayback]

Thanks. I failed physics in high school.



Ah, of course, that'll be it.

Me too!

And maybe not...as I guess spinning = the same effect wether it's having power put through it or not? Confusing myself now. Easily done!