Ducati goings on part 4 (GP15 edition)

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JanBros
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Re: Ducati goings on part 4 (GP15 edition)

Post by JanBros »

don't know, but crankmases rotating have a huge influence on the bikes handling. I've done wet/dry (same day) trackdays with my ZXR400 with ZZR600 engine in the wet and my KR1S in the dry, and the biggest adjustment in riding style when jumping from one onto the other is not the difference in weight between both, not the differnet power output, suspension or whatever, but the difference of the rotating masses of the cranks when cornering. jumping from the 250 onto the 600, you immediatly feel you have to battle the cank when forcing it into a corner.
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Fingernails
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Re: Ducati goings on part 4 (GP15 edition)

Post by Fingernails »

Would racing engines be designed to reduce inertia? I'm not as knowledgeable about engine design as many on this forum (I wanted to find another MotoGP forum which was more analytical and technical and less prone to pointless arguments than another forum, and this one is definitely it). However, I did a bit of the google-warrior thing, and found this article about the Yamaha cross plane crankshaft designed to reduce inertia. http://www.yamaha-motor.eu/designcafe/e ... &id=442641 A big crank on a road bike clearly creates inertia with obvious effects on ease of steering in a corner. But, will this be significantly reduced due to the design of and expensive materials used in modern racing engines? Or, can they only reduce the inertia by a small amount?

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speeddog
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Re: Ducati goings on part 4 (GP15 edition)

Post by speeddog »

Racing engines are fundamentally designed to be as light as possible, and have as low an inertia as possible.

But being light and low inertia does effect how easy/difficult the bike is to ride, as well as how durable the engine is.

An aggressive powerband and low crank inertia will make the bike more difficult to ride.
That can be papered over with the electronics, but it's not a perfect solution.
I think that's one of the fundamental reasons why Rossi had so much difficulty with the Ducati.
So powerbands get smoothed out, and flywheels get made heavier, just to the point that a tired or distracted rider can still turn a good laptime.

Forgot who said it, but it was along the lines of "We spend a truckload of cash to get the maximum power out of an engine, then spend another truckload of cash taming it with electronics."

It's the path that was followed with combat aircraft, make an airframe that is wildly unstable, so it can respond really quickly, then make it something that a human can fly by inserting a computer between the pilot and airframe to modify the pilot's commands.
It's an (arguably) reasonable philosophy for combat aircraft, given the environment of combat.

I don't at all think that it's appropriate for motorcycle competition.

IMO, YMMV.

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robbieguy85
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Re: Ducati goings on part 4 (GP15 edition)

Post by robbieguy85 »

Hi Gents,

I've not really posted much here, but have been reading for several years. Speeddog, on the "We spend a truckload of cash to get the maximum power out of an engine, then spend another truckload of cash taming it with electronics." I remember seeing a Video with one of the Yamaha Electronic guys a couple of years back, he said more or less the same thing. The job of the electronics is to shave off unwanted/unnecessary power.

I get your point, from the perspective that if the engine is simply too untameable, then while electronics will make it usable, it might not necessarily make it fast, as you'd potentially be shaving off power that on a smoother engine delivery would still be of use as it might not suddenly overwhelm available traction.

And here's the link to that interview - https://www.youtube.com/watch?v=0u9lq0pLMVA

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Grahluk
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Re: Ducati goings on part 4 (GP15 edition)

Post by Grahluk »

speeddog wrote:
Forgot who said it, but it was along the lines of "We spend a truckload of cash to get the maximum power out of an engine, then spend another truckload of cash taming it with electronics."
Remember that one too. Think it might have been Colin Edwards explaining testing on his his Forward/NGM bike.

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Re: Ducati goings on part 4 (GP15 edition)

Post by kenup283 »

Speaking of unstable airplanes and rotating inertia reminds me of the WW1 British Sopwith Camel . A plane who's engine had so much rotating mass for its light airframe to produce gryosopinc reactions that would pitch the plane up or down depending on left or right turns. Story goes more piolts died learnig to fly it than in combat. But it was good for those who learned how to master it. Things like approach on landing from a left bank turn rather than right turn is differnce btwn a nice flare on touch down or face planting.

For bikes, we have the tires and this crank, what I'd like is to run some numbers but in concept the effect I see of a crank rotating in opposite sense to tires woukd be to cancel out the tires reactions to changin direction.

To test this idea you imaging what an engine at 10000 rpm would be to a tire at 1800 rpm (120mph) in a fast corner entry., or exit.

The answer woukd depend on what the crank inertia ratio is to the tires. If the crank say is at least one tenth or more the inertia of the tires they would be comparable forces. Thinking further, those reaction force influence would reasonably also be a function of distance from pivot point, from which the rear tire woukd have a greater distance and perhaps influence.

Thinking of the crank versus tire inertial more. Imagine going along at 5 mph while revining the engine at 10,000 rpm. Would the bike be more resistant to changing direction. Woukd it tend to stay upright more when trying to turn left or right? I think the answer woukd be yes if engine rotates "forward" in same sense as tires, and no if engine rotates in opposite sense or "backwards" to the tires.

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Re: Ducati goings on part 4 (GP15 edition)

Post by Hanuman »

JanBros wrote:don't know, but crankmases rotating have a huge influence on the bikes handling. I've done wet/dry (same day) trackdays with my ZXR400 with ZZR600 engine in the wet and my KR1S in the dry, and the biggest adjustment in riding style when jumping from one onto the other is not the difference in weight between both, not the differnet power output, suspension or whatever, but the difference of the rotating masses of the cranks when cornering. jumping from the 250 onto the 600, you immediatly feel you have to battle the cank when forcing it into a corner.
Are you sure it's the crank? Anecdote time: I swapped the heavy-ish Enkei wheels on my RS125 for some lovely Marvics (borrowed from a friend)....same bike, plenty of difference, the bike steered significantly faster.
I have a spreadsheet somewhere where I did some calcs and comparisons of the inertia/rotational forces of various rotating bits at various speeds. Will have to dig it out.

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Re: Ducati goings on part 4 (GP15 edition)

Post by Hanuman »

kenup283 wrote:Speaking of unstable airplanes and rotating inertia reminds me of the WW1 British Sopwith Camel . A plane who's engine had so much rotating mass for its light airframe to produce gryosopinc reactions that would pitch the plane up or down depending on left or right turns. Story goes more piolts died learnig to fly it than in combat. But it was good for those who learned how to master it. Things like approach on landing from a left bank turn rather than right turn is differnce btwn a nice flare on touch down or face planting.

For bikes, we have the tires and this crank, what I'd like is to run some numbers but in concept the effect I see of a crank rotating in opposite sense to tires woukd be to cancel out the tires reactions to changin direction.

To test this idea you imaging what an engine at 10000 rpm would be to a tire at 1800 rpm (120mph) in a fast corner entry., or exit.

The answer woukd depend on what the crank inertia ratio is to the tires. If the crank say is at least one tenth or more the inertia of the tires they would be comparable forces. Thinking further, those reaction force influence would reasonably also be a function of distance from pivot point, from which the rear tire woukd have a greater distance and perhaps influence.

Thinking of the crank versus tire inertial more. Imagine going along at 5 mph while revining the engine at 10,000 rpm. Would the bike be more resistant to changing direction. Woukd it tend to stay upright more when trying to turn left or right? I think the answer woukd be yes if engine rotates "forward" in same sense as tires, and no if engine rotates in opposite sense or "backwards" to the tires.
Good post, Kenup.
Re the Sopwith, another aviation tale is of the RR Griffon, caused some takeoff issues with pilots who didn't compensate for the reversed direction of rotation compared to the RR Merlin.

As to the question of a fast spinning engine at low speeds, consider the gyro precession and the forces it produces....

Oh and I was at a mate's helping him with his Pantah (stripped belt on frt cylinder) and one of his friends turned up on a Bevel Twin... their cranks rotate backwards. :D :D

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Fingernails
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Re: Ducati goings on part 4 (GP15 edition)

Post by Fingernails »

Can someone summarise the numbers for inertia due to the wheels and the crank? The wheels are bigger than the crank, but the crank will be rotating a lot faster. There must also be a sprung weight vs unsprung weight effect, wouldn't there? I am not a mechanical engineer, as I think everyone will realise :)

Does inertia help explain famous 'turn in' problems? And other issues such as 'feel'? Mostly I've seen it described that these are probably down to frame geometry, sometimes attributed to insistence on a 90 degree V4 engine. Is this true?

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Re: Ducati goings on part 4 (GP15 edition)

Post by JanBros »

Hanuman wrote: Are you sure it's the crank?
if you pull the clutch and feel the forces diminishing rapidly, it can not be the wheels who only lose speed slowly ;)

you'll never feel it when riding your normal bike, only from jumping straight from one with a ligth crank onto one with a heavy one makes it obvious.
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Re: Ducati goings on part 4 (GP15 edition)

Post by Hanuman »

JanBros wrote:
Hanuman wrote: Are you sure it's the crank?
if you pull the clutch and feel the forces diminishing rapidly, it can not be the wheels who only lose speed slowly ;)

you'll never feel it when riding your normal bike, only from jumping straight from one with a ligth crank onto one with a heavy one makes it obvious.
I've tried that, RS125R to R6...but that's from a minnow to a whale. Far too much going on for me to discern anything (and I was trying not to crash...hardly was paying attention to crank forces :)

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Re: Ducati goings on part 4 (GP15 edition)

Post by JanBros »

Hanuman wrote: I've tried that, RS125R to R6...but that's from a minnow to a whale. Far too much going on for me to discern anything (and I was trying not to crash...hardly was paying attention to crank forces :)
than my KR1S is a trout :lol:
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Re: Ducati goings on part 4 (GP15 edition)

Post by kenup283 »

Just for fun, some good examples of a gyros reaction force can be seen in some videos of a turn skid slip indicator on an airplane.

https://m.youtube.com/watch?v=0sRrSkSJc7w

https://m.youtube.com/watch?v=wbUDYuij3Ow



Image the gyro in the vid is the rear tire, rotating forwards. When it is turned the gyro force tilts it to the outside, away from the turn. The force also depends on the rate of the turn, as in the degrees per second, of the change in heading.

I see this as a force tending to upright a bike which is rolled into a turn, and to keep a bike turned in, this force would need to be balanced by the other cornering forces into the turn.

Then pretend the gyro in the vid is the crank, and imaging looking at it from the other end for an opposite sense of rotation to the wheel. The effect would be that it tilts inwards with the direction of the turn.


Regarding effect on corning. To keep it simple, the saying goes there are fast turns and slow turns, and go fast in the fast ones and slow in the slow ones..

So thinking of a fast turn, throughout it both the wheels and crank would be spinning at there fastest at the same time that the heading of the bike is changing rapidly. Coincidently it fast turns are where yahama excel in comparison to Honda.

On slow turns, the tires are spinning slower, but so is the engine on corner entry. However, on exit from a slow corner, the tire is still spining slowly compared to the engine that spinning up to higher RPM's.

In this area the gryo reaction could also become influential, and a forwards rotating gryo woukd help get the bike upright out of the turn and on the center of tire easier and quicker.


Where I am going is, if Yahama has an opposite sense rotating crank, then it would help in fast corners when you enter high in the rev range, and if Honda have a forward rotating one, it could help on the exit of slower turns and upright braking stability.

The Honda compromise bieng the rider needs to work harder to go fast through the fast turns, and the yahmah compromise is the rider needs to work harder to get it up out of a slow turn.

Again just ideas, haven't run any numbers, need some realistic figures to work with.
Last edited by kenup283 on Mon Mar 16, 2015 7:58 am, edited 1 time in total.

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JanBros
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Re: Ducati goings on part 4 (GP15 edition)

Post by JanBros »

kenup283 wrote: Then pretend the gyro in the vid is the crank, and imaging looking at it from the other end for an opposite sense of rotation to the wheel. The effect would be that it tilts inwards with the direction of the turn.
here you go wrong (imho, I don't know much about gyro's, but it's what my common scense says).
the effect of the gyro will not change if you change the direction it is spinning.
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kenup283
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Re: Ducati goings on part 4 (GP15 edition)

Post by kenup283 »

JanBros wrote:
kenup283 wrote: Then pretend the gyro in the vid is the crank, and imaging looking at it from the other end for an opposite sense of rotation to the wheel. The effect would be that it tilts inwards with the direction of the turn.
here you go wrong (imho, I don't know much about gyro's, but it's what my common scense says).
the effect of the gyro will not change if you change the direction it is spinning.

Best thing to demo this is to take the front wheel off your bicycle. Hold the axel with both hands like your arms are a set of forks or a swing arm. Get the wheel spining and rotate your body around.

It is a strange feeling but you can see how the wheel tilts out when it is rotating forwards, and how it tilts in when spining backwards.

Also do this starting with the wheel leaned over at an angle as it woukd be in a turn.

Then can see how when spin is fwd it uprights itself, and when spin is rev it dips further into the turn, as you rotate your body around.

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Re: Ducati goings on part 4 (GP15 edition)

Post by robbieguy85 »

Perhaps not quite in the right area, but, if you ever get the chance to hold a spinning computer hard drive, this is also quite apparent. Typically they spin at 7200rpm, at least for home ones, internally they work like this;

https://www.youtube.com/watch?v=hUAI8HSk204

Basically, if you pick one up when it's spinning it makes your hand move and it feels a bit weird, that's only a very small piece of kit, so I can imagine how a larger lump of spinning metal in a bike could have similar effects.

Note: I'd not really advise holding a spinning HDD, unless you've an old spare that's redundant and has nothing important on, but it's perhaps a way of feeling something similar.

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Re: Ducati goings on part 4 (GP15 edition)

Post by Hanuman »

kenup283 wrote: Best thing to demo this is to take the front wheel off your bicycle. Hold the axel with both hands like your arms are a set of forks or a swing arm. Get the wheel spining and rotate your body around.

It is a strange feeling but you can see how the wheel tilts out when it is rotating forwards, and how it tilts in when spining backwards.

Also do this starting with the wheel leaned over at an angle as it woukd be in a turn.

Then can see how when spin is fwd it uprights itself, and when spin is rev it dips further into the turn, as you rotate your body around.
Even better, perform this exercise when seated in a swivel chair with your feet off the ground.....

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Re: Ducati goings on part 4 (GP15 edition)

Post by oldboyonrgv »

I just fell off my swivel chair.......

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Re: Ducati goings on part 4 (GP15 edition)

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oldboyonrgv wrote:I just fell off my swivel chair.......
:D

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Re: Ducati goings on part 4 (GP15 edition)

Post by kenup283 »

I did some looking and found this reference on the topic of calculating the effect of rotating parts on cornering.

Scroll down a few pages to ser where they present the equations and an example problem for a motorcycle.

https://books.google.de/books?id=T_Wlqu ... cw&f=false


Basically there are some key variables influence the magnitude, so this could be a nice optimization problem to play with, but once say you have fixed interia of tires and crank, then which way the crank spins and its speed relative to the tires (in other words the overall gear ratio) are the things that drive the result.

In summary it looks like for a given turn you can get through using 2-3 less degrees of lean angle for the same corner speed when the crank is going reverse direction. Said another way, it takes less lateral grip to make the same corner. The benefit is then if you do get down to the same lean angle (grip limit) as before then you can then go through faster.

Last year I made some figures on what 3 deg extra lean angle would be worth in time through a corner. I was trying to figure out what MM getting 63 deg out of his bike gained him relative to say another rider at 60 deg. I was surprised that it was quite significant. Something like half to one tenth a second in a single turn looked plausible depending on how fast of a turn it was and how much of the turn he held the extra 3 deg for.

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Re: Ducati goings on part 4 (GP15 edition)

Post by kenup283 »

Here are some charts I mentioned above.

To read the first chart, the left side (40 m radius) is a 60 mph turn, and the right side of chart (160 m radius) a 120 mph turn, for 60 deg lean angle.

Take the lower line, which says MM holds 63 deg lean for 10 deg of arc length of a turn versus 60 deg lean, then he is gaining from 0.02 sec to 0.03 sec., as you look across the line from left to right. The next line above is 20 deg arc and so on.


Image


The next chart is just corner speed to lean angle for given turn radius. These are approximations based on the weight leaning into the turn balancing an assuming centripetal accelraton V^2 / R

Image

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Re: Ducati goings on part 4 (GP15 edition)

Post by speeddog »

Watch this video to understand how the chassis will react when a spinning object (crank or rear wheel) is rotated.

https://www.youtube.com/watch?v=aZlT26lF5Fw

With a forward rotating crank, the chassis will yaw to the left when it's leaned left, and yaw right when leaned right.
This opposes the rider's desired motion when tipping the bike into a corner.
When tipping in, the rider countersteers, IE Turning the bars to the left to steer the wheels out from under the bike to the left, creating a lean to the right.
Additionally, the yaw input on the front wheel leans the bike, as the reaction to the front wheel being turned to the left is it leans right.

So a backwards rotating crank would make the bike tip in easier, and flick upright easier.

Reality intrudes into this wonderful benefit of a backwards rotating crank, though.

The mass moment of inertia of the rear wheel is going to be *much* higher than that of the crankshaft.
IIRC, a MotoGP rear tire and wheel weigh ~30 pounds, versus a crankshaft of ~10 pounds.
The mass moment of inertia is predominantly a function of radius squared, so the drastically larger diameter of the wheel compared to the crank will make it the dominant part.
The weight and size difference result in the wheel MoI being roughly 200x the MoI of the crank.
Even if the crank is spinning 20x faster than the wheel (engine at redline and bike at 70mph or so) it's still at a 10:1 disadvantage.

There is some benefit from the flywheel effect of the clutch assembly, as it rotates backward, but everyone's does AFAIK.

Reality does intrude the other direction, though, as you've only got to beat your opponent by an inch after 18 laps or so....

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Re: Ducati goings on part 4 (GP15 edition)

Post by freighttrain »

Very interesting stuff kenup..

thanks to you and the other for the info and research..
So, has it been confirmed that the GP15 has the crank rotating in reverse?
Did Dovi's mention it? Or it here say as of now?

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Re: Ducati goings on part 4 (GP15 edition)

Post by speeddog »

In this video, at the ~1:00 mark, the starter is engaged, and it torques forward, meaning the shaft it's hooked to rotates backwards.

It *could* be plugging into a jackshaft, but I doubt it, from the location.

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Re: Ducati goings on part 4 (GP15 edition)

Post by JanBros »

speeddog wrote: The mass moment of inertia of the rear wheel is going to be *much* higher than that of the crankshaft.
IIRC, a MotoGP rear tire and wheel weigh ~30 pounds, versus a crankshaft of ~10 pounds.
a motoGP tire/wheel will not weigh 30 pounds, it will be much much less. my guess would be about half.
a ZZR600 crank weighs 23 pounds. MotoGP cranks are on the heavy side to smoothen out powerdelivery so a GP inline crank will be in the same range I guess.
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