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Old 10-12-2011, 05:37 AM   #121
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Awesome!


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Originally Posted by sakurama View Post
Chris is modest here.



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Old 10-12-2011, 06:46 AM   #122
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Originally Posted by thecosman View Post
Troidus is close to the answer. The bike was designed as a complete system but it is hard to go directly through the order listed. Everyone has to give and take a bit. Even neglecting the suspension design there are a lot of constraints on the placement of the gear shafts, the primary one being the crank placement. The I4s you see around have much different packaging constraints than my V4 so I am not surprised (or worried) that my shaft positions are not the same as everyone else's.

One of my design goals was to get the crank closer to the bike's C of G to make rotating the crank around the roll and yaw axes of the bike (roll=lean angle and yaw=turning the corner) easier, therefore making turning easier. This goal is nearly achieved with Husaberg's latest engine design that places the crank directly under the seat and the cylinder nearly horizontal. Although my engine has nowhere near the extreme amount of crank relocation that the Husaberg does a little goes a long way, especially for a crank that spins at 16000rpm.

The reduction in turning effort is easily understood by taking the barbell/dumbbell analogy one step further. It is easier to spin (like a baton) a dumbbell than a barbell of similar weights. In engineering-speak we say the dumbbell has a lower moment of inertia than the barbell even though they have the same mass. If you put each one in the trunk of a car and did a 1/4 mile you would see no change in acceleration because that is linear motion and (neglecting small effects) is only concerned with overall mass. Rotational motion cares greatly about where the mass is placed relative to the pivot axis. Move mass further from the pivot and the resistance to spinning increases as the square of the distance (that's a lot). Move it closer and resistance decreases a lot. Its why light wheels make such a difference in handling even though they are a small fraction of the overall bike weight. Now imagine that the weights are spinning on the shaft of the barbell/dumbbell. With the barbell not only are we having to move an increased moment of inertia, we have to overcome the precessional forces of the spinning weight from a greater distance, requiring a greater moment force to be exerted by the person holding the barbell or trying to turn the bike. Not desirable.

All of this is a long winded way of saying the crank placement is an important part of determining bike behavior regardless of the type of suspension used. Once I got the crank where I wanted it the next step was to put the output shaft where it wanted to be relative to the swingarm pivot to have proper rear suspension behavior. This shaft placement was less crucial as I had the idler sprockets act as 'modifiers' to the chain forces therefore opening up the acceptable placement window. Once the crank and output shafts were placed then the clutch shaft had a very limited window where it could go using the desired reduction ratios. Now I had to see if gears with a common pitch size for easy hob sourcing could fit the ideal positions of all 3 shafts. Of course the answer was no, requiring subtle shifting of position for all shafts involved for the simple reason of needing gears with an integer number of teeth. This is where making compromises come in.

Other factors to accommodate are: Where does this crank placement put the cylinders and heads/cams? Can I fit a sufficiently strong chassis structure around it? Do my intakes have enough room to breathe fully? Can I fit a shock up front with a minimum of linkages? Is airbox and gastank volume sufficient? All of these factors and more result in a fuzzy position of most of the important components that only gets clearer as you assign levels of importance to their parameters and then walk down the line and work out what I hope to be an optimal compromise.

gotta run.


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I really tried to follow that, got the most basic premise.

I had to stop reading when my head started steaming

Your bike is going to be a stunner, can't wait to see the end product
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Old 10-12-2011, 09:14 AM   #123
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Quote:
Originally Posted by thecosman View Post
One of my design goals was to get the crank closer to the bike's C of G to make rotating the crank around the roll and yaw axes of the bike (roll=lean angle and yaw=turning the corner) easier, therefore making turning easier.

This is why this thread rocks! I haven't ridden nearly enough bikes or hard enough on any one of them to have thought about this concept but once you put it in print I am thinking DUH, of course that's the idea! Thanks!
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Old 10-12-2011, 09:44 AM   #124
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Quote:
Originally Posted by thecosman View Post
Now I had to see if gears with a common pitch size for easy hob sourcing could fit the ideal positions of all 3 shafts. Of course the answer was no, requiring subtle shifting of position for all shafts involved for the simple reason of needing gears with an integer number of teeth. This is where making compromises come in.
Here's another "DUH" moment for me. No such thing as a sprocket/gear with 16.4 teeth on it.
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Old 10-12-2011, 09:53 AM   #125
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>>I'm still sorting images but I remembered taking this shot and thought it appropriate here.

Sweet, thanks for posting the pic.


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Old 10-12-2011, 10:46 AM   #126
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Originally Posted by Easy-Z View Post
Here's another "DUH" moment for me. No such thing as a sprocket/gear with 16.4 teeth on it.
Shoulda seen my last set of sprockets, there were enough teeth chewed off to equal 16.4... sadly that woulda been on the rear.
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Old 10-14-2011, 11:47 AM   #127
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It's so cool you got to meet and spend time with Kevin Schwantz. He's definitely one of the heros of that era in racing. And, interestingly, relatively un-crippled and still in love with motorcycles.
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Old 10-17-2011, 10:29 AM   #128
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Yes, Schwantz is one of the greats. I am amazed that he goes out into competition with a bunch of club racers and allows them to race wheel to wheel with him for a good show.


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Old 10-19-2011, 10:36 AM   #129
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Nice!

I just got permission from Tony Foale to use some of the illustrations from his book in my posts. It will definitely make explanations of some of the concepts easier. I'll include them in the forthcoming front suspension post and then will go back and update the rear suspension/idler posts with some images.

Chris
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Old 10-19-2011, 11:47 AM   #130
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The Front End

The main reason for me to start building chassis in the first place was the front suspension. As a mechanical engineer it surprised me that a system with so many inherent drawbacks became the de facto standard for high performance motorcycles. From purely an engineering standpoint the idea of combining long lever arms with sliding elements is just about as bad a base design as you can get yet for some reason they have managed to become standard on 99%+ of all motorcycles manufactured.

The following 2 images show the main shortcomings of the concept of telescopic forks. Several of these images were taken from Tony's book which is available on his website along with other software that helps with bike layout and setup.





The heavy braking and cornering forces generated by the front tire are transmitted to the frame though a long lever arm requiring a strong and heavy frame structure. This increased mass is cascaded though the entire design requiring many parts that are a bit bigger and heavier than they could be with a more efficient front suspension design.




The necessary clearances in the fork bearings and the ability of each fork leg to compress independently puts high bending stress on the front axle and allow slight chamber change of the front tire as it is loaded. The tendency of modern bikes to have large hollow front axles is intended to minimize this problem but again does it at the expense of bulk.


The other thing that pushed me away from telescopic forks is the desire to do something different! You can look back decades and bike design is essentially unchanged. Frame design has barely progressed past the heavy duty bicycle stage.




Admittedly, new frames like Aprilia’s RSV4 look impressive, but when put side by side you can see they are only different to a 1950 Norton in the material choice. The Aprilia chassis represents huge advances in materials and manufacturing technology and not much else. In other words we are using the latest in production technology to manufacture a design based on 1910 ideas.






The Aprilia frame does look impressive but from a kinematic perspective (moving parts and their pivot points) it is the same as a 60 year old bike which is only slightly removed from a 1910 design.

Compare that with a side shot of my rolling chassis:




Here I use the idlers to adjust rear squat and have a much more efficient load path from the front tire to the chassis. All motion occurs at pivots with rolling element bearings, there are no bushings or linear sliding elements anywhere in the main load path. The legs of my upright are rigid, allowing for a light axle assembly that is still extremely rigid. The lever arm from the frame to the tire contact patch is reduced by approximately 30%, which if all other things are equal give a structure more than twice as stiff for a given weight. Or I can make an equivalently stiff structure at a much lighter weight or do something in between. Regardless of how you arrange the control arms to make the bike act a more efficient structure can be made resulting in a lighter overall bike weight.

This brings up a point I wish to address. Most of the time when you see a motorcycle design with an alternate front suspension (we call them Funny Front Ends, or FFEs) you will then hear the experts (armchair and racetrack) say ‘it won’t work’ or ‘brake dive is good’, or any of a number of criticisms. Some of these criticisms may be valid but my problem is that in the past 20-30 years nobody has even tested them! There have been no advanced FFE bikes since the Britten V-1000 in the early 1990s. That team took a huge development bite with limited resources and by the end was making great progress in getting the bike to work as an overall package. Unfortunately, John’s passing put an end to the project and left motorcycle innovation to people who refuse to innovate: established race teams.

So with all of these supposed problems with telescopic forks why have they become the performance standard? One of the reasons is that when they were introduced in the 1930s they were better than the alternatives. The alternatives were more geometrically complex and since there just was not the level of understanding to what motorcycle dynamics means back then the more complex systems could be designed to provide horrible behavior. With forks as long as you have the rake angle and offset correct in one wheel position the suspension behavior is quite predictable throughout the full travel. With the more complex pivot systems you could have the rake trail correct in one position but way off as the wheel moves though its travel, making a bike that handles unpredictably, not a good trait. Design and analysis tools have come a long way in the ensuing decades allowing me to eliminate bad design as a concern.

Another reason they work well is that forks have gone though costly and intensive development to minimize their shortcomings. Upside down forks, TiN coatings, pressurized damping systems, large front axles, and other detail designs all evolved to address shortcomings: increased bending stiffness, lower sliding friction, consistent damping, increased lateral rigidity. These improvements all have their associated costs: larger and more parts, more expensive processing leading to increased cost and weight.

Forks are not all bad, in fact they have one great positive: they are easy to package and fit on the bike. All you need is one heavy duty pivoting mount (the headstock) and you’re done. Springs, handlebars, and damping are all integral to the design and make use of forks easy. However, some of the techniques used to improve performance have drawbacks. The large diameter USD forks now in use can limit airflow to the radiator leading to cooling problems. Ducati’s GP team had that exact issue with the GP10. The solution is to have a bigger frontal profile thereby increasing aero drag, not a good compromise in my book. Perhaps one of the main drawbacks is the use of round sliding elements. This is highlighted in modern GP design in that the round cross section has equal bending stiffness in all directions so to have a fork that can withstand heavy braking without excessive deflection leads to a fork that is too stiff when leaned over to provide any compliance to the wheel. This requires bike designers to have to design lateral flex into the entire frame structure to allow the bike to behave reasonably well over bumps in turns.

To me these compromises, including designing laterally flexible frames, is going too far. Instead of making changes in the rest of the bike to compensate for telescopic forks’ shortcomings I decided to nip the problems in the bud and design a bike without those compromises.

That is what led me to FFEs. I’ll continue on in another post but gotta go for now.
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Old 10-19-2011, 12:41 PM   #131
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Just so you know threads like this ruin my life. Im so sick of making spreadsheets and want to go back to the fab shop.

keep up the good work, and i love how you are willing to "teach" all of us "poser mechanics"
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Old 10-19-2011, 12:58 PM   #132
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Quote:
Originally Posted by thecosman View Post

The Aprilia frame does look impressive but from a kinematic perspective (moving parts and their pivot points) it is the same as a 60 year old bike which is only slightly removed from a 1910 design.

Compare that with a side shot of my rolling chassis:


Your fork design is impressive , but from a kinematic perspective only slightly slightly removed from 1930's girder fork design?
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Old 10-19-2011, 01:39 PM   #133
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spreadsheets for all

Tex, you should see how many spreadsheets are involved with this project!


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Old 10-19-2011, 01:54 PM   #134
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not much new under the sun

Ishdishwishfish, you have a good point. This design is kinematically similar to a girder except that in a girder design the control arms are steered. The frame needs a normal headstock just like telescopic fork frames so a lot of the inefficient use of material is still there.

Moving the steering axis from the headstock to the upright also allows me to use much longer control arms which makes the suspension dynamics much more consistent and also allows more suspension travel. The increased suspension travel is a minor benefit for a roadrace bike but will be invaluable for the adventure bike version. The consistency of suspension dynamics is extremely important for any style bike.

I am not the first person to come up with this configuration. Norman Hossack was the first guy (i think) with one of these setups and the design is known as a Hossack-style FFE. My design has a lot of different details than Norman's and I have the arms set up to provide different behavior than what he likes. In general it is tough to come up with an original mechanism but easy to 'improve' on existing stuff.

When you consider the design ideas behind a bike like the 1948 Vincent Black Lightning I feel that technical design has only gone backward since then.


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CosentinoEngineering screwed with this post 10-19-2011 at 05:59 PM
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Old 10-19-2011, 02:11 PM   #135
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Trying to keep momemtum going

I'm flattered by the response to this thread. It seems like the ADV rider forum is more open minded than most other race oriented boards that I frequent. Its nice to have a willing audience.

That said, while your viewing and asking questions is a great morale booster for me I am trying to get the project moving along at a faster pace and in pursuit of that goal am posting a donations page on my blog site. There is some swag available for certain levels of donations but anything is accepted.

http://moto2-usa.blogspot.com/2011/1...gs-moving.html

Please don't feel required to give anything, I will keep the project and this post going regardless of donations. Especially in this economic environment I know how tight money can be. However, if you really like the project and want to help keep it moving (and have some spare cash!) then any contributions are gladly accepted and will result in even more posts!

Thanks again for following the project.


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