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Old 09-29-2011, 05:35 PM   #106
Z50R
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Originally Posted by thecosman View Post

That said, the line drawing you see is a mishmash of his graphical construction techniques and some equations of my own. The specifics of what is what and why are secret. Sorry about holding out but this is a lot of hard won information that is the intellectual basis of what I am basing my project around. Giving a clear description is basically giving away my IP.
Thanks for sharing what you are able to. I looked into how motorcycle frames are designed as part of my senior project research at college. I did not get very far. Please do us all a favor, write down everything you know in a manuscript and let the rest of the world have it in your will. IP is your paycheck and it would be stupid to give it away now but it would be shameful for your life's work to disappear when you are done.

The thing I was most impressed with in my research was that motorcycle/bicycle chassis design is still (after 100+ years) unexplored territory. From what I could tell, frames are still designed empirically as the equations to design them entirely mathematically are still too complex to solve. I am sure some of the larger moto or bicycle companies have a few more equations solved than the public knows about but I can't find evidence that any frame has been optimized other than by using what is known to work from previous test rigs.
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Old 09-29-2011, 07:06 PM   #107
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>> I looked into how motorcycle frames are designed as part of my senior project research at college. I did not get very far.

>>The thing I was most impressed with in my research was that motorcycle/bicycle chassis design is still (after 100+ years) unexplored territory.

I also was surprised at the lack of information and the amount of repeating the same thing as last year or doing what the other guy is doing because he is doing it. Basically nobody is telling what they've learned but the knowledge is out there.

If you are still interested in the 'why' definitely pick up a copy of Tony's book. If you are interested in the 'how' then John Bradley's 'The Racing Motorcycle: A Technical Guide for Constructors, vol 1 and 2 is great. I'm on a chassis design mailing list hosted by eurospares.com. Tony Foale is a participant as is other respected builders like Ian Drysdale and a load of DIY guys who are more than willing to answer questions. MM of eurospares.com has a good list of relevant reference books for motorcycle design located here.


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Old 09-30-2011, 09:04 AM   #108
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Old 10-02-2011, 03:45 PM   #109
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rear idlers

Many people are curious about the idlers I use in the chain run. Most suspect they are for tension control and are partly correct. Each idler has a specific purpose and ideal position. They are fixed, not spring loaded, and are adjustable in the sense that a different tooth count sprocket will alter the squat/rise behavior.

The reason for why I use them and the methodology of where I should put them is taken directly from Tony Foale's book in the chapter on rear suspension. In this chapter there are references to various ways of adjusting rear squat, mostly used on dirt bikes as their large suspension travel makes variations in squat behavior extreme. These large variations in the behavior make a bike more difficult to ride to the limit in varying conditions. Horst Leitner's design is shown in that chapter along with several other designs including mine. The reason for using one of these various techniques is to control how the rear suspension reacts to the pulling force in the chain in various suspension positions. In my design the top sprocket is active when the top chain run is in tension, eg, when you are on the gas. The bottom sprocket is active when you the lower chain run is in tension, eg, are off throttle. This simple separation of function allows us to change the behavior of of and off throttle response independently, which is nice when trying to fine tune handling to 99.999999%.

Rear suspension reaction to the chain can be described by the position of the center of gravity of the bike, wheel locations, and the line defined by the swingarm and the line defined by the appropriate chain section. By drawing a stick figure of the bike on graph paper and finding the intersections of these lines you can see what the squat behavior of the bike is. Actually, you can see what that squat value is at that suspension position is. As the suspension moves in its travel the value of the squat will change. Sometimes this is good and sometimes bad. By working in reverse: knowing wheel position, swingarm location and the desired squat value, you can determine where the chain run should be. If the chain doesn't happen to line up with your existing sprockets (highly likely!) you put an idler in to nudge the chain run into the proper location. This is where CAD comes in very useful. Drawing lines and arcs is what it is made for and makes finding the optimum idler position across a range of suspension travel much more manageable. Racers usually work to adjust this squat value by changing sproclet sizes and where possible by moving the swingarm pivot though the use of variously machined inserts. To me having to relocate the most heavily loaded pivot on the bike is silly when you can use an easily placed and adjusted idler. This is yet another negative aspect of racing on production motorcycles, you are limited in the modifications you can do to the frame so have to develop complex solutions to simple problems.

Anyway, the top idler affects on-throttle squat and the lower idler controls off-throttle rise but with roadrace bikes the current vogue is to minimize the engine braking through various ECU maps so that the off throttle behavior is greatly reduced. This would make the lower idler superfluous from a bike response point of view, however, having only a top idler would then make chain tension vary excessively through the suspension travel. So the lower idler is really there to minimize the variation in chain length and not for squat control.
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Old 10-02-2011, 04:00 PM   #110
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>>I'm trying to design a dual sport bike and I'm woried about the pull from the counter sprocket causing to much
>>squat on acceleration and anti squat on engine braking because my counter sprocket centre will be about
>>110mm away from my swing arm pivot (thats as close as I can get the swing arm to the engine)
>>Will some fixed idlers like you have be the answer to lessening that effect?

This is a perfect place to use Tony's line-drawing construction technique. A large sprocket to pivot distance does not necessarily mean you will have excessive squat but fixed idlers will allow you to adjust squat value to what you want it to be. The key will be to draw what you have and see how it compares to other bikes or your previous version. Deciding what squat value to optimize to is also another variable. I'm not sure what adventure riding requires for roadrace I like little to no squat and little variation through travel.


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Old 10-03-2011, 03:29 AM   #111
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Thanks for explaining that mate it helps a lot.
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Old 10-09-2011, 07:25 AM   #112
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Old 10-09-2011, 09:36 PM   #113
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I'm finding this really cool. Especially as I had an idea for a motorcycle engine/frame/driveline that has spots of overlap. I had no idea where to start as I've never done anything like this.
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Old 10-11-2011, 10:19 AM   #114
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starting is the easy part!

Finishing projects seems to be the tough one! I find it helpful to have a project outline and some rough task categories. The biggest design/fabrication project is really just a series of smaller ones strung end-to-end. Its easy to get frozen when you look at a big project as one discrete task. I like to make the first task to be breaking the project down into many more manageable tasks. When you go into project mode and have a (long) punch list of simple tasks it is easy to make progress. If you have to figure out what to do every time you go into the shop it tends to eat a lot of time. Us tinkers rarely think of ourselves as project managers but that is implicit in laying out a project. The better it is done in the beginning the smoother progress is.

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Old 10-11-2011, 10:52 AM   #115
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Sorry for dropping out for a few days, I had some prep to do for the trip to Barber Motorsports Park for the AHRMA vintage race festival and a whole lot of driving to do too.

I got the engine into a relatively presentable assembled state and it looks pretty convincing!





Only a few more components to be finished (crank, primary gears) and then it is ready to start for the first time. That will be a huge progress marker for the project.

At Barber we had a great time and I recommend a trip there for any racing history fan. Their multi-floor museum is filled with exotic and not-so-exotic bikes and a lot of F1 cars too.

This was one of the larger AHRMA events and had special guest Kevin Schwantz, the 1993 500GP world champion, there actually racing a vintage Manx that was brought over from New Zealand by famed tuner Ken McIntosh. There was also a nice contingent of Kiwis there to add to the general paddock mayhem. He was given a run for his money by a couple of local fast guys but was able to come up with the win both days.

Anyway, now back home I can continue the updates. The next couple of posts will be about the front suspension: the how and most importantly the why.


See you soon,

Chris
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Old 10-11-2011, 03:17 PM   #116
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From a very noob and fascinated eye.

It's my impression that you have chosen to stack the major engine components vertically.

Other engine philosophy's seem to try for compactness either on the horizontal & vertical plane (L shape) or group the components radially and try to centralize the mass.

If I am perceiving it right and obviously taking the State Secrets Act into account, can you disclose your reasons?

And by the way, hats off to you Sir!
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Old 10-11-2011, 05:43 PM   #117
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Originally Posted by kamanya View Post
From a very noob and fascinated eye.

It's my impression that you have chosen to stack the major engine components vertically.

Other engine philosophy's seem to try for compactness either on the horizontal & vertical plane (L shape) or group the components radially and try to centralize the mass.

If I am perceiving it right and obviously taking the State Secrets Act into account, can you disclose your reasons?

And by the way, hats off to you Sir!
Remember, he designed the engine to fit the frame, and the frame is designed to accomodate the suspension. The suspension is the innovation here, even though the engine is cool, too.
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Old 10-11-2011, 07:12 PM   #118
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Remember, he designed the engine to fit the frame, and the frame is designed to accomodate the suspension. The suspension is the innovation here, even though the engine is cool, too.

Yeah the engine is just a side shoot.

Cant you tell that, geez
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Old 10-11-2011, 09:04 PM   #119
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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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Old 10-12-2011, 02:03 AM   #120
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Chris is modest here.

Schwantz was pitted under our tent and we had dinner with him Saturday night. Jamie knows how to pull off a race weekend and Chris knows how to build a bike. I've met three presidents and numerous celebrities and yet it was humbling to hang out with Kevin (and he's as sweet as can be too) and I was really lucky to be part of the weekend. I'm still sorting images but I remembered taking this shot and thought it appropriate here.



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