Lots of assembly required.....

ratski,

BMW's telelever is one of their older front ends that is a copy of work done by Saxon-Motodd in the 80s and 90s. You can see a lot of various designs at http://www.tonyfoale.com/gallery/FrontEnd/index.htm.

Their newer front end on the K1200R is called, appropriately enough, the Duolever and is a variation of the Hossack style front end. It is a lot closer to Norman's original design than mine, especially with the scissor-style steering linkage. BMW got some static from the builder community by not acknowledging that their design was nearly an exact copy of the original Hossack. They have since relented and even had him as a guest to their GP tent at the 2007 Laguna GP. I met him there an we talked bike design for a while. He felt that BMW was on the cusp of entering and dominating racing. He made great front ends but I guess you can't hit them all.


Chris
http://moto2-usa.blogspot.com/
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First I would like to echo some of the other members by saying thank you for sharing this whole process with us. I find it is waking up parts of my brain that have been dulled by my fold tab A into slot B job.

Now some questions;

1. Are the upper and lower control arms equal length and will the rake/trail stay consistant through full articulation?

2. Are the braking forces separated from the suspension movement?

3. If the front suspension is very rigid and the frame is just as rigid, what kind of side loading will the front tire be subjected to while turning? ( Would it cause a "hop" or "chattering" while exiting a corner under hard acceleration?)
4. If you connected one side of the lower control arm to a torsion bar and relocated the hydro damper to the lower frame rail below the control arm,(in extension), would there be a noticeable drop in weight, center of gravity?
5. Would radiant heat adversly affect said damper in that location?

Just some thoughts.

I'm in.

I'm in for $50 to get the t-shirt. When my ship comes in I want my name on the cases!

Gregor

PS Chris has started a thread for technical questions about general fabrication and building so check that out and spread the word: Some Advice Required?

scmopar, there's more images on the blog and at the website: http://www.cosentinoengineering.com/moto2/index.htm

Chris
http://moto2-usa.blogspot.com/
Chip in and help!

KZjohn,

No problem, it's nice to have an audience!

To answer your questions:

1. They are unequal length and trail changes slightly. I don't care about rake angle as that is not a main controlling factor for handling, trail is what I am concerned with.

2. I do have some dive but not as much as telescopics. So no, they are not completely separated. Having a FFE does not automatically mean anti-dive. I could set it up to have more dive than teles if I wanted to.

3. The chassis is rigid and the upright legs are stiff in the braking direction but I never said anything about lateral leg stiffness. There is definitely a need for lateral wheel compliance for absorbing bumps when leaned over but I feel using the frame for that is not the best way to go about it. With my front end arrangement I can have less lateral than longitudinal stiffness by having non-round upright legs, which I do.

4. Yes, switching to a torsion bar in the lower arm and relocating the damper lower would result in a lower C of G but not likely a decrease in overall weight. However a low C of G is not necessarily a good thing. It would also require a stronger control arm as it would now be loaded in bending, not just compression.

5. Hard to say if heat would be an issue. A small air gap and a cooling air stream go a long way. Ducati's 999 and later models have the rear shock right next to the exhaust pipes and seem to suffer no shock overheating issues.



Chris
http://moto2-usa.blogspot.com/
Chip in and help!

Honda tried the lower CoG thing with the 84 NSR500 GP bike, which had an upside down chassis. Fuel down low, expansion chambers sweeping up over the engine. IT was disastrous...

Really depends on the bike though. I helped build a bike with a belly tank, and high exhaust, and airbox. It works wonderfully (wins every race)

Forgive my uneducated musings, but some more thoughts/opinions;

The CG needs to be above the axles for a bike to act like a bike. There needs to be a certain amount of polar moment of inertia. I see it in my head this way, when a bike tips into a corner, the wheels are trying to run under the bike to keep it uprite much like a toddler will run to keep it's body under it's big head.
My thoughts about relocating the front spring/damper lower were more about centering the mass than just lowering the CG. From a rider's stand point,(where I have most of my experience), if you can lower and center the mass it will make the rider's job easyer to go faster with more confidence. I race dirt bikes over long distances and conserving my energy is a high priority. If I can keep the weight lower on the bike it takes less effort to transition from side to side. You can build the most advanced, kick ass bike ever to roll a wheel on planet earth, if the rider is uncomfortable or unconfident on it, it will finish last every time.

Surely you jest!!

I'd like to see the bike, I'm always interested in seeing creative engineering solutions that work. Honda went a little too far I think, they had lots of issues with weight transfer working the wrong way and fuel sloshing around creating some weird issues.

The guy on the Duc is still trying to ride the bike. If he could just get his foot down to upshift....

"Champions never quit!"

Funny, I had that red & white team in mind when I said that.

That guy on the Duc!!!!! No 46, thats Valentino Rossi aka The Doctor. Multiple multi class world champion...... Good as he is just cant get that Duc working for him, maybe his engineer needs to read this thread? lol

>>My thoughts about relocating the front spring/damper lower were more about centering the mass than just
>>lowering the CG. From a rider's stand point,(where I have most of my experience), if you can lower and
>>center the mass it will make the rider's job easyer to go faster with more confidence. I race dirt bikes over long
>>distances and conserving my energy is a high priority.

For a roadrace bike a low C of G leads to slow turn-in performance. Mass centralization is nearly always good but sometimes you need to put something where it wants to be instead of where I want it to be. The front shock location provides a linkageless solution with the forces acting as directly as possible on the relevant parts to maximize feel and minimize play/hysteresis.

>>You can build the most advanced, kick ass bike ever to roll a wheel on planet earth, if the rider is uncomfortable
>>or unconfident on it, it will finish last every time.

Absolutely.


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

Hey Man, here ye be! It's a Honda RS125 with a CRF450 engine in it. The fuel in the chin fairing, and the fuel tank is now the airbox (converted to down draft intake) The bike weighs 165lbs, and makes 71HP at the rear wheel. Lots of fun!!!

Sorry, I don't think I have a picture with the fairing off

any more info? There's a debate going on over in the perfect line about hp vs top speed and they would like to see this.

I appreciate your sharing of engineering concepts. I'm enjoying the read.

Sorry for dropping off there, got a bit busy there and didn't have time for updates. I did get a chance to do some cool machining for the front suspension (how appropriate) that is on the blog.

The last post was starting on the backgrounds of why I didn't just bolt a pair of forks on the bike and called it a day. Those reasons, and also liking a design challenge, propelled me forward.

Since I had decided not to use forks the question was what to use? Examples of people from Tony Foale to John Britten showed there were many ways to skin the cat. Which method would I use? To help make a choice I looked at some of the issues current GP bikes were having. Those were late 1990s and early 2000s, the last years of the 500cc two stroke 4 cylinder bikes and beginning of the 990cc 4 strokes. The 500s were absolute beasts, 200+Hp and a power curve guaranteed to spit you off at some point. The 990s had a better torque curve shape but even more power. What the current designers were doing was stiffening up the frames to deal with the big slick tires and violent power delivery. This increase in stiffness had unwanted and unforeseen side-effects while the bike was leaned over and going over irregularities in the pavement.

When a bike is leaned way over the suspension is no longer in line with the bumps in the pavement so is less effective in absorbing pavement irregularities or even subtle braking and acceleration forces. As tires improved (due to competition) lean angles increased as a consequence of higher corner speeds. GP bikes were now starting to enter territory where corner speeds were high and the resulting lean angles were making the suspension ineffective.



The problems of increasing engine power and lean angle have continued on to today, perfectly shown by Casey Stoner in the following image.



This image is stunning. 60+ degrees of lean is incomprehensible. I highly recommend looking at some of the 1000 frame per second video of Stoner going through a corner. His form of slightly spinning the rear wheel sideways while dragging his elbow is poetry in motion.

Because all GP and 99.9999% of production race teams use telescopic forks that have a round cross section the only option to introduce lateral flexibility to deal with bumps is to have the entire fork and headstock assembly move. Round cross sections have equal stiffness in all directions since all the material is the same distance from the center of the profile. If you have a plastic pen try to bend it. It provides the same resistance regardless of which direction you try to bend it in. Not try to bend a ruler along its flat direction then along its narrow direction, it provides extremely different stiffness depending on the direction because its profile is not symmetric about its center axis.

This is the core what I think is a big flaw with telescopic forks. If you make the forks big enough to provide stable braking using sticky tires and big brakes then the forks are too stiff when leaned over and the bike skitters over bumps. If you make the forks small enough to be supple under bumps then they deflect back excessively under braking resulting in an unstable bike under braking. Both situations are not good. Non-round sliding elements are troublesome in that any torsional load (which there is a lot of in a motorcycle front end) tends to make them bind, obviously not a good characteristic for a suspension element. We can see how the use of forks required teams to have complex frames that were stiff in one direction and less stiff in others. This made a frame designer's tough job even tougher. Now they had to hold the shaking engine, swingarm pivot, shock mount, rider seat, and handlebars all very rigidly yet allow the lateral flex needed by the front wheel/fork assembly. Not easy to do and not easy to subtly change one without affecting the other.

To me, this was a great reason to eliminate the sliding action of forks with several pivoting motions of linked control arms. It would allow me to use rigid structures to create the suspension movement and 'flexible' structures to allow controlled sideways flex.

Now I knew to use a control arm system the choice was which style to use? I wanted to easily be able to change lateral stiffness while keeping suspension movement accurate. Once you go to control arm style suspensions there are several layouts that can be used. Although they look very different from a physics perspective they are all identical:



Looking at these I felt the best solution for my priorities was a Hossack style. It would allow me to create strong triangular structures to control the suspension movement and easily predictable and replaceable structures to provide the lateral compliance. Difazio and hub center styles can have problems with steering lock and also have lower control arms that are loaded in multiple directions.

These are the stiff parts:



these are the 'flexible' parts:



After picking and choosing what I felt to be the best design points we had a front end that fit all my requirements:

-low stiction/friction
-stiff where needed
-flexible where needed
-easily changeable 'flexible' elements

My first design was a bit elaborate. it had roller bearings on all the upright pivots but had a complex welded structure as the upright. I may have went a bit overboard with these parts but it was my first time and I didn't want anything to fail under normal use.



This bike lasted 2 years and taught me a lot. A hell of a lot. For the first redesign I wanted to be able to make front ends more easily. I made the compromise to eliminate the roller bearings in favor of heavy duty plain rod end bearings which would allow a much simpler design.



I ended making a lot of these with various cross sections, wall thicknesses, offsets, etc, in the search for what produced the best results. We collected a lot of data and was even able to see chatter of varying frequencies and amplitudes in the suspension travel data as the design evolved. From this frequency information and the easily characterized rectangular upright legs it was a simple engineering exercise to change the stiffness to minimize or eliminate the chatter.

Front wheel chatter (purple) line:


The lessons learned through the past few designs have resulted in the latest design. It has all the benefits of the all roller bearing setup while adding the easily definable and changeable legs of the rod end bearing setup.




That pretty much covers the how and why of the FFE front suspension. From here I'll talk about general frame design and swingarm stuff.

That's all for now.


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

Well worth the wait, looking forward to the next instalment.....