| Author | Message | ||
     Spiderman |
From what I learned in physics class centrifugal force is an imaginary force? Maybe I was high at the time but that's what I remeber hearing. (Had to stir something up) | ||
| Dynarider |
Imaginary force? This isnt Star wars & you aint Obi Wan.  | ||
| Spiderman |
You know what I mean there Ben Wa Ball. As in it isn't there.  Like "Whatever" at Hooters | ||
| Bomber |
Blake . . . .'Priller published a book a couple of years agao (I sourta Kinda Figured you'd have a copy {smile} that the site Dyna's talking about is quoting from, illustrations and all . . .. it's a good read (the math is a little murky for me, but likely a before breakfast snack for you {smiling again}) . . . .if ya like, I'll get the name and like that to ya . . . . | ||
| Dynarider |
Oh Oh, you werent supposed to mention Hooters & Whatever in the same sentence. She might get jealous. | ||
| Spiderman |
I know | ||
| M2me |
This diagram really helps to explain what I was trying to say earlier about "hanging off" to the outside in slow speed turns. Notice the position of the rider relative to the bike in the middle picture. Now, compare that to the rider on the right. They are in almost the same position relative to the bike. So if you can say that the rider on the right is "hanging off" to the inside, you can also say the rider in the middle is "hanging off" to the outside. Doing this helps in slow speed turns.   | ||
| M2me |
I remember a way to describe centripetal force from high school physics. Think of spinning a weight in a circle on the end of a piece of string. The real force that is acting on the weight is the string constantly pulling the weight to the center of the circle. Without the string, the weight will obey Newton's first law of motion: An object in motion tends to stay in motion along a straight line unless acted on by an outside force. The outside force is the centripetal force imposed by the string. This brings up an interesting point. What really makes a motorcycle turn? The friction at the tire contact patch. Without that, you can throw everything else out. You won't be able to turn. | ||
| Blake |
Greg, <sighhhh> Just when I think I've gotten away, you suck me back in again.  This really is getting silly and not much fun. "You however, have on occasion made statements that, if true, would indeed render moot the laws of physics." Again you toss out inflammatory rhetorical generalities. Please show me where I've said anything that contradicts the laws of physics. Your attempt to deny the coexistence of angular and linear momentum in a rolling wheel is only the latest." I said the exact opposite. Try rereading my last response to you. "Reading" is fundamental.  What I actually said was,
"You asked for Steve_A's help. Then you ignore it when he says a german PHD could not adequately describe this subject with 50 non-linear equations." Actually, I believe that Steve was talking about a comprehensive dynamic characterization of a motorcycle, not just a simple model adequate for ascertaining the governing mechanism that causes a motorcycle to turn. His reference to "50 nonlinear equations" was therefore not specifically applicable to "describing this subject" as you contend. Also, the guy was a tire engineer for Metzeler. What do you imagine a tire engineer would be trying to ascertain from a motorcycle dynamics model? Do you think that he might have been trying to accurately ascertain, for a variety of scenarios, the detailed loads that act upon the tires, especially throughout the contact patch? Do you think he might want those loads so that he could then apply them to his detailed computational tire models? Can you see how complex that scenario might get? I can. There are two major components on all motorcycles that behave nonlinearly, the tires and the suspension damping. Why do you suppose he needed 50+ nonlinear equations? Do you think he needed that level of complexity to ascertain that gyroscopic effect hinders getting a bike at high speed to lean and turn, that in reality it is good ole steering, traction, and centripetal force that do the job? Did you notice what else Steve said? In the very next sentence, he clearly stated that "...simpler models predict trends... . Isn't that what we are discussing, the general trend/mechanism that causes all motorcycles to turn? That is what I've been discussing. If you could build an infinitely rigid motorcycle with no suspension, no engine the thing would still turn via the same exact basic mechanism that allows all motorcycles to turn. Even if the tires were infinitely stiff/hard, as long as there is friction, the thing would turn, and it would do so via the same mechanism that allows all motorcycles to turn. What does that tell us then? It tells us that we can neglect all that complicated stuff that you are so concerned about; it doesn't affect the basic mechanism that causes a motorcycle to turn. "You also seem to have ignored his statement that some long distance wheelie riders use electric motors and gyroscopic precession to steer their bikes." Again, maybe try actually reading what I actually post for a change. I guess you missed my question to Steve, Whaddya think Greg? Think they are anywhere near the same magnitude? "C'mon Blake, you're not really that stupid. This discussion has always been as it applies to motorcycles." Doesn't matter what it applies to. Linear and angular momentum have no "interaction" one with the other; a "relation" between the two is possible as you described, an "interaction" no, not possible. "If you keep to the point and leave out the insults this discussion will more useful." I fully agree. Why don't you do that? You initiated the sharp tone, not I. I'm happy to reciprocate though. I think your first comment was to the effect that I was in "denial" or some such thing. I ignored that. Then you popped off condescendingly something about me "further confusing the issue." You have escalated from there to chiding me about "high school level physics", continually accusing me of "ignoring all the facts", stating condescendingly that "Blake, Blake, Blake, you disappoint me" and most recently insinuating that my contributions here are "stupid". Unfortunately I do not yet posses the grace to weather such condescension and insult without rebuttal, so like I already said, I'm happy to reciprocate. "I have never disagreed with the laws of physics..." Really? After I post the simple equation governing the gyroscopic behavior of a motorcycle's front and rear wheels, an equation that clearly and irrefutably shows that as speed increases, the rate of precession (rate of lean) decreases and/or the applied moment (steering effort) increases. To which you condescendingly replied, "Blake you really need to quit trying to prove everything on paper. The real world is just on the other side of that page. High School level Physics is what lead you to some of those silly conclusions." You have also asserted that... "Gyroscopic forces are what allow high speed motorcycle maneuverability. Imagine you have leaned way over in the first part of a high speed chicane. How do you bring the bike upright so you can quickly lean in the opposite direction for the second part of the chicane? Why you take advantage of something called gyroscopic precession by counter steering of course." and "What I do disagree with is (that) Gyroscopic forces and GYROSCOPIC PRECESSION are a great hindrance to high speed motorcycle maneuverability." The above statements clearly contradict the simple valid equation that I have repeatedly offered along with detailed explanations. Restated in plain English... The required amount of torque or moment (M) applied through steering effort to generate a given rate of gyroscopic precession/lean (f') in a motorcycle's front wheel assembly that is spinning at a speed (g') and has an Inertia (I) is equal to the product of the rate of precession (lean), the speed of rotation, and the inertia, namely that (M=f'g'I). Solving for the rate of precession aka the rate of lean (f') instead of the applied moment (M) we get... As you can clearly see, if the speed of wheel spin (g') increases, the steering effort (M) must increase proportionally in order to maintain the same rate of precession. Of course I am ignoring the significant additional effort (applied moment) that would be required to cause, not just the wheel assembly itself, but the entire bike to lean; that very significant additional applied moment is proportional only to the rolling-axis inertia of the bike and the rate of lean; it is independent of the bike's speed and so can be neglected as applies to our discussion. So on one hand we have the laws of physics that dictate that the faster a wheel spins the harder it will be to turn and also that the faster a wheel spins, the slower it will precess (lean). You on the other hand disagree. You think the fast spinning wheel helps more quickly lean a bike. | ||
| S320002 |
Actually Blake what I said is that you're not that stupid. Think of it as a complement! Using a few simple equations, and declaring that you have created an accurate mathematical model of motorcycle steering, is like placing a few pixels on a computer screen, and declaring you have created an accurate digital replica of the Mona Lisa. Maybe I should leave you alone for a while. You seem to be showing some signs of frustration. Just remember if you say something that's way off base I might call your hand. Greg;-) | ||
| Blake |
M2me, I agree with everything you just said. I hereby rescind my bullshit alert and apologize for being such a stickler. Sorry about that.  And thanks for trimming down the pic so I could fix the page.  | ||
| Blake |
Greg, There you go dodging the issue again. I post a lengthy well considered response to each and every point that you raise. You respond with a blurb of misdirecting rhetoric. Neither did I declare that I have created an accurate model of motorcycle steering, nor did I use a few simple equations in my outline of what such a model would entail. Rather, the equation that I have repeatedly posted is offered to refute your contentions with respect to the gyroscopic effects of a motorcycle's front wheel. You see, your assertions are blatantly contradictory to the laws of physics as represented by that one equation. I've invested a lot of time, effort, and consideration in this debate. You fail to reciprocate. How about answering the questions in my last post instead of throwing out a flip misleading response. And here is one more for you. When you are wrong, do you admit it? I'm guessing no. | ||
| M2me |
Blake, Thanks, apology accepted! I hope you or anyone else didn't take what I wrote 1/3/03 at 10:48 pm the wrong way. I was just trying to add a little levity to what was getting to be a heated discussion. Only Richieg150 commented on it. I thought it was pretty funny myself. But I was serious then and I'm serious now when I say that this is very interesting and educational reading. | ||
| Blake |
M2me, Nah, didn't give it a second thought. Come for a visit and I'll give you a ride around Oak Hill Raceway. You *may* change you definition of "hanging off." ![:]](http://www.badweatherbikers.com/buell/clipart/proud.gif) | ||
| Blake |
There are two problems with each of the three diagrams posted above (originally by Dyna). One of the errors is physics related, the other is method related. Can you identify the errors? | ||
| Jim_Witt |
Blake, If you have some spare time (which you seem to) you might want'a check this site out throughlly. Some interesting things here including some programming code and animation. I haven't been able to get everything to work yet but I'm trying. Cheers, -JW:> | ||
| Jima4media |
To me there are two primary forces at work in turning - slip angle and camber thrust. If you had a flat bottomed steel wheel on ice, you wouldn't be turning too much. Jim | ||
| Hans |
Hanging off at high speed at the inside of the turn steers the bike by the yaw cause the asymmetrical wind drag.  Hans. | ||
| S320002 |
Blake, Many of your responses are very long. Well considered? Some of them are. Others do not seem to be. As regards the formula that you keep posting. I have repeatedly stated that I agree that a gyro is more stable at high speed. It does not however eliminate gyroscopic precession as a necessary component of high speed steering. Your statement that it is a great hindrance implies that if it were eliminated it would make steering easier. Not so. As you should clearly see I do not disagree with the physics, just some of your statements. By the way, if you would plug some numbers into your equation it might be useful in defining what you consider hard steering. You make it sound like the steering head bearings feel nearly welded at high speed. In answer to you last question. I have never had a problem admitting it when I'm wrong. It keeps the blood pressure down and mine has never been high. Greg;-) | ||
| Jima4media |
Hans and Greg, I have to agree with you on the last two points. Either hanging your leg out at high speed or gently pushing on one side of the handlebar with one finger is enough to start a lean. Then it is the rake and trail geometry that takes over and the slip angle and camber thrust that gets the job done. See, I didn't mention gyroscopic precession at all in that statement. Jim | ||
| Mikej |
I just like to go around corners without falling down.  | ||
| Joey |
That's it! From now on, I'm only reading posts with pictures or oversized formulae! I have created a monster! All from some silly joke at which nobody laughed. | ||
| Mikej |
"Just goes to show you ... it's always something." | ||
| Davegess |
So how does all this apply to side cars? ;o> | ||
| Hans |
Skiers have their pockets full of high speed gyroscopes, doing the slalom. (Shhh, don`t tell anybody). Hans | ||
| Blake |
Greg, "You make it sound like the steering head bearings feel nearly welded at high speed." I think I actually stated something to that effect. That is exactly correct. At high speeds, the steering axis is attached to a gyroscope. Gyroscopes by definition strongly resist, relative to manual actuation, being rotated out of plane. Check out the simulation results for the constant radius turn (page 5) and for the lane change maneuver on page 8 of this interesting study. It shows very clearly that steering effort increases with speed and that steering slows with speed. The investigation also includes some slalom simulations, but unfortunately only for one speed. The gyroscopic hinderance to ease of maneuverability is clearly evident even though the steering action was in no way aggressive. The initiation of a constant radius turn was executed over approximately 2.5 seconds to an ultimate lean angle of only 0.2 radians (11.5o). That is in no way "aggressive" turning. Yet still, the results show conclusively that from 10 m/s (22 mph) to 20 m/s (45 mph) to 50 m/s (112 mph) to initiate the same lean angle requires both more effort and more time. This is due to the gyroscopic effects that must be overcome in order to turn the front wheel and to lean both front and rear wheels, as well as the spinning engine into and out of the turn. What do you think? Pretty much agrees with that equation I keep posting doesn't it? You might also note that the intent of the study was to evaluate and compare two entirely different analysis programs. The results of the two programs in analyzing the behavior of an RSV Mille agreed exceptionally well. That is a very good indication of the validity of the results. I agree with Dyna; the internet is amazing. Blake PS: I come up with about 4 Kg-m2 for the inertia of a front wheel assembly and about 6 Kg-m2 for the rear. At a speed of 112 mph (50 m/s) the torque needed to cause both to precess at a roll rate of 90o/s is over 100 FT-LB, that is only for the wheels, nothing else. Note that the peak roll rate in the study mentioned above is approximately 15o/s for the constant radius case. Peak torque is approximately 20 N-m (15 FT-LB). | ||
| S320002 |
Excellent post Blake. Although I would describe it as "gyroscopic resistance to steering". A roll rate of 90 deg/sec is reasonable for a pro in a quick transition corner although few of us are likely to flick it that fast. Generating 100 FT-LB of with a pair of clip ons would indeed require some effort although I wouldn't go so far as to compare it to welded steering bearings. Well done. Greg | ||
| Blake |
Greg, You know, I thought the same thing about the 90 degree per second roll rate being extreme, but after reviewing the simulation results from the Italian study, and after replaying portions of last year's moto road races in my head, and after realizing that the bike needs to accelerate to peak roll rate then decelerate back to zero, I wouldn't be surprised at all if peak roll rate is more in the realm of 180 deg/s. The effect of the bearings "feeling" like they are seized comes when you NEED to turn faster but cannot marshal the effort to do so. It's as much of a psychological effect as reality. Next time you are cruising down an open divided highway, try slaloming back and forth across the dashed line as quickly as possible. You may see what I'm talking about. I put in over 600 miles lapping the local track this past year, the gyro effect was very evident. You are right though, in everyday riding, it's not a big deal. | ||
| Bomber |
good resource for this kind of data is the following "How & WHy of Motorcycle Design and Technology" by Gaetano Cocco, ISBN 88-7911-189-2, www. giorgionadaeditore.it | ||
| Davegess |
Reading all these numbers you begin to see why, although most MC races are small people they crush you fingers when you shake hands. You gotta be bretty strong to make a bike change directions at 100 plus mph. |
