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 Motorcycle Safety
 Physics and the theoretical
 Virtual gyroscopic gamera and measured proof that leaning causes turning
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JanK
Male Junior Member
85 Posts


Ljubljana, Ljubljana
Slovenia

BMW

R1200R

Posted - 07/23/2018 :  9:10 AM                       Like
When a video camera is rigidly mounted on a motorcycle, the camera rolls with the motorcycle frame in corners. In the resulting videos the horizon tilts to the opposite side. In 2010 a self-leveling gyroscopic camera was introduced on MotoGP motorcycles. Through the use of gyroscopes, accelerometers, GPS receiver and a servo motor, the camera is kept level in real-time, providing a more dynamic view of the race.

When I saw this, I had an idea to simulate it in software. I invite you to check out the videos at https://www.youtube.com/playlist?li...VjjESf0efpMN where the results are demonstrated. The sensor data is recorded separately from the video and, during post-processing, the video and the sensor data are combined to duplicate the effect of the gyroscopic camera.

Since the data is available for the entire duration of the video, one can add features not possible with the physical gyroscopic camera, such as drawing the projected path of the motorcycle and simulating the effect of blurry peripheral vision.

I imagined that such videos could be useful not only for "dramatic MotoGP-like videos" and for analysing racing lines, but also for safety purposes. E.g., a student could be riding in front of an instructor and the deviation from the instructor's (presumably impeccable) line clearly seen on the video. Alas there has not been much interest and the whole project will be documented in an article to be published this fall.

Incidentally, the snippet between 10s and 16s in the video https://youtu.be/R3h9q0udjPo provides proof of what some of us (and physics) have been saying for some time now: leaning precedes turning, since a lean is necessary to generate centripetal force needed to curve the path into a circle. Thus leaning causes turning.

The vertical line indicates the path of the motorcycle. The top end follows the path of the camera, whose height was very close to the height of the COG of the motorcycle+rider. The bottom end follows the path of the intersection of the ground with the vertical line through the camera. So a line tilting to the left or to the right means that the motorcycle leans to the left or to the right, while the movement of the top of the line indicates the actual path of the COG of the motorcycle.

On the 8-times slowed down snippet of this video, https://youtu.be/HhGTrHvsFDA, it can clearly be seen that, at the start of the turn, at around 0:17, the bottom end of the line moves to the outside while the top end of the line continues without changing direction.

If you watch the top end closely, you can see that it points to a point just to the right and down of the red arrow sign and that it does so from 0:12 to around 0:21. By that time the motorcycle has leaned appreciably to the left.

This lean generates centripetal force, which then starts to change the direction of travel of the COG and initiates the turn. It is only then that the top end starts to veer towards the left.

If the leaning was caused by turning, the bottom end would never cross to the outside, since COG would start moving to the left before the motorcycle leaned. This clearly isn't happening in the video.

James R. Davis
Male Administrator
17321 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 07/23/2018 :  10:02 AM Follow poster on Twitter  Join poster on Facebook as Friend  
I appreciate the effort and technical skills you have put into this, but I'm dismayed that you would ruin it all with your junk science claim that leaning causes centripetal force. It does not.

When you put your bike on its side stand, which direction does your front tire point? That, friend, is simple geometry and gravity, not centripetal force.

Nevertheless, a bike can be turned with leaning - though slowly and without much precision. A simple application of mere ounces of forward pressure on a hand grip (countersteering), however, results in substantial speed and precision of turning in the opposite direction. Surely you are not trying to suggest that is a lean maneuver? The RESULTING lean comes from the forces generated by changing the direction of the front tire which THEN develops a lean as you suggest.
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JanK
Male Junior Member
85 Posts


Ljubljana, Ljubljana
Slovenia

BMW

R1200R

Posted - 07/23/2018 :  2:31 PM
I should have been more precise. By lean I mean roll angle, as defined by the upper picture in https://imgur.com/a/NUtcBvv.

Note the formula for the $F_s = mg \tan \varphi$. When $\varphi$ is 0, there is no transverse force and no turning. Turning does not magically change $\varphi$, instead the change in $\varphi$ causes the force $F_s$ - the centripetal force.

And yes, countersteering pressure - on the left handlebar in the turn shown in the video - provides the force needed for the front wheel to turn to the right, thereby rolling the motorcycle body around the COG to the left and providing the $F_s$ needed to get the motorcycle to go left.

Finally, the motorcycle itself, i.e., the body or the chassis does not need to be rolled at all for a turn to occur. It is enough for the combined roll angle to be non-zero. Looking at the figure (c) in the lower picture in https://imgur.com/a/NUtcBvv, if the $\varphi_i$ were the same as $\Delta\alpha$, the body roll angle would be 0 - the motorcycle would be vertical, but the "dynamic" angle would be $\Delta\alpha$ and the motorcycle would turn.
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James R. Davis
Male Administrator
17321 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 07/23/2018 :  2:46 PM Follow poster on Twitter  Join poster on Facebook as Friend  
Nice try.

You'll note that even in the graphic you referenced, the roll angle is the result of the bike ALREADY traveling in a curve. i.e., The chicken came before the egg.

In any event, had the bike been traveling in a straight line while leaned over, it would have fallen down as there would be NO centrifugal/centripetal force, though, as I said before, the geometry of the bike and gravity would have caused it to begin turning to the left on its way to the ground. (Said differently, if the handlebars were locked with the wheel pointed straight ahead, it would have simply fallen without any tendency to turn at all.)

Now it's possible that you will reply that my example is not fair because unless the steering column (that is the ability to change the direction the front wheel is pointing) is allowed, then turning can't happen no matter what you did. I almost agree with that and so, I'll give you a hint at another counter-argument you can use: if the width of the front tire is less than that of the rear tire, then leaning DOES cause a TRIVIAL change of direction from a lean. Do you want to go there next?

But let's get back to basic physics, shall we? You seem to be claiming that centripetal force causes a change of direction. Wrong. It causes the lean angle. Torque is what you need. Specifically, turning the steering stem.
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JanK
Male Junior Member
85 Posts


Ljubljana, Ljubljana
Slovenia

BMW

R1200R

Posted - 07/23/2018 :  4:26 PM
Yes, basic physics would be a good place to start :) Then we may see exactly where our view of the world diverges :)

To have any body in a uniform circular motion, you need two things: a constant tangential speed and a constant acceleration perpendicular to velocity.

Remove the acceleration, otherwise known as the centripetal force, and the body flies off on a tangent.

For this basic picture it is completely irrelevant which body we're talking about and how precisely the centripetal force is generated.

Do we agree on these statements?
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Eagle Six
Starting Member
8 Posts


Snowflake, Arizona
USA

Kawasaki

ZX14R

Posted - 07/23/2018 :  4:52 PM
Hi Jan,

Quite the project you have there and Thank You for the invite. I can appreciate the time and effort you put into it. I'm new to this forum and this may not be the best place to start, but I would like to comment on a part of your project that has yet to be responded to. With that said, I wish that you will receive these comments as constructive.


quote:
Originally posted by JanK
....I imagined that such videos could be useful not only for "dramatic MotoGP-like videos" and for analysing racing lines, but also for safety purposes. E.g., a student could be riding in front of an instructor and the deviation from the instructor's (presumably impeccable) line clearly seen on the video. Alas there has not been much interest


For myself, I understand why there has been only little interest. Your video system appears to be overly complex and simply points out what is already there and easy for instructors and students to understand without the graphics and speed displays. Actually, I feel these interfere with the visual and clutter up what is obvious.

In my experience there is benefit for students to see and review both perspective, the horizon held to the frame, or allowed to float dependent on lean angle. I use them both effectively.


quote:
Originally posted by JanK

....the camera is kept level in real-time, providing a more dynamic view of the race.


Actually I feel this is a less dynamic view, however the purpose is more for the audience pleasure of viewing these televised events, saving them the sea sick syndrome.

For students, neither a camera mounted rigid (no roll), or on a pendulum mount (horizon stays level with the viewing frame are the best, or close to what they should be seeing in turns. The best view (perspective perhaps) comes from an action cam mounted to a riders helmet. When we are aggressive in the turns and get leaned passed perhaps 15 degrees, we should be tilting our head attempting to keep our vision level with the horizon. As we lean much further, say maybe 50+ degrees, it is getting difficult to tilt (cock) our head to keep our vision level, so we see some tilt, but not as bad as when the camera is prohibited from rolling.

If we video what our students shouldn't see, we are not doing them a favor. So, I think some tilt of the horizon to the frame is realistic. I see the value in using all three, rigid mount (to show the extreme lean angle effect), pendulum mount (to increase the viewing pleasure) and helmet mount, which is the closet to reality that the student should also see providing of course the instructor shooting the video is using proper techniques.


quote:
Originally posted by JanK
....simulate the effect of blurry peripheral vision.


I think this is a poor simulation at best and of little to no value. If I have blurred vision I shouldn't be out riding. Any off-vision effect in our peripheral is caused (or effected) by the motion (dependent on our speed and proximity) to the objects in our peripheral vision sector. Maybe I'm way wrong on this, but the blur effect you put in your sample just doesn't represent anything I see when riding.

This is my opinion Jan, others of course will agree or disagree. I'm neither an authority on riding, on instructing, or making training videos. I've just been around for a while, dabble in all these, but just thought I would respond as you sent out the invite.

Best Regards......George
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James R. Davis
Male Administrator
17321 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 07/23/2018 :  5:13 PM Follow poster on Twitter  Join poster on Facebook as Friend  


JanK,

I've challenged some of your assertions and made some of my own. You've elected to ignore mine and now attempt a new direction - to what end is unclear.

In any event, I don't play like that.

Thanks for your participation and contributions.
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scottrnelson
Advanced Member
6912 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 1090 Adv R

Posted - 07/24/2018 :  7:02 AM
The slow motion video at least shows "out tracking". Where the wheel has to go in the other direction a little bit before the bike leans. I think it was Orville Wright (maybe Wilbur?) who first wrote about that when they were making bicycles before they started flying.

People today tend to focus on counter steering and "push right to go right", but if you think of it in terms of out tracking, it's consistent at all speeds, even super slow, while counter steering isn't. That's how I've always thought of it for both bicycles and motorcycles.
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