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galileo
Ex-Member
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 Posted - 09/19/2009 : 11:52 AM
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quote:
Originally posted by James R. Davis
This has come up many times on the site and the logic of it seems to escape even the most technically savvy readers.
Of course you don't feel lateral forces other than trivial ones resulting from putting your body in a posture that is other than in-line with the bike. In a turn your bike is leaned over. Your lateral forces are felt as increased weight - in-line with the bike, not as centrifugal force trying to slide you off your seat.
That is why you need only know how much weight you gain as compared to your resting weight in order to determine those lateral forces and, as a resault, the bike's lean angle.
James,
I think the load gained would only determine the lean angle if the rider was vertical with the bike. If I lean off, the g'meter does show a horizontal g force just like it would in the car. However, it's only a function of how much I lean off relative to how much I "should" lean off.
Even an attitude indicator would only show the lean angle of the bike, and not the lean angle of the rider. The two can be considerably different.
There is an interesting thing, at least to me, that I've discovered. If I feel pressure on the inside handgrip during a curve, I'm leaning too little. If I feel it on the outside handgrip I'm leaning too much. There is a sweet spot where the pressures are neutral once the curve is established. This sweet spot makes it very easy to make a symmetrical turn. However, I always lean the same amount except lately when playing around. I have my advisory speed lean and my .51 g lean for my infinite 8's. If I have pressure on the inside hand grip I'm going a little faster. If it's on the outside grip, I'm going a little slower. When I glance down at my speedometer, it always confirms what I feel. |
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whittlebeast
 Junior Member
30 Posts
St Louis, MO
USA
Yamaha
FZ1
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Posted - 09/19/2009 : 2:11 PM
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quote:
Originally posted by galileo
.....but it seldom measures side forces anything greater than a number very close to zero in turns. The amount it's off is a function of how much I lean my body into a curve. (I don't hang off.).......
It seems the real reasons for leaning off are to keep something from dragging......
To solve the problem you have to get your head around the fact that the accelerometer is straight with the bike and not straight with the world. The 2ed issue is the thing I call hanging off can not be ignored as most people assume. Last is that you have to come up with some sort of smoothing (averaging) trick to get any sort of reasonable results. I sample at 20 samples per sec and then smooth from there.
Lets start with the assumption that the bike is cornering at one gee and that the rider is perfectly straight with the bike. If all is perfect the bike will be at 45 degrees to the world and the vertical vector will be 1.414 (happens to be the square root of 2) straight thru your butt, seat, shocks and tires and to the ground. Things get a little messy as the contact patch of the tire has move a little to the inside of the turn but lets ignore that for now and assume the tires are real narrow. All is good and easy with the calcs.....
But now lets assume the bike is still cornering at 1 gee but the bike is 90 degrees to the world and the rider is now hung way off the bike by pure tallant. What would you expect the gee meeter to read? 1 gee vertical and 1 gee horizontal as the bike is still straight up and down and so is the gee meter.
Now is when the math gets fun. Lets assume the same corner, same speed and same geez but the bike is leaned over at 30 degrees from vertical and the rider is hung off to make up the rest of the balance act. This hanging off is a little tough to measure in a photo but we can sure back into the number with a little vector math.
Think about that for a couple of days. When I get to work Monday I will post the calc of how the math all falls out to a fairly easy solution. The devil is still in the details but I can help you get thru the basics.
Regarding hard parts and leaning off:
It is my opinion that hanging off if your bike is not scraping and you still have chicken strips on the outside edges is a waist of time and effort. Once you get the the point of being able to squarely planting that last two inches of tire on the ground then any additional leaning must be done by the rider. The knee or elbow hanging out is mostly a gauge for telling when the tires last two inches are going to be square with the surface and the end of the traction circle is near. Once hard parts start dragging continue to drag them till they are no longer in the way but remember that this is a very sketchy (and dangerous) way to get them out of the way as every pound of force that the peg/exhaust/kick stand pushes down is vertical force taken away from the only two contact patches you have to work with. [This kind of advice is unwelcome on this site and will not be tolerated more than once. JRD]
Here is a pic of my FZ1 http://www.ncs-stl.com/fz1/Front3_4.JPG
Hope this helps
WB |
Edited by - whittlebeast on 09/19/2009 2:25 PM |
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galileo
Ex-Member
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Posted - 09/19/2009 : 2:52 PM
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Whittlebeast,
What I passed over is that you have a 3 axis g meter. Mine is only 2 axis. Now I understand completely and the calculation becomes straight forward.
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sporty
Senior Member
311 Posts
north liberty, ia
USA
Harley-Davidson
Dyna & Sportster
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Posted - 09/19/2009 : 7:30 PM
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Now, has anyone come to the realization that
with a 3-axis (orthogonal) accelerometer,
orientation of the sensor becomes meaningless?
Pop quiz question #1: calculate the acceleration.
-W
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DeaminRacing
Starting Member
2 Posts
Harpers Ferry, WV
USA
(Unknown - Other)
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Posted - 05/07/2010 : 10:50 PM
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quote:
[i]Anyway, what is the purpose of all your hard work in developing this instrumentation?
James, I'm somewhat embarrassed to post my purpose here as it's not quite as serious as the rest of the discussions here - however it is bike related. At the same time I'm amazed that I've been able to get this working to the point that I have in the limited free time that I have available.
I'm actually not recording the lean angle data, but instead using it to calculate a steer angle to keep the bike upright. It helps that the bike is only 1/4 scale.
Here's a link to the video if anyone is interested:
http://www.youtube.com/watch?v=GX56jMII2FU
It still needs plenty of work, and will probably never perform as well as I'd like, but it's the first project of this type that I've seen designed with such limited resources...
Dave |
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James R. Davis
Administrator
14935 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 05/07/2010 : 11:11 PM
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You will get no razing here for your efforts or discussion about it.
Actually, I applaud your efforts. You will learn a great deal about dynamics and answer a lot of questions you didn't know enough to ask before you started.
We gave a lad trouble who posted questions about his efforts to construct a machine to help teach riders how to do a stoppie or wheelie - but that was because of the objective of the 'trainer' and the fact that he thought he could train either without any way to cause weight transfer.  That is, we support educational efforts, but nothing that is antagonistic to motorcycle safety. Your effort, it seems to me, is a learning tool for yourself and involves an attempt to understand the physics or dynamics of motorcycle behavior. |
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scottrnelson
Advanced Member
5262 Posts
[Mentor]
Pleasanton, CA
USA
KTM
990 Adv, ST2, XR650L
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Posted - 05/08/2010 : 9:24 AM
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quote:
Originally posted by DeaminRacing
Here's a link to the video if anyone is interested:
http://www.youtube.com/watch?v=GX56jMII2FU
Thanks for sharing the video. It looks a little wobbly, but when I occasionally get out my Jeremy McGrath Stunt Cycle, it's wobbly too. And I'm not usually as accurate steering it as you seem to be.
I think you've brought a new meaning to the term Parking Lot Practice. |
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