Gyroscopic effects
in [Motorcycles]
|
From: S'mee on 9 Jul 2010 11:15 On Jul 9, 6:13 am, "?" <breoganmacbr...(a)yahoo.com> wrote: > On Jul 9, 2:10 am, CindiK <cindi.k...(a)gmail.com> wrote: > > > I know the angular momentum of the driveshaft in shaft-driven bikes > > makes it impossible for them to wheelie. > > Anything that small in diameter has *no* significant angular momentum. And on cue Krusty the kiddie loveing kook chims in with his utter lack of knowledge.
From: S'mee on 9 Jul 2010 11:17 On Jul 9, 5:20 am, "Snag" <snag_...(a)comcast.net> wrote: > sean_q_ wrote: > > S'mee brought this up in another topic, but since > > it's likely to get buried there I thought it deserved > > a thread of its own. > > > Of course as a spinning object a motorcycle wheel is > > subject to gyroscopic effects. The question is, how much, > > and are they significant? > > > I can think of two gyro effects to consider: > > > (A) Because a bike leans in a turn, its wheels rotate > > (or pivot) about a horizontal axis through the contact patch. > > > (B) In a curve, the wheels also rotate about an axis > > vertical to the road surface. If you enter a turn northbound > > and come out heading east, both your wheels have been rotated > > 90 degrees to the right. > > > I'm pretty sure everyone here has at one time or another held > > a spinning toy gyroscope in their hand, given it a sudden > > twist and felt the "strange" reactive force. However, > > on a moving motorcycle changes don't happen that abruptly. > > The faster the bike (ie, the higher the rotational inertia > > of the wheels, which means the higher the potential for > > gyro effects), the more gradual the turns. > > > Well I don't have any metrics. My guess is that type (A) isn't > > all that significant, especially for me. My chicken strips are > > probably as pristine as the day the tire was made (I ride for > > pleasure, not because I've something to prove). > > > Type (B) causes a precessional torque on the wheel through > > a horizontal axis tending to force it back to the vertical. > > This can be demonstrated using the Right-Hand Rule > > on a left hand turn (the easiest case because all rotations > > are clockwise): > > > Point your right index finger away from you (the direction > > of travel) with your thumb pointing straight up. Your 2nd > > (long) finger points to the left, representing the axle(s), > > the axis of wheel spin. The Observer's POV is the place > > on your palm where these 3 fingers "meet". > > > The Observer (a fictional construct for purposes of clarity) > > looks along your long finger and sees the wheel spinning > > clockwise. Then he looks upwards along your thumb and sees > > the wheel *turning* clockwise. Ie, to the left from > > the rider's POV. According the Right-Hand Rule, > > the precessional gyroscopic torque acts on the wheel to rotate > > it clockwise about the axis represented by your index finger, > > resisting the force acting to lean the wheel over to the left. > > Steer to the right and the same gyro effect resists -- not > > the lean itself, but the rotation into leaning that direction > > as well. > > > BTW I just did a quick test and verified the above, using > > the handiest "gyroscope" I could lay hands on -- in this case > > an electric fan (it's been a hot day here). > > > Again, is this effect strong enough to be significant? > > I don't know. If anyone does I'd appreciate them > > commenting on it. > > > SQ > > Gyroscopic precession is what makes countersteering work . Those forces are > significant enough to make a bike that weighs several hundred pounds lean > into a turn ... heh, didn't i mention that elsewhere? > Got Guns ? Yep and I oil them with both sythetic AND dino AND mineral oils. -- Keith
From: sean_q_ on 9 Jul 2010 11:59 Further to my last: > I can think of two gyro effects to consider: > > (A) ... > > (B) ... Oops, I overlooked the obvious: (C) Turning of the wheel around the steering axis. Similar to (B) except at an angle to the vertical. To demonstrate this, use the same right hand configuration except tilt your thumb towards you to represent the steering rake angle. The long finger is still horizontal, but the index finger now points at an angle upwards. A left turn is initiated by a countersteer to the right, meaning, from the Observer's POV, a counterclockwise torque from the handlebars around the thumb axis. The resulting precessional torque is counterclockwise around your index finger, trying to force a lean to the left. This contributes to the countersteering effect but is not solely responsible as other forces act as well. Thanks for Mark Olsen for this link which describes the action clearly: > http://en.wikipedia.org/wiki/Countersteering#Gyroscopic_effects SQ
From: sean_q_ on 9 Jul 2010 12:01 sean_q_ wrote: > Thanks for Mark Olsen Oops, my bad - it's "Mark Olson" SQ
From: sean_q_ on 9 Jul 2010 12:13
Mark Olson wrote: > http://en.wikipedia.org/wiki/Countersteering#Gyroscopic_effects Thanks for the link. It seems to be accurate and clearly written. ps. Thanks also to all contributors in this and the "Paradox" thread. To those whose views disagree with each other: You can't both be right... but you can both he wrong! Heh heh. ;-) SQ |