Gyroscopic effects
in [Motorcycles]
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From: Snag on 9 Jul 2010 07:20 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 ... -- Snag Got Guns ?
From: Mark Olson on 9 Jul 2010 07:51 Snag wrote: > 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 ... Gyroscopic forces are significant in motorcycle wheels. And they contribute to countersteering. But they are NOT *primarily* why countersteering works. There have been plenty of peer-reviewed papers on how motorcycles steer. The phenomenon is well understood by academics who have studied it and almost unknown to the vast majority of riders. http://en.wikipedia.org/wiki/Countersteering#Gyroscopic_effects
From: ? on 9 Jul 2010 08:11 On Jul 9, 4:51 am, Mark Olson <ols...(a)tiny.invalid> wrote: > Gyroscopic forces are significant in motorcycle wheels. And they contribute > to countersteering. But they are NOT *primarily* why countersteering works. Gyroscopic forces work in *exactly* the same planes as rake and trail work in, but the forces aren't significant at the speed you ride at on the street or at legal highway speed. Even at 120 mph, the front wheel is only turning around 1600 rpm and, since modern wheels and tires are so light, there just isn't much flywheel effect. OTOH, the atttitude gyros I tested had tiny flywheels turning 100,000 rpm, and if I moved an unplugged gyro from one bench to another while it was spinning down, I had to be careful not to change its orientation so fast that the gimbals hit their stops. I had one gyro jump right out of my hands...
From: ? on 9 Jul 2010 08:13 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.
From: tomorrow on 9 Jul 2010 08:40
On Jul 9, 7:18 am, "Snag" <snag_...(a)comcast.net> wrote: > CindiK wrote: > > On Jul 8, 10:26 pm, sean_q_ <nos...(a)no.spam> 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 > > > I know the angular momentum of the driveshaft in shaft-driven bikes > > makes it impossible for them to wheelie. > > Bullshit Yes, but it is vintage, classic, succinct, and comfortingly familiar reeky traditional bullshit! |