Gyroscopic effects
in [Motorcycles]
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From: sean_q_ on 8 Jul 2010 23:26 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
From: ? on 8 Jul 2010 23:57 On Jul 8, 8:26 pm, sean_q_ <nos...(a)no.spam> wrote: > Again, is this effect strong enough to be significant? Yawn. Here we go again with FAQ about whether a motorcycle wheel acts like a gyroscope... No, because the wheels aren't turning fast enough to have much angular momentum and the tire contact patch is causing moments that are far stronger. You'll only notice the forces of precession if the wheels are off the ground and you don't ride that way 99 and 44/100% of the time. > I don't know. If anyone does I'd appreciate them > commenting on it. Look up "flywheel" on Wikipedia, I think the formula for calculating angular momentum is in that article. I once worked as a gyroscope technician, doing quality control tests on attitude and directional gyros for aircraft use.
From: S'mee on 9 Jul 2010 00:48 On Jul 8, 9:57 pm, "?" <breoganmacbr...(a)yahoo.com> wrote: > On Jul 8, 8:26 pm, sean_q_ <nos...(a)no.spam> wrote: > > > Again, is this effect strong enough to be significant? > > Yawn. Here we go again with FAQ about whether a motorcycle wheel acts > like a gyroscope... > > No, because the wheels aren't turning fast enough to have much angular > momentum and the tire contact patch is causing moments that are far > stronger. > > You'll only notice the forces of precession if the wheels are off the > ground and you don't ride that way 99 and 44/100% of the time. > > > I don't know. If anyone does I'd appreciate them > > commenting on it. > > Look up "flywheel" on Wikipedia, I think the formula for calculating > angular momentum is in that article. > > I once worked as a gyroscope technician, doing quality control tests > on attitude and directional gyros for aircraft use. Liar.
From: CindiK on 9 Jul 2010 05:10 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.
From: Snag on 9 Jul 2010 07:18
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 -- Snag Got Guns ? |