ok, maybe I should not have said "impossible to ride", but if you take a normal bike and give it a shove it will go pretty far before it falls over
if you give the bike in that photo the same shove, it wont get far.
Ive seen it demonstrated on some TV/PBS/Science channel program a while back.
A human learns to balance a bike with little flywheel action (super light tires and wheels) - but on a riderless bike the gyro effect makes a real difference.
either way, the important point for the bots is that two flywheels spinning the same speed in opposite directions do cancel each other out.
edit: ok, I checked some of Joes "here" links. I think maybe we are saying the same thing different ways.
The gyroscopic effect is not what keeps a bike from falling over while its being ridden, I agree with that. The way the front fork is angled and the patch of the wheel being infront of the center line of the fork - yes, that makes the front wheel want to stay straight, and it moves the contact patch under the bike as you lean left and right
but the gryo precession does make the front wheel turn left and right as the bike leans. The author of the first 'here' link at first dismisses this, but towards the bottom of the post he asserts it is a factor when riding hands-free:
Quote:
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if the rider lets go of the handlebars, the front wheel is free to precess about the approximately vertical steering axis. By following the right-hand rule, we see that as the bicycle leans to the right the front wheel precesses to the right, and as it leans to the left it precesses to the left. This is precisely the correct direction, but not necessarily the right amount, to help keep the bicycle upright.
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BTW, this all becomes very important when bike riders try to ride a full sized motorcycle. Because of the mass of the wheels, at high speed if you turn the handlebars to the right, the motorcycle will lean left, and go left. Many new motorcycle riders learn this the hard way, going off the road at the first high speed curve they encounter on their new motorcycle (myself included!)
The obvious way to see how much the gyro effect helps to keep a bike upright? Turn it upside down, then push it over, and see how fast it falls down. Then stand it upsidedown again, spin the back wheel up to speed, and push the bike over and see if it falls down at the same speed. (stand back when you do this! :^)