Driverless cars are already in existence. Would riderless motorbikes be a possibility?
(Continued)
Our previous answers to this question have generated a whole new mailbag of correspondence. Readers might also like to look at a feature dealing with this question (5 September 2015, p 32) 鈥� Ed
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鈥� Motorcycles and bicycles stay upright not because of the gyroscopic effect of the rotating wheels, as an earlier correspondent suggested (3 March), but due to constant steering and adjustments of body position.
The former is more important as the rider steers into a potential fall. Bike geometry can favour or hinder this. Gyroscopic effects are unimportant except possibly at very high speeds with heavy motorcycle wheels.
Tim Lewis, Landshipping, Pembrokeshire, UK
鈥� My understanding is that the gyroscopic theory has largely been discredited.
It does have a small influence on balance and rideability. But compared with the mass of the engine, transmission, frame, tank, fuel and rider, the mass of the wheels isn鈥檛 nearly enough to counter the unstable equilibrium of having the centre of mass quite high up and poised over the two points touching the road.
The insignificance of the gyroscopic effect has been demonstrated rather elegantly by David Jones and later Hugh Hunt. They mounted an extra wheel on a bicycle beside its front wheel but off the ground. This added wheel can be rotated in either direction. When spinning the same way as the front wheel, it has the same angular momentum as it.
Even when the extra wheel is spinning several times faster in the opposite direction to the bike wheels 鈥� thus more than counteracting the gyroscopic effect of both 鈥� the bike remains perfectly rideable and steerable. This is also true when riding without holding on to the handlebars for those who like to show off.
鈥淏icycles with tiny wheels that make no gyroscopic contribution are still perfectly rideable鈥�
People have also constructed bicycles with tiny wheels that make almost no gyroscopic contribution. Again, these are still perfectly rideable.
It has been explained to me 鈥� in somewhat oversimplified terms 鈥� that the main reason for a bike鈥檚 stability is that when it starts to lean to one side, the front wheel wants to turn in that direction. This causes the bike to turn that way, exerting a lateral inertial force that pushes the bike back upright.
Amusingly, many classic bike owners also ride modern performance motorcycles that have tiny wheels compared with those on their old Norton, Triumph or BSA bikes. But they simultaneously cling to the myth that scooters are less safe than their old bike because the wheels are smaller.
Sam Edge, Ringwood, Hampshire, UK
鈥� I have to contradict your correspondent who suggested that riderless motorcycles are a way off (3 March). Yamaha has a humanoid robot that can ride a standard motorcycle 鈥� and very fast, too. And Honda has created a bike that follows its dismounted rider like a faithful dog.
J. Peter Thoeming, East Ryde, New South Wales, Australia
鈥� A video of Yamaha鈥檚 Motobot racing bike versus MotoGP world champion Valentino Rossi suggests the problem is nearly solved ().
Pete Steggle, Blenheim, New Zealand, Another earlier response asked whether driverless trams are a possibility (3 March). It seems they already exist 鈥� Ed
鈥� Driverless trams are a distinct possibility because the rails avoid the need for steering, and automatic points manage the route where it joins and separates from others. Collision avoidance systems are already available in cars.
Problems do arise in taking on a driver鈥檚 other responsibilities, such as monitoring passenger behaviour, allowing extra time for those who board very slowly or ensuring people don鈥檛 get jammed in closing doors.
Prospective passengers would need to press a button to stop and board the tram, but might need a password to obviate mischievous operation causing delays.
It is all possible, of course, but doubtless someone would find a method of upsetting the system in a way that a diligent human driver could avoid.
Peter Peters, Sherborne, Dorset, UK
鈥� Driverless trams already exist. A number of airports, including Chicago O鈥橦are and London Gatwick, use driverless shuttles to transport passengers between terminals. These are on reserved tracks, so there is no danger from other users, but it is a start.
David Clarke, Seaford, East Sussex, UK
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