Quote:
Originally Posted by aschen
A minor interjection then I can let it die, I promise.
If the weight is at 5 o'clock it still exerts a 20N force. It just does not create as much torque on the wheel, which is the important aspect here. Only a component of the force is orthogonal to the wheel so less torque is created on the wheel and less power will be required of the device to keep it steady.
You can imagine in our example of coasting along at 6 oclock, the device creates no torque and would require no force to keep in place (with the hypothetical frictionless conditions).
This follows intuition as if you made a completely dumb and passive device to ride in the wheel on rollers it would "want" to stay at the bottom. IT would require more and more torque to have it advance along the wheel, until it maxed out at 3 oclock
sorry, I like to think about this sort of stuff
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I think it is interesting too. Bike races are won by small differences in the power of the engines (riders) and those engines are already very weak, so hidden motors don't have to produce much power to make a difference.
For example, the rider with the fastest time up Alpe d'Huez in the 2015 Tour de France pedaled at 340 watts for 40 minutes, ascending a 8% grade at 21 km/h. He lost the Tour overall victory by 1m30s. If he'd had sometime like 30 watts more, he'd have won. Or something like 15 watts more on that stage and a couple of the earlier stages. Or about 30 watts more on an early stage where he lost 1m30s in crosswinds.
At 11 m/s (25 mph), to get 30 watts from this concept would only require a 0.27 kg weight. Right? 0.27 kg x 10 m/s^2 = 2.7 N. 2.7 N x 11 m/s = 29.7 watts. So, about a tenth of the 2 kg weight we've been talking about. And a tenth of the battery.
Modern carbon bike wheels are pretty deep, there is some volume to work with in there.
Racers are followed by team cars carrying spare wheels and bikes. Changing wheels (for flat tires) is common, changing bikes is increasingly so. A racer doesn't necessarily start the day's race on the same bike or wheels that he finishes on.
The UCI (sports governing body) is using magnetic field sensors to screen bikes for motors, because (I think) the existing seattube motors contain permanent magnets, and then confirming by removing seatposts and bottom brackets to look inside the frame.
They have bought xray machines to some races, but those are not mobile and I don't think they are used that much. At each race there are say 200 riders and 400 bikes and 600 wheels strewn over 160 km of public roads, busy start and finish areas, team cars and trucks and buses. Impractical to physically impound all that equipment and run it through an xray and be assured the wheel used in the race is the same as the wheel that was xrayed.
A hidden motor that does not use permanent magnets, and is concealed in a component or a part of the frame that cannot be non-destructively opened, and that looks identical to current race bikes, would be hard to detect using the sport's current screening methods.