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Out of phase electric bike

Out of phase power delivery balances human input
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Conventional electric-assist bikes have motors that power the bicycle chain via a sprocket. The rider pedals as normal, but the motor supplements the power by turning.

The problem is that while the motor runs with a constant power output, the rider's legs do not. The rider pushes down, developing more power on each down stroke than when the feet are at the apex and nadir.

As a result, the drive power is not stable. It feels like you are cycling downhill or with a tail-wind, but (wo)man and machine are not working as one.

I suggest that instead, the motor should drive the chain via a pair of eliptical gears, each at 120 degrees leading and lagging the footpedals. There would be three phases of drive force per pedal cycle: two electrical, one human.

In the same way that three phase electricity generates a (nearly) smooth power output in industrial motors, this drive mechanism will deliver easy and complementary power.

FloridaManatee, Mar 11 2004


       I remember some bicycles had an elliptical chainwheel for the rider. Didn't catch on. The electrical way of doing this is to regulate the speed of the motor :)
Ling, Mar 11 2004

       Since your bike is electric anyway put a torque sensor on the hub or a strain sensor on the chain. Then use that signal to control the torque of the motor. Saves weight and complexity. (There is still complexity in the electronics but you buy that as a chip).
kbecker, Mar 11 2004

       /(wo)man and machine become one./   

       Wire the batteries directly into the cyclists leg muscles.
Mungo, Mar 11 2004

       Why not put a set of toe clips on the pedals or a set of clipless pedals, and learn how to spin? As one leg pushes down, you pull up with the other.
bicyclerider4life, Dec 24 2005

       I think the point is that even if you learn the pull-while-pushing technique, you still generate much more torque while your feet are moving vertically than you do at the top/bottom of the stroke. It would be at that point that the electrical assist would be most appreciated, especially when going up a steep hill. (+)
gardnertoo, Feb 03 2007

       A pedaling person will generate two power pulses per revolution, seperated by 180 degrees. This holds regardless of if the person is using one leg at a time or two (pulling while pushing). Motor supplimental power could be applied in two pulses per revolution at 90 degrees from the human powered input, resulting in a 4 phase system, 2 human, 2 electrical.   

       In this simple form the motor cannot put in more power than the human. If it did then the two phases powered by the motor would make the drive power 'unstable' again. This makes it difficult to provide large amounts of supplimentary power.   

       A more sophisticated system would target a constant power output, monitor the human generated input power and subtract that amount of power from the motor output, resulting in consistent, smooth output power supplimented by the human.
codesuidae, Feb 07 2007

       On modern bicycles with elliptical chainrings, the drive is designed to draw maximum power from the rider on the up/down stroke, and to give their legs a brief rest at the top/bottom. My applying a motor-assist to this part of the cycle, you shorten this rest and could conceivably add to the fatigue of the cyclist.   

       Perhaps as an alternative, you could drive the system *in phase* with the cyclist. They'd get the same rests, and you'd be able to apply the benefits of the research into non-circular chainrings, but the cyclist would feel superhuman. Kinda like that exoskeleton freight loader in Aliens...
Defiler, Feb 07 2007

       At the bike dealer or at a central location, place a very adjustable stationary bike. Potential customer rides bike after getting seat pedals and handlebars just the way he likes them.   

       During each customers ride, the special bike tries various levels of timing and assistance. Customer votes on each offering and eventually leaves with a custom programed chip for his bike. Maybe chip/rider have the ability to make some small adjustments while in use as grade and conditions change.
popbottle, Oct 28 2014

       So humans create oscillations in torque. You want to cancel this out by having artificially oscillating electrical torque.   

       Hmm, why not have a damper? Actually, bicycles already do this. When the amplitude of torque oscillations is high and frequency low, for example climbing a hill in too high a gear, you can see the speed of the bicycle change with the angle of the cranks. This effect must happen constantly, but as the frequency goes up and the amplitude goes down it becomes progressively less noticeable. I think this is because of the damping or buffering capacity of the bicycle. A moving bicycle can actually absorb a little of the torque differential, so that the change in bicycle speed is not always directly proportional to the input torque.   

       The mechanisms behind this are multiple and compound. Apply torque to the pedals and a few things happen. The pedal axle bends a little, the crank bends a little, the whole frame flexes.. the chain will stretch a little. Then the tourque reaches the wheel where it is applied at the hub. Here, the hub may twist as the torque is applied asymmetrically. Then, the whole spoke-rim combination may deform. Lastly the wheel will revolve inside the tyre a little (or a lot, tearing off the valve stem if you're a little overenthusiastic and under-inflated). When you apply much lower torque at a different crank angle, all this flex will unwind and apply stored energy to the forward motion of the bicycle. Neat.   

       The other aspect to the damping is the flywheel. IC engines utilize flywheels to damp their own torque oscillations, by exploiting the non linear relationship between input torque and rotation rate. Bicycles constitute an interesting 2 layer momentum storage system where input torque pulses are converted to angular momentum in the wheels rotation and linear momentum in moving both the bicycle, wheels and rider forward.   

       In short, I'm not sure such fine motor control is necessary considering the buffering capacity of the system.
bs0u0155, Oct 28 2014


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