Any Advantage?

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classic33

Leg End Member
To having motors in both wheels on a bike?

Only the one battery is a clear disadvantage I can think of.
 
To having motors in both wheels on a bike?

Only the one battery is a clear disadvantage I can think of.
You can switch between effectively front wheel drive and rear wheel drive depending on conditions / circumstances to get the optimal assistance to handling characteristics, dynamically.
 
D

Deleted member 26715

Guest
Getting them to run at exactly the same rpm would be interesting, taking into account different tyre pressures
 

Oldfentiger

Veteran
Location
Pendle, Lancs
Getting them to run at exactly the same rpm would be interesting, taking into account different tyre pressures
If each motor is provided with the same watts, then the rpm of each motor will be automatically compensated resulting in the same linear effort from each wheel.

Power equation P = nt/9550
P in watts
n is rpm
t is torque (Nm)

Any difference in wheel or tyre diameter is accommodated in the Newton Metres of torque.
 
D

Deleted member 26715

Guest
If each motor is provided with the same watts, then the rpm of each motor will be automatically compensated resulting in the same linear effort from each wheel.

Power equation P = nt/9550
P in watts
n is rpm
t is torque (Nm)

Any difference in wheel or tyre diameter is accommodated in the Newton Metres of torque.
Too clever for me, try dumbing it down, in my simple mind, you can put the same power in, but depending on the different forces within the motor (friction) &/or drivetrain, then taking into account that the rolling diameter of the wheels may not be exactly the same how do you ensure that both wheels turn at the speed they need to. Along with the fact that when the front wheel is turned (to go around a corner) then the longitudinal speed of each wheel will be different.
 

Oldfentiger

Veteran
Location
Pendle, Lancs
Too clever for me, try dumbing it down, in my simple mind, you can put the same power in, but depending on the different forces within the motor (friction) &/or drivetrain, then taking into account that the rolling diameter of the wheels may not be exactly the same how do you ensure that both wheels turn at the speed they need to. Along with the fact that when the front wheel is turned (to go around a corner) then the longitudinal speed of each wheel will be different.
Don't worry, I have a simple mind too :smile:
The wheels are not connected mechanically, so they are free to rotate at whatever speed they need to. If you have the same power (watts) being supplied to both, then the motors will produce the same effort.
As the speed is governed by the power equation, the speed and torque is free to vary provided it satisfies the equation.
Put simply, if the rpm increases, then necessarily the torque reduces, and vice versa.
So, if you have one large wheel and one small wheel, the larger wheel will rotate slower but will require more torque. Smaller wheel faster but less torque.

Here's a scenario:
Two people riding a tandem up a hill.
Each person is capable of exactly the same power output.
Captain is driving the front wheel, stoker is driving the back wheel.
Front wheel is smaller than the back wheel.
Captain pedals faster than stoker.
Captain is spinning, stoker is grinding, but they both put out the same power.
Dunno if that helps?

As an aside, I presume that the power is legally limited to 250 watts?
If this is true, then you can only have 250 watts shared between the two motors, so a single battery should give similar performance whether one 250W motor or two 125W motors. Slight variance as larger motors are more efficient than smaller motors.
 

numbnuts

Legendary Member
:hyper: Three wheel drive :hyper:
 

T4tomo

Guru
Don't worry, I have a simple mind too :smile:
The wheels are not connected mechanically, so they are free to rotate at whatever speed they need to. If you have the same power (watts) being supplied to both, then the motors will produce the same effort.
As the speed is governed by the power equation, the speed and torque is free to vary provided it satisfies the equation.
Put simply, if the rpm increases, then necessarily the torque reduces, and vice versa.
So, if you have one large wheel and one small wheel, the larger wheel will rotate slower but will require more torque. Smaller wheel faster but less torque.

Here's a scenario:
Two people riding a tandem up a hill.
Each person is capable of exactly the same power output.
Captain is driving the front wheel, stoker is driving the back wheel.
Front wheel is smaller than the back wheel.
Captain pedals faster than stoker.
Captain is spinning, stoker is grinding, but they both put out the same power.
Dunno if that helps?

As an aside, I presume that the power is legally limited to 250 watts?
If this is true, then you can only have 250 watts shared between the two motors, so a single battery should give similar performance whether one 250W motor or two 125W motors. Slight variance as larger motors are more efficient than smaller motors.
Strange tandem you're imagining there!
 
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