£2,000 toy fund - but what to spend it on ?

[jackhandy]

Yeah, Right!

 

[Storcker]

If you put a watt-meter on a hub-motored electric bike, you'll find that power consumption goes up as rpm goes down, such that maximum power consumption is at zero rpm. The same happens to torque, so you get maximum torque at zero rpm; however, maximum power occurs somewhere on the range between half an 3/4 maximum rpm - don't get torque and power mixed up. Torque is the amount of force that will pull you up a hill; power determines how fast you go up the hill. You can have a massively powerful motor that can't get you up a hill because it has insufficient torque.

My original claim is that with all motors restricted to a legal output of 250 watts it is possible to have a direct drive hub motor produce that amount of power from the slowest riding speed possible, for arguments sake 5 mph. As any crank drive bike is also legally restricted to that same output the motor regardless of gearing to the back wheel will produce no better hill climbing ability.
As the maximum power allowed is 250 watts, approx one third of a horsepower, then a crank drive bike only has the same power available to climb hills as long as the hub drive motor produces 250 watts at a low riding speed. 250 watts is 250 watts regardless of any gearing on a crank drive bike. It is possible to have a motor produce an output of 250 watts from very low revolutions yet the controller restrict the power output to 250 watts as the revs rise.
As I understand it all brushless motors use an alternating current, unlike brush motors, giving far more control over the output of the motor via the electronic controller. What you describe is just connecting a motor to a battery with no controller and in that situation maximum power will indeed be at fairly high revs as the motor is not under control. There are many electric motors used in machine tools that require huge power from zero revs to start a heavy but varying load moving and to accelerate it but be kept under control as loads vary. i can see no reason why the same cannot be done on an Ebike.
Some seem to be under the impression that my belief that hub drive can be just as good hill climbers as crank drive is due to me having a Storck or that I am saying my Storck can climb as well or better than some crank drive bike, I do not believe that but nor do I believe having a few gears between the motor and the wheel make a bike a good hill climber.

 

[Deleted member 4366]

I think you're still getting torque and power mixed up. Power is the rate at which you apply torque. It's torque that provides the force which drags you up a hill. You can drive an electric bike up a vertical hill with a 1w motor, but it won't be very fast. You can also have a 10kw motor that can't get you up a 5% slope because it doesn't have enough torque.

You could have a 250w direct drive motor that can pull you up a steep hill from a standing start, but I've never seen one on an ebike yet, although some of the new ones are getting better. The designers are always trying to balance size, weight, torque, power and efficiency, but everybody has different requirements. The Storck Raddar's not bad for a light person or someone a bit heavier that can pedal hard, but no good for an over-weight, aged, lazy, undiscerning normal person like me. I need a high-torque motor.

 

[flecc]

My original claim is that with all motors restricted to a legal output of 250 watts it is possible to have a direct drive hub motor produce that amount of power from the slowest riding speed possible, for arguments sake 5 mph. As any crank drive bike is also legally restricted to that same output the motor regardless of gearing to the back wheel will produce no better hill climbing ability - - - - - - - - - -nor do I believe having a few gears between the motor and the wheel make a bike a good hill climber.

Our e-bikes never have only 250 watts available, they would be useless if that were so. The 250 watt limit is a legal nicety that isn't strictly observed in practice. Those currently on the market mostly have in the region of 350 to 550 watts of net power available, hub motors typically more powerful than crank drives which have the benefit of driving though the gears.

And your statement on gearing the motor drive is simply wrong, why do you think cars have gears? Suitable gearing enables a motor to run at it's optimum torque/power combination point up any gradient at a speed that the gradient/power combination permits. A fixed gear hub motor can only have that torque/power ideal at one road speed, so if a hill gradient is too much for that combination, climb failure is assured.
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