Torque

[fishingpaul]

One £1800 +48v bionx powered bike is claiming to have 35n/m torque peak, with its powerfull rear mounted hill climbing hub motor,the lower priced tonaro £1100 bike is claiming to have 90n/m torque available,with its through the gears 36v motor,is this due to using contrasting and possibly missleading methods of calculations,or is one truly more than twice as powerfull than the other.

 

[tillson]

A torque figure in isolation is pretty meaningless in terms of giving an indication of power. Power (P) is the product of torque (T) multiplied by the rate at which the the motor or wheel rotates (W). The rate of rotation for this calculation is measured in radians per second and is known as the angular velocity. There are 2 x Pi radians in one revolution, so a motor shaft or wheel rotating at 1 revolution per second will have an angular velocity of 2 x Pi radians per second (Pi = 3.142) so 6.284 radians per second (W)

Taking Power (P) = torque (T) x angular velocity (W)

Therefore, Torque (T)= P/W . If (P), the motor power is fixed at say 250 Watts, by altering W, the output torque is also varied. If W is lowered (reduction gearing, slower bike) torque (T) will increase (better hill climber) And if W is increased by high gearing (fast bike) torque (T) will reduce (poor hill climbing). This is why crank drive bikes are so versatile, you can vary the W part of the equation with the bikes gears.

So, returning to your original point, torque in isolation is not any indication of the power which a motor delivers for the reasons given above.

 

[scarrabri]

A torque figure in isolation is pretty meaningless in terms of giving an indication of power. Power (P) is the product of torque (T) multiplied by the rate at which the the motor or wheel rotates (W). The rate of rotation for this calculation is measured in radians per second and is known as the angular velocity. There are 2 x Pi radians in one revolution, so a motor shaft or wheel rotating at 1 revolution per second will have an angular velocity of 2 x Pi radians per second (Pi = 3.142) so 6.284 radians per second (W)

Taking Power (P) = torque (T) x angular velocity (W)

Therefore, Torque (T)= P/W . If (P), the motor power is fixed at say 250 Watts, by altering W, the output torque is also varied. If W is lowered (reduction gearing, slower bike) torque (T) will increase (better hill climber) And if W is increased by high gearing (fast bike) torque (T) will reduce (poor hill climbing). This is why crank drive bikes are so versatile, you can vary the W part of the equation with the bikes gears.

So, returning to your original point, torque in isolation is not any indication of the power which a motor delivers for the reasons given above.

So does that make the Tonaro Bighit brilliant at climbing hills ,because mine sure gets a move on,very best wishes Brian.

 

[NRG]

Yes, you can liken hub motors to being stuck in top gear. Like driving your car in top all the time, it will drive OK on the flat and climb some moderate hills but when the hill gets too steep the motor 'bogs' down and you slow down. Now change down a gear and the gearbox multiplies the torque getting you up the hill.

 

[oigoi]

One £1800 +48v bionx powered bike is claiming to have 35n/m torque peak, with its powerfull rear mounted hill climbing hub motor,the lower priced tonaro £1100 bike is claiming to have 90n/m torque available,with its through the gears 36v motor,is this due to using contrasting and possibly missleading methods of calculations,or is one truly more than twice as powerfull than the other.

The tonaro uses the ratio of it's gears to multiply the torque available. The bionx does not have this ability. I think NRG describes it well, if the Tonaro was stuck in it's top gear it would have a similar torque to the bionx.

What someone needs to make is a hub motor that has different gear ratio's in it. I mean shimano make an 8 speed hub, so why not have something like that with the motor incorporated into it?

 

[flecc]

What someone needs to make is a hub motor that has different gear ratio's in it. I mean shimano make an 8 speed hub, so why not have something like that with the motor incorporated into it?

It wouldn't need to be so complex with an internally geared brushless Hall sensor motor in a legal e-bike, since two gears are all that's needed with the wide power band of these motors. The gears would be one like the present one with the coincidence of torque and power curves at around 10 mph, and the lower gear with that point at about 6 mph.

This would ensure strong hill climbing from 4 mph through to where the upper gear could take over at about 9 mph, giving strong acceleration potential to the legal limit. This would be best designed with the gear change automatic, immediate and totally enclosed, leaving the rider to concentrate only on the cycling aspects. Power control could be by either throttle or pressure sensor as at present.

 

[andyh2]

Yes please, when can we get one?

Would it be a really difficult thing to design and build or is it that there are really large markets where if you want more power from a hub motor you can get it without the same legal restrictions as here?

 

[flecc]

It is difficult, two possible approaches.

One is like that of the SRAM Sparc motor, having the gears and motor as separate entities, but that makes for a very large hub which will add weight as well. N.B. The Sparc does not drive through the gears.

The other is to use the existing single epicyclic reduction gearing arrangement in a typical hub motor, using it in two modes. For example, a 3 speed hub gear uses a single epicyclic, the sun gearwheel is fixed and the drive to the hub is taken from either the planetary gears mounting or the ring gear (outer rack) for the high and low gears with the input drive to the other one. The middle gear is just the chain sprocket driving the hub shell direct with the planetary gears doing nothing.

The difficult problem in a hub motor is to arrange two power take off points from the epicyclic with appropriate ratios. The hub would have to be larger to accommodate a rotating ring gear as well as the planet gears, and the auto changing mechanism.
.

 

[mike killay]

I live in Swansea which is very hilly. In practice, my Enduro needs numbers 1, 2 3 5 and 8 gear cogs.
3 is best for starting off on the flat or moderate hills. 8 for the flat or downhill and 2 for steep hills, down to 1 for very steep hills or if the battery is tired. I find that gears 4, 6 and 7 are mainly unused.

 

[trex]

Oigoi:

What someone needs to make is a hub motor that has different gear ratio's in it.

If you put a gearbox to the rear wheel hub motor, you will need two clutches instead of one. The arrangement sprocket for chain, clutch, gearbox input, gearbox, clutch, motor needs to fit in the 140mm of the rear dropout. The cost of the mechanical gears alone (without the motor) will be in the region of $100 for 10,000 units. Is it viable?
BMC has two versions optimized for speed or for torque, not both. The Ezee motor seems to have the best compromise between torque and speed. In hub motors, the controllers already do a very good job at increasing the torque at low speed but the loss of efficiency is up to 70%.

 

[banbury frank]

Hi

Our Hub motors are the V8 off motors pure GRUNT direct drive with a 5 year warranty only 2 moving parts the main bearings they will pull a 12 stone + rider up hills no pedaling.

We don't Give Torque numbers as we can change by windings in the motor it is then RPM per volt also rim size

Our motors will pull a 20 stone rider along no problem

That is because they can output up to 1,500 watts 48 volt 15 AH battery 33 AMP controller

Al our kits and bikes are Electronically limited to 15 MPH

on our web site is my younger brother who weight is 12 stone on a very steep hill no pedaling this is our old kit just click on commuter

we will have a new web site coming soon very fast Loading

Showing our new bike climbing steep hills NO pedaling

also a video of a bike doing 28 + MPH on private land

If you don't believe me come to Banbury and try one we are open 7 days a week

Frank