A somewhat newbie question on torque sensors....

[pedalingDave]

Hi all, as one of my N+1s, I've had a front hub powered Brompton (nano kit) for a while which runs off a cadence sensor. I'm considering getting a Fazua assisted road bike and was just trying to make sure I understood how a torque sensor works.

Fazua quote assistance levels as

white 0% or 0W
green 75% or 125W
blue 150% or 250W
pink 240% or 400W

Presumably this means that if I am in the green mode and I'm putting in 100w of power pedalling, the assistance gives me a further 75w (175w in total). So this means at 166.6w from me, the system provides 125w of power on top (so 291w in total) but if I put in 200w in the same mode, the power assists remains at 125w as that is the upper limit for that setting ?

At the other end in pink mode, for that same 166.6w, it adds in 400w (566w in total). And in any mode, if I am providing anything over 166.6w, the power assistance will be hitting its top level of assist ?

Just trying to understand how it works!

Cheers

Dave

 

[Woosh]

Presumably this means that if I am in the green mode and I'm putting in 100w of power pedalling, the assistance gives me a further 75w (175w in total). So this means at 166.6w from me, the system provides 125w of power on top (so 291w in total) but if I put in 200w in the same mode, the power assists remains at 125w as that is the upper limit for that setting ?

that's correct.

At the other end in pink mode, for that same 166.6w, it adds in 400w (566w in total). And in any mode, if I am providing anything over 166.6w, the power assistance will be hitting its top level of assist ?

that's also correct.

 

[vfr400]

If those figures are correct, the torque sensor is being used as a switch.

The Bosch system uses algorithms that are based on torque multiplication, but they integrate other factors, like pedal speed and bike speed from separate sensors.

What I'm trying to say is that a bike with a torque sensor is not necessarily going to be like a Bosch system. A torque sensor is just another sensor. You can gones that just give on and off signals and ones that give a signal proportional to torque, and it's what you do with the signal that counts. Even ifthe sensor gives a proportional signal, you can use a power algorithm that says give 125w of power if the sensor shows a value above a threshold value and add some other factors, like the length of time that the torque is above that value, which means it's being used as a switch.

The figures that you provided show an assistance multiplication level, but it looks to me that they've chosen an arbitrary power of about 180w as being 100% human effort, then expressed the motor power in proportion to that unless those figures are maximums and you can get any amount below that by not pedalling so hard.

You have to ride the bike to see how it works in relation to the above. Most people have been riding their bikes for years and wouldn't even know how their system works.

I don’t know how old your Nano kit is, but the ones I tried were very rudimetary. Even cadence based systems have improved a lot since.

 

[pedalingDave]

Thanks for both those replies - makes sense. Off to try a few bikes methinks...

The Nano is about 3 years old and has a very clear "surge on" and "sudden off" but that was entirely for the purpose of city commuting and local errands where I had no desire to either exercise or get sweaty but just avoid the car and hence was perfect (still is!).

Any new road e-bike is for those days where I fancy getting some exercise and distance in but I'm feeling a little lazy (I've got a normal road bike for when I am minded to go and suffer). Plus I'll put some wider rubber on it so I can head off the beaten track - perhaps even some bike packing.

Thanks

Dave

 

[vfr400]

If you replace the controller with a KT one, you can eliminate that surge. it's because your controller uses speed control. It gives maximum power at start, then decreases it when the motor approaches its target speed. The KT controller gives the option of power control, where you get a different but fixed amount of power on each of the 5 levels. Those statements only apply to the pedal assist. Throttle works independently as a speed control.

 

[Nev]

I rode tested a Fazua powered road bike (Cube Agree) a few months ago. It was great on the flat and small hills, but very poor on really steep hills. If you already have good cycle fitness or not to many steep hills where you live you will probably find its fine, but I was rather disappointed with it.

 

[pedalingDave]

Thanks - will look at a KT controller.

The Fazua is genuinely for when I am feeling lazy and don't really want to honk up the steep hills as aggressively. I'll ride the steep ones on my normal road bike on other days so this will just take the edge off
Dave

 

[Nev]

If you can manage steep hills un-assisted no problem, then I am sure a Fazua equipped bike will be fine for you. I really wanted to like the one I test rode, and was unhappy that it just was not powerful enough for me on steep hills.