SPD and torque sensing drive

[gw8izr]

Hi all, I'm about to push the button on a torque drive for my mountain bike, my days of TT pushing 130 inch gears is long behind me, these days I just spin a nice low gear and bimble around enjoying life.... but I just cant manage without my clips.

Thinking about how the axle sensor measures the degree of assist required I cant work out whether my normal pulling up on the idle half of the crank cycle is going to upset the torque sensor or my guess being it will actually reduce strain on the drive train by smoothing out the power delivery?

I'm sure I'm not first to have thought about this so inject some logic into my thinking please?

 

[danielrlee]

Torque is usually measured at the crank or bottom bracket, so the forces the individual pedals are subjected to are not important.

 

[gw8izr]

Torque is usually measured at the crank or bottom bracket, so the forces the individual pedals are subjected to are not important.

Thanks for the reply, this is my concern, the torque apears to be measured by the twist in the crank axle so that implies a necessity to reverse that twist to create the sensor value?

 

[danielrlee]

As long as the direction of rotation is the same, whether you're pulling up or pushing down on the pedals does not alter the direction of force at the crank.

 

[gw8izr]

As long as the direction of rotation is the same, whether you're pulling up or pushing down on the pedals does not alter the direction of force at the crank.

For sure, although the motor control system will have to interpret a different signal both amplitude and phase) which is where I came into this thought process. I know for sure that with clips I deliver power over a much greater rotational angle, so as far as I can tell the only effect will be to reduce peak load and smooth out power delivery demanded from the motor and passed through the drive train - which will be a good thing.

The first eMTB I tried was ten years ago in Norway and was built by an engineer friend from Sweden with no regard to subtlety. It had some kind of torque sense to deliver power, which was considerable! I was enjoying tootling about on it until I aplied power to lift the front wheel over a kerb wherupon it threw me off the bike ;-) I'd like to avoid this with my build.

 

[sjpt]

There was an article in the CTC (whoops, Cycling UK) magazine a few months ago that argued pulling up on the cranks can increase short term power but reduces efficiency (on the human side, not related to its effect on drive train, torque sensor etc). This is because the muscle pulling action is less efficient than the muscle pushing action. However it is still worth having clips to maximize the power around the 12 o'clock to one o'clock region of the crank cycle.

 

[gw8izr]

There was an article in the CTC (whoops, Cycling UK) magazine a few months ago that argued pulling up on the cranks can increase short term power but reduces efficiency (on the human side, not related to its effect on drive train, torque sensor etc). This is because the muscle pulling action is less efficient than the muscle pushing action. However it is still worth having clips to maximize the power around the 12 o'clock to one o'clock region of the crank cycle.

Yeah its the 'scissor' action at bottom and top that makes the difference I think, you can hear the difference on the turbo trainer with and without. I do reckon the up pull is advantageous (to me anyway) as I can certainly feel the burn in the top of my legs so obviously using different muscles. Its like the advantage of pretty pedaling, once its programmed into muscle memory you cant stop it, but I'm old and fat these days so its all academic really

 

[sjpt]

I never managed to make effective use of the pull up even when I thought it should be helpful; so I was pleased when the article justified my lazy cycling habits ... now lazier with age and the electric.

 

[gw8izr]

I'm too old to worry these days but the only thing that bugs me is when I see people pedal with the instep over the pedal axle

 

[gw8izr]

Well it stopped raining! It was still very windy but that never changes here.

So I decided to take the bike round a quick 5 mile circuit to shake it around a bit and see if anything falls off, I’m pleased to report nothing did.

I was into minds as to whether to fit the thumb throttle, I did in the end as I thought it might be useful when pulling out of junctions. I’m not sure it makes that much difference but it’s there so I’ll see how it goes.

I do have a question about operation of the thumb throttle , When pedalling along up a hill I can feel the assistance as expected but as soon as I touch the throttle the assistance cuts out, of course as you continue to open the tap then the assistance comes back and away you go. Is that generally how it works?


(Edit) forgot to say the stock gearing with 42 tooth front ring it’s probably okay but for my use I think I’ll try the smaller 32 t. ring anyway

 

[Woosh]

I do have a question about operation of the thumb throttle , When pedalling along up a hill I can feel the assistance as expected but as soon as I touch the throttle the assistance cuts out, of course as you continue to open the tap then the assistance comes back and away you go. Is that generally how it works?

the throttle has priority over the pedal sensors.
As soon as you open the throttle, even just a little bit, you'll feel the step change.
You soon work out how much to push depending on the gradient and speed.
I must admit, I don't like keeping a thumb on the throttle much, use it rarely on hill start before changing down a gear or two.

 

[Nealh]

With a throttle it takes over the assistance full stop when applied, there may be a split second time lag between throttle operation and the PAS cutting out.

 

[gw8izr]

the throttle has priority over the pedal sensors.
As soon as you open the throttle, even just a little bit, you'll feel the step change.
You soon work out how much to push depending on the gradient and speed.
I must admit, I don't like keeping a thumb on the throttle much, use it rarely on hill start before changing down a gear or two.

Perfect, that’s exactly how it’s behaving, so there’s nothing to worry about thank you.

I’m not sure I’d use it much but it’s handy for testing and setting up the gears et cetera.

The really good news is the assistance takes all the pressure off my inguinal hernia which means I can actually get back out on the bike again