Watts being used vs. PAS level

[Bruce Arnold]

I noticed something interesting today. I usually try to use the lowest PAS level that works for me at the moment. Given that I usually don't do high-speed runs, I ride the most in Eco or 1. Today I was cruising along on a level stretch and noticed that I was in 2, which I'd used a couple miles back to get across an intersection quickly. The same glance at the LCD showed that I was riding at ~16 mph and using in the neighborhood of 250 watts. I bumped it down to level 1, and the watts rose to 325. Whoa -- I'm curious now. Set it back on 2, watts dropped back to around 250. I tried moving a little faster, 18 mph, and the normal shape of the universe re-asserted itself; fewer watts in level 1 than in level 2.

The only explanation I can see is that at 16 mph in 2, I was more or less ghost pedaling, but to maintain the same speed in level 1, I had to put a bit more effort into it. More torque into the torque sensor would raise the output, right?

What do y'all think? Anyone else notice anything like this, and is there a better explanation?

 

[rich c]

Torque sensing with your bike?

 

[harryS]

That is a puzzle. Physics predicts that you will use the same power (watts) at a given speed. Maybe you were still accelerating in PAS in your first try in level 1?

 

[Bruce Arnold]

Torque sensing with your bike?

That was my guess anyway.

 

[Bruce Arnold]

That is a puzzle. Physics predicts that you will use the same power (watts) at a given speed. Maybe you were still accelerating in PAS in your first try in level 1?

Once I noticed it, I did my best to maintain an even speed on both levels. But it takes more pressure on the pedals to maintain 16 mph in 1 vs 2, and the bare minimum in level 2. That's why I suspect that torque sensing is the cause. Because of how torque sensing works, there is some overlap in power output between levels.

 

[Bruce Arnold]

Maybe some other CCS riders could try the same thing. Find the speed where, given your weight and road conditions, it takes more effort in level X and next to no effort in higher level Y to maintain the same speed. Take a look at the watt readout and see what you find.

 

[Chris Hammond]

So here's my 2 cents (poor man's theory). There seems to be an algorhythm in the controller that I think is designed to avoid overloading the motor at low speed. This only shows up in higher assist levels, so level 2 or higher. You can demonstrate this to yourself by accelerating in S mode from a stop. When you start pedalling, instant power readings will hover in the 400W range until 16-18 mph, after 18-19 mph you will feel the kick of more power and see power readings jump to 900-1000W. This test works best on a slight to moderate incline where you are accelerating more slowly than you would normally be. Obviously do not use the throttle.
At any rate my theory is that the controller is holding back power at this slower speed in level 2, but allows the full ~400 W that level 1 normally sees to be delivered.
Of course, I could be entirely wrong, and my wife would be happy to agree with that.

 

[Trail Cruiser]

So here's my 2 cents (poor man's theory).
At any rate my theory is that the controller is holding back power at this slower speed in level 2, but allows the full ~400 W that level 1 normally sees to be delivered.
Of course, I could be entirely wrong, and my wife would be happy to agree with that.

I think you are spot on. I saw this controller algorithm by Juicebikes which Tora calls dynamic assistance.


http://juicedbikes.com.au/bikes/2017-crosscurrent/

I think that is the baseline assist level by cadence sensor. On top of that, I think there is also an overlay of additional output coming from the torque sensor.

A torque sensor map will look like this (example shown from Yamaha PW-X)



So the aberrantly higher power reading on PAS 1 compared to PAS 2 is most likely coming from the torque sensor activation.

 

[Bruce Arnold]

So here's my 2 cents (poor man's theory). There seems to be an algorhythm in the controller that I think is designed to avoid overloading the motor at low speed. This only shows up in higher assist levels, so level 2 or higher. You can demonstrate this to yourself by accelerating in S mode from a stop. When you start pedalling, instant power readings will hover in the 400W range until 16-18 mph, after 18-19 mph you will feel the kick of more power and see power readings jump to 900-1000W. This test works best on a slight to moderate incline where you are accelerating more slowly than you would normally be. Obviously do not use the throttle.
At any rate my theory is that the controller is holding back power at this slower speed in level 2, but allows the full ~400 W that level 1 normally sees to be delivered.
Of course, I could be entirely wrong, and my wife would be happy to agree with that.

I've noticed that same thing, Chris. It's very noticeable at around 18 mph, suddenly you feel this surge. Your theory makes sense to me.