How does PAS work on the Zen Photon?

[Cybersnow]

While this is not a problem I am curious about how the bike handles PAS. Since the bike has a torque sensor can you get maximum torque in the lowest PAS setting? I have noticed that the watt display can hit 1500 or max in the lowest PAS setting and that gets me wondering how it works. I am very familiar with Bafang kit motors that use just a cadence sensor but know very little about the M620. On a relatively flat road I can definitely feel the difference in the amount of effort to pedal, but on a steep hill (without changing gears down from 11) on PAS 2 it quickly hits max wattage. Now understand this isn’t a complaint as there are plenty of lower gears in the Rohloff, I am just wondering how PAS with a torque sensor.

 

[scrambler]

The basic principle of a torque based pedal assist is that it delivers a power proportional to your own input.
The PAS level you choose normally determines what that max power is, but the actual power depends on how much you put in.
That said, there are many subtilities in the settings and the combination with the cadence sensor input, so what max power can be delivered with any PAS under max input condition can vary.
Zen will obviously be the best place to answer that, but it is possible that even in low PAS under a very strong input, it could deliver peak power.

You could want a low PAS that does not multiply your input too much under average pedaling strength, yet if you really apply maximum pressure on the pedal, that could be because you momentarily really need more power.
If Zen settings can create such a configuration, that would actually be great as you would not have to change PAS just because you need momentarily peak power.

 

[Jeremy McCreary]

I have noticed that the watt display can hit 1500 or max in the lowest PAS setting and that gets me wondering how it works.

That reading is probably the electrical power supplied to the motor. How much mechanical power you're actually getting out of it will depend on where you're operating on the motor's efficiency vs. cadence curve, where efficiency = (mechanical power out) / (electrical power in).

If your cadence is varying during your tests to figure out how your PAS works, the varying efficiency could well muddy your observations.

Example: My Specialized mid-drive hits max efficiency at a cadence of 80-90 rpm. If I keep a steady exertion up a hill, I can definitely feel motor power falling off below 70 rpm and even moreso below 60 rpm.

 

[Cybersnow]

So the Zen has a cadence and a torque sensor? My old BBSHD only had a cadence sensor and the PAS setting determined the level of”power” provided if you were maintaining a minimum required cadence. I am trying to understand the relationship between PAS setting and actual ”power” provided. Zen advertises a torque of 160Nm but my son‘s 85Nm 750 watt e bike seems to have at least the same power as the Zen. I am trying to figure out why and how to increase power provided on steep climbs.

 

[Jeremy McCreary]

So the Zen has a cadence and a torque sensor?

In a typical mid-drive, motor shaft speed is tied to rider cadence in a fixed ratio. Result: The motor's efficiency vs. cadence curve — a baked-in property if the motor itself — will be convex upward with a peak in a specific "optimal" cadence band (also baked in).

This motor effect has nothing to do with the bike's ability to measure true cadence (crank speed in rpm).

But for safety reasons, any ebike is likely to detect and act on the presence or absence of crank rotation — even those with torque-sensing assist. Unfortunately, most so-called "cadence-sensing" ebikes do only the rotation detection part.

My mid-drive measures both rider torque and true cadence. That gives a (rider) power-sensing PAS.

 

[Jeremy McCreary]

I am trying to figure out why and how to increase power provided on steep climbs.

For a torque- or power-sensing mid-drive, the simplest way to maximize mechanical motor power out for a given effort and assistance level is to find out your own motor's cadence sweet spot and use your gears to stay as close to it as you can.

This will maximize mechanial motor power out, but ground speed may well suffer in the process.

Q: Anyone know the M620's cadence sweet spot?

 

[Gionnirocket]

So the Zen has a cadence and a torque sensor? My old BBSHD only had a cadence sensor and the PAS setting determined the level of”power” provided if you were maintaining a minimum required cadence. I am trying to understand the relationship between PAS setting and actual ”power” provided. Zen advertises a torque of 160Nm but my son‘s 85Nm 750 watt e bike seems to have at least the same power as the Zen. I am trying to figure out why and how to increase power provided on steep climbs.

Yes.. The m620 has both cadence and torque sensors. Your m620 has a CANbus controller and there's not much you can change without hacking the firmware. In general the higher the PAS the more easily the motor will output power thus requiring less torque input from you to do so.
The motor does like to spin but I'm not sure of the sweet spot as far as cadence goes as it has so much torque output that it's hard to know when it's struggling. That said I try to keep it spinning around 75 which is my sweet spot and the motor responds as desired. Obviously being in the right gear and PAS play a part. If your not feeling that, try a higher PAS and/or lower gear.
Staying in gear 11 on a steep hill is most definitely bogging the motor... Especially since I believe you changed to a 52t (equivalent) chainring. Trying to stay in gear 11 all the time defeats the purpose of having a Rohloff. Steep hills I'm usually in gear 6 and that's with a 44t chainring.
The 52t chainring is not for climbers and is definitely loading the motor on hills if not in the lower Rohloff gears.
As a side note... I believe your Photon is a one off (welcome to the club) with the m620 as Zen switched to the Ananda motor soon after announcing the Photon Ultra. Why they kept the same name doesn't make sense to me.
I don't believe any other of the Photon Ultra bikes with the m620 that were pictured being built were ever delivered.