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.

 

[Cybersnow]

The current set up is pretty equivalent to a 52-12 and is great on the road. I typically ride in gear 11 but the comparison we did using the Aventon bike was calculated so we were using the same gearing ratio (sorry dont remember exactly what the gearing was). Of course climbing steep hills is done in a much lower gear as gear 5&6 make the climb much easier. I did look at dumping the Rohloff and going to a chain system but when doing the math found no gearing advantage and certainly more maintenance issues. I have been talking to Luna Cycles about a different controller but again more issues than improvement.

 

[Gionnirocket]

No experience with the CANbus version but from what I read and my experience with the UART is that they leave the factory more aggressive than most want. Mine is now tuned down and very smooth and predictable.
I'd use the lowest gear that doesn't have me spinning out.

As for PAS... I'm using the 9PAS option and have my first four very tame for minimal assistance and to exercise.
On hills I'm typically in 5 - 7 so I'm guessing you should be in at least 3.

Personally I wouldn't use a super charged controller as you'll be tearing things apart in both riding and repair.

 

[Cybersnow]

There were two key issues that had me eliminate the different controller, one was the distance was dramatically reduced and the other was Bafang’s advice to not overheat the motor. I dont think I can change the number of PAS levels, so I guess the most reasonable answer is to keep the cadence up, increase PAS and decrease gearing (and ket my 100 lb wife on her current 54 lb bike just beat me to the top.

 

[juggernaut]

Nowhere in your posts have you mentioned your actual cadence. And based on your experience with the m620 it sounds like you are not spinning the cranks fast enough, hence your disappointment with this motor.

The m620 is the Ferrari of e-bike motors……it loves to rev. If you can do that the m620 is the gift that keeps on giving. Few cyclists will ever exploit the max efficiency of the m620 because it is around 135. So the secret to extracting the maximum performance from the m620 is to spin the cranks.

For reference I have attached the efficiency curve of the m620 (vs the new m630).

 

[Gionnirocket]

Nowhere in your posts have you mentioned your actual cadence. And based on your experience with the m620 it sounds like you are not spinning the cranks fast enough, hence your disappointment with this motor.

The m620 is the Ferrari of e-bike motors……it loves to rev. If you can do that the m620 is the gift that keeps on giving. Few cyclists will ever exploit the max efficiency of the m620 because it is around 135. So the secret to extracting the maximum performance from the m620 is to spin the cranks.

For reference I have attached the efficiency curve of the m620 (vs the new m630).


View attachment 187784

This all may be true...
But like a Ferrari even at low rpm and far from peak efficiency the motor puts out more than needed to satisfy.. though maybe using a few more electrons than one would like.
I'm thinking slow steep climbs for instance... It just keeps going when geared correctly.
And on the opposite end when I was feeling pumped myself and keeping up with the motor I've achieved 6.5wh/mi on a 30mi trip with a fair amount of hills and an 80lb build.
ymmv

 

[PCeBiker]

My cadence is 0, and I have no idea what "normal" cadence is, but isn't 140 rpms faster than anyone would be able to spin the crank?

And if so, why would Bafang make a motor top out at 140 instead of lowering the top rpm in favor of more torque at lower speeds/rpms?

 

[Gionnirocket]

My cadence is 0, and I have no idea what "normal" cadence is, but isn't 140 rpms faster than anyone would be able to spin the crank?

And if so, why would Bafang make a motor top out at 140 instead of lowering the top rpm in favor of more torque at lower speeds/rpms?

That's its maximum efficiency... and I'll add On Paper. Not that you need to be there for normal use. It still works well leading up to that.
If you drove most sport cars only in their efficient power band you'd have to own an oil tanker as well as have a close relative in the sheriff's office and DMV.

 

[juggernaut]

This all may be true...
But like a Ferrari even at low rpm and far from peak efficiency the motor puts out more than needed to satisfy.. though maybe using a few more electrons than one would like.
I'm thinking slow steep climbs for instance... It just keeps going when geared correctly.
And on the opposite end when I was feeling pumped myself and keeping up with the motor I've achieved 6.5wh/mi on a 30mi trip with a fair amount of hills and an 80lb build.
ymmv

Yes the m620 does deliver at lower cadences because of its bulk torque. However this isn’t the first time I’ve heard posters on this forum being disappointed with the output of the m620, which has been due to their low cadences.

 

[juggernaut]

My cadence is 0, and I have no idea what "normal" cadence is, but isn't 140 rpms faster than anyone would be able to spin the crank?

And if so, why would Bafang make a motor top out at 140 instead of lowering the top rpm in favor of more torque at lower speeds/rpms?

Car manufacturers also build motors that most people will never exploit maximum revs, power nor maximum efficiency (max torque) in their day to day driving……..but there are always those few.

 

[PCeBiker]

That's its maximum efficiency... and I'll add On Paper. Not that you need to be there for normal use.

Car manufacturers also build motors that most people will never exploit maximum revs, power nor maximum efficiency (max torque) in their day to day driving……..but there are always those few.

At least with a car, all the human has to do is hammer the throttle, but with an M620 the human has to wing it up manually to 140 rpm.

I didn't know if that was humanly possible, but they do it all the time in spin class depending on what studio you go to,..

So I guess that the M620 was designed for girls step through e-bikes.

I think @Gionnirocket has one of those??

 

[Gionnirocket]

At least with a car, all the human has to do is hammer the throttle, but with an M620 the human has to wing it up manually to 140 rpm.

I didn't know if that was humanly possible, but they do it all the time in spin class depending on what studio you go to,..


View attachment 187793



So I guess that the M620 was designed for girls step through e-bikes.

I think @Gionnirocket has one of those??

The tripod mounts/dismounts without injury.

I think you're taking a white paper analysis of one characteristic as gospel.
The motor has many attributes and finding a happy medium that's user friendly is most important.
It's loss at 75rpm in my experience is negligible

 

[Jeremy McCreary]

Nowhere in your posts have you mentioned your actual cadence. And based on your experience with the m620 it sounds like you are not spinning the cranks fast enough, hence your disappointment with this motor.

The m620 is the Ferrari of e-bike motors……it loves to rev. If you can do that the m620 is the gift that keeps on giving. Few cyclists will ever exploit the max efficiency of the m620 because it is around 135. So the secret to extracting the maximum performance from the m620 is to spin the cranks.

For reference I have attached the efficiency curve of the m620 (vs the new m630).


View attachment 187784

Wow, my mid-drive's cadence sweet spot is 80-90 RPM, and happily, mine's about 82-92 RPM these days. The M620 would be roughly 75% efficient at these cadences. Since I spin out at ~105 RPM, I'd never come close to the 85% peak.

 

[PCeBiker]

The tripod mounts/dismounts without injury.

I think you're taking a white paper analysis of one characteristic as gospel.

Well,.. I guess, but if I ever bought a mid-drive with a choice of motor, I'd pick the M630, especially when my preferred cadence is 0.

I hope it comes with a throttle?