Bafang BBS02 48V: PAS vs. shifting gears

[happybear]

Hello!

Setup
I've got BBS02 48V. The settings are attached, and also available at:

Bafang config - Pastebin.com

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pastebin.com

https://imgur.com/wnEBlTl

https://imgur.com/tikPzO0

https://imgur.com/QQQhAdM

The key display settings are:
PAS levels: 9
Max speed: 55 km/h

I have a 9-speed cassette, 11-34.

"Problem" description
Let's say I ride at PAS level 3 and gear 6, I like my cadence, but don't mind increasing the speed a bit.

When I reach a certain speed, the motor stops helping. I can engage it by either increasing the PAS level or shifting to a higher gear. Either way my cadence gets less comfortable: either easier, or harder than I'd like.

I choose to shift to gear 7. But shortly I get the same issue albeit at a higher speed. The motor stops helping again. And I have the same dilemma: increase PAS or shift to the next gear.

Questions
1/ Why does shifting to a higher gear engages the motor? I only have the speed sensor. The gear sensor is currently not used, but the behavior is the same when it's active.

2/ Are there settings I can tweak to make my pedaling smoother? IDK how to formulate this clearly, but I'd like to have a more natural feeling of controlling speed with my cadence. I realize this may not possible without the torque sensor. Yet I'm willing to try different controller settings.

I've searched the forums, but couldn't find the answer to my questions. Please share the link if they were asked before
Thanks!

 

[Diggs]

Why does shifting to a higher gear engages the motor?

Because you slowed the cadence. The Bafang drives track not only speed but cadence.

Are there settings I can tweak to make my pedaling smoother?

I'm not sure what you are asking here. Have you read through the programming guide? - A Hacker’s Guide To Programming The BBS02 & BBSHD

The second page of programming above controls how quickly and strongly the drive responds to changes.

 

[seanchad]

If I remember right either keep current or current decay are setting which dial back the power once you reach a particular cadence. As above poster mentioned that website is great for programming guidance. There are forum posts knocking about with settings you can download and try too.

 

[E-HP]

The PAS on the BBSXX motors is a simple cadence triggered PAS. It doesn't matter how hard you pedal (like a torque sensing PAS), or how fast you pedal (like a real cadence PAS), so as long as the cranks are spinning, it will give you a fixed level of assist, based on the PAS level. Fundamentally the PAS levels are speed based, so a certain PAS level equals a certain speed or throttle position. So, the short answer is to get in the gear and speed that most closely matches what you like, then fine tune the speed limit % for that level, higher or lower to get it to what works best.

As you discovered, you can have several combinations of gears and PAS (throttle) levels that you can use to achieve a certain speed result, but you could play with the Grin simulator to study the differences in the various combinations to determine what is most efficient, etc.

Here's an example of a bike in PAS level 6 set up to go around 15 mph:

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

This simulates increasing the PAS level (increase in throttle) with the same gearing to achieve 17 mph:

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

This simulates changing the gearing to achieve 17mph with the same PAS level to achieve 17 mph.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[richj8990]

He's really running into the same little issues many of us have had even on a geared hub drive. One of the solutions is to fine-tune the watt output per PAS level. You have 9 PAS levels! That should be enough to fine tune it. Play around a little bit with the current input and see if there is a slight but noticeable difference in the power per PAS level. That ends up a good match for: level pavement, slight inclines, etc., stuff that you normally do with the bike. After doing some modest current adjustments you'll get a good set of PAS watt outputs that will match what gear you are in for the terrain. I know what he means: say for example 150 watts on level pavement is a nice output for a high gear and casual cadence under 70 RPM. 250 watts is not, it's too much. So you have to choose either PAS level 1 or 2 (or in his case maybe 3) to be around 150 watts and the rest of the levels go up in watts from there. Don't be surprised if you usually only use 3-4 levels out of 9, that's normal. It is what it is for cadence-based PAS. And it's not a bad thing, there are great things about it, it's just that it's not really usable through the whole watt range.

 

[happybear]

All, thank you very much for your input and links to the guide and the simulator. Looks like Current Decay and Keep Current are the settings to play with.

@Diggs why do you say my cadence get slower when I shift to a higher gear? I feel like I keep pedaling with the same cadence. Also, if I stay on the same gear and reduce my cadence, the motor does not kick in.

@E-HP I get the idea, but this is probably not a good fit me. I'd have to adjust the selected PAS levels way too frequently. E.g. today I commute on flat paved roads and can probably stick to the preferred levels throughout the ride. But tomorrow I hit hilly trails in a park and use multiple gears and PAS levels as I go up and down.

@richj8990 I understand that I can change the PAS level, thanks. 9 levels do provide smoother experience than 5, albeit with more fiddling. But I was more curious about the gears aspect.

Finally, don't these statements contradict each other? Emphasis mine

Because you slowed the cadence. The Bafang drives track not only speed but cadence.

The PAS on the BBSXX motors is a simple cadence triggered PAS. It doesn't matter how hard you pedal (like a torque sensing PAS), or how fast you pedal (like a real cadence PAS), so as long as the cranks are spinning, it will give you a fixed level of assist, based on the PAS level.

 

[Diggs]

why do you say my cadence get slower when I shift to a higher gear? I feel like I keep pedaling with the same cadence. Also, if I stay on the same gear and reduce my cadence, the motor does not kick in.

When I slow my cadence or speed my motor kicks in. How much and what that speed is depends on your programming. You can see mine here in another forum devoted to Bafang programming. Bafang drives are sensitive to both speed and cadence. What the algorithm is I don't know. My level 3 is programmed for 15 mph and a max of about 550 watts. If I drop below that speed it will bring on motor assist (up to 550 watts) to get me back to 15 mph. If I'm above 15 mph it slowly tapers off assistance until there is none at all by 15.5 mph. If I am in a lower gear and pedaling like crazy the assist tapers off before I hit 15 mph as I mentioned the drive is aware of both cadence and speed.

or how fast you pedal

I would disagree with this based on the 7,000 miles I've done on my BBHSD. It is aware of both speed and cadence (at least the way mine is programmed) but how it ties the two together I'm not sure. I can be pedaling along at 15 mph with moderate assistance and downshift so I am pedaling like mad. The assist will taper off around 13 mph instead of 15 even though I haven't changed the assist level. It's just that I'm pedaling faster. So the Bafang seems to see both cadence and speed.

@add - Here's the chart I was looking for that shows that increase in cadence decreases motor watts. The two are related, I just didn't know how. I'm assuming the BBSHD is similar.

 

[giblet]

All, thank you very much for your input and links to the guide and the simulator. Looks like Current Decay and Keep Current are the settings to play with.

@Diggs why do you say my cadence get slower when I shift to a higher gear? I feel like I keep pedaling with the same cadence. Also, if I stay on the same gear and reduce my cadence, the motor does not kick in.

@E-HP I get the idea, but this is probably not a good fit me. I'd have to adjust the selected PAS levels way too frequently. E.g. today I commute on flat paved roads and can probably stick to the preferred levels throughout the ride. But tomorrow I hit hilly trails in a park and use multiple gears and PAS levels as I go up and down.

@richj8990 I understand that I can change the PAS level, thanks. 9 levels do provide smoother experience than 5, albeit with more fiddling. But I was more curious about the gears aspect.

Finally, don't these statements contradict each other? Emphasis mine

The stock settings are useless from Bafang.

Try this: BBS02B - my look at driver settings

The settings worked perfectly for my use case. The information and graphs are also very useful to get an understanding of all the settings.

 

[happybear]

@giblet, thanks! My settings are far from the stock ones. But I appreciate the link, interesting tidbits on RPM / cadence.

 

[richj8990]

When I slow my cadence or speed my motor kicks in. How much and what that speed is depends on your programming. You can see mine here in another forum devoted to Bafang programming. Bafang drives are sensitive to both speed and cadence. What the algorithm is I don't know. My level 3 is programmed for 15 mph and a max of about 550 watts. If I drop below that speed it will bring on motor assist (up to 550 watts) to get me back to 15 mph. If I'm above 15 mph it slowly tapers off assistance until there is none at all by 15.5 mph. If I am in a lower gear and pedaling like crazy the assist tapers off before I hit 15 mph as I mentioned the drive is aware of both cadence and speed.


I would disagree with this based on the 7,000 miles I've done on my BBHSD. It is aware of both speed and cadence (at least the way mine is programmed) but how it ties the two together I'm not sure. I can be pedaling along at 15 mph with moderate assistance and downshift so I am pedaling like mad. The assist will taper off around 13 mph instead of 15 even though I haven't changed the assist level. It's just that I'm pedaling faster. So the Bafang seems to see both cadence and speed.

@add - Here's the chart I was looking for that shows that increase in cadence decreases motor watts. The two are related, I just didn't know how. I'm assuming the BBSHD is similar.

Really? There is no assist at all after a certain speed...

You know what I think that is. I've never had a BSSxx, but I think there is a very low level of assist, but because mid-drives normally don't show watt output, you can't see it or feel it. The reason I say that is because on a couple of different displays, both KT and SW900 for a hub drive, if I program it a certain way the watts will fall way down to under 20 after a certain speed (downhill, or after downhill on a flat section). They will go to like 11 watts. So there is a tiny bit of assist but you can't feel it. The watts will not go to 0, I think it needs to keep a bit of power going just so it's easier to ramp up later when you slow down.

I hate that lack of assist so I change the programming to where it provides a minimum of about 50-70 watts after a certain speed. It's either imitation torque for KT or the equivalent of that on SW900.

 

[happybear]

but because mid-drives normally don't show watt output, you can't see it or feel it

What do you mean by 'don't show'? All decent BBS-compatible displays can show you either Watts or Amps, or both at the same time. E.g. P850C shows W numerically and A graphically (as shown below), or you can configure it the other way around.

https://imgur.com/NWKEL2a

I prefer amps numerically, but I feel like the precision is about 0.5A. Also, from my experience, 0.5-1A provides very little assistance and it's hard to keep such a level steady when pedaling.

 

[Diggs]

Really? There is no assist at all after a certain speed...

I keep mine set to display watts and yes, it drops to zero (0) after a certain speed depending on my assist level (and programming). This is one of the things I like about the BBSXX. I get power only when I need it, not when ever I pedal.

 

[richj8990]

What do you mean by 'don't show'? All decent BBS-compatible displays can show you either Watts or Amps, or both at the same time. E.g. P850C shows W numerically and A graphically (as shown below), or you can configure it the other way around.

https://imgur.com/NWKEL2a

I prefer amps numerically, but I feel like the precision is about 0.5A. Also, from my experience, 0.5-1A provides very little assistance and it's hard to keep such a level steady when pedaling.

22W is pretty much what I would expect to see. That's not zero. That's similar to what happens when I'm in speed control on a hub drive controller. It's between 10-20 watts. It think this is normal.