Bafang PAS - hows it work?

[JayCee]

Could somebody please explain how the BBSxx PAS systems work? I know they're not torque-sensing, but do they keep constant cadence, ground speed, or what? What is the effect of the different settings (1-9)? Thx.

 

[fredfire]

they keep constant cadence based on the assist level you choose.
Let's say you select PAS 1, it will go faster or slower depending on the gear you selected with your shifter, but cranks will turn at same speed (or try to reach that speed if you choose level 9 and are in the smallest gear, it will take a lot of time to get at speed)

The ground speed is used to apply speed limit set on the onboard controller. That max speed you can select it in the password protected menu.

 

[JayCee]

they keep constant cadence based on the assist level you choose.
Let's say you select PAS 1, it will go faster or slower depending on the gear you selected with your shifter, but cranks will turn at same speed (or try to reach that speed if you choose level 9 and are in the smallest gear, it will take a lot of time to get at speed)

The ground speed is used to apply speed limit set on the onboard controller. That max speed you can select it in the password protected menu.

Do the levels simply adjust the maximum assist power level? Also, is programming something that is commonly done if you're not a tweak? Wondering if I should buy a programming cable.

 

[WoodlandHills]

Sorry, but this is incorrect information. The Bafang does not keep cadence, it does not count cadence and it certainly does not sense cadence. Bafang has a cruise control/autothrottle that is turned on when the pedals move. There is a sensor to verify pedal movement, but not pedal speed or cadence: it just looks to see if pedals are moving forwards or backwards. If backwards it cuts the PAS, if it is in operation. If forwards, it turns on the PAS or keeps it on if it is in use.

The PAS has 9 throttle settings for the autothrottle each with a maximum current and rpm which can be changed using the programming cable and a PC. Depending on your gearing you may find yourself running up against the max rpm for a given PAS setting this will be felt as surging where the motor pulls out power when it exceeds a set rpm and them adds it back as the rpm drops below the set point. Perhaps setting the maximum rpm to 110% will mitigate this, but I don't have a PC to try.....

The lack of an actual pedal assist system is the only real failing of the Bafang drives compared to the high priced Bosch units with their sophisticated torque sensing systems.

 

[JayCee]

Sorry, but this is incorrect information. The Bafang does not keep cadence, it does not count cadence and it certainly does not sense cadence. Bafang has a cruise control/autothrottle that is turned on when the pedals move. There is a sensor to verify pedal movement, but not pedal speed or cadence: it just looks to see if pedals are moving forwards or backwards. If backwards it cuts the PAS, if it is in operation. If forwards, it turns on the PAS or keeps it on if it is in use.

The PAS has 9 throttle settings for the autothrottle each with a maximum current and rpm which can be changed using the programming cable and a PC. Depending on your gearing you may find yourself running up against the max rpm for a given PAS setting this will be felt as surging where the motor pulls out power when it exceeds a set rpm and them adds it back as the rpm drops below the set point. Perhaps setting the maximum rpm to 110% will mitigate this, but I don't have a PC to try.....

The lack of an actual pedal assist system is the only real failing of the Bafang drives compared to the high priced Bosch units with their sophisticated torque sensing systems.

I'm sorry, but I totally don't understand your response. What is the system servoing? It sounds like you're saying that engaging PAS simply provides a fixed amount of power assist, regardless of conditions. Is that right? OR - does the motor spin up to a fixed RPM, but the power assist attempting to get it there is current-limited by the PAS setting?

On a related note - do you think a programming cable is a must-have item? Thx

 

[WoodlandHills]

The PAS is effectively a throttle lock with 9 settings. In use it functions exactly like a mechanical throttle lock on a motorcycle. The motorcycle speed will slow on hills and speed up on descents. On flats it will stabilize at what ever speed the power matches the drag. The only addition to the Bafang system is a maximum rpm for each PAS setting that is measured in % of rpm. In the motorcycle analogy, the motorcycle can overspeed when descending a long hill, but the Bafang will not (in theory). As the rpm exceeds the maximum it will reduce current and the bicycle will slow to below the maximum rpm at which point the Bafang will add current and it will speed up to over the maximum rpm. This cycle can be repeated indefinitely and is usually described as "surging". Interestingly, it seems to occur most often on the flats or on gentle hills in my experience, but with different gearing the effect may be present on descents too.

 

[WoodlandHills]

Sorry, but this is incorrect information. The Bafang does not keep cadence, it does not count cadence and it certainly does not sense cadence. Bafang has a cruise control/autothrottle that is turned on when the pedals move. There is a sensor to verify pedal movement, but not pedal speed or cadence: it just looks to see if pedals are moving forwards or backwards. If backwards it cuts the PAS, if it is in operation. If forwards, it turns on the PAS or keeps it on if it is in use.

The PAS has 9 throttle settings for the autothrottle each with a maximum current and rpm which can be changed using the programming cable and a PC. Depending on your gearing you may find yourself running up against the max rpm for a given PAS setting this will be felt as surging where the motor pulls out power when it exceeds a set rpm and them adds it back as the rpm drops below the set point. Perhaps setting the maximum rpm to 110% will mitigate this, but I don't have a PC to try.....

The lack of an actual pedal assist system is the only real failing of the Bafang drives compared to the high priced Bosch units with their sophisticated torque sensing systems.

I'm sorry, but I totally don't understand your response. What is the system servoing? It sounds like you're saying that engaging PAS simply provides a fixed amount of power assist, regardless of conditions. Is that right? OR - does the motor spin up to a fixed RPM, but the power assist attempting to get it there is current-limited by the PAS setting?

On a related note - do you think a programming cable is a must-have item? Thx

Engaging the PAS by moving the pedals simply provides a fixed amount of assist, regardless of conditions. You could program your motor to spin up to the same rpm in each PAS level and current limit the assist to different levels if you wanted by setting the maximum rpm levels all the same. For my liking I would set the rpm limit to the highest level possible to try to mitigate the surging, but I live in an iOS world and programming is only done through Windows, so I haven't tried yet.......

 

[LyonNightroad]

It's worth pointing out that PAS can be used to lock in a given cadence or a given power amount or both.

I've noticed alot of the vendors are shipping their ESC with the PAS set to Cadence (speed) limit with moderate power limit as well and typically put the throttle on current limit mode. This is a good setup. If you add external cruise control to the throttle then you can get a pretty cool setup where you can use either current limiting (Which I find to be the best way to achieve long battery life) or cadence limiting (the more comfortable way to pedal).