Regen for heavy cargo bike question

[Evelosimo]

I am interested in locking the clutch on my geared hub motor to get regen for better braking. I modified a Juiced U500 by adding a BBS02 mid rive to tow a 200lb trailer as well as carry about 300 to 350lb on the bike, including rider, bike and gear for a total of about 500 to 550lb. This has worked pretty good, I have a few steep grades I need to either climb or slow down on, none of them are very long but I have noticed that I would benefit from having regen for braking purpose as I have on another bike I also use for the same purpose.
The sensor less Bafang BPM I have on the front of U500 is a good motor for carrying cargo so I would like to keep it if possible. I have previously considered upgrading it with a better controller like a Phaserunner or Baserunner but it seems to be a difficult motor to find a controller for. Would anyone know if I need to upgrade the controller to benefit from regen braking once the clutch is locked? I am not interested in recharging the battery through regen, only increasing braking power.

 

[amberwolf]

The sensor less Bafang BPM I have on the front of U500 is a good motor for carrying cargo so I would like to keep it if possible. I have previously considered upgrading it with a better controller like a Phaserunner or Baserunner but it seems to be a difficult motor to find a controller for. Would anyone know if I need to upgrade the controller to benefit from regen braking once the clutch is locked? I am not interested in recharging the battery through regen, only increasing braking power.

Since we don't know what controller you are using, we can't know if it supports regen (or any other feature). You'd have to check your controller's options (does it have a manual?) for whether it supports regen or any other electric braking, and how those braking modes work (simple on/off, or variable, etc).

Assuming you need a new controller, then if you don't need regen, but just electric braking, you can pick a controller that supports FOC and negative current for braking--this will actively force current in reverse direction in the motor, so that it places reverse rotational force on the motor, actively braking it.

Because this is using up power to create the braking, rather than recovering power from it, this will heat the motor, wires, and controllers more, so if you do a lot of rapid acceleration and deceleration, things can get quite hot...but it does much better at braking.

Because FOC controllers' throttles (and braking) control current to the motor, not speed (voltage), you can probably also get finer braking control, rather than the simple on/off that most controllers' simple regen gives, even if you are using the regen version of the FOC braking rather than the negative current version. (if the controller supports both you can test the differences).

On/off braking can be problematic (especially on the front) because you only get one level of braking that you have to preset (if you have any options at all), and it is harder on the whole system than braking you can vary and "roll onto" (even if you do it fast because you need hard braking) rather than just instantly slamming it on every time.


Just note that if the motor is sensorless, the controller you choose must also support sensorless operation for all the functions you want it to have.

 

[Evelosimo]

Thank you for the explanation Amberwolf, very much appreciated, this makes sense. I have a FOC phaserunner controller on our other bike with the regen activated by the throttle once the brakes are on, it is pretty awesome. I have already tried many times to find out about the stock controller on the U500 but as for many commercial ebikes, the info is not available and I doubt it has regen capability. I also tried replacing the controller with a Grin baserunner without any success, it seems that the Bafang BPM is a difficult motor to find a controller upgrade for. Probably someone with more knowledge may have better luck, the throttle would only work once the bike is rolling which would be ok but with a heavy load, it is not so easy. It looks like the best option would be to change motor and controller to get regen. Currently, I have a 203mm rotor in the front which is pretty good considering it is on a 20 inch wheel but i have noticed that the caliper gets out of alignment really quick with the heavy load which is why I was looking into regen. Who knows, maybe I could even try 220mm rotors, it sure would be a lot less work and money than replacing the whole front motor.

 

[amberwolf]

if the caliper misaligns thenthe fork is probably bending the mounting tab or it's weld, or rotating the tube/stanchion.

or the caliper-tab adapter is bending...unlikely the caliper itself is bending.

larger rotor to makehigher braking forces will make alighment even worse, espeically with the caliper having ot be spaced even farther form the mount tabs and placing evne more torque on them.

 

[Evelosimo]

if the caliper misaligns thenthe fork is probably bending the mounting tab or it's weld, or rotating the tube/stanchion.

or the caliper-tab adapter is bending...unlikely the caliper itself is bending

Indeed, most likely the weak point is the spacer I added when I upgraded from 180 to 203 in the front. I will try with the simpler solutions first, see if applying the rear brake first will lessen the stress in the front whenever I am hauling the trailer, that may help solve the problem. At least the brakes are still working well, it just gets noisy and start wearing unevenly whenever they go out of alignment.
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