Regen Braking

Regenerative Braking

In EM's original system, regen braking is accomplished by a push button on the left handlebar. It only has one level but is also affected by the throttle position and the “clutch” lever.

The Kelly controller's factory setting for the regen braking was 20% (of maximum motor current). The allowable range is 5 to 50%. My first experiment with the controller was to reconfigure the regeneration. Although on my concrete driveway 20% seemed reasonable, it proved to be too much for loose downhill dirt and it locked the rear wheel. I tried 10% which seemed as though it might be reasonable on soft dirt. I also tried 50% to see what it did. That was very enlightening as the braking was quite strong for about one second on concrete and then it freewheeled with no regen braking whatsoever. I had to get back on the throttle in order to reestablish regen braking.

The Kelly controller user manual explains this behavior as follows, “Regeneration has braking effect but does not replace the function of a mechanical brake. A mechanical brake is required to stop your vehicle. Regen IS NOT a safety feature! The controller may stop regen, without warning, to protect itself or the battery (it won’t protect you!).” My guess is that 50% regen was causing a battery over-voltage condition. I did not experiment with the maximum level of regeneration that did not cause the protection to occur as 20% was already too much for dirt.

Later, I also ticked a checkbox to enable “ABS” in the configuration software. There was no description of what it is or how it might work other than, “A novel ABS technique provides powerful and smooth regen.” This seemed to be a big benefit as locking on dirt was no longer a problem. Of course, the mechanical rear brake could still lock the rear if you wanted it to slide.

Test of a brake light switch to actuate regen braking

Brake Pedal Regen?

One could argue that the only reason regen braking is desirable is to extend the battery life. Adjacent is the setup I fabricated to test regenerative braking using the rear brake pedal. This was an effort to make it more natural than the handlebar button EM provided.

My main objective with this design was something quick and dirty as a proof of concept. Ultimately, a progressive system using a linear potentiometer and some signal conditioning electronics may be preferable (although a lot more work).

As an aside, the EM swingarm pivot bolt is quite elegant, lightweight, and inexpensive to make in small quantities. It's just a threaded aluminum shaft with an aluminum nut at each end.

Inconclusive Brake Pedal Regen Testing

Adjusting the actuating point of my design is difficult, but the switch is well-protected. Unfortunately, the K&S switch I found on eBay was very poor quality.

I also considered using a Hall-effect switch or a mechanical micro switch, but both have drawbacks. I wanted the regen braking to take effect first, and then the hydraulic brake would begin to actuate with continued pedal travel. Initial testing showed the regen braking was too strong, and I reduced the maximum permitted regen current from 20% to 15%.

The downside of regenerative braking is that it's not possible to “drag the rear brake” while simultaneously controlling the throttle and clutch as can be done with an ICE bike. I am used to doing this for very tight (nearly full lock) turns. However, the EM offers excellent low-speed control – so learning a different technique may be worthwhile.

Cindy and I both felt the system's behavior was not repeatable. But instead of working the bugs out, I had a better idea to try. It is described in the Progressive Electronic Clutch section.