Over the last few days I have installed and tested the AuxD 2-button accessory from Grin and updated my CA3's to firmware version 3.1b16 on both of my bikes.
After spending considerable time tuning the speed gain parameters on an empty road with an even downgrade and then descending over varying terrain, I am mostly happy with the new feature. Thanks, teklektik and Grin, for supporting this. Having a speed control on long descents frees me to concentrate on riding the bike and to enjoy the scenery. It also allows me to capture the maximum energy* possible on downhills. The system works as I expected it would.
I say "mostly happy" because the best speed gain settings are an acceptable but imperfect compromise between too much initial overshoot, more than 3 excursions about the set speed, and perceptible higher frequency motor surging while the system attempts to hold the set speed. I can live with 2 overshoots and barely perceptible surging at the set speed, but I may try to fine tune the gain parameters further. I do have the odd sensation that if I pedal while engine braking, I can feel the motor attempt to compensate for the slight variation of speed with each pedal stroke in syncopation with my pedaling.
My bikes weigh about 140kg loaded, and I'm using DD hub motors with 30-35mm stator. CA3 is set for 1000 watts maximum (at 52 volts nominal) when driving normally, and -1500 watts in regeneration or up to the controller limit (up to about +3000 watts) when plugging, controlled by ASI BAC2000s. I set up 18 discrete speeds between 12 and 80 kph to be selected with the AuxD buttons. Speed gain parameters on the Gold Rush running the Edge1500 motor are PSGain=1.8, IntSGain=250, and DSGain=250. On the Pursuit running the Nine Continents M3006RC, the parameters are: PSGain=2.0, IntSGain=300, DSGain=300.
One bug or glitch: On one of my test rides, the CA3 recorded a MaxS of 87.9 kph, while my GPS track recorded a maximum speed of 65.3 kph. My speedometer signal is coming from one of the motor's Hall sensors, so there can be no faulty reed switch. And, "natural" regeneration occurs somewhere between 65 and 70 kph with these motors.
*The ASI controller's "engine braking" uses a combination of regeneration and plugging. Regeneration converts mechanical energy into stored battery energy and is desirable when it can be used. Plugging consumes battery energy to impart a reverse torque on the wheel. The two modes on the ASI controller have considerable overlap depending on speed and commanded braking force. The transition between regeneration and plugging varies depending on speed and braking force, lower speed or greater braking force increasing the likelihood of plugging.
When a speed limit lower than the current speed is set, it is possible for some braking to fall briefly into the plugging domain as the CA3 attempts to reduce quickly the vehicle's speed. Plugging may also occur even if net negative battery current is flowing, such as on steep descents where speed is moderate (25-30kph) but braking force is high. When some component of engine braking is plugging the motor core temperature will rise quickly, evidence of wasted energy. It is for this reason that I am looking for a way to disable plugging on my ASI controller.