Variable regen

Both manuals list the brakes as “Binary Power Regeneration.” Pressing the left lever slightly closes a switch, and the controller applies a fixed amount of regen. There is no in-between. Variable regen means the harder you press, the more the motor slows the bike. This guide covers how stock regen works, what a progressive setup needs, and the limits that do not go away.

How stock regen works

• The left lever does two jobs: it pulls the rear mechanical brake, and its brake light switch tells the controller to start regen.
• When regen is on, the controller kills the throttle. The manuals say to make sure you are not on the throttle when you release the lever.
• Both manuals say regen sensitivity would be adjustable in an upcoming mobile app. CONFIRM: whether that app setting ever shipped, and what it adjusts
• A stuck lever or touching switch wires also triggers regen, which is why a dead throttle is usually a brake switch problem. See Electrical troubleshooting.

What the manuals warn about

• Regen is not a reliable way to stop the bike. It can stop working suddenly, especially near a full charge, because the pack has nowhere to put the energy.
• Regen is strong and can sometimes stop the bike by itself, so use it with caution.

Those warnings still apply after any conversion. Variable regen changes how regen feels. It does not make it a brake you can count on.

What a progressive setup needs

1. A position sensor. Something has to measure how far the lever or pedal moves. Common choices are a magnetic angle sensor such as the AS5600 on a pivot, or a Hall-effect sensor like the ones used in throttles. The foot brake conversion uses an AS5600 on the pedal pivot.
2. A controller that accepts it. The controller needs an analog brake or regen input and a setting that scales regen to that signal. A controller with only a brake switch input cannot do this, whatever sensor you fit. CONFIRM: whether the stock RCR controller or the CTY2’s Kelly KLS-S has an analog regen input, and its voltage range
3. If it does not, a different controller. That is a much bigger job: it has to match the pack voltage with margin, the motor, the hall sensors, the throttle, the display, and the key fob. See Performance and controller.

Limits set by the battery

Regen is charging. Every amp of regen goes back into the pack through the same BMS that protects it on the charger, so the charging limits in the manuals apply.

• Charge current. Both manuals list 5 A as the recommended charge current and 10 A as the maximum. Hard regen can push far more than that. If your controller lets you set a regen or battery charge current limit, set it with that rating in mind. CONFIRM: the BMS charge-path rating for short regen peaks on each pack
• Full pack. The BMS stops charging at 4.25 V per cell. On a full pack, regen can fade or cut out with no warning. Do not rely on it for the first part of a ride after a full charge.
• Cold pack. The CTY2 manual gives 0 to 45 °C as the safe charging range. Regen into a pack below freezing is charging it below freezing.

Safety rules for any conversion

• The friction brakes must work completely on their own. Regen adds to them; it never replaces them.
• Keep the brake light switch. The brake light should come on whenever regen is applied, and so should the throttle cutoff.
• Design for sensor failure. A signal that is out of range, unplugged, or stuck should turn regen off and leave the friction brake working. It should never apply full regen by itself.
• Start with a low maximum regen setting and raise it in steps.
• Test with the rear wheel off the ground first, then at walking pace in an empty lot, then at speed. Test on a full pack too, since that is where regen is least predictable.
• Modification and non-standard parts void the warranty under both manuals.

If you have not worked on a controller and 72 V wiring before, have a shop that does e-bike electrical work make the change. A wiring mistake here can cut your throttle, lock up regen, or damage the pack.

CONFIRM: Alexander: the controller and sensor wiring used on the foot brake build, the regen current limit you settled on, and how it felt on the road