[HighKalibre]

I work on large mine size diesel-electric wheel loaders. The engine drives a large generator which supplies power to 4 wheel motors. These have a very complex control system too them. These use resistive braking instead of regenerative braking, same idea the energy is just used differently. wasted as heat through a bank of resistors instead of "topping" up the batteries.

We also have electric trolley buses that run off overhead lines. when they brake or travel down hill the motors turn into generators and pump electricity back into the grid.

Lemme get to my point. The way I know regenerative braking to work. You can't power the motor to move the vehicle at the same time as you're making it generate power. if that makes any sense.

With the wheel loader for example. you step on the throttle and power is supplied to the motors to move the vehicle. The moment the operator takes his foot off the throttle. Power is no longer being supplied and all 4 motors turn into generators, pushing power through the resistor bank and slowing the loader down.

If you were to use the drag brake as you suggest. When the batteries fall below ~80%, the drag brake engages and tops the batteries up.

The batteries being at 80% and then applying a 20% added load to the motor might slow the vehicle down to the point where the drag brake is doing nothing for the vehicle. Voltage gives you speed, as your motor slows it'll draw more amps from the battery. Further draining it, the cycle continues until your battery is dead. Sorry if its overly exaggerated

Have you thought about coupling a small 12v or even 24v alternator to the motor to keep the batteries topped up. To me this would seem like a smaller overall load then the drag brake. In this way you could still use the motor to generate power when traveling down hills or during braking applications. coupling the alternator to the motor (depending on the size of motor you are going to use) may or may not grossly affect the rotating mass of the motor.

In which case an idea just came to mind. An electo magnetic clutch (EMC to simplify) to activate/deactivate the alternator drive. Once you're up to speed the EMC could activate and the alternator would top your battery up as needed.

Or also if you wanted to try and collect the wasted heat energy from the exhaust or cylinder head. What about a thermocouple/thermopile to generate power? mind you it may be more involved than you would like

Ignore me if this makes no sense