ford442 wrote:I see how to form the 3 phase rectifier bridge from AC to DC now.
Does that hook up to the motor with 3 wires?
Yes, you could use a 3 phase rectifier like this. One quirk of using this method is that the motor must be spinning above a minimum speed in order to charge the battery. If you are below this speed, no power is generated and there is no braking force provided. This would not be a good brake.
On the other hand, an appropriate motor controller has a better way to generate power. Without going into the exact details, a good motor controller will connect and disconnect the motor's phases at just the right moments to generate power at any speed.
The controller to look for is one that supports variable regen - this way you can apply the correct amount of brake that will allow you to keep going down the hill at a constant speed instead of coming to a full stop. If you got a good controller like this, there would be no need to modify your motor or add a secondary motor and you would have proper braking too.