Most of the info out there on bendy limbs in c4d seems to refer to custom built, offered for sale, or otherwise different items than the built in bendy option in character builder in r20.
For the built in rig, it appears to not be automatic, but rather to require that the plates on either side of the bendy joint be moved in addition to increasing the bendy slider. Doing so, though, doesn’t allow the limb to return to a straight position once the bend is completed without also moving the plates back, or else it ends up like this:
If you instead move the plates to the ends of the bones (hip and ankle in this case, it works ok using only the knee control, but none of the built in functions or other controllers engage the bend (foot roll, foot controller, etc)
Have I missed some simple way to use the bend without having to animate either the plates or the bendy slider back and forth in addition to every move? Seems like there must be a more automatic way to engage it.



















loops on the hips are also fine that way.