Trailer brake controllers, hard to custom build?

[Apothus]

Working on a robotics project. I am planning on using electronic trailer brake hubs as brakes (not much of a hack there). However I want more control than a conventional brake controller that just works off the tail lights. I have hopeful I could do something proportional.

My expectation is that these brakes are just a coil in a field. Hopefully A basic H-Bridge circuit can controll them with some form of proportional PWM control.
Has anyone done anything with these before or even laid their hands on a pair? I dont want to shell out for parts i may not be able to control.

[firehopper]

most trailer brakes are a electromagnet that attracts to the drum, its attached to the brake shoes via a mechanism, as the wheel turns it rotates the mechanism and that applys the brakes, the controllers I've seen are connected via brake line or another method, and is usually proportional too

[Apothus]

Thanks firehopper for your patience . I should have just read the wiki page before posting here . Silly me that had all the answers