Shahid Sheikh wrote:

> The problem is that the motor has a small flywheel attached to it
> which keeps it going for a while after the supply has been shut off.

  This is empirically proven?  (In other words, you *have* tried
disconnecting the power and it *does* keep on running more than wanted?)

> This is for a model train decoder and I'm trying to figure out how I'm
> going to implement an emergency stop.

  Relating to a previous reply, do you need emergency stop on power
disconnection (e.g., off rails) or emergency stop when the controller is
so operated?

  Most, if not all small model trains have the characteristic that the
motor stops very quickly when the power is removed, even with a flywheel
which may be fitted to improve this.  This is so unrealistic that
controllers are specially made to simulate "inertia", and the "emergency
stop" control simply zeroes the "inertia" analog (which may be digital
or analog, the latter usually a capacitor).

  The situation you describe is very unusual, the opposite problem.
Naturally, most of us are quite surprised this would happen!

> The motor's speed and direction are controlled by a PIC using PWM.
> Right now I dont have any plans of using back EMF for speed control so
> I'm trying to find a braking solution that doesn't use back EMF.

  We don't see the connection.  Back EMF *is* used for braking,
independent of whether you want to measure it, by simply shorting the
motor.  You could use relays as suggested, but if you have a MosFet H-
bridge already in place, switching on both ground-side FETs and neither
supply-side one will do the job perfectly.
--
  Cheers,
        Paul B.