I have an omni drive proof-of-concept machine i'm working on right now, uses just 2 motors to do swerve drive and am using a solenoid to actuate the disc brake on a part of the machine.
Yes, yes i know that you can't use solenoids, but if anybody ever needs to have a way to do it easily outside of first i've found it works very well.
We used got our disc brake and the caliper for it from
Northern Tool at a great price. Also an awesome place to get big tires cheap too, among other things... its like harbor freight on steriods for some stuff
-Q