In 2015 we incorporated a pneumatically actuated bike brake into our robot.
The disc was coupled to the belts that drove the lift. The software was setup to automatically engage the brake when the commands to the motors that drive the lift were below a value that would cause motion (that way we didn't have to explicitly engage and disengage the brake with every command).
The brake and caliper are this one:
https://www.amazon.com/gp/aw/d/B003W...IIL&ref=plSrch
Renders from our CAD model here:
http://imgur.com/a/17HN6
It would also be worth checking out 971s robot from the 2014 season:
https://picasaweb.google.com/m/zoom?...portHeight=416