Anyone know anything about disc brakes?

Found this. maybe relevant to someone's interest!

Chainstay mounted cable caliper with cable along toptube:

That setup was done, just because we could - and to see how well it
worked (which was fine). The Avid mech arm can be re-installed every
60 deg, because it sits on an hex key. The return spring was
re-positioned to provide a similar return force. The frame was
designed to handle the earlier version of BB7 caliper, which had a
longer arm, but I did not have one handy to modify by the time this
project happened. The pictured setup is on a MTB tandem, and there is
no shortage of braking power.