We used a hook made out of two pieces of 0.25" lexan that was mounted onto the end of a 1x1 which slid on another 1x1 via the VEXpro linear motion kit. The hook was tied to a strap that went down to a winch. The winch was powered by a 775pro on a 100:1 versa planetary with two 0.5" ratcheting wrenches on the output shaft so that the shaft could only turn one way. As the winch turned, the strap would be let out in order to raise the hook. A constant force spring would extend the 1x1 lift and some surgical tubing would pull the 1x1s backwards away from the robot. When all of the strap was let out and the lift was at it's maximum extension, we would line up the hook against the bar and then continue turning the winch which would then spool the strap in the opposite direction. After getting lined up on the bar, the climb would take about 3 seconds. After the match we would then pull off one of the external gears in order to reset the climber for the next match. The entire mechanism ended up weighing around 6-7 pounds.
https://youtu.be/TjlrXFp4Ru0?t=140
https://drive.google.com/open?id=0B8...UxoTDhwc2pTbnc