Can your robot slowly drift back down after end game or must it be at a complet stop?
<G05> Scoring Determination - Scores will be assessed after all objects in motion, when the ARENA timer displays zero seconds, come to rest, or 10 seconds after the timer displays zero seconds, whichever comes first. The final score of a MATCH is the total of points assigned under Rule <G04> less any assigned PENALTIES.
(emphasis mine)
So, yes, your winch should probably have a ratchet. 
Thank you very much