well our current links are very low resistance and are able to carry very large currents, a few stats-

feather - 100amp
light - 200amp
middle - 500amp
heavy - 1000amp (very cool!)

however originally we made our own. At the bottom of the shaft there were two half circle cresent moon shapes of copper which were separated by a few mm. On the bottom of the removable part of the link there was a large round disc of copper which connected the two at the bottom. This screwed threw a thread in the centre of the half circles. This was very simple yet effective and we were actually congratualated by the robot wars crew the first time we entered.