RE: RC Shark
Taken from the article:
"Thoughts turned to the actual tail drive which had to be articulated to give the required undulating motion, and this turned out to be quite simple and consists of 10 segments made from 25mm x 18mm x 38mm long rectangular Tufnol tube. The first segment is bolted to the aft bulkhead and each subsequent segment attached to the next by means of top and bottom brass plates screwed to one segment with a pivot pin in the next. The gap between the segments is minimal to limit the movement, and the last segment carries an M4 stud onto which is fixed the actual tail. The drive consists of a Como Drills 11:1 ratio gearbox which in turn drives a 6:1 worm reducer and on each end of the wormwheel shaft is a crank arm, each arm being set at 180 degrees to the other. Each arm has a crank lever which in turn drives a push rod passing through an O-ring gland attached on the aft bulkhead. This is attached to a piece of of picture wire which makes a nice stranded brass cable and this passes through guides on each segment to be finally attached to the last segment."
Because he didn't think the tail would be able to turn the shark, he fitted a water thruster with a flap that diverted thrust out through the gills in order to steer it. The bodywork is fibreglass, and the rear tail section is silicone rubber. The tail itself is a sandwich of brass and silicone. Apparently it works quite well, and with the water thruster disengaged, the tail actually powers the shark forward without a loss in speed!