I recently had a call from a company that makes underwater documentaries and they asked if I would be interested in lending them my submarines Faux Fish and Bogus Batoid for use in one of their upcoming films. Never being one to turn down an opportunity to show off my subs I immediately said ok. The only thing was that the subs, which were built to be human-powered and run in a straight line, would have to be converted to battery power and be fully maneuverable. Fortunately, whenever I design a sub I try to design into the drive mechanism the ability to accept motor powering. The reason for this is that a motor will give a constant, consistant power output that will allow any tuning inprovements to the sub to become apparent. This is really important for testing a non-propeller type sub, where you have variables such as fin or wing frequency and amplitude, shape and size, angle of attack and stiffness. With pedal power, the operator gets fatigued after a relatively short period of time and power output drops off.
Faux Fish is propelled through the water by moving its tail side to side just like a real fish. The operator sits in a recumbent position and pedals in a linear motion. The tail moves 1/2 cycle for each leg extension. For testing Faux Fish, the tail was made to be driven by a pair of pneumatic cylinders to simulate the linear pedaling motion that would be used in the man-powered version. The circuit also contains a number of air switches that allow the cylinders to operate 180 degrees out of phase in a reciprocating motion and pneumatic limit switches ensure that the tail has reached the end if it’s sweep before it reverses direction. The speed is easily controlled and the whole tail can be pivoted while sweeping for turning. Variable rate air springs between each tail segment allow the operator to control tail rigidity. This setup would be using the tail for propulsion and steering, but would not allow the sub to travel backwards. For the best maneuverability I could replace the dive planes with electric trolling motors and just use the tail for steering. I need to review both setups a little closer to determine which will best suit the application. Maybe I can incorporate both into the sub although interior volume is pretty limited.
Bogus Batoid is propelled through the water by flapping its wings like a manta ray. Like in Faux Fish, the operator sits in a recumbent position and pedals in a linear manner. That is where the similarity ends. The linear motion is converted to rotary motion through a pair if one-way clutch sprockets on a drive shaft. This shaft then drives another parallel shaft through a 5:1 ratio. The second shaft operates a scotch yoke mechanism which in turn makes the wings go up and down. The rubber sheet in the wings gets stretched from the force of the water and causes the leading edge of the wing to rotate into the direction of movement of the wing.
I have a couple of options to power this sub also. The first would be to drive the first shaft using an electric motor, chain and sprockets. This would give a smooth rotation and wing movement as opposed to the choppy motion created by linear pedaling. This method would allow the sub to propel itself by flapping its wings. I will have to evaluate the other control surfaces tho see how effective they are in an open water environment. The second method would be to attach a trolling motor to the rudder shaft on the bottom side of the sub. The motor would be linked to the stern planes so that it would not only steer but pivot up and down.
In addition to the drive modifications on both subs, I will be installing new buoyancy and trim tanks that will be easier to use and will eliminate the necessity of using foam blocks and lead weights to get the sub trim and buoyancy correct.
Details of the conversion to follow.