Drive and Steering


FINALLY!
The steering and drive systems took significantly longer to design and install than I was hoping, mostly due to many many mistakes, miscalculations, and lack of adequate planning. Very frustrating.
Note: The orange cable in this picture goes from a battery on my work bench to a motor driver to test the drive system.

Steering

The steering system is electric with manual tiller backup. The black and white parts are 3D printed on my printer. The blue and silver blocky thing is a waterproof giant scale servo from the Radio Control (RC) hobby world. It has gobs of torque for being so small and should be strong enough to turn the rudder. It is back-drivable so the tiller can be used to steer, without removing the servo. However, for electrical-safety reasons the servo's cable must be unplugged before using the tiller.

The tiller is made from a large red oak board that I think came from Scholar's Retreat, aka THICUT, aka what used to be my grandmother's house in Connecticut. It was warped in all directions but I was able to cut out a few pieces that were flat and straight enough to be usable. You'll notice it is darker than regular red oak due to weathering. I sanded it only enough to make it smooth and left most of the weathered surface, then varnished it.



The rudder is made from the large piece of quarter sawn red oak that I found at Home Depot. (See earlier post). That board is sandwiched between to thinner oak boards (also from Home Depot!) to make a 3 layer "super" plywood-like plank.

The narrow thing between the rudder and the black thing above it is the rudder post. It is a piece of 3/4" stainless pipe, threaded on both ends. The rudder's design is what's known as a "balanced" rudder. The rudder post is aft of the front edge of the rudder. The small part of the rudder in front of the rudder post reduces the force on the servo (and tiller). This layout is significantly different than rudders like those found on the back of sailboats. This is why the RC servo should have enough torque to turn the rudder.

Drive System

Forward of the rudder in the picture above is the stuffing box and propeller shaft. The white stuff around the black stuffing box is polyurethane sealant. It keeps water from getting to the wooden keel. The stuffing box, like many things on the boat, is an unusual design/experiment. Inside that black 3D printed part is a ball bearing between two rotary seals. The design is based on shaft seals used in electric motors and is supposed to seal out water completely. I give it about a 47% chance of doing that!

Moving onto the dreaded, frustrating, PIA drive system. After much trial and error, MUCH trial and error, the final design consists of a chrome-moly high carbon (but not stainless) steel shaft. Yes, it will rust if not coated in grease or painted. The black 3D printed part to the left of this picture is the thrust bearing housing. This assembly is what pushes on the boat. It is glued (with polyurethane sealant) and screwed to the oak keelson which is the strongest part of the hull.


Aligning the motor with the propeller shaft requires either extremely precise mounting or an adjustable mounting. I opted for the adjustable version. The drive motor hangs from an upside-down yoke whose screw holes are all slotted so I can move the thing left/right and up/down until it is perfectly aligned with the prop shaft.

Between the motor shaft and the prop shaft is flexible coupler that allows for the inevitable very small misalignments. It too is made of 3D printed plastic. I'm really curious to see if it holds up!


I actually did some math to figure out how much power the motor needs to have. The end result looks way too small. Yet another experiment. I plan to leave room around the motor so a longer version will fit in if this one is not powerful enough.

Next task: Installing the frames, also called ribs.







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