The flapping foil propulsion drive based on Cardan gear mechanism

This was a test of attentiveness .
The leading edges of all blades in a Voith Schneider Propeller always point in the direction of rotor rotation.
In a trochoidal propulsor, the leading edge of each blade points against the flow, as in flapping foil propulsion.

Cycloidal Rotor in Motion | Voith Schneider Propeller:

 

Yes, you understood and drew everything correctly.
It is possible to combine a leading heave Tusi couple mechanism and a slave pitch Cardan gear mechanism.
I wouldn't want to place a servo motor on a moving part, increasing inertia. Furthermore, the servo motor might not provide the required pitch change rate.
And besides, one electric motor is still simpler than two.

 

Ah, Victor....Nah.

You do you, but for what it's worth, I'd do something like salvage two bicycle wheels, put them one atop the other, and use them as a tiered external Tusi gear(s). Find or make another set of wheels of exactly 1/4 R and, well, figure out a way to get them to mesh without slipping. Your specialty.

Use a single central motor with arms that terminate in axles/bearings for the whatsis, smaller, inner planetary gears.

Out at the rims of the smaller gears, where your foil masts and pivots are, use small, DC stepper motors bolted to the gears, above and below (or fine, just above, or in between) for fine contol of pitch. You don't need much rotation, they're very high torque and very precise and pretty cheap and light. Don't even need that much force if your mast is back 25% from the leading edge or wherever it needs to be for neutral twisting moment. I found some potential sources somewhere I could dig up as examples. It looks like they're the kind of thing the ABB Dynafin guys employ. "Modular."

You really do want the vertical separation, I suggest. I think you're flailing your poor mechanism to pieces without it. The prodigious jerk (not me, haha) at foil reversal is harsh enough as is, without asking it to be withstood by a single arm and joint. Spreading the load to much bigger gears/wheels and sharing it between top and bottom gearsets might really help to address the strains you've reported. Might even consider a bit of damped suspension on your foil masts/steppers. I loves me some damped suspension. Or just use foil braking--yeah, much better. I think this scheme wouldn't need the drag and interference of guides.

Would take some fair electronic skullduggery to figure out the stepper program, but that's right up your alley, and free, and you're retired. You certainly already know the motion required. Same deal with synchronizing two foils, either driven off the central motor or having two "modular" motors. Motor tech and control and compactness is pretty impressive these days.

You could take it as a "spur" (huh) to undertake something to prove why it WON'T work. Like @montero has threatened to do to illustrate why I'm full of baloney on my crackpot suspension and planing schemes on other threads. Wouldn't need to be physical, just virtual.
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PS--also, I'm a big fan of trying to work with the water's resistance sorta synergistically, playing tug-of-war with it rather than just brutalizing and fighting it and forcing it where you think it must go. Use the fact that motors/servos have some amount of "give" in them, or surely can be made to, so that you're persuading the water to take the path of least resistance, not just rigidly churning it up. Give a little, take a little. Judo. Wu wei. I'll go back on my meds now, and put down the hookah ...

 

Or.....

Scrap all the above, and use the Cardan gears for compactness and because you already have them. But use a set above and below, please, if you aren't already. I speak for the pivots.

If you substituted little steppers for your slave mechanism, could you not just flip your foils so you don't have to rotate the whole shebangy around to reverse direction? Stay in the same plane of oscillation, just swivel your foils so the trailing edges are where your leading edges were. Whatever --in front rather than behind. Keep oscillating as before. Not sure how one gets side thrust. I'm not much good on steering. But at least there'd be reverse.

Tracks optional, but if you used them and located your drive mechanism vertically in between them, you'd have vertical separation for support of your foil mast while not needing to duplicate the gear mechanism. You can get 2m heavy-duty sliding door tracks, or make your own with, say, FRP antenna tube and U-groove rollers also used on barndoor-type sliding doors. I can show you what I do. Results not guaranteed.

 

I have no doubt that everything could be done completely differently, for example, using linear electric motors.
But that would be a completely different story .

LinX Linear Motor Demonstration:

 

I think the main design goal of the Voith Schneider Propeller was for maneuverability. It avoids the propeller/rudder combination. I assume in that respect your design achieves the same goal?

 

I'd like a drive that achieves the same goal, but it won't be as elegant as the Voith Schneider Propeller.
Voith Schneider can instantly change thrust from one direction to any other.
With the Cardan Gear, the thrust direction will change sequentially, like an Azipod—to move, for example, from one side of the boat to the other, you need to sequentially move through +90, +45, 0, -45, and -90 degrees.
I hope experiment will reveal how convenient this will actually be; the use of flapping foil propulsion as a steering device has been little studied.
I'd also like to test the drive's ability to function as a sailing boat hydrogenerator.