Premise:

This is my take on the concept of an open source outboard motor. Inspired by the original open source outboard by Makeshift_, I wanted to design one that had a bit more customizability, with varying options for cosmetic appearance, as well as having more options for disassembly and maintenance. It also takes some more retro design cues, from the design of the British Seagull outboard motors. I hope that it can perform as a platform for further community mods and designs.

Dimensions (L x W x H): 94mm x 54mm x 178mm
(the height of 178mm can be changed by adjusting tube and shaft lengths)
Whilst this has no official scale, not having a full size prototype, I think it would work well with 1:6 scale figures and boats. I have several boat hull designs on my Thingiverse page that fit well with this if scaled up.

Update 01/07/22:

Added a flywheel cap for the Seagull style engine. This should really be printed on a resin-style printer as I don't think FDM can do the resolution for the text.

Update 03/02/22:

Added three new propeller options: A random sketchy 3-blade prop from my design archives (probably not a very good prop but it looks different), and two seagull-style propellers, of four and five blades. Again, probably not very good props, but they look neat!

Update 10/02/22:

Added a version with a mock exhaust pipe, to further resemble a proper Seagull outboard. The drawback is the loss of the integral servo, so steering will need to come from elsewhere. To help with this, I've added a couple of control horns that fit over the boss that the tiller handle mounts onto, this should allow the attachment of a servo pushrod.
The exhaust requires an 80mm length (or Driveshaft-Tube-Length minus 20mm), OD10mm x ID9mm Brass or Aluminium Tube to complete, plus a further M2 x 4mm screw that screws the tube into the adapter plate. Drill Ø2mm through one side of the tube 4mm from one end to make the mounting hole.
The exhaust mount plate gets screwed in place in lieu of the servo, and the two exhaust outlet pieces should sandwich together in place of the normal anti-ventilation plate. The computer render shown above should aid with assembly.
I wouldn't really recommend this particular build configuration as losing the internal servo will be a bit annoying, but it's nice to have in case anyone wants to try it.
Also added another big 4-blade propeller from my archives, and it's own 3-blade version.

Required Hardware:

Sadly, not everything can be 3D printed. Below is a list of items that will need to be bought in order to make this a functional motor:

• M2 x 10mm Screws - 8pcs
• M2 x 4mm Screws (it's possible to cut the 10mm ones down) - 4pcs
• M2 Nut - 9pcs
• M3 x 20 Thumbscrew - 3pcs
• M3 Nut/M3 x 4mm Threaded Insert - 2pcs
• Micro Servo - 1pcs
• 2212 Brushless Motor - 1pcs
• 3 x 6 x 3 Bronze Bushings - 3pcs
• M3 x 6 CSK Screws - 4pcs (for motor)
• OD5mm x ID4mm Brass or Aluminium Tube
• Ø3mm Brass Rod
• Ø1mm Brass Wire

OPTIONAL:

• S163A Bevel Gear (module 0.5, 16 teeth, 3mm shaft) - 2pcs

The optional bevel gear replaces a 3D printed gear, and means that you only need to drill 1 hole through the propeller shaft instead of 3. The propeller could also probably be epoxied in place if you really don't like crossdrilling.
The brass rod could possibly be substituted with aluminium if you want it easier to crossdrill, but I wouldn't fancy finding out what galvanic corrosion and galling might occur in the bushings.

Tools:

A suggestion for what will be needed for assembling this outboard:

• Screwdriver with selection of bits
• Hammer
• Scalpel or hobby knife
• Hacksaw or jeweller's saw
• Pin-vice or drill
• 0.12mm drill bit(s)...they can break
• 3mm drill bit or 1/8" drill bit
• Cyanoacrylate (superglue) or epoxy glue

OPTIONAL:

• M2 thread tap - recommended!
• Needle file for cleaning burrs

Assembly:

Included in the files is an assembly guide with step-by-step pictures for the assembly of the motor.

1. Mount the upper gearbox housing bearing in place. This should just press-fit home. Tap the hole in the top of the gearbox housing, then choose what anti-cavitation plate you want, and screw it in place.
2. Cut a length of 3mm brass rod to the size pictured, and crossdrill the two holes with a 1.2mm drill bit in either a pin vice or a rotary tool. It takes ages with a pin vice, but it does work. To get the holes started, it may help to put a small notch in the rod with a hacksaw or a file. Mount the gear and bearings as shown. Cut a small (~5.5mm) length of 1mm wire to act as a key for the printed gear if you are using it. The gears may need fettling to fit the shaft depending on your print quality. using a 3mm clearance drill to ream them out helps a lot. Mount the propeller by threading a piece of 1mm brass wire through both propeller and shaft, and bending the ends over. It may help to anneal the wire first with a flame.
3. Cut the main drive shaft to length, and fit the gears similarly to the previous step.
4. Pass the main drive shaft through the upper gearbox bearing. Cut the shaft tube to length, and insert it into the upper gearbox housing. Press it down all the way, and then fasten it with an M2 x 4mm nut and bolt. Sandwich the propeller shaft assembly between upper and lower gearbox casings, and fit 3 sets of M2 x 10 bolts and nuts. The propeller should turn, but it may be slightly stiff until after the motor is run in.
5. Choose either 2x M3 x 4mm heat-staked threaded inserts or 2x M3 nuts and fit them to the transom brackets. The nuts will need to be glued in place with either cyanoacrylate or epoxy. Screw the two bracket mount halves together with M2 x 4 nuts and bolts, then sandwich them between the two transom brackets and, using 2x M2 x 10 bolts and nuts, fix the two transom bracket pieces together. Similarly to the propeller, use a piece of brass wire to mount the driveshaft tube buffer. Pay attention to the angle of your boat's transom, as this will affect which mounting holes in the transom brackets to choose.
6. Remove the motor shaft as described and mount it to the motor mount plate, choosing which style of power unit you want to build.
7. Using the old motor shaft, assemble the tiller arm with epoxy or cyanoacrylate. The '30s style fuel tank has a few cosmetic end caps to choose from, and a spare thumbscrew makes the fuel filler cap. Tap the hole for the tiller arm M2, and fit the tiller arm with an M2 x 10 screw. Mount the servo in place. The servo screws should pass through the motor mount plate and catch the fuel tank which sits over the servo body. If building the '80s version, the fuel tank may be omitted.
8. Finally, insert the drive shaft tube through the bracket mounts, and into the motor mount plate, ensuring that the drive shaft passes through the motor and rotor. Tighten the rotor grub screw onto the shaft, and fasten the shaft tube with an M2 x 4 bolt and nut, ensuring that the gearbox and power unit are aligned. The chosen cowling can be added to the '80s version at this stage with two M2 x 10 screws. Tap the holes beforehand for best results.

Notes:

• If you don't want to buy a thread tap, you can heat up the M2 x 10 screws with a flame and then thread them into place prior to assembly. This creates an internal thread without stressing the plastic, but it's a tricky process. You can burn yourself or add too much heat and burn the plastic if you're not careful.
• You can change the length of the outboard motor by cutting the drive shaft and shaft tubes to your desired length, so long as you retain the 40mm of difference between them
• It is possible (and I did this for the prototypes) to make your own 3 x 6 x 3mm bushings by sleeving three pieces of brass tubing, soldering them together, then sawing off 3mm lengths. The tube sizes required are ID3 x OD4mm, ID4 x OD5mm, and ID5 x OD6mm.
• The motor usually comes shipped with its own mounting screws, they are in the hardware list only for the sake of completeness
• I'd suggest getting the lowest KV rated motor you can find, for the torque required to push a lot of water. That said, I haven't experimented with motors with a higher KV rating.
• Buying M2 socket cap screws means that, compared to phillips head screws, they will strip less often. Additionally, the motor grub screw will then use the same screwdriver bit as the rest of the engine, simplifying things somewhat.
• The original motor shaft is 1/8", which is replaced in this design by a 3mm rod, leaving a diameter difference of 0.175mm. This isn't usually a problem; the motor's grub screw handles the difference, but it can happen that the rotor begins to interfere with the stator. If this happens, you can sort it by carefully shimming the axle with a piece of aluminium drinks can. There is a company that sells a 2212 motor with a 3mm shaft, but I've not yet had a chance to test it out.
• If you can find a 1/8" brass rod for the drive shaft, you can carefully turn the gearbox end of it down to 3mm with a drill, file, and vernier calipers (or a lathe). That way, you can bypass the problem with the motor shaft being undersized.
• It may be a good idea to waterproof the servo somewhat to protect it from corrosion. There are several internet guides available on how to accomplish this.
• A good way to get a nice seam finish on the two gearbox halves is to sand or scrape the seam smooth after they're screwed together.

Safety:

Be very careful with this outboard once it's built. The propeller is small, but it still uses a big RC aircraft motor. Whilst not sharp, the propeller blades can abrade through skin and clothing in seconds, and as such need to be treated with extreme caution when the motor is connected to a power supply. Don't do anything daft with it, and all use of this design is at your own risk.

Links:

This motor claims to have a 3mm shaft as opposed to a 1/8 (3.175mm) shaft which would make it far more suitable for this design. It is, however, more expensive:
https://www.aliexpress.com/item/32806847021.html
This is the more standard type:
https://www.aliexpress.com/item/4000595532593.html
Any 9g micro servo should fit, similar to these types:
https://www.aliexpress.com/item/4000903734519.html

The design files that wouldn't fit on thingiverse:
https://drive.google.com/drive/folders/16xC3SVB21H21on5wyYQx5eWvVzqJP8xH?usp=sharing

Video:

Another short clip of one of the prototype motors being test run on a 2-cell battery. It was still using ball bearing races at this point, which later changed to bushings after they all rusted shut. The boat is a large scale printed version of my 'Meeuwtje' dinghy: https://www.thingiverse.com/thing:4832048