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[Andy M]

I have mentioned this outboard on a couple of posts already.
 I thought it deserves a post of its own,
 it seems to work, I have only tested it in the bath so far, but holding the boat must be loading it more than if it was free running. I am hoping it holds together, with the aid of my modifications, additions and reinforcements. I hope to try an open water test soon.
 I have printed it in PLA, I imagine abs would be better.
 The print includes bevel gears, but I decided right away to use brass gears instead.
 Print also includes a left and right hand set of props, supposed to fit onto a flat on the shaft with a steel flat bit, I ditched these too and used an m4 threaded 4mm propshaft section instead, with a 35mm 2 blade prop.
 It has 3 bearings, one each end of propshaft and one just above the motor side bevel gear. A solid coupling is used to connect 4mm stainless driveshaft to the motor.
 The print has a watercooled motor mount, mine leaked, but I sealed it carefully with a couple of coats of superglue, excess being wiped off very quickly. A light sand on the inside and my motor slid in nicely.
 The original designer had used a water pump, I used a waterscoop instead, it goes up through the leg and  through the motor mount. I bent a bit of snake outer to its final bendy shape by heating it and using paper stick type cotton bud with one bud cut off up the tubing as a cheap bending 'spring' to stop it flattening out.  It goes in the back of the leg and has to miss the propshaft, but theres ample room.
 The silicone tube to the waterjacket had to have a spring put up the middle to keep it from folding on the 90 degree bend.
 I am going to detail the mods and reinforcements I have added if anyone fancies trying one.

[Andy M]

The motor I am using is a 4 pole 2838 4500kv. It was midway down the kv range of the motors on the specification sheet that came with the motor.
It has loads of power mounted in my Sea Rover, I am using same prop on my outboard so should be similar thrust, if not the same, maybe a bit down due to drag of lower casing.
Still produces bath emptying amounts of thrust. 😁

[Andy M]

Here is a pic of the other outboard on thingiverse, it has a few different bits for different styles.

[Andy M]

Some background, a video and some dimensions

[Andy M]

Here is a video showing my Sea Rover, using same motor and prop and a 3s pack.
My bath test of the outboard was only on 2s pack and it was still very impressive.


https://youtube.com/shorts/k6gPbSjp4gk?feature=share

[CarlC]

Really interesting post.


The photo of the two other outboards are my builds. They use the Open Outboard Motor Mark II design from Christian Pomeroy's Thingiverse.


I personally prefer the open version that is a bit like a Seagull. The first one I built used a 1400kv motor and printed gears. It works very well but is a little over powered. I have built one with a 1000kv motor and its great, but still a bit powerful for a Seagull. I have just received some 930kv motors so that will be my next build.


Look forward to seeing what modifications you do.

[Andy M]

I have had a seagull so I will definately be printing one, and probably the other one too.
 I am going to make a few tiny changes on my next version of this one, first of all, the anti cavitation plate as printed, has 2 weak tabs to bolt it on, and its too small. If these tabs snap off, it leaves the lower gearcase screws loose, so I am ditching the printed plate bit and doing a completely new 2mm plasticard one the same size as my enlarged version on my first outboard, welded to the midsection, exactly where it was but not using gearcase bolts and weak tabs. I reinforced these on my mk 1 version so they should be ok. Hopefully. Need to get a test happening soon on open water. Need to fix the hole in my inflatable dinghy soon, I want to take it just in case I need to rescue my boat.
I do have a good few ideas I want to try on these outboards, I think they have good potential. I even thought about scaling up to 150%, using 6mm shafts and associated scaled up hardware, the bearings are available if I try it, and not much dearer.
I think it is worth sticking with these, I printed a couple of extra sets of parts to experiment with and modify. I have one more set of hardware ordered, but it can easily be transferred into a different outboard if I want.
I love the extra potential boat builds that are opened up by having an outboard. It is so easy to swap between hulls.

[CarlC]

Really interesting on the modifications for the anti cavitation plate, having looked at a number of 3D printed outboards that is a common weakness. The larger plate on the outboard with the cowling is only held in place by one bolt, threaded into the plastic, so I am not holding out huge hopes for it surviving long term.


The other issue I hit with my builds was that the instructions suggest replacing the motor shaft with a 3mm shaft and shimming it. This didn't work for me as the original shaft was 3.175mm and it caused some vibration issues. I have replaced the 3mm shaft with a 1/8 inch (3.175mm) brass shaft and machined the lower end to 3mm for the bearing and gears, seems to work a treat. In fact, it got another 3 hours use today, with a good hour of that being by a 9 year old with a throttle heavy finger.


I have just received the nylon push fit bevel gears so my next build will be with them, rather than 3D printed gears, fingers crossed they will work and be an improvement.


I agree with you, since I built the outboard I have been looking at building a whole variety of boats I would never have considered before. I think a working, easy to build outboard could spawn a raft of interesting model boats.

[Andy M]

All commercially available ones have been expensive. Hopefully this one will be reliable as well as being relatively cheap.

[Tug Fanatic]

The motor I am using is a 4 pole 2838 4500kv........................

Andy

Are you sure about the 4500kv. With a 3S 11.1v supply that would be nearly 50,000rpm!

[Andy M]

Its all I have, I am just going to run 2s,it never broke apart at full beans on 2s in the bath.
I did run 3s on my Sea Rover using same motor and prop, but it is a very solid mount for all the hardware, not sure if my outboard is up to that.....reinforcements or not.

[Martin (Admin)]

Some background, a video and some dimensions

https://youtu.be/fYpT2TCFHKk

[Andy M]

Awesome, I have a re-awakened love for outboards having started experimenting with this one.
Scaled up Keil Kraft Cresta?
I have been brainstorming about mods to the outboard and new project too.

[Andy M]

Andy

Are you sure about the 4500kv. With a 3S 11.1v supply that would be nearly 50,000rpm!

I was wondering if you can calculate if the motor is overloaded with a 35mm prop? It had no prop info.

[tsenecal]

I was wondering if you can calculate if the motor is overloaded with a 35mm prop? It had no prop info.

4500kvm is WAY too much

using an ancient windows app called FECalc (fast electric calculator)  I have no idea how accurate this is...  but...

using a motor in its database that is 4500kvm, and 3 cell 2100mah lipo, and a 35mm octura x series prop...   
under load:
31000+ rpm
139 amps
7.85 volts
1000+ watts
43 mph
55 second run time

dropping to a 2200kv motor and 3 cell 2100mah lipo with the same 35mm prop:
under load
20,000 rpm
37 amps
10.22 volts
384 watts
3.5 minutes run time
28 mph

dropping to a 1100kv motor:
12000 rpm
7.26 amps
10.93 volts
80 watts
17.5 minutes run time
17.5 mph


if you want me to run those numbers with a different size prop, let me know.

[Andy M]

I will be running 2s, I dont have any lower kv motors apart from aircraft ones, aircooled.
So I really have to just stick with my 4500 ones at the moment and hope finances improve enough to invest in lower kv motors.
I ran the same motor, esc and prop in my Sea Rover and it wasnt way too much, it was rapid but nothing extreme and that was trying it on 3s.
It has a standard propshaft setup, I wont subject my plastic outboard to 3s.

[tsenecal]

the Fast Electric Calculator has a "Prop Wizard" function.  given a specific motor and battery combo, it will try to find the "best" prop for that setup...  using your 4500kvm and 2s lipo, it recommended an octura x430 30mm prop.   It only knows about the props in its database, and those are all racing props, so take its advice as you will.

[Andy M]

Here is the prop I used on the Sea Rover on 3s, 35mm diameter, not quite an x type.
I was running it on a river so never kept it full throttle for more than a few seconds, the esc and motor were quite warmish hot,
I had no cooling on the motor or esc at that point. The outboard now has its own cooling system, which seems to pump water fine.
The Sea Rover still has the other motor of the pair I have. It will be getting a copper coil on the motor and I have already converted the esc to watercooling.
I was thinking about the amps, I ran it on 3s, with a 35amp esc, would that not have popped really quick or have I been incredibly lucky to stop when I did?

[Andy M]

I have to withdraw what I said about the outboard design needing reinforcing, after trying a new nozzle, different PLA and different heat settings, I have managed to produce outboard bits that I have 100% more confidence in.
 Due to managing to produce very tough and usable bits, I am going to skip showing the reinforcing stage that I did on the Mark 1.
 Only thing is, I dont see much point in continuing with completing a second outboard using the red, weak prints and having to reinforce them.
 They do show up better in photos than my tough black ones, so I am showing all the parts I use in red just so the details show up better.
Starting at the gearcase, this has a bearing seat each end, these take 4mm id, 10mm od and 4mm thick flanged bearings. 3 bearings are used in the outboard, the other one being above the bevel gear in the bottom end of the midsection/leg?
 The gearcase has screwholes fore and aft for bolting it to the midsection, which has recesses to take 2 m3 nuts.
 I bought an assortment of allen bolts, nuts and washer in m2, m3 and m4. I was only after the m3 sizes but it was cheaper than buying them as batches of 5 or 10 of one size. Several lengths of bolt are required
 The outboard uses only m3's, some of mine were too long, so you may see up to 3 washers in places on it. Or extra bits of bolts sticking out.
 I went for steel bolts, I can get stainless ones in exact sizes later.
Onto the top of the midsection goes the cooler mount, this bolts on with 2 of the the aforementioned '3 washer-ised' bolts into captive nuts in the midsection
 It has a clamp that takes another bolt and nut to tighten onto the watercooled engine mount. The mount/cooler has spiral channel running through it, when I was printing it in red, I monitored the printing of this bit very carefully, worried about any stringing blocking the channel, but it was printing very cleanly with no little blips or any strings.
 The black bits I have been printing do have stringing, but it is completely extra to the print, once it is pulled off, the print is perfect below. My priner has printed miles of filament, the extruder is quite worn and might not be retracting properly. Thats my theory, I will test it when I get a new bit.
 For now though, I wouldnt print the cooler in black, due to the stringing, so I am going to use my original, sealed with superglue, one that is in Mk 1, and seal another red cooler in the same manner.
 I have 2 of the brushless motors, so I may as well print 2 outboards.
 I have been looking for lower kv motors in this size, 28mm diam, but I haven't seen any at 1100kv.
 Anyway, the hood/lid/cowling clips onto the motor cooler mount plate. A small weak clip holds one end, it isnt under any load unless you dont feed it in carefully. I intend to reinforce this with pla or replace this clip system with a metal version.
 I made up new anti cavitation plates from 2mm plasticard, these will glue to the midsection instead of flimsy brackets on the original printed version which was too small anyway.
Thats pretty much it for the actual outboard, I will get to the mounting brackets later and some more modifications.
 

[Stuw]

the Fast Electric Calculator has a "Prop Wizard" function.  given a specific motor and battery combo, it will try to find the "best" prop for that setup...  using your 4500kvm and 2s lipo, it recommended an octura x430 30mm prop.   It only knows about the props in its database, and those are all racing props, so take its advice as you will.

is this the site you mean for the calculator? May be of use if so! Thanks...
https://www.radiocontrolinfo.com/rci-fe-boat-calc/

[Andy M]

Any chance of a calculation using 2s and a 25mm prop?

[tsenecal]

can you post pics and dimensions (diameter, length, diameter of shaft) of the brushless motors?  i might be able to help you find some lower KV ones.

[tsenecal]

is this the site you mean for the calculator? May be of use if so! Thanks...
https://www.radiocontrolinfo.com/rci-fe-boat-calc/

that site is A fe calculator, but the version i have is actually a windows program, and the "database" of information is an editable text file, so i have added quite a few motors whose info i have found, and quite a few propellers to the data that is available on the website.

[tsenecal]

Any chance of a calculation using 2s and a 25mm prop?

using the same 4500kv motor on 2s 2100 mah lipo with a 27mm prop (smallest i have in my database)
29000 rpm
41.26 amps
6.87 volts
283 watts
3.13 minutes run time
31.24 mph

2200kv motor on 2s 2100 with a 27mm prop
15800 rpm
8.45 amps
7.29 volts
61.61 watts
15 minutes run time
16.86 mph


(just to see, i went ahead and ran the 2s 27mm on the 1200kv motor)
dropping to a 1100kv motor:
8000 rpm
1.49 amps
7.38 volts
11 watts
86 minutes run time
9.19 mph


seriously, it looks like dropping from your 4500kv motor to even a 2200kv motor would do wonders for your amp draw and run time.

and yes, i would guess that you are playing russian roulette with your 40amp esc

[Andy M]

Thanks, the motor is 28mm diameter, the outboard can take a motor up to 45mm long, more if you leave the cowling off, or make up a deeper cowling. Mine is 38mm long.
I have already bought 25mm props,
The esc says 35, so its probably 25!
Anyway, I dont plan on even using full throttle now I know some numbers.....
If it is 35amp, I can probably run short bursts of 3/4 throttle on the 25mm props. I am planning on transferring the mechanics into a tough black shell soon, or do I just go ahead and test my reinforced weaker print anyway? It is ready for testing, but I am not.