Weed eater engine conversion

[Harshana]

My first propeller (or the model propeller) is done using a piece of regifoam. Instead of the hacksaw, I used a desk knife. That's how I got the concept right. I suggest you to do the same with your first one.

What I have fitted to the motor is my first real prop. What I have photographed is building my third prop. second one I had to throw away due to a imperfection on the nylon block. I came across a air bubble on one of the blades (I know its very strange to have air bubbles in nylon blocks)

Here in Sri Lanka you can find lathe shops in most suburban areas. So nylon blocks (cylinders) are not very rare commodity as its widely used for making bushes etc.. I am lucky to live close by to one of those shops.

Cost of the nylon (ie 1.5" thick 4.5" diameter was around LKR 550/- ie around USD 4/- rest is my energy and electricity.

About performance.

I couldn't find a small enough metal propeller. So I have never used a metal prop. Therefore I can't compare it with a metal propeller.

Prop1 : 4.5" dia and 3x1.5" pitch
I cannot rev more than 20 ~ 30% with the prop submerged in water due to load.
So far I have used my motor only twice, both occasions on the same lagoon. These days wind and waves are large, hence couldn't get a proper feeling of thrust. Due to large waves, boat goes up and down and the prop shoots out of the water on large waves.

I think it should perform much better on calm water. It should be better than pushing the boat while swimming with fins (that's the closest I can get ).

Prop3 : 4" dia and 3x1" pitch
Revs slightly better, not much difference on thrust (again tested under the same conditions).

I'm thinking of making a 2 blade metal prop with a piece of 14 gauge metal sheet. Let you know when its done and how it performs.

Sorry for the long mail. Let me know if you have more queries.

Thanks,
Harshana

[American_Yankee]

Thanks for all of that information, Harshana.

I bought my metal propeller from Young Manufacturing P.O. Box 30, Mountain Grove Missouri 65711 (417-926-3075) This is a T-10 model, which is a two blade aluminum prop. The T-10 is a counter clockwise prop that fits a 3/8 inch shaft, and is 5 3/4 inches in diameter. The prop sells for $14.95 plus $5.00 Shipping. I believe they take a money order for $19.95. The prop comes with one roll pin. Sorry, I don't have their website right at hand... but if you Google them, you can get it.

Looks like you're in salt water, in that lagoon. You may want to go with a stainless prop instead of aluminum, for corrosion resistance.

Are you running the same drive shaft cable that was on the brush cutter? If so, is it a cable or a solid drive-shaft? The pictures indicate you built some kind of adapter for the end of the brush cutter shaft, right? Or, is it something you adapted from some other application?

Thanks again.

[Harshana]

Hi American_Yankee

My bush cutter is virtually unchanged. I mean't I haven't done anything to it that is permanent.

First change is, I tuned the exhaust chamber by 180deg so exhaust fumes goes towards the back. The way this machine is designed, you can simply unscrew two screws holding the exhaust chamber and turn it by 180 and fix. This could have been a major problem, but solved thanks to the way it has designed.

Second is how I have mounted the engine to my platform. I'm using the screws at the handle and screws at the bottom of the engine where the stand is mounted . Again, no permanent changes.

Third is how I have mounted the propeller. I disassembled the geared part that has the cutting blade and fixed my part that takes the propeller.

Its a solid shaft cutter. Here's a simple drawing that shows how I fitted the prop.



Main thing note here is two allen keys that are tightened on to the grooves. Those two allen key bolts transfer the torque to the inner part that I got machined.
The machined piece that's mounted to the outer tubing has two screws going through the outer tubing (so it want come off). It also has another screw to tighten it to the outer tube.

Hope this helps. I'll try to post some more pictures.

Harshana

[American_Yankee]

Hi Harshana,

Thanks for the additional information, and the drawing. That's a pretty neat way to adapt a propeller. I'm in the process of building a complete replacement shaft.... pretty much an exact copy of the one Helicopter John posted on here. I have received almost all of the parts I need.

What is the brand name and model of the brush-cutter you used? Helicopter John and I purchased a new Honda GX35 engine and clutch assembly, and I don't believe we can reverse the exhaust, without modifying the engine cowling.

Good job on your conversion, Harshana... now if you can just smooth out those big waves! LOL

[Harshana]

Hi American Yankee,

My bush cutter is a used one I bough it for LKR 10,000/- ie around USD 75/-. I think motor is in very good condition. My model is Robin NB04. It's a 42cc engine.

Good luck with your conversion.


Has anyone used same / similar engines like mine (Robin NB04, bush cutter). My concern is will the shaft with its original mount is strong enough. I have noticed specially when turning the boat (engine), its bit hard. There's lot of resistance. Has anyone had any situation getting the shaft / outer tube broken ?

Harshana

[buttales]

wow great thread fella's, took awhile to read 88 pages but u have some great contributors to this thread. figured i'd post up to claim to be the first to cram a weedwacker thru a hobie drivewell. flamesuit on lol

[HelicopterJohn]

Hi buttales,

I think I recognize the propeller. It looks like an R/C Airplane propeller. How fast does it push your boat?

John

[buttales]

hey john, like u i fly rc mostly electric 3d but i have a trex 450 also. i also race 1/8 offroad and onroad both electric and nitro. i've had it up to 6mph on the gps in open choppy water but the gps was bouncing up tp 6mph. in calm flat water it goes way faster but i've never taken a gps reading. the boat is a hobie adventure about 27in wide by 16ft long.easy peasy on the prop using a ryobi gearcase, the prop is a tractor or puller not a pusher turned upside down

[American_Yankee]

Originally Posted by buttales

wow great thread fella's, took awhile to read 88 pages but u have some great contributors to this thread. figured i'd post up to claim to be the first to cram a weedwacker thru a hobie drivewell. flamesuit on lol

Hi Buttales,

I'm curious about the power settings you're using on the Honda motor, as I have the same motor and clutch to power a Otter Stealth 2000 duck boat. That's a nice sea bass also! looks like that policewoman would like to take it home with her!

[buttales]

fish and game is a better poser than me lol..... couldn't get a good grip of it's mouth and held it by the gills all sideways i'm usually around 1/4 to 1/2 throttle still breaking in the motor. what prop are u using, the t8 or the t10? i was going to use a t8 prop and cut it down to 4 or 5 in but had these props lying around that i don't fly anymore

[American_Yankee]

I haven't actually got mine together yet. Still gathering components and welding, machining. I have the T-10, that I plan to try out first. I'll just have to see how it marries up to the Honda, and the duck boat. I'm pretty much trying to copy Helicopter John's design, as he used the Honda 4 engine also. I've had a couple of detours... we all know how that goes. My little Toyota 4x4 truck has decided it needs a new head gasket, at only 117,000 miles! So the boat motor has been put on hold for a little while.

[buttales]

i'm most envious of john's talent and equipment, i know of a few people that fly rc helis that have a mill and lathe and have all custom and tricked out prototype parts on em. i'd love to be able to build and exhaust extension off the muffler that routes the exhaust thru the outer tube of the drive shaft going down to the water. i guess most people are building the mud style long tail motor but i think it's muruama or something like that, have a brushcutter gearcase with a 1.9 to 1 gear ratio so i'm suprised that no one has tried it yet instead of trying to build your own gear reduction.

[buttales]

i looked for the spelling, it's maruyama model b27l turbo with 1.9 to1 gear reduction. i know most are to cheap to consider using this but if want want something under 15 lbs to power a boat

[American_Yankee]

Originally Posted by buttales

i looked for the spelling, it's maruyama model b27l turbo with 1.9 to1 gear reduction. i know most are to cheap to consider using this but if want want something under 15 lbs to power a boat

Thanks, I haven't heard of that one, who sells them? I'll have to check it out. Is that what you used on yours? Did you seal the seams with silicone? Is the inner shaft cable or solid rod?

[buttales]

you will have to google maruyama b27L turbo to get to maruyama website then go to dealer network to find a retailer near u. the u.s. distributor is in texas. i don't have their gearcase.... didn't find out about it till after mine was built. i'm using a ryobi gearcase which is 1.2 to 1 which seems to be the norm for most manufacturers. on their website they have a parts diagram that shows a 7mm solid shaft. the part # for the gearcase is 232718. i suspect this could be a 60 to 90 dollar part.... the whole brushcutter is about 500 dollars and comes with a 5 year commercial warranty. i'm pretty sure this gearcase will be the cat's meow with the t8 prop