Weed eater/whipper snipper engines

[valet_dave]

Hi All,

Okay, this might sound ridiculous, but we have a few people at work that are doing a "junk yard wars/scrapheap challenge" type competition, which involves using weed eater motors to run various types of hulls (foam, plywood, fibreglass, single hull, multi hull) approx. 1300mm x 400mm for a series of boat races/trials.

There seem to be plenty of people that have used weed eater motors, but not much detail on how successful they are in RC boats. Some of the questions to demonstrate my ignorance are as follows:

1. Do these motors have a high enough RPM to provide a reasonable speed or do you need some kind of gearing or modification?
2. Is "torque steer?" a problem (ie. if the engine is revved hard from idle, can the boat be made stable enough, or do you need to look at a non longitudinal configuration to stop it from rolling over.
3. What size/diameter prop would be most efficient?

Cheers,
Dave

[turtle]

i used a homelite 25cc weedeater engine went with direct drive in my enforcer gator and havent had any problems

[dwr9]

Weedeater motors have been used for years in r/c boats. Homelites are probably the most popular, but almost all brands have been used. Some have built in rev limiters in the coils also. I'm no expert on weed eaters, but you should probably be able to get 7 to 8,000 rpm and with the right hull and prop you should be able to get to 30 or 35 mph. If you want to do some modifications to the motor more performance is there. If you look in the menu on the main page here you will see some info on hopping up one of these things. Weed whacker motors have lower rpm but a decent amount of torque so they will turm fair sized props. An Octura x482 or Prather 275 or 280 are popular I believe. You could also try an Octura X470/3. A larger carb than stock(Walbro WA-167 for one) and a tuned pipe are the easiest mods. Torque steer is more of a problem with surface drives than with submerged drives, but surface drives generally give better performance. Doug

[Ozpulse]

Hmmm? You dont work in the aviation industry do you?? I have a fully modded homelite 25cc here if you want to get the jump on your workmates! Other than that look for a Kawasaki weedeater motor they have one of the best power to weight ratio's.

Cheers,
Chadly..

[John]

I built a boat a few years ago using an engine out of a 28cc Talon whipper snipper from Bunnings.

Went reasonably well with a Prather 275. From memory I got around 50kmh out of it.

Google Video of Whipper Snipper Boat

[valet_dave]

Originally Posted by Ozpulse

Hmmm? You dont work in the aviation industry do you?? I have a fully modded homelite 25cc here if you want to get the jump on your workmates! Other than that look for a Kawasaki weedeater motor they have one of the best power to weight ratio's.

Cheers,
Chadly..

It's very tempting, especially when you consider my complete lack of building skills, but my ego isn't worth driving that far! In fact, my failure in this project is probably going to be part of the fun.

[valet_dave]

Originally Posted by John

I built a boat a few years ago using an engine out of a 28cc Talon whipper snipper from Bunnings.

Went reasonably well with a Prather 275. From memory I got around 50kmh out of it.

Google Video of Whipper Snipper Boat

That is absolutely awesome, I can't believe how you can throw it into the turns. The Talon is exactly what I had in mind. Mind you, I've got no hope of producing what you have there, but I'll post the photos in a few weeks so you can all have a good laugh.

Can you tell me what kind of length and width you are running with that hull?

[John]

I don't have the boat anymore but from memory it was 40inches long and about 12inches wide

[valet_dave]

Okay, the project is continuing after 2 months, and we are now seeing why ignorance = failure.

I ended up making a "boat" out of folded stainless and a 25cc Talon weed eater motor. Because buying ready made parts was not part of the competition, we have also had to make our own dodgy prop out of stainless.

The twin blade (120mm diameter) job we came up with, simply stalls the motor, or breaks the prop shaft, partly because the engine doesn't seem to have a clutch, which means the prop is spinning when it hits the water.

Manufacturers only seem to go to a maximum of 80mm diameter. This seems too small for a weed eater engine which produces much lower RPMs when compared to one of the off the shelf RC motors. Does anyone have any opinions on this?

I've also got a problem where the prop shaft goes out the transom at a very shallow angle, meaning that half of the prop will be exposed if the boat ever gets fast enough to create a draught. I've read that some props work in these conditions, but I can't seem to find out when, or how this would work effectively. Can anyone tell me if they have seen this work?

Cheers,
Dave

[valet_dave]

See attachment for dodgy prop and shallow position. Thought you might get a laugh out of it.