I'm planning to build a very basic version of a hovercraft with a leaf blower inflating a tarp 'skirt' wrapped around a sheet of plywood. There a number of youtube videos featuring DIY hovercrafts like these. However, I would like to take it a step further and add a petrol motor with a propeller from an rc plane for forward movement like in these two videos:
Problem is I am clueless about motors. I am considering getting this one for my upcoming hovercraft build:
Though how would I mount or attach the propeller? Obviously, this kind of motor wouldn't be designed specifically with a propeller in mind. And the other question is whereabouts would I mount it? I'm guessing that a propeller might be attached to something spinning like a fan? It looks like there are two circular things on this motor in the pictures but I'm not sure if one of them is a fan or not.
Additionally, would anyone have any idea what size / pitch etc of propeller would be suitable for a motor like this?
And looking at the motor, would it be possible to get an idea of the start up sequence? For example, all I know is that you'd have to pull a cord to start the motor. After that, would it be in idle or neutral or something like that? And then would there be throttle control and some kind of release for the acceleration?
I guess it's pretty obvious from my questions that I am clueless about motors / engines etc. However, if I can get working with something like this, I think it will improve my knowledge in this area which would be beneficial for me later down the track for different types of projects and tasks. So I think it would be a valuable learning experience.
To be effective, propellers (diameter, number of blades, blade pitch and taper) MUST be matched to the motor, taking into account the motor shaft RPM and power output.
This is not at all a trivial undertaking and you should do plenty of research. Don't choose a motor until you have some idea what the power output your hovercraft may require.
You might start by talking to the folks at a nearby RC plane hobby shop, or go online to the many hobby forums. Consider also starting smaller: use a standard model plane motor and matched propeller, to see how it works with a scale model hovercraft.
jremington:
This is not at all a trivial undertaking and you should do plenty of research. Don't choose a motor until you have some idea what the power output your hovercraft may require.
One thing I have noted from my research is that I do need a considerable amount of power to drive the hovercraft forward at decent speed. I have seen a youtube video where someone used a single high powered leaf blower for propulsion for their DIY hovercraft and it was incredibly slow. Basically snails pace. There's another video which shows two leaf blowers being used (looked like they were fuel-driven) and the speed was not too bad but the cost of buying two likely gas-powered leaf blowers would be pretty steep. In one of the videos I linked earlier, a 20CC motor from a weedwacker was used on a DIY hovercraft with decent success. The motor I am considering is a 2 stroke 49CC (suitable for dirt bikes, quad bikes etc) so should be a bit more powerful than the weedwacker one.
jremington:
You might start by talking to the folks at a nearby RC plane hobby shop, or go online to the many hobby forums. Consider also starting smaller: use a standard model plane motor and matched propeller, to see how it works with a scale model hovercraft.
I admit I'm still clueless about how to attach the propeller to the motor. I have asked on one of the biggest rc hobby forums out there but I'm still waiting for a reply. Ive also e-mailed sellers of 49CC motors and repair / service centers of dirt bikes and they have no idea. The tricky thing is I need someone who is both knowledgeable about the kind of petrol motors that are used in dirt bikes etc and also RC hobby equipment as well. Though interestingly, with one of the videos I linked, it was a pair of teenage high school students who worked out the attachment on their own.
Don't forget to look to the small active airports. Those private plane pilots have a lot of knowledge and you may find a few who are working on their own propeller driven projects.
jremington:
Look for "shaft couplers". They come in all possible sizes and lengths. McMaster Carr has everything, at a price.
Ah great. Thankyou.
jremington:
Your first mistake is in choosing a motor intended for use with a chain drive.
Oh that is interesting to hear. Someone on another forum commented that that particular motor was a suitable choice for my hovercraft project and that I needed to purchase a chain for it. According to him, the motor pulls the chain and the chain pulls a cog which in turn pulls the fan. Or is there more to this which would make this motor an unwise choice?
According to him, the motor pulls the chain and the chain pulls a cog which in turn pulls the fan.
That is certainly one possibility, which involves putting together an extra shaft on a ball bearing mount, with chains and chainwheels chosen for proper gear ratios to match the motor and propeller RPMs, all onto a sturdy and carefully aligned framework. Do you have machine tools handy for the construction?
Or, use a sturdy shaft coupler to mount a properly chosen propeller directly onto a suitable motor with an extended shaft.
jremington:
That is certainly one possibility, which involves putting together ball bearing mounts, extra shafts, chains and chainwheels chosen for proper gear ratios to match the motor and propeller RPMs. Do you have machine tools handy for the construction?
Yea that would be out of my knowledge base. And I probably wouldn't have the tools anyway.
jremington:
Or, use a sturdy shaft coupler to mount a properly chosen propeller directly on the shaft of a suitable motor.
Would it be possible to recommend some suitable motor types that would have similar or greater power comparable to a 2 stroke 49CC? Or tips on what to search for on sites like ebay?
I guess I'd need to know what the alternative is to a chain driven system.
I recently learned that someone successfully used a lawnmower engine in their hovercraft for propulsion so that could be another option. I do have a feeling that lawnmower engines don't use chains.....correct me if I'm wrong.
I looked at this site again and there are some good options but very expensive.
Though I'm a bit puzzled when comparing some of the specs.
There's an engine selling for over $100 which has 1.2HP but also has an insanely high RPM (13500.) A higher priced model at over $400 has 5.6HP but a lower RPM (7500.) So if I got this right - the cheaper model has a significantly higher RPM but produces a lot less power? Previously, I was under the assumption that a higher RPM would produce more HP.
Since you don't say which engines you're looking at I'll guess that they are not the same capacity. A high revving 10cc engine still won't produce the same power as a low revving 100cc engine.
One very important point: props designed for electric motors cannot cope with the much higher stresses of a petrol motor (they will shatter and can kill).
MarkT:
One very important point: props designed for electric motors cannot cope with the much higher stresses of a petrol motor (they will shatter and can kill).
Very good point. I was planning to use a wooden propeller which I presume are intended for petrol rc planes. Additionally, there will be a protection cage around the prop.
I think Ive pretty much decided that I'm going to use a lawnmower motor instead of the 49cc motor.
From one of the videos I linked, I like the inclusion of the throttle / kill switch cable located near the seat. In any case, it would be good to prevent the hovercraft from running off on it's own when I'm first starting it up on the ground beside it....any ideas on how to do that when the motor's at idle speed?
RoadMan:
Very good point. I was planning to use a wooden propeller which I presume are intended for petrol rc planes. Additionally, there will be a protection cage around the prop.
Don't presume, check that the prop is rated for the power source.
MarkT:
Don't presume, check that the prop is rated for the power source.
Oh yes and I'll definitely enquire about which size prop to get to match the horse power and rpm of the motor.
By the way, would anyone have any budget suggestions on building a duct and cage / barrier around the motor and prop for protection? Surprisingly, I couldn't find much on youtube or google about that. I admit I like the look of those circular 'cages' they use on the back of the air boats like in the Florida everglades. It would have to be removable rather than permanent so that I could get access to the motor and prop when they're not in use.
