Please could someone size me a motor and prop to push a feather

[daveimi]

As above really, looking to build a fan powered feather for the champs next year. Looking for a big brushless and matching prop w/ adapter to push it along. Will like buy a few as the design uses two or four depending.Going to be plugged into a massive lipo. I can't work out how big I need to go and which prop I need to generate the required push. All help like desperately appreciated.

[maddox10]

Hovercraft idea? Pinball anyone?

[daveimi]

on wheels but fan powered lol

[maddox10]

Ah, wheels. Using a fan to power a turbine, what drives a small generator?

[overkill]

While think an air propelled bot is never going to win a match, it would be interesting to see. Here are some ideas:

Rather than use propellers, use ducted fans meant for jet aircraft models; they produce more thrust in a smaller diameter package. Some of the Hobbyking ones come with matched motors. The enclosed fan blades will be safer and probably less breakable.

Steering the bot is going to be interesting; you won't really have a reverse as such although you could mount the fans at both ends to give you thrust in both directions. Steering left & right has several options: using moving vanes like hovercraft use is probably too delicate to survive a full combat match. You could possibly mount the fans on swivels and move them to steer like a jet ski does. If you use two fans at each end, you could try proportional mixing to turn the bot. This is the simplest from a mechanical standpoint but might not produce sharp turns. Finally, you can use wheels with Ackerman steering but again, that may be too delicate to survive long.

My favourite steering idea is to use three fans in a 120 degree radial pattern and control them with an OMX-3 omni directional mixer. It may or may not work but an omni directional air powered bot would be really unique!

If you go for air-powered steering, use ball transfer rollers rather than wheels. They are compact and tough, plus you can mount them on the top & bottom of the bot for full invertability.

[daveimi]

Yeah the plan was to have either a fan facing in each dirEcton to give fwd, back, left and right translational movement. The other idea was two props side by side to give the same as tank style steering but using fans instead of wheels, ie reversing one fan to steer.

It would just be something different no one has tried yet.

[overkill]

I used a spring scale to measure the pulling power of one of my two wheel bots; it was around 5Kg of force, which is nothing special but enough to get around the arena. Looking at the thrust figures for ducted fans at Hobbyking, even the large ones have a thrust under 4Kg and most are much less. To get the same pushing power as a two wheel bot, you are going to need a pair of fans at least 70mm diameter; here is something that might work: http://www.hobbyking.com/hobbyking/s...Rotating_.html



This has 2.2Kg of thrust so a pair would give about the right amount of force. They use 1,900 watts each to achieve that, so you will definitely want a large Lipo to run them. Also keep in mind that fans will probably deliver much less thrust running in reverse as they are not designed to do that.

[daveimi]

Yeah starting to wonder about bothering lol...