Comment by Ao7bei3s | Hacker News Reader

Comment by Ao7bei3s | Hacker News Reader

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They have been in civilian (private/commercial) use for a few years (since 2008 or so). Mostly for taking pictures from above -- they are relatively well-suited for that. (And for fun flying of course)

For transporting big things: it's more efficient to have larger rotors than to have multiple rotors.

For transporting really big things: see above, and helicopters have been around for a long long time; "we" (not me) have decades of experience with helicopters; you probably really want something that is safe and reliable. You can't just scale up your model.

As for quadrocopter piloting: right now, all pilots crash. Repeatedly. Luckily, repairs are cheap (unless you happen to carry an expensive camera). For a full-size aircraft, crashing is probably not an option, so add lots of dev/testing time for safety features and pilot training.

BTW (somewhat unrelated): One huge problem with (smaller) quadrocopters is the many people that start new copter projects and get nowhere instead of contributing to one of the existing major projects or reusing its soft/hardware. Some of these projects are already way beyond what a single person or even a small team can achieve in a few years work.

I wonder which project you believe require the most help?

Would be fun to have a small working group in Manchester (UK) - shout if you're in the area and are interested.

Sorry for the late reply, and sorry, I'm not in the UK.

I'm using UAVP-NG (http://ng.uavp.ch/).

It's open source, there is a custom operation system (NGOS) and half a dozen hardware revisions and also a few side projects such as a 4x-BLC. There are over a dozen people actively working on that project now and I believe they've created a nice, easily extensible, platform to base future work on.

On the downside, it isn't the cheapest project. For students like me that can be a bit of a hurdle. Also, you're likely not going to get around soldering the PCBs yourself. (It looks much harder than it is.)

But do have a look around and check the various projects out for yourself before you pick one.

BTW, if you have any questions, please do shoot me a mail. I like mail. Or drop by #uavp on Freenode. The people there are mostly harmless^W^Wvery friendly (as long as you've read the FAQ first ;) [edit: And now we're waaay offtopic. Sorry.]

Hey, cheers for the info. I'm slowly getting a picture of where things are and if I'm likely to be able to contribute at all. For a robust platform to extend in software would be the fun I was after. I've started a Manchester group - there's an amazing 3 of us: http://www.facebook.com/groups/523358144381052/ The kit I've found at a cheapISH price so far is: http://www.seeedstudio.com/depot/preorder-crazyflie-nano-qua...

Can you explain the physics behind why it's more efficient to have larger rotors than multiple rotors?

Two reasons. First, surface area. For an equivalent surface area, one rotor results in a much smaller craft than 4 rotors.

Second, precision machining. It is much easier to balance 1 set of rotors weighing hundreds of pounds than it would be to balance 4 of them. I'm guessing your typical quadcopter is too small right now for this to be a real concern.

Balancing props is a very real concern, but for another reason than efficiency: unbalanced props cause more vibration and lead to reduced image/video quality due to the rolling shutter effect (image looks wobbly). That being said, many people don't bother with propeller balancing.

Size of the aircraft is a very important point, but there are other reasons besides the two you mentioned. Generally, larger motors are more efficient than smaller ones. Larger, slower, props are more efficient than smaller, faster, ones, because Thrust ~ Rotor Speed^2 but Power ~ Rotor Speed ^ 3. Why? I don't recall, sorry. I'm more interested in the software. (If you do figure it out though, let me know.)

Because KE is proportional to v^2, and then you get another factor of v since the volume (and thus mass) of air through the rotors per unit time is proportional to how fast the air is moving.

At least that's my guess. And if I'm right, it's also why, to a first approximation, the power generated by a windmill is proportional to the cube of the wind speed.

To first approximation, the power needed to generate a given thrust is inversely proporional to the rotor diameter. See here;

http://en.wikipedia.org/wiki/Momentum_theory

"The primary reason a helicopter becomes less efficient as it shrinks is that the Reynolds number decreases as the scale decreases. The lower Reynolds number, a measure of the viscosity of air relative to the other forces acting on it, means the air appears thicker to whatever is passing through it, so the drag increases disproportionately compared to the lift." - http://www.ae.utexas.edu/faculty/422-dr-jayant-sirohis-resea...

It's a scale-dependent effect of air.

I would have thought the big contribution to this kind of dynamic balancing would be the eventual ease of piloting it would give. It still might not make sense efficiency wise though.

Exactly.

Seeing this and saying: "These are just helicopters, but smaller" isn't very helpful.

The big difference between these and "real" helicopters (either realsize ones or RC helicopters) is that now these things are using a super fast feedback loop to find their balance.

This could definitely one day help piloting real helicopters: just like these feedback-looped quadcopters are way easier to fly than the RC copters...

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