Replies to This Discussion

Permalink Reply by Michael Molloy on March 31, 2009 at 8:46pm

Sound very cool, but from a systems safety approach i can see MANY points of failure and a very complex system and I think it would end being heavier and less efficent than just having the motors out on the booms, there are some light motors out there now.

• ▶ Reply

Permalink Reply by Brandon Angelo on March 31, 2009 at 9:18pm

hmmm. I can see the belts causing some concern, but where else can you see the system failing?

• ▶ Reply

Permalink Reply by Michael Molloy on March 31, 2009 at 10:46pm

Belts were a concern and the complexity that goes with them, but i was also concerned with the pitch control linkages, grips etc, one bump of a blade can damage all those mechanisms, a motor prop saver and prop would be alot less complex..

• ▶ Reply

Permalink Reply by Caleb Chamberlain on July 31, 2009 at 8:44am

It seems to me that the real advantage of a quadrotor is its mechanical simplicity; it makes a fantastic test platform as far as rotorcraft go, since a crash isn't as big a deal as if you crashed a heli.

But in my experience a quadrotor is less efficient than a similarly sized heli - doesn't get as good flight times. As pointed out, it is also less maneuverable, and less stable (requires relatively high-bandwidth computer control for stabilization).

So... if you want a maneuverable aircraft that is super stable, and that has long flight duration... it seems like a quadrotor is not a good option. By making variable pitch rotors, you lose mechanical simplicity, so that compared to a regular heli, you have extra complexity, less stability, potentially higher cost, and worse flight times. Unless you are just building it for fun (which I can definitely understand) why not just use a heli?

(BTW, I think that a variable-pitch quadrotor design like you are describing would be REALLY COOL, regardless of whether it makes perfect sense from an engineering standpoint)

• ▶ Reply

Permalink Reply by Gian Carlo M. on July 30, 2009 at 12:15pm

I don't fly Quads but I intend on building one, and one of the things that bother me about them is the lack of maneuverability. I see a bunch of videos of them but I end up thinking...: boring (except for the FPVs).
That's another reason why I want to build a tilt-rotor quad (more reasons and discussion here: http://diydrones.com/forum/topics/tilt-rotor-quadcopter-for).
I think Michael is right on saying that it adds another layer of complexity, but maybe you can reach an equilibrium between complexity and efficiency. It's worth trying.
What's the current status for your project?

• ▶ Reply

Permalink Reply by Brandon Angelo on August 2, 2009 at 4:36pm

hey sorry for the delay, havetn been pn this site much. this is for a research project and we determined that it would make sense to put off the construction of the quadrotor and get the´meat´ of the project started on a tradition heli to save time. BUT thats wrapping up and im beginning to look back at building this thing; after much deliberation, we deterined that this may not be the most efficient design for the job but ere doing it anyway because it would be the most badass thing we could think of (words of my phD mentor). I have picked up some quadtails from this AWESOME site. ( http://www.cnchelicopter.com/servlet/the-1488/HeliArtist-TREX450-CN...) it works fin on the trex but im worried about not having thrust bearings and the centripital force siezing up standard bearings. as for a conroller, I have decided to use the propellor by parallax. its a very powerful microcontroller running at 80MHZ. we further plan on plememnting our cnotrol system in assembly to minimize latency.

in response to a couple of your comments-

flight time- i~m not too worried with this one. once the thing is running autonomously extreme aerobatics arent a priority (yet...well see where the project takes us) and with a total of 16 pretty ide blades i think were going to hacve thge lift capacity for a couple of big batteries. im thinking 2 2500-3000 mAh lipos. with 4 450 sized brushless that should be about 40 minutes flying.

maneuverabliltiy- 4 variable pitched hubs. ~(-4-10 degrees) that is all.

continue later. on vacation with the fam

• ▶ Reply

Permalink Reply by Caleb Chamberlain on August 2, 2009 at 5:30pm

That's great! Keep us updated; I want to see this thing fly. :-)

• ▶ Reply

Permalink Reply by Jack Crossfire on July 31, 2009 at 10:15am

Around here we're mostly interested in autonomous systems & not model building for its own sake, so in terms of an autonomous system, the fact that it's a quad rotor isn't the limiting factor in maneuverability.

• ▶ Reply

Permalink Reply by Xander on July 31, 2009 at 2:57pm

Caleb, I've got to question your assertions. I've seen quadrotors get near 30 min of flight time, something I have not seen in an electric heli (maybe they can get there, but I doubt they can do much better). And while they might not match a 3d heli for maneuverability, I think they'd match anything you'd dare put an autopilot in. As for stability, they are inherently unstable, but seem if anything to be easier to electronically stabilize. From everyone I've spoken to, they're as easy to pick up as coaxial helis, if not easier.

Example of a quad being rather maneuverable: http://www.youtube.com/watch?v=74SxyuJgkKk

I dont mean to attack you, but I see these points brought up fairly frequently and dont really know where the facts are that back them up.

I do agree though that removing the mechanical simplicity of a quad likely isnt a great idea. It's kind of its selling point. I would be looking for some MAJOR benefits before I'd consider doing that.

• ▶ Reply

Permalink Reply by Gian Carlo M. on July 31, 2009 at 3:34pm

Xander, that's a great video!
Maybe I was wrong about the maneuverability!

• ▶ Reply

Permalink Reply by Caleb Chamberlain on July 31, 2009 at 7:32pm

Xander,

Good points; I'll touch on each of them:

You wrote, "I've seen quadrotors get near 30 min of flight time, something I have not seen in an electric heli (maybe they can get there, but I doubt they can do much better)."

And I've seen a quadrotor do a full hour; I guess the question isn't whether long flight times are possible, but whether you can achieve long flight times efficiently. I haven't collected hard data, but my understanding is that as motors and props become smaller, they become less efficient - less thrust per watt. Certainly this depends on the actual hardware. But, loosely, four smaller props, each with extra spillover drag on the tips, spun by smaller motors with individual motor controllers... compared to a single, more efficient motor, controller, and prop. Maybe the benefit is marginal, I don't know.

You wrote, "And while they might not match a 3d heli for maneuverability, I think they'd match anything you'd dare put an autopilot in."

Very true. I guess I was thinking aerobatics, which you don't do with a quadrotor - you can't fly upside down, etc. And few people do autonomous aerobatics. When it comes to response time, though, a quad is probably more maneuverable - more quick to make attitude changes - simply BECAUSE it is unstable. So, maybe I spoke too soon.

You wrote, "As for stability, they are inherently unstable, but seem if anything to be easier to electronically stabilize. From everyone I've spoken to, they're as easy to pick up as coaxial helis, if not easier."

Having developed autopilots for both helis and quadrotors, I don't agree that quads are easier to electronically stabilize; depending on the heli, you may not even HAVE to stabilize it electronically. And they may be as easy to pick up as coaxial helis once you've built them, developed a controller, tuned gains, etc. But Brandon seems to be talking about building one from the ground up, which isn't exactly trivial.

You wrote, "I do agree though that removing the mechanical simplicity of a quad likely isnt a great idea. It's kind of its selling point. I would be looking for some MAJOR benefits before I'd consider doing that."

Yeah, that is the crux of the issue. A quad typically trades mechanical complexity for electronic complexity. making a design that is more mechanically complex than a heli, AND one that is electronically complex, seems harder to justify, especially if, all other things being equal, it MIGHT be less efficient than a standard heli, and is at best equivalently efficient.

• ▶ Reply

Permalink Reply by Gian Carlo M. on July 31, 2009 at 11:54pm

Ok, I'm starting to get discouraged about building a quadcopter... :)

• ▶ Reply

• ‹ Previous
• 1
• 2
• Next ›
• Page