Replies to This Discussion

Permalink Reply by james sowell on August 24, 2012 at 9:03pm

http://diydrones.com/profiles/blogs/open-source-g10-quad-frame    somthing like this with all ars up?

DeveloperPermalink Reply by Randy on August 24, 2012 at 9:47pm

hmm..ok.  Maybe we do this because it keeps the props higher off the ground so they are less likely to be broken?  I have certainly seen people put the motors on the bottom of the arms.

The best way would be to try it both ways and then, if you're using an APM2, compare the Roll-in vs Roll an Pitch-In vs pitch in the dataflash's ATT message.

Permalink Reply by Jesse Shaw on August 24, 2012 at 9:50pm

this is interesting. i think that yes initially your corrections would be very small. however the problem would be when some great outside force tipped the copter too far over and it would flip. the example in my head is that of balancing an 8ft 2x4 in your hand. it's easy to control while within a few degrees of vertical... but along comes a gust of wind that knocks your balance out of kilter, all of a sudden you're going to have your hands full keeping that 2x4 from crashing to the ground

(admittedly this would be hard without some sort of engine failure)

Permalink Reply by Will Snodgrass on August 24, 2012 at 10:04pm

I'm trying to visualize this, but much like muscle memory, overcoming the common can be quite a trick.

Please forgive the broken rotor (which should help illustrate how I'm in a position to try what your saying out) So Obviously take what you see in this pic, remove the legs and then flip the motor 180 degrees right? If you take a closer look at the motor I'm using it has a prop shaft coming out the "bottom" so I can mount my rotor on either side....But from what I gather it would be best just to flip it because that would allow me more space to get payload above....Obviously there will have to be some sort of minimum landing skit below, but using small carbon rods it wouldn't take much.....30 grams? With the total weight of the quad 480grams (bare frame).

Permalink Reply by Will Snodgrass on August 24, 2012 at 10:11pm

This would change things from a pull to a push.. the APM2 deal with that?

And this may sound like a really stupid question, but in your analogy using a single string holding a payload would of course require more input to balance.....but were using more then one string here no?

I just keep picturing this attempt at the Star Wars skidder bike that has 2 props beneath it (like a hovercraft) and hovercraft just slide all over place.

DeveloperPermalink Reply by Randy on August 24, 2012 at 10:28pm

As long as the thrust from the motor is still down, I don't think the APM2 will have any problems.

Permalink Reply by Greg Fletcher on August 24, 2012 at 10:41pm

Like this

?

Permalink Reply by Greg Fletcher on August 24, 2012 at 11:37pm

Standard issue ArduCopter.

DeveloperPermalink Reply by leonardthall on August 24, 2012 at 11:54pm

Hi, I came across this paper when looking for control designs for Quads.

http://eprints.qut.edu.au/33767/1/33767.pdf

This paper says "the system exhibits an unstable oscillation when the CoG is below the rotor, pure divergence when it is above the rotor, and neutral stability when coincident with the rotor."

My understanding is that the best case is when the rotors line up with the CG but it is also where the rotor position error changes the characteristics of the system the most.

So it looks like your gut is right. :)

Permalink Reply by Will Snodgrass on August 25, 2012 at 12:54am

Ok, I have a couple of the Turnigy HAL frames on the way..... The skids are made of carbon fiber and VERY small....  Within the dome I am going to put the APM2 on the top of a stack within the protective bubble at dead center, but as close to the top as will fit.(Below it will be power distribution, at the very bottom the battery...but all still on top of the quad within the bubble) Im guessing that because the higher the APM2 (and ergo it's sensors) is mounted, (Like a lever) it will feel the quad leaning and be able to correct for it far sooner than it would be if mounted below. (Does that sound right?) and using the motors and mounts I showed you before only flipped 180 Degrees. And the Direction of the motors reversed.

What do you think?

Permalink Reply by Raymond Choat on August 25, 2012 at 1:28am

Why would flipping the APM board over be better? I would of though flipping motors and props over and leaving APM like it is? Read my ealier reply and how switching props would allow you to not change rototion of motor with APM change of program. In reality the rotation changed with flipping of motor so swapping prop with prop on next arm would do the trick. Of course flip all props on hubs to face upward in the real world.

Permalink Reply by Raymond Choat on August 25, 2012 at 1:17am

With motors moved to bottom of arms facing down instead of the normal facing up. Instead of reversing the motors, would it not be easier to switch propellors on a nieghboring arm, with the props flipped over so the top of prop would be up to the world.  This would reverse Yaw, so you would have to also reverse your yaw control in Mission Planner. No rewiring (for those with soldered wires) just moving props to next arm over (also flipping prop to face up correctly) and reversing Yaw setting.

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