hey again all! I thought it would be cool to have a dedicated thread for guys who build bigger hex and octocopters with apm where we can share tips and advice regarding tech specs, builds, code, firmware and whatever else comes up.
Firstly, how many of you are building bigger AP rigs with APM? We've been building all our commercial SteadiDrone RTF kits with APM with great results.
so, who else is out there, lets get chatting.
John, I understand what you're saying. But at the same time, I've seen some evidence that well engineered vibration damping can make everything smoother. One video I saw, the quad was so quiet, it was really shocking. And I think that's evidence that vibration damping makes the system better.
The DJI arms... well that's not engineered vibration damping. That's obviously un-engineered softness in the system, which can make everything bad.
So, I'm doing some competitive research now. I like your system better than the Cinestar, but probably not as much as the SkyJib. Some features on the Skyjib just seem to be a little more robustly built.
As far as the web page is concerned, this page here is great!
1) Yeah, and you definitely are a winner here with the pop-in bullets. Seems like everybody else requires hand connecting the bullets. Not a huge deal, but you have a nice feature there, assuming it works.
2) The weight of aluminum boom clamps wouldn't concern me too much. We can't be talking about that much weight, realistically. I understand the plactic boom clamps are cheaper than an arm. But I think replacing a boom clamp would require a lot more work than simply pulling a broken arm and plugging in a new one?
3) Yes, I'm not too worried about damping the camera. I'd use that in any case. But I've just seen some evidence that damping at the motors makes everything quieter, and that has to be better in my mind. Anyway, just something I'm interested in, it doesn't look like the other guys are offering anything either.
As for the position on the APM2, I saw one of them moved the GPS/Mag out onto an arm. That's a great idea. Very much like a helicopter, which seems to have a good result.
I really wish they had designed the APM2 differently, that would make it easy to mount the GPS/Mag section remotely. You could do it by using some wires to connect the daughterboard, but that brings the flash card along too, and I'm not so sure about that. I'd love to see a daughterboard that contained just the flash card (and maybe the FrSky Rx mounting), and then just some solder pads for the GPS and Mag connections. Then a separate remote mountable GPS/Mag card.
Anyway, I do like your design better than the Cinestar. One thing I like about the Cinestar is the captive nuts they use. That's a nice feature. But another nice idea would be to use threaded studs embedded in the plastic, and then simple nylock nuts to secure them. I'm not sure what you have, but in no case should assembly rely on screws threading directly into plastic, or aluminum, even. Although I see now that you are using nylon hardware, so all of this is moot. I guess the nylon screws are for breakaway?
But generally everything on the Cinestar looks pretty flimsy.
The Skyjib seems to have more robust boom blocks, etc.
One thing I really like on the Skyjib is the boom nacelles. That helps with the aerodynamics. One problem that multi-rotors have is the "vortex shedding frequency" which is a source of vibration that I think most people are not aware of.
But the best way to reduce vortex shedding is with a helical strake:
This is something simple to do that is worth experimenting with to see if it improves things.
The Skyjib might look slightly more 'robust' but again does not feature motor arms that can be removed, and if you want to it's dismanteling the entire frame to do so, and keep in mind pricing here, our main aim is to fill a gap for guys who just cannot afford 1995 USD for an airframe, or even 1750 USD for the cinestar, our top end octo eight full airframe kit with removable arms is only about 695 USD, you can almost buy three of our frames compared to a single skyjib and ours is the same size, same 20mm booms, custom lightweight motor mounts and other features and IT LOOKS GREAT!! :)
I totally understand, and I agree. Yours does look like a good value, and I am interested.
Do you included any type of landing gear with your kits? I don't believe that I have seen any in the pictures.
I have considered making some fairing for the outer portion of my arms. I know that I am getting vibes and also losing efficiency from drag on the blunt boom. I get a wicked whistling noise every now and again too.
Totally agree. I just envision a scenario where everything seems fine and then you get into a certain frequency and suddenly everything breaks apart (literally).
I actually have some some nice high speed cameras as work, for a computer vision inspection system I am working on. If I find some time it would be interesting to capture some 2000+fps video of different copter arms and motor/prop combinations in action.
That would be awesome.
Yeah, this needs to be done with some engineering work, not just have everybody go out and mount their motors on jello.
I suspect there might be some kind of effect where vortex shedding excites the arm to vibrate, which in turn starts the motor vibrating. Or vice-versa. So some damping can help this feedback loop.
I've designed and busy printing test prototype nacelle / vortex remover thingy, will show pics soon.
Hey again guys, after doing some research into the aerodynamics of tubes and how to best get rid of vortex shedding etc, I've come up with the following simple very light weight mount that just clues to the tubes, we will give it a test but should remove most of the shedding directly under the props. Let me know your thoughts, here are pics along with our nex SteadiDrone h6x RTF kit (without camera gimbal)
Good idea - streamlining the entire arm would be wasteful but cool looking.
Those of us using square tubing arms are creating an entirely different set of vortices.
"Under arm" motor mounts now have factual support for their use. We put the shafts pointed up simply for convenience it seems.
I think that even with round arms, there might be some small advantage to point the motors down. Of course it's less safe when landing.
Duran, that looks interesting. I like it. Did your research show that it is more effective than simply wrapping something helically around the arm? I noticed GM started doing this on their car radio antennas back in the mid-90's. They simply wrapped something around them and it eliminated the whistle and whip they used to have.