Overlapping Propeller Designs

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flytofly

Member
jes1111 said:
It's to do with the air columns (they effectively offer resistance to lateral wind) and the shorter arms (so response to disturbance is quicker). National Geographic Magazine uses a coax-8 and stated in a video (can't find the link right now) that it was much better for wind stability than their previous flat 8.
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Great feedback. i need to search for that episode.

Jes, are you flying an MK coax 8? If so, where can I find mixer info? I believe most people are using larger diameter props with a steeper pitch on the bottom motor which is set to spin faster?

Thanks
 
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flytofly

Member
matwelli said:
View attachment 8410

decided to try it out on my Y6 - bit rough but the mounts are all done, and esc wireing bodged...just need to add flight controller and test her out tomorrow
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Nice! Looking forward to seeing your results. What would be awesome is thrust comparison between single, coax and overlapping props.
 
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matwelli

matwelli

Member
no idea on the eficiency, need to test it, but she was hovering at 38% throttle

Maiden flight, as usuall windy (need to be up around 5:30 am at the moment for a still day, but the forcast tomorrow looks good)

was worried with the increased blade area (over a coaxial) it would get "lifted" during gusts, but over all seemed to sit nicely

not an exciting vid, but i like to document my flights/new builds

http://youtu.be/I_NOEVHe72M
 

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flytofly

Member
Mat, thanks for sharing. Are you using the same props for all motors? I wonder if using a steeper pitch on the bottom would make any difference? Maybe spinning slightly fast than the upper prop.
 

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R_Lefebvre

Arducopter Developer
DwarfStar flew for the first time last night. It flew perfectly right off the bat. I loaded in some suggested gains, and the results were perfect. I just tuned them up a bit and it's all set. No weird noises or visible vibrations. Smooth as butter, and just a typical APC SF hum from the props suggest nothing strange is going on. Rock solid stable. And ridiculously overpowered.

630mm Octo capable of lifting 5kg.

View attachment 7236 View attachment 7237View attachment 7238

So far so good. I'll provide more info as I get it.
 

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F

flytofly

Member
That is one beautifully built machine! Very clean. How much overlap do you have? could you upload an overhead picture showing 2 props overlap amount? Thanks!
 




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R_Lefebvre

Arducopter Developer
I flew it last night, and I wasn't as happy, but maybe it's not a problem. So the conditions were, maybe a 10-15 km/h breeze, whereas the night before it was dead calm. I took off and noticed a twitching. I started working the PID's, and it took a while before I realized I had accidentally set them back to defaults, so they weren't where I was the night before. Anyway, I was totally in "PID Tuning Mode" and not thinking straight. I couldn't get the PID's tuned, it was just twitchy. I was worried maybe in turbulent conditions there is some bad wake interactions.

This morning I got my head on straight and realized that I was trying to tune PIDs, flying very low, mostly in ground effect, downwind of a pine tree in a breeze. Just about worst case scenario.

I'm going to test more tonight.
 

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R_Lefebvre

Arducopter Developer
Two more flights last night. Conditions were dead calm again, and it flew perfectly. I tuned the PID's, and I think I was way out of range before, was the problem. I'll just wait for some wind to see now.

But otherwise it flies brilliantly. It's way way way overpowered. It can climb faster than my 600 heli. I think I got almost 15 minutes from 2 4S5000 packs, which beats the eCalc calculation a little bit. I think that typically I will want 4 4S5000 packs, because the maximum current draw of this thing is much too high for 2 20C packs. I'd need like 40C packs at least. The average draw is much lower than 20C, but when I punch it, it's way too much.
 


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R_Lefebvre

Arducopter Developer
No payload yet. I don't really have a solid plan for AUW. I have planned for at least 1kg however, representing small P&S and a solid gimbal that doesn't vibrate and buzz like most do.

I flew it last night in some light but turbulent winds and it went OK. I had to dial back the PID's more, but it's stable. Well, probably as stable as a MR can be. It's hard for me to draw a good conclusion since it's been a while since I flew my quad, and my SRH is rock solid.
 
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Fat Corgi

Fat Corgi

Member
Hey [MENTION=3314]R_Lefebvre[/MENTION], did you ever do anymore testing with your overlapping octo rig? What happened in the end?
 

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R_Lefebvre

Arducopter Developer
Well, yes, I ended up using it a little bit and got pretty good results. It was very very stable. Not saying it's more stable than anything else, but certainly not less stable, which some people thought it would be. The only real disadvantage was it does make quite a bit of noise and vibration. Due to wake interactions. It wasn't a problem though because the way that I built it, the vibes on the camera were very low. And the flight time was short at 9 minutes when I had the camera on, which is a bit lowish. But that was due to 12" props not the design.

So, it worked out pretty well I'd say. But I had a crash and never got around to rebuilding it.
 

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Rockli

Member
Good question. I think as long as you don't have all the motors on the bottom going all one direciton, and the top motors in the opposite direction

added a new question:
could you upload an overhead picture showing 2 props overlap amount?
 
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R

Rockli

Member
R_Lefebvre said:
kloner, not overlapping just partially, not a full coaxial. There is theory that says that you can overlap up to 40% of the disk area without losing efficiency (which you do with a Coaxial), and I proved it out in testing. I allows you to shrink an octo to a more manageable size.

Here's a picture of my layout.

View attachment 6269
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Good Job!
I think you to shrink an octo to a more manageable size.
 
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