Overlapping Props

They are lovely powerful motors and that quad will be wicked , It reminds me of my 450 with 1200kv NTM motors from zero to 60 feet in 4 seconds
 
I have a Reptile frame just sitting here. I also have some extended arms. You have inspired me, ringalong! The motors and props look brutally sinister! You gonna take your pets for rides?? Haha! Then you could have a real dead cat!!!!:)
 
I do. I have T-motor 3508 380kv undamaged from my last flight/crash(that's my way of redistributing parts from build to build Haha) I just need new props. I have everything else. I'm going to damage the budget and get some T-motor props this time. See how they do. Mine won't be 8oo like yours. Closer to 650. I really should finish the other 2 I have started. Or not.........We'll see. Wait. What? Oh look! Squirrel!!
 
Finished manipulating all of the motor mounts, and got one completed this evening. Three more to go :)

IMG_2142.JPGIMG_2143.JPGIMG_2144.JPG
 
Got it in the air. I am not sure if this frame is going to work out though. It was vibrating a lot, and I am not sure how to correct that without larger arms or a stronger frame. It was up and down vibrations not side to side.

Super quiet though.

http://rl.dyndns.info/MySite/quad17.m4v
 
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Slow motion to show what it is doing. I played with gains a little, but lowering and raising did not seem to affect what is going on here. It would be so stable if it was not for these vibrations :(

I will try a larger battery later in hopes it is a weight issue.

Any recommendation?

 
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It looks and sounds great! On my old Reptile frame(the crashed one), I added another spacer on each side at the center between the front and back arms. For better stability I mounted my battery underneath. I made a battery bracket out of aluminum. That may have added stiffness as well. It's probably something simple like a couple of loose arm screws. So frustrating.
Maybe something like the lateral upper strut mount support on performance cars. Takes the flex out of the unibody. You could take a 1/8" X 5/8"strip of aluminum and run it across the bottom of the frame from left to right arm mounts. Use slightly longer screws to mount it to the arm bracket. I may have done that by accident when I made my battery holder. Food for thought........
 
This project did not survive :(

I had a custom 2.5mm carbon fiber frame cut, and the tips of the arms still vibrate. I think the plastic arm mounts are just not strong enough for the 4216 motors. This sux!!!!! Now I am deciding what to do.

This is the best built hex frame that I could find that I could use the e1200 on that is under 900mm. I don't want too large of a frame.
http://copterlab.com/foldable-hexacopter-kit

Any other suggestions or ideas?
 
ringolong said:
This project did not survive :(

I had a custom 2.5mm carbon fiber frame cut, and the tips of the arms still vibrate. I think the plastic arm mounts are just not strong enough for the 4216 motors. This sux!!!!! Now I am deciding what to do.

This is the best built hex frame that I could find that I could use the e1200 on that is under 900mm. I don't want too large of a frame.
http://copterlab.com/foldable-hexacopter-kit

Any other suggestions or ideas?
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Vibrations? Mount what you can with jellos, balance the motor hums and props, add some vibration dampening to the motor mounts, something like a gel or foam in between the plates. It was a problem I experienced using CF props and aluminium frame hahaha.
 
It's large vibrations, not really jello. The motors and props are balanced from the factory, maybe I will tighten them and see where they land on the balancer.

It is an up and down vibration, not side to side like a prop is out of balance.
 
The arms will raise a little before the opposite arm on the same font or back side when it is sitting on the floor when I pick up on any arm. Its the mount that is flexing.
 
Is it ok for the tips of the arms where the motors are to vibrate?

It looks like a lot of people are having this same issue with 15 inch props too.
 
ringolong said:
Is it ok for the tips of the arms where the motors are to vibrate?

It looks like a lot of people are having this same issue with 15 inch props too.
Click to expand...

It could be we were wrong when we said that as long as the props didn't touch it would be ok. Since you're props and motors are balanced the only thing left is the prop clearance issue. My guess, not a proven fact, is there is a shear force in action at the tips of the counter rotating props. Sort of like how a torque converter in an automatic transmission works. That is likely the cause of the arm tips vibrating and could be the cause of the arm oscillations. You have the front and rear motors changing speeds constantly while rotating in different directions. The more I think about it the more I'm convinced that we, or at least, I was wrong to think there wouldn't be an issue with the props that close.
I used 15X5.5 props on mine with no problem but I had a few inches clearance. You could try some 11 or 12" just to see if the tip vibrations go away. I think you are spot on about the mounts being the weak link and causing the arm oscillations. I have seen quite a variety of aluminum mounts listed online. Maybe there is a design that would work for you.
If the smaller props eliminate the tip vibration then I would suggest that you seriously consider extending the rear arms. You could do it by using arm extensions like the ones from Phoenix Flight Gear or by replacing the arms with ones the right length. You are using quality materials, motors and props so it is likely a design issue rather than components.
I don't have a background in fluid dynamics, but from building and racing cars and motorcycles way back when we learned a lot about turbulence and shear forces.The mounts are an obvious problem. The shear at the props tips is just my guess. I think you could fix this for far less than the new frame you are looking at.
One more thing. Like you, I no longer buy the cheap stuff. Since using only the best that I can afford (and checking the prop balance) I discovered that it is no longer necessary to use isolation materials for mounting cameras or any other equipment for that matter. Again. I think your current problem is solvable by a design adjustment. It would be rare to work perfect the first time.:)
 
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