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Old Jul 22, 2012, 11:07 PM
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TheFernMan's Avatar
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Multirotor Arms: Round vs Square?

I have a question.

Do you prefer round or square arms?
What have your experience been with either? Advantages and disadvantages of both?

My experience has lead been that round arms have a tendency to twist and hard to level. Carbon fiber is strong for arms and wont bend at the ends like square arms can.
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Old Jul 22, 2012, 11:47 PM
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United States, CA, Fresno
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Round:
Pro:
Easy to source
Easy to add thrust angle to improve yaw performance on static yawing rigs
Boom Clamps are more durable
They will allow the motor mount to rotate in a crash absorbing some of the impact
Light Weight

Con:
Harder to keep motor thrust angle perfect
Bend fairly easily


Square
Pro:
Motor mount is 90 degrees on top and wont rotate
very sturdy and dont usually bend
can be easy to source in Al

Con
Boom clamps can be more prone to failure at the 90 degree joint
harder to find in CF
Snap rather then bending
Heavier


I have flown and built 3 rigs with round and 2 with square....

I dont know if i have a preference
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Old Jul 23, 2012, 10:21 AM
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That's a good analysis, I used only square twice and was happy, now I am using U-shaped dual-channel aluminium that's ultra-strong. They're usually used as rails in sliding glass panes in olden-style showcases.
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Old Jul 23, 2012, 11:53 AM
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Square arms are strong (I can prove it...) and easy to install.
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Old Jul 23, 2012, 12:21 PM
recep
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Boom clamps add weight. On my carbon boom y6 they add 120 grams in case of a hexa this number goes up to 240. 40 grams per arm. I dont even count the landing skids. With a square aluminum you just mount them.
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Old Jul 23, 2012, 05:21 PM
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Quote:
Originally Posted by vineet_p View Post
That's a good analysis, I used only square twice and was happy, now I am using U-shaped dual-channel aluminium that's ultra-strong. They're usually used as rails in sliding glass panes in olden-style showcases.
What kind of material are your center plates composed of?
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Old Jul 25, 2012, 08:41 PM
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Square arms are better for a simpler build. If youre out of the frequent crashing stage i would recommend using 10mm x 750mm carbon square tube and you can strengthen them by inserting 8mm carbon rods. You can get this cheap from HK. Surprisingly strong.
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Old Jul 25, 2012, 09:10 PM
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Quote:
Originally Posted by Stunt Double View Post
Square arms are better for a simpler build. If youre out of the frequent crashing stage i would recommend using 10mm x 750mm carbon square tube and you can strengthen them by inserting 8mm carbon rods. You can get this cheap from HK. Surprisingly strong.
I found the square tube. It says 750x10.5. I don't see the carbon rod
http://www.hobbyking.com/hobbyking/s...idProduct=9012

Is that the correct one in the link?
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Old Jul 25, 2012, 10:57 PM
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Yes thats the correct link for the carbon tube. Here is the link for the 8mm rod:

http://www.hobbyking.com/hobbyking/s...w_8x750mm.html

Ive been using this setup for tricopters and so far its worked really well. I was a bit concerned about it being too weak but no. The carbon tube can split in a crash but you can fix it up easy with CA. Compared to the wood ive used in the past this stuff is much more rigid and lighter and also you can hide your motor wires inside the tubes too.
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Old Jul 26, 2012, 04:17 AM
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Thanks for the link, I've add it to my wish list
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Old Jul 26, 2012, 05:26 AM
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Quote:
Originally Posted by TheKnightFerrin View Post
What kind of material are your center plates composed of?
I don't know aht it exactly is, but it's a sort of thermosetting fiber. I cut it out of a student's examination board/pad.

Vineet
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Old Jul 26, 2012, 08:19 AM
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How's the torsional strength for the carbon set up? I'm finally out of the frequent crashing stage.
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Old Oct 28, 2012, 02:53 PM
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I'm revisiting this.

Most of the higher end multirotors use round carbon tubes.

Anyone know why versus using some square aluminum tubes?
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Old Oct 28, 2012, 03:16 PM
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This thread got me wondering, why arent we using square carbon fibre tubing?

I can agree that getting motors level with round tubing is a pain. Especially with the motor mounts I have. The way its designed means that as you tighten it, it slowly rotates around the arm. This makes it harder to level the more you tighten it.
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Old Oct 28, 2012, 03:25 PM
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Quote:
Originally Posted by malcr001 View Post
This thread got me wondering, why arent we using square carbon fibre tubing?

I can agree that getting motors level with round tubing is a pain. Especially with the motor mounts I have. The way its designed means that as you tighten it, it slowly rotates around the arm. This makes it harder to level the more you tighten it.
i have a Talon V2 frame and thats where this started. After i ordered replacement motor mounts, i installed them yesterday and i saw something i didn't see the first time around a few months ago.

when using a bubble level on the motor mount itself and laying the arm with the bracket flat on the floor, i could turn the motor mount till it was level. seem easy but it took a few minutes each arm. something that i didn't have to worry about with square arms.

you could use square carbon fiber arms, but i assume you'll still need arm blocks to mount to center plate and mount the motors.
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