Comment by I.S. on April 25, 2011 at 8:14pm

Nice job.

what arm size (length, profile, thickness)are you using?

Comment by Gerard Toonstra on April 25, 2011 at 11:33pm

15x1.5mm square tubing, 30cm long for each arm. Screwed together on the sides using 20x2 alu strip bent at 90 degree angle. The tricopter I built before had close to 45cm armlength from center to rotor. I shortened this down a bit to get more stability. Props closer to the center travel less up/down to rotate the model in the xy plane, so should be quicker in regaining the set attitude, allowing some more aggressive PID settings. I decided on 30cm more as an intuitive choice rather than anything scientific. Getting the props too close increases the influence of one over the other due to turbulence at tips and downward air flow. When going forward, front props may leave more of a turbulent wake for the aft props if they're too close together. It's probably something of a tradeoff between transport, acrobatics, weight and turbulence interactions.

Comment by robert bouwens on April 26, 2011 at 1:20am

goed gedaan!

Comment by I.S. on April 26, 2011 at 5:05pm

The thing is that I am also trying to build a scratch quad with square alu tubes of about 25-35cm.

I am looking for 12x12x0.5 like Arducopter, 10x10x1 like Mikrokopter, or something in between.

but right now all I have found is 16x16x1.5mm, don't you think this is too much?

How heavy/stiff trade off do you feel your quad has?

 

On the other hand, do you guys pay attention of what kind of alu is it? 6063, 7075,...? people here doesn't seem to care but I don't know how relevant it could be.

Comment by Gerard Toonstra on April 26, 2011 at 11:30pm

It feels heavy-ish, but the props I have are 10x4.7 with about 600-700g thrust. in terms of stiffness, the 0.5mm should already be enough. I considered U-tubing once, but that might be too much subject to torsion. The best I could find was at an online-shop for metal in Holland: http://metaalwinkel-metalen.nl/index.php?item=5&aitem=70. But I didn't like the prices and just went for the 1.5mm one. I'd say it'd be very difficult from the looks of it to get it so thin. Maybe some specialty online modelshop would have it for the fine work.

Terms of weight/flying time... I think I had it in the air for 5 minutes and that burned 2200mAh. My battery is a Turnigy 3.6Ah and another 5.0Ah. That should give me 8 and 11 minutes respectively. Doesn't sound like much, but it's enough really. I just wanted something finished for now and alu tubing doesn't cost much in comparison to the rest. If I want something else in the future, I can always replace the tubes.

I didn't pay attention to 6063 7075 or anything like that. Just didn't go for "anodized" stuff, as that would be heavier I think?

Comment by I.S. on April 27, 2011 at 4:55am

@Gerard

Thanks for your info.

 

I suppose you're using 3S lipos, don't you?

5mins with 2.2Ah, doesn't sound much not. I wish getting those numbers with a compact camera hanging, but I might be overoptimistic.

I have some Arducopter arms and also feel that 0.5mm thickness is enough for flying (maybe not for crashing ;) ), but I rather have extra flying minutes than extra strength.

The link you posted says "Al Mg Si 0,5 F22", this looks to me like some 6000 series alloy, which seems to be the general purpose one, which I suspect is good enough.

In the beginning I thought it will be easy, but Aircraft aluminium thin square tubes looks like exotic fairy dust.

Maybe I am not looking in the right place.

http://deskontu.com/ofertas-recientes/113

Comment by Gerard Toonstra on April 27, 2011 at 12:41pm

Hmmm... have you tried an antenna shop that sell material for e.g. yagi antennas?  That's one of the best bets... other than that, perhaps one of the arducopter guys can tell where they got the alu material from.

Comment by I.S. on April 27, 2011 at 1:24pm

Thanks for the advice, I don't know any antenna shop that don't just sell pre-made things, but I will keep trying.

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