My daughters and I have built several quadrotors out of aluminum and also a mini quad out of kite parts (see beatty-robotics.com for these). But for this next project, we decided to make a quadrotor out of carbon fiber. We applied everything we learned on our previous builds and also tried a few new ideas that we hadn't tried before. 

 

The arms of this new quad are made out of (4) 8" lengths of 3/4" square carbon fiber tube. On our past builds, the motor mounts often bent (and had to be replaced) on "hard landings," so this time we dispensed with the motor mounts altogether. We drilled the mounting holes directly into the arms (as shown in the picture below). That may be worse. It might just break the arm instead of bend the motor mount (which would be a worse failure mode obviously). We'll see how it goes. I noticed recently that the 3DR kit also appears to use the same technique on their aluminum arms.

 

The center plates are made out of two 6" x 6" squares of carbon fiber. In previous builds, we always stacked multiple plates vertically to mount all the electronics and store all the gear. In this case we decided to "go wide" instead of "go tall."  The idea was to flatten it out and make it more crash resistant, and to reduce overall weight and parts by having fewer plates, fewer fasteners, and no standoffs at all (the arms separate the plates). It also provides more of a fixture-surface for the arms and it gives us a place to store the ESCs and all the wires (We solder our own Power Distribution Unit out of Deans connectors). We'll see how that works.

Next, we wanted to try the switch idea that I had discussed and asked about in the forum. We have installed a decent-sized (but relatively light) illuminated automotive toggle switch. When the quad is stored in the house, the battery will be disconnected, but out in the field, we'll use the switch to turn the quad on and off. It's very quick, easy, obvious (red), and it can be reached without putting your hands in the path of the props. We're hoping this will be convenient and safe. In retrospect, it might have been even better (safety wise) to put the switch on the outside edge of the underside. (Note: I'm aware that 20 amp automotive switch may or may not be suitable for the ultra-high amps of a quad rotor, but refer this Forum post for our extensive discussion on that subject). We'll see how it goes.

We've had a lot of trouble with landing gear in the past. We've tried a number of approaches and none of them have been satisfactory for us. On this build, at least initially, we decided to test out the 3DR landing gear pieces available in the DIY-Drones store. They seem like they are going to work well. 

I have uploaded pictures of the completed quad as well as an image of our CAD drawing and a few in-process pics. It's too wet to fly today, but hopefully we will be able to post a video soon. 

 

 

Views: 4189

Tags: arducopter, carbon, deans, fiber, quadrotor, switch

Comment by Marko Kleine Berkenbusch on October 14, 2011 at 10:25am

Hi Robert,

Congrats on a very nice-looking quad frame. I have been using the 'sandwich' and go-wide method for most of my quad frames so far and I don't see a reason not to do it this way. Along the same lines, I used to make my own motor-mounts out of Delrin plastic and fiber-glass plates, but have lately resorted to just bolting the motors straight to the arms (I use aluminum rather than CF, but other than that it is the same idea) - much easier, lighter, and thus far without any noticeable disadvantages. Keeping it simple never goes out of fashion...

I  completely missed your discussion about on/off switches - I actually use the exact same RadioShack switch you are using (I picked the blue variety, though ;-)). You can see it sticking out the left on the first picture of this blog post: http://www.diydrones.com/profiles/blogs/quad-with-optical-flow .

I have also used this switch on another, slightly larger quad (1.2kg AUW) - I have not had any issues with the switches whatsoever so far (plenty of crashes, but none that could be attributed to the switch)... I think being able to quickly turn off the quad via switch can be much safer than having to fiddle with battery connectors...

Marko

Comment by Ian Lee on October 14, 2011 at 12:12pm

Looks almost exactly like what I have in mind for my next frame.  Where did you source your carbon fibre?

Comment by Robert Beatty on October 14, 2011 at 12:36pm

Marko:

Thank you. It sounds like both of us are moving in the same direction, which is good to know that at least some of these ideas make sense. I like your quad. :)

--Robert

Comment by Robert Beatty on October 14, 2011 at 12:44pm

The carbon fiber is from DragonPlate (www.dragonplate.com), who have been excellent to work with. I made the plates from 1/16" solid carbon fiber sheet (glossy on one side, rough on the other). I made the arms from Braided Carbon Fiber Square Tubing 0.75" x .75" x 24". Carbon fiber is expensive as compared to the aluminum that I was using, but thus far I really like it. Note: They don't make carbon fiber 1/2" square tubing, but the 3/4" actually works very well.

 

Comment by Ellison Chan on October 14, 2011 at 1:20pm

Just wonder, because I use lexan sheet for my centre plates.  How's the flex on the carbon fibre?

The lexan flexes quite @ 0.06 inches, but once sandwiched between aluminium tubes, it's extremely stiff.  The lexan sheet cost under $5, how does that compare with carbon fibre?

Comment by Robert Beatty on October 14, 2011 at 6:07pm

The carbon fiber has very little flex at this thickness. The carbon fiber is much more expensive than Lexan. The main selling point is a high strength-to-weight ratio.

Comment by healthyfatboy on October 15, 2011 at 9:21pm

Out of curiosity, why aren't wood arms used like on tricopters? I know the v2.5 tricopter on rcexplorer.se just mounts the motors directly to the arms. Maybe it just flexes too much?

It seems like a cheap way of doing it and easy to replace if you break an arm.

Comment by Ellison Chan on October 15, 2011 at 9:27pm

Well, I use 4 trex 450 tail booms for arms, and the total weight is about 30 grams.  Not sure if wood can beat that in weight.  It takes two tail boom cut in half to make four arms at $1.00 per arm.  Not sure if wood can beat that.

Comment by Robert Beatty on October 16, 2011 at 11:16am

healthyfatboy: I prefer working with aluminum or carbon fiber rather than wood, but there are quadrotors, both home made and commercial, that are made out of wood. 

 

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