A great exercise in using CAD and 3D printing to improve drone design from MAKE and 3D Systems:

My job at 3D Systems gives me the 3D tools to tinker at a high level. The highest level, really, considering we’ve got scanning, design, and 3D printing right here. I’m a lucky guy. So when my quadcopter started to show some of its design flaws, I took to a Batcave’s worth of equipment around here that’s just waiting to be used.

Comparison: Redesigned boom in green, original boom in purple. Notice the huge difference in leg length.

There were a couple of issues with quadcopter design that kept me up at night:

  1. At the end of each boom, where the motor mounts, there is a thin section. The motor mount section is actually thinner than the rest of the boom and has no support. As a result, during a hard landing (I never claimed to be a particularly good pilot), the leg would snap right off.
  2. Those perpendicular legs that stick out at the end of each boom support the quadcopter during landing. But the original legs were only about an inch and a half long, plenty long to land the quadcopter normally. But I’m also a sucker for aerial photographs, and if I wanted to mount a camera under the quadcopter, these short legs didn’t give me enough clearance to land, unless I wanted to land on the camera.

The Fix

Now, I know what you’re thinking, and, yes, I did consider a whole load of duct tape. But that wouldn’t give me the warm fuzzies like a redesign with pretty 3D printed components. Besides, a redesign would be a good learning experience with the software that I sell.

I started by scanning the original boom, which I had no problem with otherwise, and working from a model based on that scan data. The original sidewall of the boom was about .375 in. tall all the way across (with a rounded edge at the bottom) until you reached the motor mount, where it suddenly dipped to about .1875 in.

Comparison: Redesigned boom in green, original boom in purple.

Comparison: Redesigned boom in green, original boom in purple. Notice the huge difference in leg length.

Comparison from the other side. Notice the huge difference in leg length.

Comparison with original boom in the foreground. From this side you can see how the boom thins out at the motor mount above the leg.

My redesign added thickness to the boom overall. I also squared off the edges and tapered the sidewall length from the body side of the boom down to the leg. The redesigned boom starts at about .5625 in. thick by the body and slowly tapers down to about .375 in. thick by the leg. The leg side is much stronger than it was at only .1875 in. No more snapped legs. Smiles. Kittens rejoice. Cured meat for everyone.

Now on to the leg length issue. I did a couple of things here. First, I made the leg longer, almost doubling the overall length from 1.875 in. to 3.5625 in. But I also added some extra strength by thickening the legs pieces and crossbar by .125 in. each, and I moved the crossbar so it’s parallel to the ground. I wanted to make everything thick and burly, as you can see. That way the risers would be able to withstand the stress upon impact with the ground.

The redesigned boom was printed on a ProJet 6000 SLA 3D printer.

The redesigned boom was printed on a ProJet 6000 SLA 3D printer.

3D Printing and Fitting

To manufacture the piece, I went with the 3D Systems ProJet® 6000, which is a high-definition crossover SLA (Stereolithography) 3D printer that’s easy to use in an office environment. It took around 15 hours to complete the print, and it looks amazing. Perfect detail and a nice smooth surface finish. Now if I could just get one of those bad boys for my home, I could start my own RC vehicle company.

Bolting the boom onto the chassis was essentially uneventful. It fit perfectly the first time without any modification, hammering, tooth grinding, cursing or anything of the like. So I’ve got the first of four stronger quadcopter booms, which will provide plenty of clearance for a gimbal or rigid-mounted camera on the bottom.

Views: 1281

Comment by mdisher on January 18, 2014 at 7:54am

So, uhm, when can I order a set?, or actually like a dozen?

Comment by R. D. Starwalt on January 18, 2014 at 9:04am

Now you have to build the frame and toss it around the office like in the old video where the fellow stomps on it, and finally tosses it out the office building window to the parking lot below -- no damage.

That will get you total street cred in the multirotor frame club.  ;)

(can't find the link to that video after searching 30 minutes..)

-=Doug

Comment by Luis Morales on January 18, 2014 at 2:06pm

could not find the arm one either but its seems its a standard test there

http://www.youtube.com/watch?v=OTZs_mDXW4k

Comment by Luis Morales on January 18, 2014 at 2:07pm

so now i am curious about your design, apart from he support change is there any advantage in terms of vibrations? the original ones are horrible in that aspect.

Comment by Gary McCray on January 18, 2014 at 3:45pm

A few Things;


Probably nice to credit Nick Chwalek the original author (I honestly didn't think Chris had gone to work for 3D Systems.)

He said it took 15 hours to print (I presume 1 leg) and regardless at what theses printers cost, I think an RC vehicle business is a bit optimistic maybe for people who want really, really expensive RC vehicles.

Making the motor mount plate thicker is a great idea, the only reason I can figure out they didn't in the first place might be so that they could use slightly shorter screws???

And the longer landing gear is nice if you actually are going to try an sling a camera under one of these although a whole lot of people make add on gear for just that purpose.

Also, although the clones are both too fragile and too flexible, the original DJI arms are plenty strong, rigid and low vibration.

The Flamewheel clones are the bad ones with flexible flimsy arms

I have 3 of the original DJI ones and haven't broken anything more than a prop yet and I have seriously tried - Trees, rocks, pavement and even a concrete wall.

If he was injection molding them and selling them for a reasonable price I'd buy a set to give them a try.

But I like the seriously heavy duty Iris Zytel arms better.

Comment by R. D. Starwalt on January 18, 2014 at 5:56pm

I must be nuts... been at it all day (off and on) looking for that video.

Here it is:  http://www.youtube.com/watch?v=b5rjDVgJAVQ&feature=youtu.be

This is a DJI office. Notice the logo on the sides of the archway as he goes to toss the airframe out the window.

(Whew. I feel better..  ~snicker~)

-=Doug

Comment by mdisher on January 18, 2014 at 8:05pm

I would be all over these.  Unlike some, I have about a half dozen, legit, broken DJI arms.   Some of the crashes haven't been that bad either.   I've never actually broken one at the motor mount though.   I have seen where the knock-offs are much thinner up there.   Photo below shows where mine break, usually.  These were handy for a quick photo.

If I were to make them, I would make them longer as he's done, but I'd make them so that they could be 'trimmed'.   30 seconds with a dremel and you'd have the same stand off as the original arms if that's what you want ;)  

I have personally avoided DJI knockoff 450/550 frames, though I did get a HK 330 frame to transplant my QX350 which was also smashed up beyond repair and it's OK but clearly not DJI quality.

I have started buying black arms because rumor has it, they are the stiffest/toughest.   Time will tell.

Comment by Gary McCray on January 18, 2014 at 9:46pm

Hi mdisher,

I know it is possible to break DJI Flamewheel arms, I haven't manged to do so yet, but others have.

However I have kicked it up a notch with my latest though:

Hoverthings Flip Sport Frame, a 380 sized copter that uses the same DJI motors as the Flamewheel (and I am using a 4 in 1 ESC under the center plate.

Those arms are CNC milled fiberglass and look like G10, they are very very stiff and very very tough.

I have already had several sub-optimal hard object encounters and the only thing to prove fragile at all has been props.

PX4 build in wiki is here: http://copter.ardupilot.com/wiki/hoverthings-flip-sport-quadcopter/

The Flip is designed for DJI motors and ESCs so might be worth an upgrade if you are having durability issues with DJI Flamewheels.

Comment by Mike Bristol on January 18, 2014 at 11:25pm

mdisher, dude I like your parts mat ;) 

Chris, what do you think the strength of that material is compared with ABS?

Comment by Andrew Rabbitt on January 19, 2014 at 9:16pm

Chris, while you've got the printer still warm...

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