3D Printing Frames For Off-The-Shelf Multirotors

So what do you do when you aren't quite ready, financially or in terms of ability, to do a DIY quad build but you have a 3D printer and a couple off-the-shelf toy multirotors?

You take apart the old frames and design and print new ones!

Full disclosure, this actually came about due to necessity seeing as I broke both of the frames and had to fix them in order to keep flying. But let's stick with it being planned. ;)

The two frames that I worked on are for the Sharper Image DX-2 and the Eagle Pro 6-Rotor Wifi Drone. Both of these multirotors are pretty fun toys to fly around the house/yard, nothing special (though the Eagle Pro does have a wifi camera) but fun. I won't be doing any kind of reviews on them, mostly because the frames are broken and I don't have before pictures, but also because I'm sure the reviews exist elsewhere. Feel free to ask any questions though!

Sharper Image DX-2

I worked on the DX-2 first which has a very simple set up, nothing more than the 4 motors, 4 LEDs and the central board/battery.

I used SketchUp to design the frames due to it being very easy to use. I've also used it in the past for many different projects and I feel most comfortable with it, In the future I plan on learning Fusion360. Using calipers I measured the motor diameter and the spacing for the mounting holes for the board as well as a rough length for the arms.

The design went through a few iterations and testing (and failures) before I was inspired by a design I found on Thingiverse. 

(The picture below is the assembled middle frame above but moret than anything I just thought that it was a cool picture)

Those frames were fine but they were much heavier than the frame that came with the toy originally so I had to fly at about 80% throttle just to get off the ground. In addition it was difficult to get the diameter of the motor mounts just right and since PLA isn't flexible (well, not enough to make this design work) I had to tape the motors down to keep them from flying out, which totally happend and was fairly entertaining.

Here are the 2 frame designs in Sketchup.

Fortunately I found the design mentioned above which inspired me to use the bit of flexibility that PLA does have to grip the motors very tightly and keep them from flying out. This also allowed me to reduce the weight to about two-thirds of the original frame weight.

At this point everything was working great, despite the reduced weight I didn't really notice any longer flight times which is fine since that wasn't the goal anyway. I did end up breaking the frame at some point, I think there was a little too much tension in the curved parts so when I hit a wall it snapped. I'll probably make some adjustments but at the time I just printed another and it's survived so far.

Future plans include detaching the battery and soldering on a JST connector for some more power flexibility. I'd also like to come up with a way to mount the LEDs that are just hanging off right now. I may even try to add an FPV camera but that probably won't happen, we'll see.

Eagle Pro Hexacopter

This one was much harder to design, the issue came when I needed to mount the motors. I thought that it would be easy and that I would have a similar design to the DX-2 but the motors aren't direct drive, there's a set of gears that slow the actual prop relative to the motor. I thought about just changing it to direct drive but thought that I should try to keep it as close as possible to the original implementation at first.

Unfortunately the build area of my Prusa i3 MK2 isn't big enough to keep the same arm length as the original frame and wrap all around the gear housing so I had to do some interesting designing to grip the motor and housing. The design that I came up with allowed me to use the full size of the print bed and maximize the arm length. I printed about 6 or 7 different iterations of the end grip section before I felt good about it which thankfully only took about 8 minutes each rather than the full 4 hours for the final frame. However the arm length I was able to print as a solid piece didn't allow the props quite enough clearance and during flight they would just barely hit each other and you could hear it clicking the whole time.

Here's an image of the gears.

This is a screenshot of the frame in Sketchup. I tried to cut as many holes as possible in the frame to cut down on weight. I didn't actually weigh this one but it seemed to fly fine around 60% throttle.

This is the first and only print of this frame. As I was putting it together I realized that I measured the screw holes on the circuit board wrong and couldn't screw it together so I had to use a bunch of tape again. The original frame also included removable landing feet which I tried to integrate but the natural shrinking of the printed plastic made the holes too small and I couldn't attach them how I wanted. The next iteration will fix all these things. I also plan on reattaching the camera that came with it but didn't get around to it this time. 

Future plans include reattaching the camera, designing the arms to be 2 parts so I can make them longer and keep the props from hitting, switching to direct drive and again possibly adding an FPV camera.

Conclusion

These were a couple of pretty fun experiments, I love having a 3D printer and designing prototypes like this. There's definitely some more work that I need to do on both of them but I'm fairly pleased for now.

The next steps I have in mind are to keep improving the designs and eventually to do a complete DIY build with a printed frame.

If you guys have any questions feel free to ask! Thanks for reading!