I recently built a foldable Quadrocopter for FPV, the KlappQuad.

It’s basic form is inspired by the FQuad from Warthox. I own one of these and like it a lot, but I always wanted a foldable version. Also, in order to use a brushless gimbal for the camera, the frame needed some other modifications.

The KlappQuad has a 3 piece body. The lower two plates form the rigid body, holding the foldable arms and the landing skid in place. Also the RC receiver, the flight controller and the AV sender are mounted on this rigid section of the copter.

On top of this section, hold by four soft rubber spacers, a third plate is mounted, holding the gimbal assembly (including it’s electronics PCB) and the LiPo battery (to provide inertia). Since they need to have clear view to the sky, the GPS antenna from the flight controller and the OSD (also containing a GPS antenna) are mounted on the top plate. The rubber spacers (in conjunction with the high mass of the LiPo battery) provide decent vibration decoupling of the camera from the rest of the copter.


I use a Naza Light as flightcontroller and it’s GPS antenna is supposed to be mounted on a small spike in order to get best reception. To minimize the folded size of the KlappQuad, I mounted the GPS antenna on a foldable retainer:


I machined this retainer out of brass stock on my lathe. The three pieced part took about 2hrs to produce (I’m somewhat out of practice and was happy to have something to machine after a while).

Folding the KlappQuad is a little bit more sophisticated than simply folding all four arms backwards:

In order to minimize the folded length, the two arms on the back are not only rotated to the back but also retractable. The arms are not hold in place by a single bold (like the front arms) but by two bolt heads, running in grooves on the under side of the arms. Milling these grooves was a nice and easy job for my Pleasant Mill…

One bolt head is guiding the shift and rotation of the arm with the long groove visible in the image above. The second bolt holds the arm in is “flight” end position. The groove for the second bolt is open at the end of the arm and visible in the following picture of the folded copter.


The above picture also shows the position of the front ESCs. The both ESCs for the back motors are concealed between the two lower plates in the back of the copter.

Since all arms slide partly between the two lower two plates when folded, using cable binders to mount the cables from the ESCs to the motors on the arms wasn’t an option. Instead, I drilled small holes into the arms (1mm diameter) and used 0.8mm silver wire to fix the cables to the side of the arms.

Here are some pictures of different stages of folding/unfolding the copter:


The folded copter measures LxBxH 47 x 14 x 14 cm with props and 36 x 14 x 14 cm without props. So it fits easily into a small suitcase (including RC transmitter, and some clothes).

The total weight (ready to fly, including Gimbal, GoPro Hero 1 and a 2400mAh LiPo battery) is 1150 gramms.

Last but not least:

It flights great so far. Here’s a video I shot entirely with the KlappQuad. I wanted to know if it would be possible to use this copter to shoot an “action scene”. A friend of mine an his son were so kind to help me out as actors :)

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