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 :)

50 weeks later: Still no final spindle motor

IMG_0644.JPGI’m still working on the final spindle (motor) for the Pleasant Mill.

As mentioned before, the Dremel as spindle motor works more or less fine, but it’s way too loud for my ears! That’s why I bought a big-ass brushless motor back in mid-2011 as kickoff for a new, self-made spindle.

I found this blog post (Google translation) on a DIY spindle and decided to use it as base for my build. I even found a PDF with detailed drawings of such a spindle on this site (Google translation).

So the build began:

I bought a piece of V2A steel stock on ebay and machined the spindle body on my lathe. It was the first time for me to machine steel. Definitely a whole different deal than the aluminum and brass stock I work with normally…

The main work was to drill the 17mm through boring into the V2A. Here’re the tools I used for this job (from left to right):






After the tough job of drilling the hole, the bearing seats were machined with the boring bar:



I hadn’t a thread cutter tool for machining inner 19mm fine pitch threads a the time. So I paused the project until the ordered tools were delivered…

Still missing the inner thread:


The 6001 ball bearings fit. However, I later replaced the RS type bearings with Z type bearings.


And that’s my trash can after boring the V2A stock:


A week later or so, the thread cutting tool arrived. Here’s the spindle housing with the fine pitch thread. The threaded ring later holds the bearing in place. It’s made out of aluminum.



The rest of the assembly.  I bought the ER11 100mm spindle on ebay. The only modification was the flattening at it’s end for fastening the timing wheel with the set screw.

The distance rings were machined out of brass by me. The timing wheel’s center hole was re-bored to fit on the spindle shaft and a set screw was added.


Here’s the lower part of the spindle after assembly. The lower brass distance ring is also visible:


And the upper part of the assembly. Again, a brass distance ring sits between ball bearing and the rest of the assembly: timing wheel, another brass spacer and finally a washer and a bolt. The spacer and bold are for adding some pretension (“Vorspannung”, not sure if this is the correct word for it in English) on the bearings.


Finally, I machined an eccentric ring for mounting the motor in the retainer clamp. By rotating the eccentric ring, the disance between spindle and motor axis can be varied by some mm to adjust the tension of the timing belt.


I’m not particularly proud of the retainer clamp itself. I tried to build it from 10mm sheet aluminum without proper tools. This resulted kind of a “substandard” piece on the whole assembly. As soon as I can get access to the proper tools, I’ll build a better, cleaner version of the clamp…

Anyhow, here’s the complete spindle with the  2.5kW 1000KV brushless motor:


The motor is most likely oversized for this. But i thought it would be a good idea to run motor and speed controller (ESC) way under their ratings in order to run both for much longer time as they usually do in their RC world habitat.

And then the real problems start: How to run such a motor not from LiPo batteries but from a power supply?! I read all kinds of warnings on this in the internet. There were some guys, saying it would be ok to simply connect a brushless motor with it’s ESC to a power supply, but a lot other guys saying that the power supply won’t last for long.

Since I didn’t want to blow up my high current power supply by connecting an RC world ESC to it, and also since I read, that running a brushless motor without hall sensors won’t work very well with quick changing loads on the motor, I started to develop my own brushless speed controller, using three hall sensors I added to the motor’s housing for closed loop operation. The power stage is driven by an Arduino. I’ll write some more details on this in my next post.

Meanwhile I bought a smaller brushed DC motor on ebay. This motor has a rotary encoder already mounted to it’s end, so I thought, it would be nice to try some PID speed controlled spindle driving with it.

One problem was, that the motor’s spindle has a diameter of only 4mm while the timing wheels all have a 6mm center hole. So I machined a special spindle adapter out of brass:



I also needed a second eccentric ring for the motor retainer:


With the new DC motor I was finally able to use the spindle for the first time. It worked well and was considerably quieter than using a Dremel as spindle motor.

However, the brushed DC motor is definitely too weak for the job. I used it to drill holes in a PCB, but only for the smaller drills. Drilling the 3mm mounting holes in the corners of the PCB failed (the spindle simply stopped…).

Here’s a video of the brushed DC spindle in action. The video also compares the sound level of my former Dremel spindle to the new spindle: