New mini drone sub 250g

partlist:

Frame GEPRC Sparrow Mini 139mm, got it from Amazon
Motoren Emax 1306 4000kv - also Amazon
KISS AIO CC - from Flyduino or n-factory
RUNCAM Split V2 -I got it from n-factory
MATEK VTX HV - got it from Amazon
FrSky R-XSR Empfänger - N-Factory
Aluminium Prop nuts from Banggood
you will need a lighter linear antenna for the VTX - the one(s) from Matek are too heavy and too long for this build. I got some from ebay

building it

The best thing about KISS builds is that they are simple (KISS = Keep It Super Simple). So, if the build itself is simple, you can add some complexity like keeping it below 250g including HD Recording...

If you want to put these parts listed above together, you will need to modify the frame a bit. There is a little notch that is used for keeping mini cams in place. but in our build, it is using too much space. You need to grind or cut it.

Make it as flat as possible, it will keep marks in the case of the Split otherwise.

Then put together the roll bar. This is a bit fiddly but the split will fit exactly. So it will be a very tight fit. If you do it that way, the minimal angle at which the split can be positioned is about 35°. If that is too steep for you, you will have to use a different frame or a different camera.

Once you got the roll bar finished, the rest is quite simple... except...

you will have to rotate the FC 90° in Yaw (either clockwise or counterclockwise). I chose clockwise, so that the USB-Port is in the Back of the quad. You need to do the rotation as the roll bar would not fit otherwise. The FC is just a couple of mm longer than wide.

But if you rotate it, it fits perfectly

Attention: even if you set the rotation in the FC GUI for the FC itself, the motors do not rotate! Motor #1 is still front left!

But the rest is quite simple - its a KISS build after all...

update the Firmware (FC and ESC) first, as it is probably not easily possible afterwards. (boot button is blocked by the buzzer)
Mount the EMax Motors to the Frame. Mind the rotation! I only used 2 screws f- we need to save weight.
Solder motors to the motor outputs of the FC. As the FC is rotated, you will have to lengthen the motor leads a bit. 1.use short standoffs (Nylon because of weight) and attach the FC with them to the frame.
solder Lipo connection. I used Xt30 (for weight and all my other builds use xt30)
connect the R-XSR receiver. It is rather straight forward: red 5v, black GND, white S-Bus, yellow Telemetry / SmartPort

solder a connection from the RX-Pad of the Runcam Split (or Split V2) to the TX-Pad of the KISS AIO CC.
In order to be able to control the Matek VTX via the FC, you need to solder a connection between the TX-Pad of the Matek to the RX3 Pad of the AIO-CC.
Connect the beeper / buzzer. The only place I found to put it is in the front of the quad. Unfortunately it will block the boot button. Maybe I can put it to the top later. If you want to put it there as I did, use some hot glue to mount it there

connect video out from RunCam to VTX
Power from LIPO directly to the Matek VTX
I used the 5v output of the Matek to power the Runcam. I read it is possible to do that directly from the lipo, but I did not dare to. The 5V BEC of the Matek is rated for 1A - so it should be fine.
Put all together (small standoffs), put the roll bar on and do not pinch cables.
Throw away the ultra heavy prop nuts from emax and get some aluminium ones from Banggood!
Test it using a smoke stopper - just to be sure you did not short something.
bind the receiver to the taranis.
Check in the KISS Gui that everything works. Test the motors one by one if they spin in the right direction. If not, exchange 2 of the 3 motor leads.

Aaaand... here you are. should be fine now. You just finished the 3-inch-KISSer. If all worked out, it should fly now.

but you will have to have a closer look at the GUI first.

Configuring the FC...

UAV Type / PIDs

We do have a quad, a receiver that speaks S-Bus and the Failsafe should kick in after 2 Seks. The default setting was 10s, but I think 2 seks is even long! I kept the standard PIDs (3 - 0,035 - 10 für Pitch / Roll und 8 - 0.05 -0 für Yaw). Of course we will do some PID tuning later..

General Settings / AirMode

I used no Air Mode on this build, just to see a difference. Airmode means (simplified), that the FC is powered on, even if there is no throttle on. Usually when there is no throttle, the FC is more or less switched off. The advantage is, that in flight, especially when doing tricks, your quad is still controllable even if you set to min throttle. The downside is that you need to be careful when landing. This sometimes causes the quad to bounce.

When using KISS you can enable AirMode by setting Min-Command to 1000.

The alternative is, in order to keep the Quad controllable even during no-throttle time, is to set an idle up switch in der Taranis. This only adds a little value to the throttle value and keeps the FC "on" even if thottle is set to minimum.

AUX functions

With the AUX Channels you can configure additional functions that can be enabled using additional switches / sticks on the FC. So you can switch beween stabelizd /level mode and acro mode, switch on the split, change power settings of the vtx and so on.

I use AUX1 to arm the quad. When switching AUX2 to high or mid position, I switch on level/stabelized mode. The Buzzer is enabled when AUX2 is high, that means when enabling the buzzer, the quad is stabelized. That may sound a bit strange, but you only switch on the buzzer when the Quad is lying on the ground.

Using another switch, which sends via AUX4, I can switch the Power of the VTX to High. Attention in Germany you may only use 25mW!

I can switch on/off the recording of the Runcam Split using the AUX3 channel. This is cool, I can switch on / off hd-Recording mid flight!

Usually, if you have such a switch, you do not want the switch to start recording when powered on. You need to change this setting via the OSD or the Wifi-Module and the App.

Advanced Tab - Lopo Alarm

I set a lipo alarm f just for safety.

13,9v only works for 4s lipos!

Advanced Tab FC Orientation

very important here you need to set the 90° for Yaw - or the copter will not fly at all or crash instantaneously!

if you rotated your FC the other way, you will have to set 270° here. Check your settings in the live view on the Data Output Tab!

Advanced Tab - VTX Config

This is very important. You need to set the right vtx type here. If that is correct, you can change power, band and channel via the taranis. For the Matek VTX you need to set it to IRC Tramp!

Band and channel is the Band and channel that will be set when powering on the FC. You can change that via the Taranis later if you want.

Verdict

It is still a bit early as I could not fly her yet. But she is a beauty the 3-inch-KISSer

And it is below 250g Puh...

Update 1st of January 18

I went for the Maiden Flight. It was fun and all went well... almost. One Crash and the frame broke. Not sure if it was my flying "skills" or the Frame...

Watch the whole Flight on youtube

update 2nd update 10th of January 18

got spare part (a new Frame) and re-built it. Flies now as before. It does not look like, there is a design flaw at the frame. Hope this one lasts longer than the last.