Cheapest quad trainer?

Hello everyone. I would like to contribute to flitetest but because I'm cheap and like to scratch build my models I don't buy much stuff. Maybe I can contribute with charing my experiences with this cheepy quad good for FPV. I have been training on this platform for more than two years now and I still think the concept is good. It is very durable and easy to fix. The quad parts costs around $100 plus shipping.

I have tested a drive train that I think is the cheapest, easiest build and good flying setup for a trainer. I wanted it to be easy to repair when crashing. And when you do crash, it will break as little expensive parts as possible so that you are able to quick fix it and fly again.

3S version. I have build it in two different sizes. With a 3S battery, 250mm booms are good (1m rod cut in 4 pieces). It will lift FPV gear and a GoPro with ease and fly quite fast.
Video example of GoPro HD flight recording:

2S version. For a very stable beginner quad that ignores a lot of wind but is slow and do not lift much you can use a 2S battery. You have to build the quad small and very light for this option. (mine has 180mm booms and weighs 430g with FPV gear and without battery)
Because of the small propellers, strong motor and lowered KV when using 2S you are able to use high P and D value in the PID controller. I use 2S in a small FPV trainer that I fly on windy days and learn beginners to fly FPV. Video of flight in tricky winds:

If you want to build a quad like this and don't know how to solder wires together, drill holes for 8 M3 bolts and use a windows computer. You have to learn it. Then this is a very easy build.

It is not a high end multicopter but a good, easy build and cheap trainer. Old multirotor airmans may think this is old news but I write this to the less experienced flyers.


Motor:

I ended up with the Emax 28-22 1200KV motor. Benefits is that its simple to mount on a 10x10 rod with double sided tape (Fästkuddar) and zip ties. It is very cheap and has straight shafts OK bearings and has lots of power. The propeller is also easily mounted with zip ties. Video of Balancing the motor. (Static test of motor prop combo. 166w 13.3A @ 11.8V)


Propeller:

I use the Slow Fly Electric Prop 8045SF +R from HobbyKing. It has a prop adapter straight thru the prop and is therefore suitable for a zip tie solution. I have tried many different ways of fasten the propeller on the motor and the zip tie solution has the benefits of low vibrations, propeller is mounted close to the motor and of course its cheap. Remember to balance the propellers.
For better handling the carbon fiber prop is suitable (not that cheap but durable).

ESC:

The HK blue series 12A is a good esc that is easy to flash with simonK firmware. Its a perfect match for the Emax motor. It is also cheap;)

In multicopters you choose a smaller propeller than what is recommended for the motor. That is because you want it to have more power for better control of the angular velocity. This together with the way the flightcontroller regulates the motors, multicopter motors often draws less ampere than you think. So my experience is that too big ESCs wont do any good. Only heavier. (Correct me if I'm wrong).


Flashing the ESC
The simonK firmware is needed for a good flying quad. Detailed Instructions how to flash esc with simonK. Easiest way to flash the BS12A is to use the Atmega Flashing Tool and USBasp AVR Programming Device. Link to SimonK firmware. Use the bs_nfet.hex file for this esc.
Warning. When flashing firmware in to the ESC there is always a risk of damaging the hardware. Once flashed you cannot go back to the old firmware.

It is not difficult to flash the esc with the tools. This is a short instruction how to flash the HobbyKing Blue series 12A with kkMulticopterFlashing tool and USBasp in a Windows computer:
1. Download and install the kkMulticopterFlashtool
2. Download and install the USBasp driver
3. Remove the shrink tube from the esc.
4. Connect the USBasp in the computer and the Atmega flashing tool in to the USBasp.
5. Start the kkMulticopterFlashtool application.
6. Choose settings as in the picture below.

7. Press the Atmega flashing tool against the esc atmega as in the picture below. (The corner on the flashing tool with a mark on it should be placed on the corner with a little round dot on the atmega.)
You kind of feel when the tool connects well with the atmega pins. 

8. ress the green run-button in the application to start. Hold the flashing tool steady against the atmega until the text in the kkMulticopterFlashing tool program says Done.
9. Make sure everything went well by reading the text created in kkMulticopterFlashing tool. Its going to tell you if something went wrong. -Done
10. You can tell you have the simonK FW when powering up the esc. It will beep once instead of the three beeps on a 3S battery. Video clip of the simonK sound.
11. I recommend to place a new shrink tube on the ESC for protection.

Link for more detailed Instructions how to flash esc with simonK
(Even thou I am cheap I want to give SimonK a small gift for his work but I cant find the paypal account. Anybody know where to send him a dollar?)

Flight Controller

Use the flightcontroller you like. For beginners I recommend the KK2.0. For a really cheap and light FPV solution I choose the multiwii just because it has a 3.3V regulator on board that I can use for the video transmitter module and it was extreamly cheap on a HK sale.
HK has a MultiWii NanoWii ATmega32U4 Micro Flight Controller that should be similar for $19.99.
-->Read your specific flight controller manual for a detalied setup.

I use double sided adhesive foam to mount my flight controllers. My favorite brand is "Fästkuddar". Mount the controller firmly. A small movement of the controller makes the quad react in a funny way.

-WARNING- Do not use the HK i86 flight controller with simonK flashed escs! The controller is buggy and the simonK FW has no built in safety.


Frame:
For the 250mm boom quad I use two 100x100x1.6mm FR4 center plates. They are probably overkill and takes all kinds of beating. Once I dropped it down from about 100m in to a field with no broken parts on the frame. In my small quad I use 1mm thick FR4 plate. That should be enough for the bigger quad as well, I think.
For the smal and light quad I use 70x70x1mm FR4 plates. (I don't know where to buy FR4 glassfibre laminated plates. I found them in the scrap yard. Any strong light material will do)

Suitable holes on the four 250mm long booms. Use a 3.2mm drill for the holes and M3 screws.

Motor mounts is fastened like this. Remeber to use loctite when tightening the motors.

Power cables
If you need to make longer power cables to the ESC from the battery plug 0.75qmm cable is OK. I think the easiest way to make the routing is to route all the cables from the ESCs and solder them all in the battery plug.

Other data
Small quad:

Diameter    345 mm
Weight        430g + battery (With FPC gear)
Battery       2000mAh 2S
Software    MultiWii 2.1 Källkod

Bigger quad:

Diameter    475 mm
Weight        XXXg + battery
Battery       2200mAh 3S
Software   

PID

Remember PID values are different on every build. I show my PID settings but you should find your specific sweet spot. Video of how to set your PIDs

Small MultiWii 2S quad PID:

Bigger KK2 3S quad PI:  I Use "P gain" and "I gain" value around 130.

Parts and prices

FPV gear

Done
I thought I would write a short story about my experience with this quad but it became quite long. Now I'm tired. (Gaps will be filled in later on.) I hope I didn't bored you to the ground and that you got something out of it...  :)   

Happy flying!