Hi!

I've built micro quadcopter 10 months ago for the purpose of learning acro mode (source: https://oscarliang.com/build-fpv-micro-q...lest-quad/ )
Oscar's blog helped a lot and I was able to make it fly but with FPV equipment micro quad flight time was less than 30 sec.
Then I have decided to take off FPV equipment but even then I could fly only for less than a minute which was quite disappointing. Quadcopter feels sluggish and lacking power.
I was trying to troubleshoot further, tested different battery types (Turnigy 300 mAh, CX-30 500mAh) but the results were not so good.
After that I have dropped CJMCU project until few days back.

As I'm very stubborn person I decided to read and learn as much as I can and tried to make it fly


What I have done so far:
- changed FET's on CJMCU - no difference in flight time
- added step-up voltage converter to power up RX to fix the issue with VD5M losing radio signal due to voltage drop below 3V

Total weight of the build: 
- 27,9 g without battery


I would appreciate any suggestions and ideas how to improve flight performance of this tiny CJMCU board  

Hi,

I have changed concept a bit.
- Replaced 7mm motors with Chaoli 8.5 mm motors from BG.
- Also replaced VD5M with micro frsky receiver from BG
- Using 750 mAh Eachine lipo

In result I'm getting way longer flight time up to 4 min but still experimentig with different props and lipo's.
I had very poor performance with 300mAh turnigy nano tech lipo. I need to investigate that.

I know there are loads of F3 boards around etc but learnig stuff on that cjmcu board is nothing but fun

Next steps:
- fishpeppers mod of fet circuit (1k resistor as described here: https://www.rcgroups.com/forums/showthre...?t=2456739 )
- replacing fet's to IRLML6244
- PID's tuning - I've no idea where to start
- figuring out FPV setup (most likely FX798 will be chosen)

Let me know if you have any recommendations :-)

wow didn't know the FET on that FC can actually handle 8.5mm motors.
For FPV i would recommend to get the TX01 VTX/Cam $15 cheaper but perform similarly to the FX797/798

about PID tuning, i wouldn't spend too much time on that, it's just too hard to see much of an effect on such a tiny rig quickly tune it like you normally do on a 250, as long as it handles the way you want then that's good I think Rate/Expo actually plays a bigger role when it comes to handling.

(13-Nov-2016, 01:39 AM)Oscar Wrote: wow didn't know the FET on that FC can actually handle 8.5mm motors.

Onboard FET's are doing fine indeed. I can fly but when I punch it feels much slower than on F3 brushed evo boards.
Also noticed that after 4min of flying battery and motors are barely warm on cjmcu and on F3 boards both are very warm if not hot. Interesting....
That is why I'd like to experiment with FET's more as they might be a bottleneck. Will see

In terms of fpv cam I just have FX798 in hand and few of TX01/02 on their way
I never actually tuned PID myself so I'm entering a whole new world. Quick research on Rate/Expo revealed it could be indeed a major player here

Thanks for the tips!

"Also noticed that after 4min of flying battery and motors are barely warm on cjmcu and on F3 boards both are very warm if not hot. Interesting....
That is why I'd like to experiment with FET's more as they might be a bottleneck. Will see"

Some very interesting follow up on that one....
I have changed FET's to a stronger ones but that was a false lead...
After that I started to trace pcb paths etc and I realized I missed the obvious ... battery losi connector is soldered to pcb board which goes to first nano switch and then to second charging switch.
I got rid of them and shorted them.
It looks that thise tiny switches were bottleneck for high current and right now flight time increased from around 4 min to 7 min without FPV.


Also I have upgraded firmware from cleanflight to betaflight as betaflight also support CJMCU however its terrible to control the quadcopter with stock PIDs

I have tried some manual values from different forums but still it feels over responsive even after playing with rc rate and expo.

Anyways for all of you still having that board of the bottom of the drawer... there is a chance to give CJMCU a second life

Cheers!

I have lost 2 motors and waiting for a slow boat delivery
Anyways it looks like there is one thing left I want to try which is introducing some changes to fet circuit as suggested by fishpepper here:
https://www.rcgroups.com/forums/showthre...quadcopter

"Additionally remove the gate driving series resistors and put them between gate and source of the fet. Now mount a 1 k resistor (0603 or 0805 will fit) on the now empty spots.
This way there is a defined level at the mosfet when the board fw is not running and the 1k resistor alows a better driving of the fet."

Apart from that I was able to get schematics for CJMCU so I can dive into that and possibly compare to other brushed controllers like Alienflight which is quite interesting opensource fc project btw.

Cheers!