I would recommend the latest Steveis firmware. I have tried flashing with Arduino, it work pretty well. USBasp is simpler though
See this for Windows: http://blog.oscarliang.net/flash-kk20-16-firmware-upgrade-arduino/
And this for Mac: http://www.rcindia.org/multirotors/updating-kk-firmware-with-an-arduino-(on-a-mac)/msg203151/#msg203151

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Thanks @SK, will try latest using arduino.

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I am getting the below error, any idea to fix this error?

C:\kkmulticopterflashtool_0.77\lib\avrdude\windows\avrdude.exe -P COM3 -p m644p -c arduino -b 19200
avrdude.exe: stk500_getsync(): not in sync: resp=0x15

Your Baud rate seems set at 19200 bits/sec . try changing it to 9600 bps .

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I tried that as well, but no luck.

Double check  the ICSP connections, Check the reset pin on KK board's ICSP connector is connected to Arduino Reset .
With which program you are trying to upload the HEX file ? Command line interface ?

I went by this docs http://blog.oscarliang.net/flash-kk20-16-firmware-upgrade-arduino/
KK RST is connected to PIN 10 Arduino.

Just a note, the power to KK is supplied by 9v - stepped down by regulator KA7805 to 5v, not sure if this will cause any issue.

If you are powering KK2 with another source, you should make sure the arduino and KK2 have a common ground . use a jumper to short arduino and KK2 Grounds.

Just tried with common ground, no luck still. Thanks @sooraj for helping me out.

Quote from: jsquadman on March 08, 2015, 08:36:55 AM

I am getting the below error, any idea to fix this error?

C:\kkmulticopterflashtool_0.77\lib\avrdude\windows\avrdude.exe -P COM3 -p m644p -c arduino -b 19200
avrdude.exe: stk500_getsync(): not in sync: resp=0x15

Is COM3 the right port? The port that your Arduino is on? You are flashing from the command line right? Have you uploaded the Arduino as ISP sketch to the Arduino? Please post the exact command you are using.
Oh, and try changing Arduino to avrisp as the programmer type.

COM3 is the port arduino is connected.
The command I used quoted on your post (above).
Yes, uploaded the sketch as ISP also.
Now tried with the 10uf capacitor between RST and GND.
Didnt try changing Arduino to avrisp as the programmer type yet, will try.

OK, tried as avrisp and new error 

C:\kkmulticopterflashtool_0.77\lib\avrdude\windows>C:\kkmulticopterflashtool_0.77\lib\avrdude\windows\avrdude.exe -P COM3 -p m644p -c avrisp -b 19200

avrdude.exe: stk500_recv(): programmer is not responding

Is your KK board powered while flashing?

Quote from: phanivyas on March 08, 2015, 02:37:58 PM
Is your KK board powered while flashing?

Thats funny

What's funny? 

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its funny because I would be so ignorant (or whatever) to ask for help

disconnect your kk board from power source if you are powering it separately while flashing (you are using ardunio as isp correct?)..

OK, now I get the below error and looks like the board is dead

C:\kkmulticopterflashtool_0.77\lib\avrdude\windows>C:\kkmulticopterflashtool_0.7
7\lib\avrdude\windows\avrdude.exe -P COM3 -b 19200 -c avrisp -p m644p -v -e -U f
lash:w:"C:\kkmulticopterflashtool_0.77\lib\avrdude\windows\kk21.hex":i

avrdude.exe: Version 5.11svn, compiled on Jan 18 2012 at 22:40:34
             Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
             Copyright (c) 2007-2009 Joerg Wunsch

             System wide configuration file is "C:\kkmulticopterflashtool_0.77\l
ib\avrdude\windows\avrdude.conf"

             Using Port                    : COM3
             Using Programmer              : avrisp
             Overriding Baud Rate          : 19200
             AVR Part                      : ATmega644P
             Chip Erase delay              : 9000 us
             PAGEL                         : PD7
             BS2                           : PA0
             RESET disposition             : dedicated
             RETRY pulse                   : SCK
             serial program mode           : yes
             parallel program mode         : yes
             Timeout                       : 200
             StabDelay                     : 100
             CmdexeDelay                   : 25
             SyncLoops                     : 32
             ByteDelay                     : 0
             PollIndex                     : 3
             PollValue                     : 0x53
             Memory Detail                 :

                                      Block Poll               Page
          Polled
               Memory Type Mode Delay Size  Indx Paged  Size   Size #Pages MinW
MaxW   ReadBack
               ----------- ---- ----- ----- ---- ------ ------ ---- ------ -----
----- ---------
               eeprom        65    10   128    0 no       2048    8      0  9000
  9000 0xff 0xff
               flash         33     6   256    0 yes     65536  256    256  4500
  4500 0xff 0xff
               lock           0     0     0    0 no          1    0      0  9000
  9000 0x00 0x00
               lfuse          0     0     0    0 no          1    0      0  9000
  9000 0x00 0x00
               hfuse          0     0     0    0 no          1    0      0  9000
  9000 0x00 0x00
               efuse          0     0     0    0 no          1    0      0  9000
  9000 0x00 0x00
               signature      0     0     0    0 no          3    0      0     0
     0 0x00 0x00
               calibration    0     0     0    0 no          1    0      0     0
     0 0x00 0x00

             Programmer Type : STK500
             Description     : Atmel AVR ISP
             Hardware Version: 2
             Firmware Version: 1.18
             Topcard         : Unknown
             Vtarget         : 0.0 V
             Varef           : 0.0 V
             Oscillator      : Off
             SCK period      : 0.1 us

avrdude.exe: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.12s

avrdude.exe: Device signature = 0x1e960a
avrdude.exe: safemode: lfuse reads as D7
avrdude.exe: safemode: hfuse reads as D1
avrdude.exe: safemode: efuse reads as FC
avrdude.exe: erasing chip
avrdude.exe: reading input file "C:\kkmulticopterflashtool_0.77\lib\avrdude\wind
ows\kk21.hex"
avrdude.exe: writing flash (53644 bytes):

Writing |                                                    | 0% 0.00savrdude.e
xe: stk500_recv(): programmer is not responding

Man - board is not dead, and it will never be, until you supply reverse polarity, or set wrong fuses.
Don't worry about that.
Retry the procedure .

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tried it couple of times, still same error.
What you mean reverse polarity?

OK guys, got it flashed.
It seems like the issue was the serial driver. It started working after reinstalling the com driver.

Thanks  @phanivyas, @SK1701, @sooraj.palakkad for spending time to debug with me.

I am using turnigy beast as motors and a 20 amp esc . It does fly quite well. Best of luck with your project ...(got the parts from hobby king )👍👍

Congrats! BTW the AIO R2 is an older version. I saw that R3 is out. It is available here: http://www.rcgroups.com/forums/showthread.php?t=2340156 I just switched over from Steveis 1.19S1 to this firmware. I haven't test flown it but it seems to have a wealth of features.

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Thanks @SK701, probably try the R3.

Congrats on the new FW. You should have at least flown with the stock FW and then flashed some thing custom, just to see the difference.
Anyways good luck with the maiden.

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Thanks @ashimda. Will update as I progress.