faq

Question	Answer
“Error, Flash download failed - Could not load file '/.axf”	Project not compiled, go to 'Project → Build Target (or press F7). Errors in code may be causing compilation to fail. Check that the number of errors is zero when compiling.
“No target connected”	Quad not powered on, you need to supply power to the board; either plug the battery, or the serial cable. If powered, check your clk and data connections. This message indicates the computer can't communicate to the quadcopter.
“Unknown target connected”	Wrong chip selected, go to “Project → Options For Target (Alt + F7)”. New window opens, switch to 'Debug' tab and on top right, press “ST-Link Debugger” Settings button. New window opens, switch to 'Flash Download' tab, select the proper chip family, press Remove, then Add, and then select the proper chip.
Internal Command Error. Error: Flash Erase failed - Target DLL has been cancelled“	Your programming wires might be too long. Try to keep them as short as possible.
ST-link USB communication error or similar popup	Disconnect/reconnect st-link from USB. This may also be a special blue board problem. read here
Select device menu grayed out	This is from video, use text instructions from post, or skip the related steps

Question	Answer
What PWM frequency is the best?	The pwm frequency changes the linearity of the motors (due to their inductance) and as such it can have an effect on flight. For 720 motors 8Khz seems to result in linear thrust. Some 6mm motors are similar. Increasing frequency reduces thrust at low throttle, so it can help with wobbles that occur while descending. 820 motors are still somewhat nonlinear even at 32Khz

Question	Answer
My quad is drifting in flight	Try the accelerometer calibration: Place the copter on a level surface, throttle low, roll&yaw center, and pitch down three (3) times in quick succession. The LEDs will blink alternating while the calibration is in process.
How do I fly acro without crashing all the time?	“There is an art to flying, or rather a knack. Its knack lies in learning to throw yourself at the ground and miss. … Clearly, it is this second part, the missing, that presents the difficulties.”