Whether it’s your first quad or you’re a seasoned builder, there’s always the potential that something will go wrong. You’ve armed and found that your quad powers on, props spins up, but won’t take off. The flight controller software needs to be told a lot about its setup and the environment to work properly. When these things don’t line up with reality, the quad goes in the wrong direction. It starts trying to correct for this, causing it to even more forcefully go the wrong way. This causes a complete flip-out as soon as you try to move. If you are running a recent version of Betaflight, your quad may refuse to lift off instead of flipping out. Betaflight now attempts to detect when the quad isn’t acting appropriately to your input and will quickly shut it down. This is much safer! If Betaflight killed your quad for this reason, you will see the “RUNAWAY” status warning on your OSD. Not all of the problems that can cause a flip-out are caught by runaway protection, but the steps you take to fix that problem are the same.
There are a lot of reasons this can happen. Today, you’ll learn how to fix this common but frustrating problem.
When troubleshooting this issue, once you’ve confirmed that the props were installed properly, the next thing you must do is take them off. When a quad spins up but the user doesn’t have complete control, it creates a dangerous situation. No good will come of trying to debug this issue with props still attached.
Are your propellers installed correctly?
- Make sure your props are all right-side up. There is almost always some raised writing on the prop, which should be installed on the top. If not, look for a subtle “C”-shape to the blades. The opening of the “C” should point downward.
Make sure all of your props are facing the right direction. The arrow on the diagram should point from the low side to the high side of the blade. In other words, if the motors were spinning in the direction shown, the high side would catch the air first. If your prop is right-side up but pointing the wrong way, you need to switch it for a prop of the opposite direction. Props come in both clockwise (CW) and counter-clockwise (CCW, often marked with “R”) types. Your quad must use two of each kind.
- In rare cases, you might be running a reversed “props-out” configuration. If that’s true, all of your props should be the exact opposite. You will still use two of each kind, and they should be installed right-side up.
More information: Understanding Props: Proper Installation, Performance and Safety
When Crash-Flip mode (also known as “Anti-turtle” or just “Turtle” mode) is on, the quad behaves very differently. If your quad does not respond to throttle but flips out when you touch pitch or roll, this is probably your issue. “CRASH FLIP” in your OSD status also indicates this.
- Check all the switches on your radio to make sure none of them may have activated this setting
- Visit the Modes tab in Betaflight. Make sure Crash-Flip mode is disabled, or set so that it is not switched on while your radio is powered up.
Related: Save Your Race with Anti-Turtle Mode
Check Motor Direction
- Plug in a battery and use the “Motors” tab in Betaflight to spin up your motors. Each should be spinning according to the diagram.
- If you have a “props-out” configuration, all four motors should spin in the opposite direction from the diagram. (Some versions of Betaflight Configurator update the diagram when the setting is toggled. If yours does, it will also show “reversed”)
Motors spin at such a fast rate that it can be hard to see which direction they are moving. You can use your finger to lightly touch the motor bell and feel the direction it’s moving in. This won’t hurt it; normally you have props attached and the motors have to spin under load.
If any motor is working opposite what you want, you need to change it. You can do this by desoldering and switching any two wires between the motor and the ESC. For most quads these days, there’s a simpler approach: adjust the motor direction setting in BLHeli. Your can read about how to do that in our article, How to configure your BLHeli ESCs.
Check Motor Reverse Setting
Betaflight needs to know which motor direction you are running (standard vs. “props-out”). The command you use will depend on the Betaflight version. Make sure the commands you use match the motor direction you have!
- For very recent versions of Betaflight Configurator, there’s a switch on the “Configuration” page to easily check this instead of the CLI commands below.
- Visit the CLI tab and type “set YAW_MOTORS_REVERSED”. (For Betaflight older than 3.2, it’s “set YAW_MOTOR_DIRECTION”.)
- For a typical configuration, you should see “OFF” (or “1”). If not, then run the command “set YAW_MOTORS_REVERSED=OFF” or “set YAW_MOTOR_DIRECTION=1”.
- For a reversed, “props-out” configuration, you should see “ON” (or -1). If not, then run the command “set YAW_MOTORS_REVERSED=ON” or “set YAW_MOTOR_DIRECTION=-1”.
If the flight controller doesn’t know which direction it’s pointed relative to the motors, it’ll make incorrect corrections that cause a flip-out.
- Connect to Betaflight. You should be in the “Setup” tab by default. The green arrow matches the direction your camera is facing.
- Tilt your quad left, right, forward and back. If the pictured quad does not follow your movements, adjust the “Board and Sensor Alignment” in the Configuration tab. Most likely, you will need to change the Yaw by 90 degrees one way or the other.
Recalibrate the Accelerometer
A poorly calibrated ACC causes the flight controller to think it is angled incorrectly, which can cause it to constantly try to flip over.
- Also in the Setup tab, place your quad so that it is level. (You can just eyeball it for the purposes of diagnosing the problem, but not being perfectly level will introduce some drift.)
- Disabling the Accelerometer in the Configuration tab will also resolve this issue, but it will prevent you from using stabilized flight modes like Angle and Horizon.
The mixer tells the quad which motors to spin in order to get the craft to angle in the right direction. This is set in the “Configuration” tab. It should always be set to “Quad X” unless you’re running an unusual motor configuration (such as a tricopter, hex, or “plus” layout).
You can wipe clean the entire configuration and update your firmware in the process to take advantage of any recent bug fixes. If you’re doing this to fix a problem, we recommend only using “stable” releases, avoiding “beta” versions of the firmware. (Note to new users, “Betaflight” does not imply it is always “beta” software; it has both “stable” and “beta” releases.)
- Take a backup of your FC settings. How to make a Betaflight backup (and restore it!)
- Reflash your flight controller and all of your ESCs. Updating Your Flight Controller & BlHeli ESC Firmware
You Might Have a Mechanical Problem
If your quad flew perfectly and you haven’t changed any parts or settings, there’s a chance that some component has gone bad.
Bad Motor or ESC
A dead motor or ESC will cause the quad to flip on takeoff. Flipping toward the same direction every time often indicates this problem; a poorly performing component doesn’t provide thrust and ends up being the “low” side when you apply power. Inspect these components carefully to see if there’s any sign of damage, and replace them if necessary.
If the angle of the quad in the Setup tab is wrong and recalibrating doesn’t help, (or doesn’t stick,) you probably have a bad Accelerometer. You can disable the ACC entirely in the Configuration tab, but stabilized flight modes like Angle and Horizon won’t work anymore. However, you can still fly this quad as long as you only use rate mode. Most serious racers and freestylers do this anyway, and it’s a great skill to learn.
Related: Learning Rate Mode
If quad in the Setup tab is behaving erratically or constantly spinning, you probably have a bad gyro. Unplug and plug your quad back in just to make sure; the gyro should recalibrate each time you power up. If the issue persists, you will likely need to replace your flight controller.