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Troubleshooting

✎

Modified 2021-07-14 by Andrea Censi

It is very very common for something to go wrong during your build. Count on it. The goal is to systematically figure out what is wrong and fix it. Mastering this process is essential to any robot project, because things will always go wrong.

The high-level bit when troubleshooting is to try to isolate the problem systematically. Rather than simply redoing part of the build or replacing a part, try to systematically verify what parts are working and what parts are not working. Your drone will not fly until everything works!

Power Issues

✎

Modified 2021-07-14 by Andrea Censi

A common issue is that your PI won’t boot or the motors won’t turn on. You should verify that each part of the drone is receiving power. The Pi indicates it has power with a red power LED. The motors indicate they are receiving power by beeping once. You can also check each part with the multimeter. Verify that there is a 12 Volt connection between power and ground on the power distribution board. And verify that the Pi is receiving 5 volts from the BEC.

Pi Issues

✎

Modified 2021-07-14 by Andrea Censi

Most of the next debugging steps require getting “into” your Pi. So if your PI doesn’t boot and display an access point, you are stuck. If your Pi is not powering on, verify with a multimeter that the Pi pins are receiving the right voltage on input. You can find a mapping of the GPIO pins here. Verify that each power pin is receiving 5 volts compared to each ground pin with the multimeter.

If your Pi is receiving 5 volts on its power/ground pins, but no red light turns on, then it might have gotten fried. This can happen if you wire or short the power/ground pins on the Pi, so try replacing the Raspberry Pi.

If it is receiving power and turning the red light on, then something might be wrong with your SD card. Verify that your SD card has the correct image flashed on it, and that it is seated in the Pi so that it can boot. If all this doesn’t work, then find a keyboard and monitor to plug the Pi into during boot, to see what is going on during the boot process. There may be an error message being printed on the screen that will give more information.

Camera

✎

Modified 2021-07-14 by Andrea Censi

Now verify that the camera is working. If the camera node is not starting in screen, use raspistill to verify that it is plugged in. You can try raspi-config and make sure it is enabled. Also it is very common for the camera cable to be plugged in backwards, or plugged into the wrong slot on the Pi. (There are two possible slots that fit the cable.) Make sure it is plugged into the slot marked “camera”, and that the cable is facing the right way. (The metal parts of the cable should be facing the pins in the slot.) And make sure it is seated all the way.

If none of these things make “raspistill” work, try plugging your Pi into someone else’s camera, and someone else’s Pi into your camera, and try all of the above debugging steps. You can also consider if the cable is bad. For example if you bend the cable too much, it will fatigue and then break the wires; or if a prop strikes the cable, it might cause the cable to break.

If your Pi and cable works with someone else’s camera but not yours, try replacing the camera. If your camera and cable work with someone else’s Pi but not yours, try replacing the Pi.

Range Sensor

✎

Modified 2021-07-14 by Andrea Censi

The range sensor passes information through the Adafruit board. Use the multimeter to verify the three wires going to the range sensor have sensible values. Check power to ground first; then check the signal wire to ground. You should see the signal voltage change in the multimeter based on the range reading (moving your hand closer and farther from the sensor.)

If that is working, then check the Adafruit board. Verify that you can read the analog range voltage reading on the appropriate pin on that board. Then verify that it is getting power.

If all that looks good, then check the connection to the Adafruit board and the Raspberry pi. Make sure the Pi GPIO pin is accurately reading the adafruit output value.

Flight Controller

✎

Modified 2021-07-14 by Andrea Censi

Finally check the flight controller. When the flight controller connects to the motors, it will make a “low beep, high beep” sound. So verify you hear the “do do do” from the motors, indicating they have power, and then the “low, high” indicating the flight controller can talk to them. If that doesn’t work, check the connection between the flight controller, ESCs, and motors.

Inside the Pi, make sure you can calibrate the accellerometer, and run the flight controller node. If those don’t work, go back and recheck your Cleanflight configuration.

Sometimes the flight controller gets wedged into a state where you can’t talk to it in Cleanflight. You can get it unwedged by shorting two pins on the board and following the instructions in Cleanflight. Once you do this though, you’ll need to set the Cleanflight configuration again.

Flight Issues

✎

Modified 2021-07-14 by Andrea Censi

Before each flight, physically inspect the drone. Make sure that your camera is mounted firmly, pointed downwards. Make sure the range sensor is pointed downwards and hasn’t gotten rotated. Make sure the flight controller board is level and firmly attached, or the IMU and gyroscope will return incorrect readings. Any of these issues could cause poor flight behavior. Also make sure each propellor is tightened down all the way.

If your drone flips the first time you try to take off, the motors are spinning the wrong way, or the props are on upside-down. If your drone makes funny noises when arming, either the props are not tightened all the way, or they are stricking a wire. Tape everything down as much as possible.

If the drone is not stable during flight, you should make sure that the props are all tightened down. Make sure the ESCs have been calibrated following as in (this video)[https://www.youtube.com/watch?v=csCBMF8P3qg].

After doing all these steps, you can try to tune the PID gains as described in our PID project.

A well-tuned drone can hover with velocity zero with some drifting, but not tons of drifiting. It should be able to hover with position hold indefinintely.