When they’ve been built and maintained properly, multirotor aircraft can be very reliable because they are mechanically quite simple. Their complexities arise from the fact that their power systems are managed by a flight controller that’s connected to the power system with a network of wires, cables, and connectors. In this article, we’ll take a look at some of the more common problems and review some logical troubleshooting procedures.
1.Multirotor drifts or yaws without control input.
This could be caused by one or more problems. First, inspect the multirotor booms to confirm that they are not twisted, bent, or damaged. If the motor mount is clamped to a round boom, verify that it has not rotated and remains perpendicular to the vertical- or Z-axis of the multirotor. If you don’t find any mechanical problems, the next step is to calibrate the magnetometer. Follow the manufacturer’s instructions for your flight controller and see if calibrating the magnetometer is the root of the problem. If the problem persists, it is possible that ferromagnetic materials came within close proximity of your magnetometer. Either replace the unit or perform the procedure to correct the issue and verify proper flight operations. Calibrate the compass before the first flight and when you’re flying in a different area. Make sure to keep away from ferromagnetic substance and other electronic equipment when you’re calibrating and flying. If the multirotor continues to drift, an advanced calibration may be required. Connect the flight controller to the software assistant and perform a basic, as well as an advanced, calibration.
2. Multirotor flies erratically or uncontrollably.
Even though multirotor aircraft have few moving parts, they are the most critical components as they provide the thrust. Lack of control is a serious issue, so the first step is to confirm that all motors are rotating in the proper direction. This is best done with the propellers removed. Mark the direction of rotation on both the motor and the airframe, in case the motor needs to be replaced. After you’ve confirmed that all motors are turning in the correct direction, verify that the appropriate left- and right-hand props are mounted on the correct motors. It’s also important to confirm that the propellers are not inverted, so take your time and double- and triple-check the mounts. If this does not resolve the problem, connect the flight controller with the assistant software and confirm that the correct mixer type has been selected. Also verify that all the speed controls are plugged into the correct ports on the flight controller. Finally, confirm that all transmitter switches are in the correct position for the desired flight mode.
3. Multirotor “returned to home” unexpectedly.
The radio range of many multirotors is approximately 300 meters, so always perform a range check prior to each flight. If the multirotor exceeds the communication range of the transmitter, it will automatically land if the fail-safe mode is active. Signal loss between the transmitter and receiver may occur if the transmitter is powered off or loses power from discharged batteries. Another cause for the unexpected switch to
fail-safe mode could be the loss of one or more connections between any of the receiver channels and the flight controller. It’s important to know that the multirotor will only return home if it’s in GPS mode and has acquired six or more satellites prior to takeoff for at least 8 seconds. Before takeoff, the current position will automatically be saved as the home point by the flight controller, so be sure to stay clear of that area when you operate the multirotor.
4. Motors or speed controls are very warm after flight.
It is important to check the temperatures of all the motors and speed controls after each flight. A motor that is warmer than the others may indicate a worn bearing or another issue that needs to be addressed. All speed controls have heat sinks to help dissipate heat. However, if you are operating your multirotor in a very hot climate, the speed controls may approach their maximum operating temperature. In this case, you may need to either add a larger heat sink to each unit or relocate all speed controls closer to the motors so the airflow from the propellers can keep them cool.
5. Multirotor oscillates or is too sensitive to controls.
Most flight controller manufacturers recommend using their default gain parameters, but you may need to change these settings if you’re flying a multirotor with custom or upgraded components. If gain is too large, you’ll find that the multirotor will oscillate. If it’s too small, the multirotor will be difficult to control. You can use the remote gain-tuning channels to tune the gains during flight to save time during setup. Follow the instructions in your controller’s operating manual to assign one of the transmitter channels in the “Remote Adjust” section of the assistant software for the gain you want to tune. Only one gain can be adjusted with one channel at any time. Make small changes in the gain, between 10% and 15%, until you have your desired control response. Set the gain sequentially for each parameter: pitch and roll, yaw, attitude, and altitude.
6. Multirotor vibrates during flight.
The problem of in-flight vibrations tends to be mechanical in nature. Inspect and rebalance your props as they may have become nicked and/or damaged. If the vibration is moderate to severe, it is likely that either a prop adaptor or a motor shaft is bent. Disconnect each motor from the flight controller and test each independently to find the problem. Replace the damaged component and test to verify the smooth operation of all motors individually.
7. Multirotor has reduced flight time.
The most common cause for reduced flight time is a problem with the LiPo battery pack. It’s critical to use a high-quality lithium-polymer charger to simultaneously balance and charge each cell. Modern chargers can also display the internal resistance of each cell in the pack and this figure should be logged to monitor battery health. Flights that discharge the battery to the nominal voltage of 3.7 volts per cell will increase the life and number of cycles you can get from the pack. Excessive depletion will cause swollen or “puffy” cells that will decrease flight time and performance. Never take any chances by flying with swollen or damaged cells as this will put your multirotor at risk. Investing in high-quality LiPo batteries will increase the reliability and safety of your multirotor.
It is important to note that increasing the payload on the multirotor will proportionally reduce flight time. Exceeding the manufacturer’s recommended maximum payload will significantly reduce flight time and make the multirotor difficult to control. Finally, remember that LiPo batteries don’t perform as well in cold weather. If you are operating in a cold environment, charge and store your batteries at room temperature if possible.
I hope these troubleshooting solutions to common problems will keep your multirotor in the air. When in doubt, it’s always better to stay on the ground and fix any concern before you fly. As pilots always say, “Takeoffs are optional; landings are mandatory.”
By: Gus Calderon
