From Multirotor Pilot Issue: 1
by Petr Hejl
Lift the copter at the tips of opposing pairs of arms and see if it stays balanced.
A GPS and compass module is a must-have enhancement that enables the use of a few very useful functions of the Naza-M flight controllers. With this module, the controller is capable of GPS position hold, return-home failsafe, intelligent orientation control (home lock and course lock), and ready to be used with the ground station module.
The module’s GPS sensor and compass are depended on by the flight controller to accurately determine the correct position and heading of your multirotor, and proper installation and calibration of this module is very important for a problem-free and smooth operation of the machine. Taking time to learn how to set up this module correctly may prevent a few very tense moments, crashes, or fly-aways.
Choosing a proper location for the GPS module is perhaps the most important thing in the process. The unit comes with a small carbonreinforced mast and some 3M VHB tape to help with the install. There are also other masts available. Collapsible masts are worth considering if you’re looking to travel with your multirotor, since they make it easy to put the copter into a transport case.
The module needs to be kept as far away from any sources of magnetic interference as possible, and our machines laden with wires, motors, and other “noisy electronics” are not exactly a friendly environment for them. As great of an idea as some shorter masts and mounts are, I can’t recommend putting the module closer to the top of the frame than at the length of the factory mast.
If your battery is mounted to the top of the center plate, choose a location as far away from the battery as possible; best near the edge of the frame on either side of your battery pack. Leave at least three inches of distance between the module and the battery. If the module is installed too close to the battery, the copter will behave very unpredictably and will be extremely difficult to control.
Clean the mounting surfaces with a small alcohol pad and use the 3M VHB tape to attach the bottom of the mast to the frame. This is my preferred method of mounting because I find that things survive better in crashes if they’re allowed to pop off . Alternatively you can use screws to fasten the bottom of the mast to the frame.
Before taping the GPS “puck” to the top of the mast, run the cable to the PMU and make sure that this cable is not pressed against any sharp edges on the frame so it does not get cut.
The arrow on the GPS unit should be pointed at the front of the copter, but its exact direction should be adjusted for magnetic declination (the angle between magnetic north and true north) in your area. The declination slightly changes with area and time and the compass adjustment is necessary for the aircraft to fly straight. The best website I found to determine the magnetic declination in your area is ngdc. noaa.gov/geomag-web. This website also has a mobile version that uses your smartphone’s location and displays a picture of a compass adjusted for declination on your phone’s screen. Turn the GPS (clockwise for positive, counter- clockwise for negative) so that the arrow on the GPS points in the same direction as the magnetic north in the picture on your phone. There are four tiny adhesive strips in the box that can be used to mark the true and magnetic north directions on the unit. Check the declination and readjust it if you travel further away from your usual flying area. Slightly adjusting the direction of the module can also help resolve situations in which the copter does not track straight (it turns right or left when moving forward, also known as a “toilet-bowl effect”). In cases when compass calibration and checking the mounting location parameters in the assistant software (both procedures described further) don’t resolve this issue, simply turn the unit (very slightly) in the direction opposite to the direction it’s trying to track in. For proper operation, compass calibration (known as “Naza dance”) must to be done every time you adjust the direction the GPS module is pointed in.
SETTING UP YOUR GPS IN THE NAZA-M ASSISTANT
Before setting up the GPS in the assistant, add all gear on your copter (the camera, battery, etc.), and make sure that the aircraft is balanced. Simply lift the copter at the tips of opposing pairs of arms and see if it stays balanced. If it tips to one side, shift the gear (electronics, battery) around until it’s balanced. For ideal performance, the Naza-m flight controller unit should be mounted as close to the center of gravity as possible, with the usual mounting location being the middle of the center plate, and the arrow on it pointed at the nose of the copter.
You’ll need to measure and enter the distance from the center of the GPS module to the center of gravity in the assistant software, under the Basic-Mounting tab. Use a ruler to measure the distance along the three axis (the value needs to be entered in centimeters, 1 cm = 0.39 in.), and enter the measured values into the X, Y, Z fields. Be sure to correctly enter whether the value is positive or negative; use the diagram in the assistant software as a guide. If your machine is very bottom-heavy, or the flight controller is mounted too far above the CG, you can account for this by adding more distance on the Z-axis; on most copters I found it to be no problem to simply measure the Z-axis from the center of the bottom plate.
Next, open the IMU calibration menu under Tools tab. This menu helps you calibrate the IMU sensors and the compass. It is advisable to check the mod values and re-calibrate after the initial install, any software upgrades, or any IMU or GPS re-installs (change of location). Hover your mouse over the “question mark bubble” on the IMU calibration screen to reveal a box that explains what the normal and abnormal mod values are, and when the basic or advanced IMU calibrations should be performed. Keep the unit away from any magnets or large metal objects when performing the calibration. A message informing you that the “MC temperature is too high” and instructing you to let it “cool off ” may appear. For some reason this message always appears during advanced calibration (up to the 2.20 assistant software), no matter what the temperature of the unit is. The IMU calibration will still proceed (watch the green progress bar in the assistant) and the message disappears after it.
ENHANCED FAILSAFE AND INTELLIGENT ORIENTATION CONTROL
If you haven’t yet, you may now set-up the failsafe under Advanced-F/S. The failsafe setting decides what the copter does in case the transmitter signal is lost, and the GPS module enables the use of Go-home&Land feature. Please, read the failsafe instructions on the assistant screen, and learn how the failsafe operates before you use it.
You can also enable the orientation lock modes under the Advanced/IOC tabs. These are a great help especially in aerial videography. Get yourself familiar with the home/course lock functions by reading the description on the assistant screen, and practice flying in these modes in open areas.
INSTALL AND SETUP A GPS/COMPASS UNIT FOR A DJI NAZA-M V2
COMPASS CALIBRATION, AKA THE NAZA-DANCE
The module needs to be kept as The basic compass calibration (sometimes called “the Naza-dance”) is an important procedure done outside of the assistant software (and not to be confused with the IMU calibration). Perform a compass calibration every time you: 1) Fly in a different location, 2) Change or re-position any electronic or mechanical components on the machine, 3) Change the direction the GPS module is pointed in, 4) When the flight direction is not straight (shifting to right/left) and 5) When the LED module indicates GPS abnormality by flashing alternately yellow and red. It is ok for this code to flash occasionally, but if the unit fl ashes this code continuously or every few seconds, switch your copter from the GPS to the ATTI mode, land it, and calibrate it.
To perform the compass calibration, bring the copter outside, away from any possible sources of magnetic interference (cars, steel reinforcement, wires above or underground, magnetite), and remove any ferromagnetic materials from your pockets (keys, cellphone). Turn the transmitter and the copter on, and then quickly toggle the flight mode switch 6-10 times between its two end positions (GPS/Failsafe or GPS/Manual, depending on your setting). The LED will turn on constant yellow, indicating the calibration mode. Grab the copter by two opposing arms, lift it slightly off the ground (keep it level), and rotate it slowly 360 degrees clockwise until the LED turns constant green (the easiest way to do this is to walk around in the small circle while holding the machine in the middle, thus the Naza-dance). Set the machine back down (LED still solid green) and lift it again, this time with the nose of the copter pointing straight to the ground. Rotate the copter slowly 360 degrees clockwise again until the LED turns off , and you’re done. If the LED keeps blinking red, flip the flight mode switch to exit the calibration mode and start over.
THE LAST WORD
Take time and care when setting up your GPS/compass and you will be rewarded with an amazing flying machine with some very useful functionality.