What's a Headspeed Governor?
The AR7210BX is equipped with an internal headspeed governor function. What this does is controlling the throttle automatically, so that the rotor headspeed of the helicopter stays consistent in flight. I.e. when you add pitch and load the rotor disk, the system will add more throttle in order to prevent from sagging headspeed, when you descend quickly the system on the other hand will have to lower the throttle to prevent from overspeeding. Usually this is what you try to do when using the throttle curves of your transmitter, but this is very inprecise and will not give reproducible results. It's much more convenient to just tell the system what rotor headspeed you want and this will maintain the given head speed for the whole flight, even when batteries go empty or the motor starts to run lean. The governor function can be used with electric heli which doesn't have a governor or "heli mode" built in the speed controler or when the governor function of the speed controller doesn't maintain the headspeed very well. For helis with combustion engine you don't need to buy a separate governor device anymore, with AR7210BX you already have it built in your receiver.
Thus the Headspeed Governor of AR7210BX can be used, the system must be able to detect the motor speed. This is done with the help of a speed sensor that is plugged to the port AX2/RPM on the AR7210BX (the AUX2 output becomes an input when enabling the Governor!). For models with nitro/gas engines usually sensors are used that determine the speed signal magnetically or optically. These sensors are mounted next to the crankshaft or clutch bell and register the number of engine revolutions here. For electric motors the motor speed can be determined electronically. For this purpose a phase sensor (e.g. BXA76013) is connected to one or two of the motor phases. Some electric speed controllers also offer a direct signal output for the rpm signal, so that no additional sensor is required.
To see how the sensor is mounted in detail please refer to the instruction manual from the sensor or from the helicopter. The speed sensor plugged to the port AX2/RPM on the AR7210BX which also powers the sensor with the supply voltage, if necessary. Note that the height of the supply voltage corresponds to your receiver power supply voltage!
Here are some installation and connection examples. As described virtually all kinds of rpm sensors may be used. Unfortunately it is impossible to try and enumerate all types. If in doubt about whether a particular sensor can be used in conjunction with AR7210BX ask your dealer to find out.
Electric drive system with external phase sensor
Connect the motor wires of the phase sensor with any two phases of the electric motor. It is recommended to solder those wires to the plugs of the speed controller. So for maintenance purposes it is easier to remove the motor from the model later. In some cases the use of only one phase wire is sufficient. Usually this is the case when the speed controller powers the system with a BEC thus there is no galvanic isolation between motor and receiver circuit. However, we recommend using both wires in any case! This ensures that the sensor provides an interference-free signal as possible.
The electronic speed controller is plugged into the throttle output [THRO]. The phase sensor is plugged into AX2/RPM input.
Electric drive system with rpm signal output from the speed controller
When a speed controller is used that provides a rpm signal output you can directly plug the sensor wire from the ESC into the AX2/RPM input on the AR7210BX. In case the speed signal wire also has power lines watch our for correct polarity. The signal wire must be on top, the minus wire is connected at the bottom of the AR7210BX pin board. In case your speed controller doesn't come with power lines and only has one wire instead, make sure this wire is connected at the top of the device. The speed controller‘s control signal input is plugged into the throttle output [THRO] as usual.
Combustion drive system (nitro/gas)
Particularly when using sensors for combustion engines check for correct polarity of the sensor power supply. Here commonly sensors are used that are designed for governor systems from other manufacturers and therefore have a special pin assignment. In this case the colors of the connecting cables may not follow the norm (The wire colors of the ALIGN governor sensor HE50H22 are swapped for example. Here red denotes the negative and black the positive pole!). So make sure the signal wire is connected on top, plus is in the middle and the minus wire is connected at the bottom of the AR7210BX pin board.