Archived: Migration from Plane 3.7 to 3.8

This is a guide to migrating from plane 3.7 to plane 3.8. There have been a large number of configuration changes, so please read the guide carefully, and make sure you do careful ground tests before your first flight.

The firmware will try to auto-migrate your parameters where possible, but it is a complex migration and there is the possibility of errors, so careful testing is critical.


If you later downgrade from Plane 3.8 to an earlier version, then any changes that were made to the RC_* and SERVOn_* parameters will be lost. Upgrading back to 3.8 (or higher) will not copy over any new param changes. This is only an issue if the user decides to downgrade. Please note that downgrading from 3.8 to 3.7 (or earlier) is very likely to cause a crash if you do not manually restore channel reversals.

Change to Servo Range Parameters

One of the biggest changes between plane 3.7 and 3.8 is the change from RCn_* parameters to SERVOn_* parameters.

In plane 3.7 and before, the range, trim and function of all input and output channels was controlled by a single set of parameters starting with RC. For example, the handling of input channel 1 was defined by 4 parameters:

  • RC1_MIN

  • RC1_MAX

  • RC1_TRIM

  • RC1_REV

these same parameters also controlled the range of output values for the first output channel. That means you could not have a different range for your RC inputs and your servo outputs.

In plane 3.8 the above 4 parameters are replaced with 8 parameters:

  • RC1_MIN

  • RC1_MAX

  • RC1_TRIM






the RC parameters control an input channel, the SERVO parameters control an output channel. This gives much more flexibility, and means that when you re-calibrate your RC inputs it doesn’t affect the tuning of your aircraft.

You may also notice that the “REV” parameters have been renamed to “REVERSED”. This is because the old parameters had a convention so that “reversed” was chosen by setting RC1_REV to -1, and “not reversed” was chosen by setting RC1_REV to 1. This caused quite a lot of confusion, so for 3.8 we now use the convention that RC1_REVERSED=0 means not reversed and RC1_REVERSED=1 means reversed.

Change to Servo Functions

The second big change is to the parameters that defines what each output is used for. In plane 3.7 the output function of the first 4 channels was hard coded, following the AETR “aileron, elevator, throttle, rudder” convention. Channels 5 and above had FUNCTION parameters, allowing their function to be set.

For example, in plane 3.7 you could set RC5_FUNCTION to 4 to make output channel 5 an additional aileron.

In plane 3.8 the functions are chosen using the SERVOn_FUNCTION parameters. You can set these on any output channel. The default for the first 4 channels is the same, but you can change it to any output type you like. This gives a lot more flexibility, and is especially useful for flight boards with a smaller number of output channels.

So if you wanted the 5th output channel to be an aileron you could set SERVO5_FUNCTION=4.

You can see more details on output functions in the Output Functions documentation.

Change to Elevon, Vtail and Flaperon Configuration

The method of setting up elevon, vtail and flaperon planes has completely changed in plane 3.8.

In the 3.7 release if you wanted to setup an elevon plane you would set the variable ELEVON_OUTPUT to an integer from 1 to 8. This then changed the behaviour of the first aileron and elevator channel to do elevon mixing. The value of ELEVON_OUTPUT controlled the possible channel order and reversal options (8 combinations are possible).

In plane 3.8 a much simpler and more flexible system is used. If you want channel 1 to be a left elevon and channel 2 to be a right elevon then you use:



the value 77 means “left elevon”. The value 78 means “right elevon”. You can then set the reversals as needed, using SERVO1_REVERSED and SERVO2_REVERSED.

Changing to this system means you can have elevons on any channel (and multiple elevons if needed), plus you can directly control the trim and range of each elevon,

The same system is used for vtail, flaperon and differential spoiler setups. Please see the following guides for more details:

Tuning Changes

Some users may notice the tuning of their aircraft changes a bit between 3.7 and 3.8. The likely cause of this is the change in the RC and SERVO parameters. With the separation of the RCn_MIN/MAX parameters from the SERVOn_MIN/MAX parameters you may find that the “throw” of your servos changes a bit, which can affect tuning.

While the automatic upgrade when you install plane 3.8 onto a plane running 3.7 should produce a very similar servo range, please do check it carefully.

Reversal Checking

Please do very careful checking for servo reversal before your first flight with plane 3.8. The automatic parameter upgrade when you install plane 3.8 should get this right, but it is very complex and there may be some situations that aren’t covered. Please make sure that both of the following are checked carefully after you update:

  • that RC inputs give the correct movements of your control surfaces in MANUAL mode

  • that the control surfaces move in the right direction in FBWA mode when you roll and pitch the aircraft with no RC input

There is a detailed guide to checking for reversals in the four channel plane document.

Airspeed Setup Changes

The parameter for enabling an airspeed sensor has changed from ARSPD_ENABLE in plane 3.7 to ARSPD_TYPE in plane 3.8. This change was made to provide a more flexible way of supporting multiple airspeed sensor types.

If you have a MS4525 digital airspeed sensor then the parameter upgrade should happen automatically and you should find that ARSPD_TYPE will be automatically set to 1. However if you have an analog airspeed sensor then you will need to set ARSPD_TYPE=2 after updating to plane 3.8.

Plane 3.8 also supports the new MS5525 airspeed sensor. That is selected by setting ARSPD_TYPE=3.

Change to THR_MAX

The THR_MAX parameter, which controls maximum throttle, defaulted to 75 percent for versions 3.7.1 and earlier. In plane 3.8.0 it defaults to 100 percent. If you had not previously changed this parameter and your plane is overpowered at 100 percent throttle you may wish to change it back to 75.