Add Main Rotor Brake demo profile

[ZZ-Cat]

Overview

This profile demonstrates how your helicopter's Main Rotor can behave like a braking system to help decelerate the Main Rotor.

How this works

When the Rotor Brake is activated, you have two braking modes: The Service Region, & Emergency Brake.

Switch SB controls whether-or-not the Main Rotor Brake is armed/disarmed & what Braking Mode will be used.

The Service Region is where your Collective Stick controls how much braking force is applied to the main rotor. There is an "Initial" braking force at your Collective Stick's centre position & below. This puts about -3° of collective pitch on your helicopter's Main Rotor Blades & is sufficient to spoil any remaining lift that may be present during shut down.

Emergency Brake is used for emergency purposes only.
This is because it instantaneously puts full negative collective pitch on your helicopter's Main Rotor Blades in order to stop the Main Rotor from spinning as quickly as possible.
This braking mode can help save your helicopter from tipping over.

How it's operated

Switch SB is used to Arm or Disarm the Main Rotor Brake in addition to selecting which Braking Mode will be used.
The Main Rotor Brake will not activate until both of your sticks are centred.
This is done to prevent the Main Rotor Brake from causing your helicopter to crash, if you inadvertently arm the brake in flight.

To arm the Service Region, simply move Switch SB on your RadioMaster TX16S to its middle position.
Centre both of your sticks to activate the brake.
The higher up you move your Collective Stick, the quicker your helicopter's Main Rotor will stop spinning.

To arm the Emergency Brake, pull Switch SB on your RadioMaster TX16S all the way towards you.
Centre both of your sticks to activate the Emergency Brake.
Your Collective Stick will not affect how much braking force is applied, in this mode. It is best to leave your collective stick centred, whilst in this mode.

You can release the Main Rotor Brake at any time by moving Switch SB all the way forwards. When this happens, any negative pitch that's applied to the Main Rotor Blades is bled off over a short period of time, before control is passed back to you.
This is done to ensure that your helicopter is in a known state before you can restart the motor.

Some things you need to be aware of

1. This profile grants you control over your helicopter's motor.
2. Two-Step Safety Arming is not present in this profile, as it is not in the scope of what this profile is intended to demonstrate.
3. Your helicopter's motor will activate as soon as your Switch SF is down. Flick Switch SF up before you switch your RadioMaster on, & check that your Switch SF is up before you power-on your helicopter.
4. If the Main Rotor Brake is activated in flight (despite the requirement of both of your sticks being centred & Switch SB being in any position other than its default), your helicopter will crash. You must ensure your helicopter is on the ground before activating the Main Rotor Brake.
5. In any of the braking modes, your cyclic, tail & motor controls are isolated.
6. You will not regain full control over your helicopter until the Main Rotor Brake is fully released.

Additional Features

Motor Control Logic

I took the liberty of including an experimental Motor Control Logic on Channel 6.

With this, your helicopter's motor is controlled in four stages:

1. Cut.
2. "Excite".
3. Ramp.
4. Run.

"Cut" is the same as "Throttle Cut" & it's where your helicopter's motor is stopped.

"Excite" is the minimum PWM signal required to get the motor to spin.

"Ramp" is the startup phase, where the motor is gradually brought up to speed.
This is perfect for motor controllers that either have no soft start or they have their soft start disabled.

"Run" is the running phase, where you can use Switch SD to select your helicopter's Main Rotor RPM. The Motor Control Logic will automatically interpolate between each switch position to avoid sudden changes in your helicopter's Main Rotor RPM.

ExpressLRS Arming & Disarming

Because this profile is intended to be used with ExpressLRS, Channel 5 is reserved for "arming" & "disarming" the ExpressLRS control link between a transmitter module & a receiver.

When you go to start your helicopter's motor, your ExpressLRS control link will also be "armed".

[ZZ-Cat]

I think that about wraps it up for this Pull Request. 🤔

I was considering adding in control logic for the motor brake. But, a.) I can do that in another PR later on; & b.) Not a lot of folks I know of (aside from myself) have the motor brake enabled in their helicopters.

With that being said, HobbyWing are about the only manufacturers I am aware of that have a motor brake.
But, hey. If someone wants it, they can always open an issue & request it too.