SITL: sailboat: add waves, tides and throttle

[IamPete1]

This adds a basic wave simulation to the sailboat SITL.
There is a enable parameter:
0 = no waves
1 = roll and pitch from waves, this works reasonably well
2 = roll, pitch + heave, this works ok sometimes, but can start to do some funny stuff in larger waves.

There are also parameters for wave length, height, direction and speed.

I think the roll and pitch is the main thing, the purpose for adding waves is to try and classify the sea state in the main code, I think the accuracy of altitude measurement would make it very hard to use to calculate the wave height on a real vehicle.

I have also given the sailboat SITL model a throttle and a parameter to turn it on and off. This will be used for testing the motor sailing functionality that will be added in the future.

[IamPete1]

rebased and added tides

[rmackay9]

LGTM, I'm not a SITL expert so I might as if @peterbarker or @tridge can give some feedback..

[IamPete1]

rebased

[rmackay9]

@IamPete1, I tested this today and it generally worked but I found one problem. If I set the SIM_WAVE_ENABLE = 1, wait for the vehicle to roll or pitch, then set SIM_WAVE_ENABLE = 0 the vehicle doesn't return to it's upright position. It seems to keep the attitude from the moment the waves were disabled.

I had a quick look at the code and I couldn't figure out what was going wrong but if you give me a hint as to how to fix it I could try to resolve it be merging.

[IamPete1]

@rmackay9 I have rebased and added a new commit that should fix the run-time disable issue, although I have not tested it.

[rmackay9]

@IamPete1, great, thanks for that. I've squashed some commits and moved to this new PR. #11986

I've done this because I'd like to get in the non-controversial parts quickly.

Re the motor support, how about if the sailboat simulator always supports a motor so that we can remove the new SAIL_OPTS parameter?

Normally we don't require setting a simulator parameter to configure the vehicle. So for example we have skid-steering and ackerman rovers.. but the user decides which they are using by providing a parameter to sim_vehicle.py. They don't decide by setting a SIM_xx parameter.

If we get rid of the SAIL_OPTS parameter we would need to be a little careful that this doesn't cause the motor to spin in reverse in SITL in cases where we have a sailboat with no motor attached (i.e. SERVOx_FUNCTION = 0). If we are lucky the servo output will be zero instead of a low PWM value and this will allow us to detect that no motor is connected.

[IamPete1]

@rmackay9 I have rebased this so it is only the throttle changes left. We could do a check for throttle > 1000 and remove the throttle output form the sailboat defaults. In either case i guess I should add a new default param file for a motor sailboat. The thought behind SAIL_OPTS was that I can add more bits for enabling wing sails and other things in the future.

[IamPete1]

@rmackay9 This now range checks the throttle rather than uses a parameter, I have updated the sailboat defaults to match and added a sailboat-motor frame that has the motor enabled

[rmackay9]

Looking good, thanks!