Lets address the issues one by one:
1) Drag equations not included for Single track:
Refer to the below section of documentation.
The section named "Drag" is not included in either of the "Dual track" or "single track" section. It is printed as a seperate section, indicating that the same drag equations are valid for both, single track and dual track mode.
2) What exactly are the external forces?
I read the documentation. As per my understanding, the "Fext" appears as an input port upon selecting "External Forces" checkbox, found under "Input signals" drop-down. This "Fext" is the external input force acting on the CG of vehical (It has to be provided by the user as an input). It is not the sum of "Drag forces + external input forces". This "Fext" is represented by notation: (
) in the documentation. The block calculates resultant external forces (represented by notation: (
)), by adding "Drag forces (
) + external input forces" (
), as shown in the below equation. It uses this (
) to calculate other forces as shown in the below screen-shot.
3) How the equations of "drag forces" calculated ? What is the purpose of gain blocks [4;4;0] and [0;0;1] ?
The purpose of "tanh()" block is to find the direction of relative wind. Although, signum function can be used for this purpose, but the issue is, it may cause chattering problem. Refer to the graphs of both the functions. Signum function has discontinuity at zero, but tanh() is continuous function, for all values.
If you observe carefully, the output of "tanh()" block will be (-1) or (1) under normal operations. It just indicates the direction of relative wind. The gain "4" is multiplied to ensure that we stay in the yellow highlighted region, as shown below.
The gain of [0,0,1] is subtracted to ensure that "z" component of the force is (-1).
The wind direction vector is then multiplied with the calculated force in order to find force vector.
4) The defaut values of "
" and "
" stated in the documentation does not matches with the actual default values. As correctly pointed out by you,
The default value of "
" stated in the documentation is: [0:0.03:0.9] The default value of "
" stated in the documentation is: [0:0.01:0.3] The actual default value of "
" is: [0 0.01:0.01:0.9] The actual default value of "
" is: [0 1e-6:0.01:0.3] But, you can observe that 1e-6 is very small and the vector [0 1e-6:0.01:0.3] will closely resemble the value [0 0:0.01:0.3]
You can contact Mathworks Technical support for the clearification.
I hope you find the information useful !