Axle forces different from equations in Vehicle Dynamics Blockset 3 DOF Block

I have a pretty simple 3 DOF vehicle setup in the following model:

I'm trying to validate the results, and after resolving the drag force discrepancies described in this question, I seem to have come across another discrepancy. The Vehicle Body 3 DOF block outputs both axle and tire forces, where, per the documentation, the axle forces seem to just be a rotation of the tire forces.

In the equations above, I believe the lhs is the "axle" forces, and the rhs uses the "tire" forces.

My calculations for the tire forces are consistent with the results of my Simulink model, as well as my calculation for the longitudinal axle force, . But I'm specifically observing a discrepancy between the model's computed lateral axle force, , and what I get when manually performing the calculation from the given equations.

For example, with , , and , I'm computing and . Somehow, though the simulink model computes the same , it's computing , which doesn't make any sense, as this is even larger than .

This discrepancy in then leads to my calculations being off for and , and this cascades into larger errors over time.

How is actually being calculated, and why does this seem to differ from the documented equations? I could figure it out if the underlying code was actually open, but since a good chunk of the 3 DOF block is implemented in P-code (see this question for context), I'm left with no choice but to ask for help.

[Paul]

Direclty above those equations the linked doc page states:

"To determine the tire forces, the block uses the slip angles."

However, those equations don't include the slip angles, only the steering angles.

Also, that would be a peculiar statement if the Fxt and Fyt are tire forces on the RHS, which makes it looks like the tire forces are input to the equations, rather than "determining" the tire forces.

Good that you're digging into all of this, but all of your findings, if only documentation errors, certainly does not inspired confidence in the underlying model.

[Daniel]

That issue with the term “slip angles” was brought up [in a separate question](https://www.mathworks.com/matlabcentral/answers/2172390-inconsistency-in-documentation-for-vehicle-body-3-dof-block?s_tid=srchtitle), in which it was determined the documentation should say “steering angles”.

“ all of your findings, if only documentation errors, certainly does not inspired confidence in the underlying model.”

I wholeheartedly agree. With this many documentation issues for a single block, I’m inclined to think I’m the only one who’s ever attempted to use the Vehicle Dynamics Blockset, and am seriously considering switching over to any other vehicle dynamics simulation tool.

[Paul]

BTW, I'm not convinced that your findings are only with the documenation. I'd be concerned abou the "drag" equations as implemented (comment).