Documentation: No road grade angles in model equations

Hello,

I was going through the documentation of blocks Vehicle body 6DOF, Vehicle body 3DOF and Vehicle body 3DOF Longitudional and all three seem to miss the road grade angles in their equations. Moreover, the blocks Vehicle body 6DOF and Vehicle body 3DOF do not have any input for road grade angle or road incline even though the Vehicle body 6DOF block has defined road grade angle in variables.

Did someone encounter this? Do you know where I can find the equations?

Is it possible to get the road incline inside the Vehicle body 6DOF and Vehicle body 3DOF blocks?

Any help is appreciated. Thank you.

[Jiri Minarik]

I will add here what I used for those who would have similiar problem.

As @Ryan Chladny suggested, you can took whole subsystem of vehicle body + suspension + wheels and then specify road grade angle as ground difference between wheels in Combined Slip Wheel blocks inputs.

You can do that by taking "sin(road grade angle)*distance_of_rear_wheels_from_front_wheels" as distance input for front wheels and for rear wheels take simply 0.

Regards and thanks to @Ryan Chladny and @Chris Erkkinen,

Jiří Minarik

Answer 1

[Chris Erkkinen]

Hi Jiri - Thank you for your careful review of the documentation! I'm the technical writer for the Powertrain Blockset and Vehicle Dynamics Blockset documentation.

Looks like you're using the Vehicle Dynamics Blockset.

Hope this response helps:

Vehicle body 3DOF - Block models longitudinal, lateral, and yaw motion. As of now, the block does not include considerations for road incline and/or bank angles. We could incorporate the incline and bank angles in the future, but we need to work with users to decide how to specify them. For example, should the block model instantaneous loads or a global road profile? The distinction is important as we'd need to account for the reaction loads while the vehicle is traversing up the side of a hill at a lateral angle and could potentially roll over.

Vehicle body 6DOF - Block models translational (3DOF) and rotational (3DOF) motion. The block implicity accounts for road incline via the gravity vector. I will take the 'road grade angle' entry out of the variable list in the documentation; I can see why that might be confusing.

Vehicle body 3DOF Longitudinal - Block does account for road incline. I will consider enhancing the documentation to include the specific road incline equations.

Thank you!

Chris Erkkinen

[Jiri Minarik]

Oh, alright. Thank you for the answer!

But how can I change the gravity vector in Vehicle body 6DOF? Because if I want to change the road incline through out the simulation I cannot just use parametres. I need access to the DCM to adjust the pitch angle for road incline but, for Vehicle body 6DOF, it is a internal variable of the block and as such I cannot change it just from Fsusp, MSusp, FExt and MExt, right?

Regards,

Jiří Minarik

[Chris Erkkinen]

Hi Jira -

Yes, you can change the road incline by adjusting the input signals, either:

• FSusp/MSusp - Suspension forces and moments at the vehicle hardpoint locations
• FExt/Mext - External force and moment acting at vehicle CG.

Chris

[Ryan Chladny]

Hi Jiri,

Presently the block does not support the direct application of a grade (which could be interpreted as a form of pitch constraint).

Keep in mind, unlike the other vehicle block equations of motion, the 6DOF block pitch or roll are not constrained and it does not have any notion of where the road surface(s) are located. Rather, the user will typically use the 6DOF block in conjunction with wheel and suspension elements which are in contact with a road while being subjected to a gravitational load.

Hope this helps,

Ryan

[Jiri Minarik]

Hey,

even though, it's very late response. I will add what I used for those who would have similiar problem.

As @Ryan Chladny suggested, you can took whole subsystem of vehicle body + suspension + wheels and then specify road grade angle as ground difference between wheels in Combined Slip Wheel blocks inputs.

You can do that by taking "sin(road grade angle)*distance_of_rear_wheels_from_front_wheels" as distance input for front wheels and for rear wheels take simply 0.

Regards and thanks to @Ryan Chladny and @Chris Erkkinen,

Jiří Minarik