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MV/MS Tire Test Rig Unexpected Normal Forces

Hello, I am looking for feedback on how the auto tire test rig is controlling normal loads.

Running the lateral slip test, with commanded normal loads of 201, 323, 485, 637 N, the actual normal loads are significantly higher (due to the mass of the wheel, hub, and carrier body masses not being compensated for. Also, the normal load varies significantly with inclination as the vertical actuation pivots with inclination.

I'm curious if anyone has any suggested modifications to the mechanism or event to control normal load? Two possibilities may be:

Set up vertical actuator as closed loop feedback control to target based on CP forces.
Release RY from "Rig_Long_Camber_Jt" and apply desired normal load as an additional mass applied to carrier body which will not be effected by inclination (Not sure this is actually possible to do a load sweep by changing the mass mid-simulation).

Thanks,
Chris

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GTT Adam

Hi @c_sells,

If you are looking to parameterize the applied load, you can define the load case via expression and subtract the mass of the additional components:

Expression Example: 3000-9.81*(MODEL.sys_comp_testrig.b_wheel_hub.mass+MODEL.sys_comp_testrig.b_rig_body.mass+MODEL.sys_comp_testrig.b_carrier.mass)

As for measuring the vertical load during the inclination, you can always create you own Markers and Outputs to crate a custom measure in a defined coordinate system.

Hope this helps!

Adam Reid

c_sells

Thanks Adam, in terms of the inclination portion of the event. I don't just want to measure the load, I want to maintain the requested contact patch normal load regardless of the orientation of the vertical actuator (or response of the tire). The reason is that this is how the tire test data I'm trying to correlate with is collected.

I should be able to add a solver variable to track the normal load at the ground reaction easily enough, but it looks like I would have to have to modify the event "lat_slip_test.mdl" to actually replace the pre-defined vertical force expression with something that actively compensates based on the error between the normal force solver variable and the requested normal force. Is that correct, or is there a way I could do this within the test rig model itself and not modify the event files?

GTT Adam

Hi @c_sells,

Rather than modify the default event model definitions, I would suggest you create your own Analysis along with a few Motions and Forces. That will create a similar event as the Lateral Slip, to which you can have complete control over timing and measurements.

Hope this helps!

Adam Reid

c_sells

@GTT Adam, Definitely makes sense. I anticipate this might be a somewhat regular simulation that I will need to do. Is there any documentation you could point me to that would give me guidelines for setting up my own library of customized events that would show up in the entity browser?

GTT Adam

Hi @c_sells,

New in version 2025.1 is the ability to add User Systems. If you have a System that you want to reuse, you can right click » Store System Entity. This will then show up in your Entity Browser palette:

You can then import this User System and use the Default Analysis with a proper End Time to accommodate the custom event you are creating.

An Analysis can not be added to this User Systems folder, however you can still create this custom event entirely in an Analysis and then export it as a MDL definition. The MDL definition can then be imported into any model and it can contain the End Time and any solver specific settings for this custom event.

Hope this helps!

Adam Reid