In this tutorial, you will learn the basics of tuning the vehicle system of a light armored vehicle (LAV). We will go through all of the powertrain components to get to a fully functional automatic vehicle. Read the Vehicle Tuning Guide for more in-depth documentation about vehicle tuning.

Prerequisites

This module assumes that Wheeled Vehicles Module 1 : Creating a Vehicle System is completed. If you haven't completed the challenges, expect that the turret graphics won't interact with the vehicle.

Tuning the Engine

The vehicle system in Vortex uses a "torque curve" model for the engine, whether it's an electrical motor or combustion engine. In the case of a combustion engine, the torque output is a relation of RPM and throttle. The brake torque, on the other hand, is a function of "delta RPM", which the difference between the current output speed and the maximum speed of the curve at current throttle.

From the Explorer, select the Dynamics Component of the vehicle system.
Under Parameters > Engine, click on the Browse button of Braking Torque Table CSV File. Find LAV_TT.csv in <Demo Scenes>\Equipment\Resources\VehicleSystems.
Similarly, assign LAV_BT.csv to Torque Table CSV File.
Under Parameters, modify the Internal Shaft Inertia to 0.5 kg.m2.
Set the Internal Shaft Mass to 50 kg.

Note

The scale of the engine torque and brake torque can quickly be modified under Inputs > Engine with Braking Torque Scale and Engine Torque Scale. This section also has Shaft Velocity Damping fields, which add friction to the engine rotation. If you the torque curves set for the engine account for internal friction, these values can be set to 0.

Tuning the Torque Converter

In this brief section, we'll tune the torque converter.

Under Parameters > Torque Converter, click on the Browse button of Ctr Table CSV File. Find TorqueConverter_CTR_sample.csv in <Demo Scenes>\Equipment\Resources\VehicleSystems.
Similarly, assign TorqueConverter_Lambda_sample.csv to Lambda Table CSV File.
Under Inputs > Torque Converter, change the Angular Stall RPM to 1,580 and the Drag Scale Factor to 2.0.

Tuning the Automatic Transmission

In this section, we're going to set the ratios for all gears (including reverse and neutral), as well as define the logic for automatic gear changes.

Under Parameters > Automatic Transmission > Gear Ratios, set size to 15.
Fill the resulting fields with the values from the table below. These represent the ratio between engine speed and speed to first differential. Keep in mind that the model for differentials can also have gear ratios, so they don't need to be taken into account here.

Gear Number Ratio
0 -14.500
1 -10.000
2 -6.600
3 -4.900
4 -3.330
5 -2.309
6 0.000
7 9.570
8 6.635
9 4.370
10 3.219
12 2.188
13 1.517
14 1.000
15 0.736
Note

Negative values represent reverse (R), a ratio of 0 represent neutral (N) and positive values represent drive (D) or overdrive (OD)
Under Inputs > Automatic Transmission, set the following fields:
- Shift Again Delay: 0.5 s
- Shift Delay: 0.4 s
- Gear Change Down: 0.45
- Gear Change Up: 0.7
- Gear Quick Change Down: 0.7
- Gear Quick Change Up: 0.95

Note

The values for gear change represent the ratio between current engine RPM and the engine max RPM. You can find the value for maximum engine RPM under Inputs > Engine. These values are calculated by Vortex from the torque table set in the engine parameters. For a more detailed explanation of gear change behavior, read Automatic Transmission.

Tuning the Differentials

Over the course of this tutorial, nothing with respect to the differential will have to be modified.

Under Parameters > Differential[n], you can set if each differential has a lock function (this does not activate the function)
Under Inputs > Differential[n] :
- Enable Lock activates the lock for each differential
- Gear Ratio 1 and 2 sets how the torque is transferred to each wheel. Like in most differentials, the torque is transferred equally to the two wheels. Note that, unlike the transmission ratios, it does not impose a relation in speed.
- Gear Ratio Input is an additional speed ratio at the input of the differential.
- Lock Max Torque is the maximum torque allowed to lock the differential. This value can possibly be used during run-time to model the transient state of the locking clutch or a limited-slip differential.
- Lock Ratio defines the desired sum of the speed ratios at both wheels when the lock is engaged.

Steering and Suspension

In this section, we'll tune the properties related to the suspension and steering of each wheel. Since there are four wheels, using the search function will be useful.

Keep in mind that the steering and suspension assembly is not fully modeled in Vehicle Presets, meaning that the software is not evaluating the masses and constraints present in a real suspension assembly. It's using the Car Wheel constraint. If you want to simulate a steering and suspension in its entirety, use the Modular Vehicle Systems instead.

Suspension

Using the search bar of the Dynamics Component properties, search for the field listed below and modify their values for all 8 wheels.

Suspension Stiffness: 160,000 N/m
Suspension Damping: 20,000 kg/s
Reference Point: -0.179 m

Since these values are Inputs, they can be modified during run-time. It's useful to modify those while the simulation is running to visualize the effect each field has on the suspension.

Keep in mind that the stiffness and damping can be modified during run-time, either manually or through scripting. More complex suspensions can be modeled by adding logic which modify those values in real time.

Ackerman Steering

Ackerman Steering applies a turning angle on steerable wheels in reference to a turning radius.

Under Parameters, check the field Steerable under the four front wheels (Front Left, Front Middle Left, Front Right, Front Middle Right).
Under Parameters > Ackerman Steering, modify the following values:
- Reference Position: -1.310 m
- Steering Max Speed: 50°/s
- Steering Ackerman Max Angle: 33°
Under Inputs, make sure the Ackerman Steering field is checked.

The Ackerman Steering can be deactivated in order to control each wheel angle manually. Under Inputs, you will find the Input Angle field in each wheel's section.

Tuning the Brakes

Brakes are simply modeled as a resistive torque on each wheel to which loss can be added (force in relation to rotation velocity). When using the integrated Braking Logic, this torque is multiplied by the Input Brake field. Brake torque and loss can also be manually added to each wheel during run-time, under Inputs in each wheel's section.

Under Inputs > Braking Logic, set the Maximum Brake Torque to 20,000 N.m

Up Next : Vehicle Presets Tutorial 3 : Adding Tire Models to a Wheeled Vehicle

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