Designing a High‑Performance Gravity Grand Prix Car Using MODSIM Workflows

For those of you joining us in Pittsburgh for a 2026 rollout event, we have created a workflow to model and customize your own easily manufacturable derby car design. The goal is simple: the fastest car wins.

Entrants will use simulation to evaluate aerodynamic performance and weight distribution to sift through the submissions. The top performers will then be physically built, using TriMech’s 3D printing capabilities.

The Two-Stage MODSIM Workflow

Entrant designs will compete in a two-stage MODSIM workflow to compete for the top-performing car. The MODSIM workflow allows us to virtualize testing from the design modeled in a single, streamlined workflow.

1. The aerodynamic performance of each car will be tested virtually. The top performers will be evaluated and ranked based on how far the car makes it over a short time window during an FEA study using the explicit dynamic solver.
2. The real-world performance of the highest-ranked cars from stage one will be physically tested. The cars will be 3D printed by TriMech Manufacturing Services and raced on a real race track.

At TriMech, we have access to advanced CAD tools, simulation software, and additive manufacturing technology. That gives us a ton of options on how we could design and evaluate these cars.

The Car Design Workflow

For this challenge, we wanted to focus on designs that could be manufacturable from a standard wood block using only a band saw or jigsaw. That means removing complex, multi-axis cuts requiring a CNC machine or the full capabilities of our 3D printing facilities.

Starting From a Standard Car Blank

The design workflow starts from a solid block of material sized to match a typical downhill car blank you could purchase online or make yourself. This block is our starting point and defines the maximum envelope of the car.

The standard car blank

From here, you can customize the car designs by removing material. The two primary driving factors to keep in mind are the aerodynamic performance and the weight distribution of the cars.

Creating the Side Profile

To keep the car designs easily manufacturable, we will use a single side profile cut. This sketch profile will be driven from a spline that you can easily click and drag.

Creating the side profile spline

The workflow to create the profile is as follows:

1. Create a side profile sketch on the car blank.
2. Use a simple spline with control points to create your own custom curve.
3. Shape the profile to balance aerodynamic drag and mass placement.

The spline-based profile lets you quickly adjust the cut geometry to test different design concepts. Once the sketch is complete, it will become our reference for removing material from the block.

Removing Material with a Boolean Operation

With the side profile defined, we can then use a Boolean operation to remove material from the car blank. Any material above the cut surface is removed, leaving us with the final outer shape of the car body.

Using a Boolean operation to cut the car body

At this stage, the car is largely complete from a geometry standpoint. However, from a simulation and manufacturing perspective, we aren’t done quite yet.

Designing for Process Automation

To efficiently test all the unique designs created, we are leveraging our process automation tools. These tools allow us to feed the updated geometry into the workflow and automatically execute the CFD and FEA studies to help identify the top performers.

Process automation for MODSIM workflows

To support the automated simulation workflow, we need a consistent and repeatable way to represent the wheel axles so that results can be compared fairly.

Defining Axle Reference Locations

To achieve consistent axle locations, we can leverage how meshes are generated in our finite element analysis.

To simplify the process:

1. Create two reference planes at the desired axle locations along the length of the car.
2. Use those planes to create a partition line on the bottom face of the car.

Adding planes for a cutting location

This partition creates a seam in the geometry. When the mesh is generated, that seam will automatically have nodes aligned along that edge.

The final cut car body

By leveraging this meshing behavior, we can reliably reference the same location whenever creating hinge connectors for the wheel axles. This removes any need to create the hinge connectors manually.

Creating hinge connectors for the wheels

Preparing for 3D Printing

The seam used to create consistent connection points in the simulation also becomes the reference for creating axle holes in the final 3D printed car.

When adding these holes, there are a few practical considerations:

• Axle location relative to the bottom surface
• Hole diameter, accounting for material shrinkage
• Post-processing effort after printing

How Will Your Car Stack Up?

At our upcoming live event, you will take part in this workflow firsthand. Bring your engineering mindset and apply it to designing the best downhill car to beat the competition.

To participate in this challenge, you will:

• Walk through the car modeling workflow with a member of our technical team.
• Adjust your side profile to control aerodynamics and mass placement within a timed session.
• Submit your design to the two-stage virtual-to-physical race challenge.

Following the event, we will be posting the simulation results and identifying the top performers. From there, we will be 3D printing the top performers and racing them in the real world. Following the races, we will review the results to crown a champion.

To learn more about applying MODSIM to your existing workflows, read our MODSIM fundamentals article here.