USAR Pro Cup Race Car - The Seven-Post Rig

The seven-post rig is a process that has been talked about and thought about by many race teams. Most teams struggle to understand how this would help their program. It is, in fact, a complicated process to learn, much less to apply. We talked with the engineers at RaceWorks in Huntersville, NC, and were able to do a full range of tests on our USAR Pro Cup race car. In doing that, we learned how the process works and how it could benefit your team.

What teams must understand, and what was explained to me by the lead engineer at RaceWorks, Joe Berardi, is that the rig is a tool that can help a race team learn more about the way its race car works. It's through equipment like the rig and data acquisition that we can better understand the systems in our race car and the dynamics at work for each race track we'll run. Throughout the following discussion, Joe's explanations and comments will be shown within the quotation marks.

The seven-post rig is just that, seven hydraulic posts, three that are attached to the chassis and four that rest under the four tires. There are two motions introduced to the race car. In one set of motions, the rig simulates chassis movement and especially the tire loads that represent the forces encountered during a baseline lap. These inputs are the result of recording the three axis forces (lateral, vertical, and longitudinal forces) acting on the car as well as the movement of the shocks.

The other motion is a more high frequency motion introduced to the tires to simulate bumps and other deviations in the actual track surface. This helps us understand how the shock and springs interact and improvements made here help maintain contact patch mating with the track surface for more consistent grip.

Objective
The objective of this work was to evaluate the performance of our CT USARacing project car at the Concord Speedway and use modern tools, including data acquisition systems and the vehicle dynamic rig to improve upon its performance. For this effort, we conducted a track test before and after a seven-post rig test session to compare and evaluate vehicle handling and performance gains.

The first stage consisted of instrumenting the car with a Pi Research data acquisition system before conducting the initial track test at Concord Speedway. The main purpose for the session was to acquire the needed information from the data and the driver about track characteristics and vehicle performance. Several setup changes were then performed in order to improve the vehicle lap times and driver comfort and to develop a baseline suspension setup that was both neutral in handling and balanced dynamically.

We actually needed to make some last minute rearend alignment changes that were interfering with the handling. Once we sorted all of that out, we could then properly evaluate the setup and make appropriate setup changes and shock adjustments. What we ended up with was a car that produced very even tire temperatures and that had good bite off the corners.

What we didn't have for this test was a carburetor that was adjusted correctly. This hurt our exit performance when trying to accelerate. We concluded that once we came back we would see a couple of tenths better lap times with a motor that would quickly accelerate.

We also were there alone most of the time and the track had been washed clean from a heavy rain days before. The last laps of the test were done on 70-plus-lap tires and a "green" track. All of that must be taken into account later on when we come back for our post seven-post evaluation which will be the practice day for the race. Newer tires, a better track surface, and an improved motor should give us 3-4 tenths better lap times.