USAR Pro Cup Race Car - The Seven-Post Rig

The vehicle was then placed on the seven-post rig where changes in springs, bars, wedge, and shocks were evaluated and analyzed as to their effectiveness. At the conclusion of the time spent on the seven-post rig the race car setup was changed to try to improve and increase grip, reduce body motions, and enhance balance and driveability. Based on the fact that we had done a dynamic evaluation prior to our test and refined it at the track, it would be interesting to see how this came out.

The race car was then taken back to the track for the Friday practice prior to the Saturday race. Its performance was again evaluated and then compared to the baseline achieved on the first track test. What we saw was what we expected. Friday's test was somewhat tainted due to hot track conditions that made the track slick.

Track Test
Joe tells us, "A track test was conducted at Concord Speedway on March 30, 2009. During this test, a Pi Research data acquisition system was utilized to obtain data from the vehicle which would give an accurate representation of both the motions of the sprung mass due to lateral acceleration, track banking, and so on; and the vertical accelerations of the unsprung mass to represent the surface of the track. Concord Speedway is a half-mile oval track located in Concord, NC. Its bumpy and 'dog leg'-shaped back stretch make it unique among other tracks on the USAR schedule.

"During the test, it was evident on the data, the car had a tendency to be tight mid-corner and snap loose on corner exit. The most challenging section of the track was through the 'dog leg' segment starting just at the exit of Turn 2 and carrying into the entry of Turn 3. It's evident from track data that the driver had to constantly correct the steering wheel and frequently be 'on' and 'off' the throttle through that section. Figure 1 shows the track data obtained from the steering, throttle, and brake versus the position on the track.

"Figure 2 is an alternative view of throttle and brake application. The darker the line color the more the throttle and brake are being applied. The throttle trace is on the left-hand map in green, while the brake is on the right-hand map in red. The two different lines around the maps represent two different laps, the outermost lap is a 17.06 while the innermost is a 17.74. It can be clearly appreciated where the driver had difficulty getting back to the throttle off of Turn 4 during the slower lap by the lighter throttle trace. On the braking trace, it's noticeable that the brakes are applied at a consistent point on the track but that for the slower lap the driver didn't need to brake as hard getting into Turn 3."

Post TestDrive File Generation Joe continues to tell us, "By placing sensors on the vehicle in key locations, data can be collected which record the exact body and wheel motions of the vehicle. These motions are then converted into a drive file which can be used as an input to the seven-post rig. This file will replicate all of the vehicle motions experienced at the track. Acceleration, braking, aerodynamics, and banking loads are all accounted for in the drive file."

"Placing the car on the rig with the exact same setup it had at the track is important for the accuracy of the drive file. This methodology allows replaying lap after lap consistently in the controlled environment of the rig where external factors, such as weather, driver error, or engine problems, don't interfere. Once the drive file is created, changes can be made to the vehicle setup and the new response can be measured. This powerful tool allows teams to "dial in" a setup for a particular track without the expense of continuous track testing.