Let's Shake it Up!
For short, we just call it a '7-Post Shaker'. It is also referred to as a '7-Post Rig'; or even just a plain old '7-Post'. Yet it's anything but 'plain'.
While a wind tunnel gauges aerodynamic performance and a dynamometer (or 'dyno') measures engine output, a 7-Post Shaker puts the chassis and suspension to the test.
This sophisticated machine is used to simulate what the race car sees when it's on the race track.
The 7-Post is actually an outgrowth of 4-Post Shaker testing which began with Formula 1 teams in the 1980's. Tom Walkinshaw and the Renault Formula 1 team was a leader in the development of this particular type of testing. It is currently used in other series such as the IndyCar, NASCAR, and sports car racing.
The automotive industry has long used 4-Post Rigs to test passenger cars and trucks. They provide a much more precise evaluation of body and suspension dynamics than just driving on the street. Manufacturers do not typically use a 7-Post Shaker on production vehicles because they aren't subject to the same aerodynamics effects as high-speed race cars.
GM Racing began developing 7-Post testing for NASCAR Sprint Cup cars back in 1997. It was a joint cooperation between Kaz Technologies, the GM Structural Development lab, Hendrick Motorsports, and Richard Childress Racing. It has since become a very effective device in GM Racing's tool box.
We call it a '7-Poster' because this device is composed of 7 hydraulic actuators (or posts) that introduce force and motion to the race car.
There is one actuator under each of the four tires (four posts) and three more actuators attached to the frame of the race car (three posts).
The four posts under the tires, called 'wheel' actuators, simulate input from the road to the tires. The other three posts attached to the frame, called downforce actuators, simulate the downforce the car sees on the race track.
The seven posts stand approximately four feet tall and are powered by a large hydraulic pump. They are precisely controlled by a computer to reproduce the loads encountered on the track. They shake it up!
A 7-Post Shaker Rig is housed in the ground. Our Chevy Teams such as Hendrick Motorsports, Richard Childress Racing, and Stewart-Haas Racing have rigs at their racing facilities in North Carolina. Earnhardt-Ganassi Racing uses a nearby rig owned by Earnhardt Technology Group.
A 7-Post Rig requires an in-ground pit approximately 10 feet wide by 20 feet long by 10 feet deep. It's pretty big! When the foundation for the pit is dug, they dig down to solid rock and then pour in concrete to create a seismic mass. In other words, there is a big concrete block that is set on rock in the earth that's heavy enough not to vibrate with the operation of the 7-Post Rig. When installed, the tops of the posts (or actuators) are level with the floor of the race shop or facility.
An average 7-Post machine costs approximately $1.5 million. There is another $1 million investment for the seismic mass, creating the pit, installation, and so on. Figure in the cost of an engineer and technician to run and maintain the rig, and you can see this is an expensive piece of equipment.
In racing, the only objective is to go fast. One of the main factors in being able to go fast is how well the tires stay in contact with the racing surface. Springs and shock absorbers are the keys to a smooth run on the road, whether on the highway or the race track.
In simple terms, the job of the shock absorbers is to control the body motions as well as the wheel motions of a vehicle. Have you ever seen a car on the freeway with a bad or missing shock absorber? The wheels are hopping up and down, the body is bouncing all over the place, and it probably can't even keep up with the speed limit. You chuckle, but this car is way out of balance and in serious need of a GM suspension tune-up!
On your personal vehicle, just like a NASCAR Sprint Cup car, the wheels basically move straight up and down relative to the chassis, yet the body moves around according to the road surface. When things are in balance, you have a smooth ride. When they're not, you're in trouble!
Of particular importance to the engineers are these three motions: 'heave' (movement up and down), 'pitch' (forward and back) and 'roll' (side to side). Each of these motions is resisted by the springs & shocks at the four corners of the car. The trick is to find the right balance point.
Also, the race car drivers' personal preferences come into play here too. Some drivers like very little body motion, while others prefer the car to move around some. The teams, crew chiefs, and engineers take this into account when performing a 7-Post test. And that's where this machine is a very nifty tool. It helps them put the car 'in balance' for the driver.
There are 22 different race tracks on the 36-race point-paying NASCAR Sprint Cup tour, and no two are exactly alike. For example, the race cars react much differently on the tri-oval at Talladega Superspeedway where speeds can approach 200 mph than they do at Bristol Motor Speedway where the corners are banked at 24 - 30 degrees and the speeds are much, much slower.
GM Engineers and Team Chevy engineers work together in directing the test procedures as well as interpreting the results.
Data is collected at every NASCAR open track test as well as test sessions at non-NASCAR tracks. A number of sensors are attached to the race car during the test to provide data from the track. The engineers make notes on how various suspension changes affect the grip and downforce of the car. Data from past year's tests is also used.
From that information, GM Engineers create drive files that simulate the track and downforce inputs to the race car. This gives them a virtual lap of the race track itself. The drive file enables them to test various suspension springs, sway bars, and shocks to develop suspension set-ups for the different race tracks.
Back at the shop, the race car is put on the 7-Post Shaker, which allows them to re-create the behavior of the car on the track in a controlled environment. It simulates a variety of conditions and suspension loads, and also recreates bumps and other irregularities on the track surface. One run on the Shaker takes only about a minute. The engineers make changes, go back, and run it again. One day of 7-Post testing can be equivalent to three days of track testing.
The results enable the Chevy teams to find the base package they want, and to look at extra ways to fine-tune their settings. They continue to improve what they take to the race track on a week-to-week basis, just as the GM engineers continue to develop technology and provide resources to support the teams on every level.
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