There are still people who believe that they are able to determine the quality of the shock absorbers by how often the vehicle 'see-saws' after strong compression. In fact, for a long time there was no other sure method, other than to remove the dampers and then to test them. Perhaps, if need be, to drive the vehicle on a very bumpy road surface and to have a second person monitor the process. If the wheels lose road-contact for a longer period then the dampers are definitely useless. After two short test runs, modern testing devices, are much more exact in their evaluation.
In the above figure the surroundings of the test-bed have been removed. What remains, is an electric motor which, through an eccentric, (not really visible) causes an exactly defined (black) spring metal sheet to be moved. This spring metal sheet has on the right, an axle connected to the (red) plate on which the vehicle wheel stands. Apart from the eccentric, the engine also moves a heavy flywheel mass (below on the left with arrow). When the maximum wheel speed is reached, the motor is switched off and only the flywheel mass causes drive. The left side of the spring metal sheet is raised and lowered with a certain frequency according to the wheel speed. With the same frequency, the plate with the vehicle wheel on it, now moves. If this has a different oscillation height (amplitude), with more or with less damping, this is possible through the spring metal sheet. Below the plate the electric travel sensor can be seen, visibly linked by a cable. It transmits the deviations of the plate with slowly reducing wheel speed to the computer analysis.
The red plate as a standing area for the vehicle wheel, is connected with the black spring metal sheet only through the axle, and not directly.