P10221: Baja 1 (Baja Driveline Test Development)

Stand Vibrations

Stand Vibrations, Method of Analysis:

Although the frequency of the engines vibrations can be assumed based on the rpm the amplitude of the vibrations was unknown. For this reason it was determined that the best course of action would be to find the natural frequency (mode) of the stand and ensure that it is nowhere near that of the engines rpm. This helps to ensure that any vibrations that are created by the engine do not get amplified.

The engine rpm will range between 1750 (idle) and 4500 (600 rpm above max). It is unsure of whether the input frequency correlates to every revolution or to every time there is a power stroke in the engine. If it is the later then the frequency is half the rpm, or a minimum of 14.58 Hz. If the frequency correlates directly to the rpm then it would have a maximum value of 75 Hz.
Using SolidWorks Simulation vibration analysis and a somewhat simplified model of the stand, in which all connections are assumed to be ideal, the first five modes of the stand were calculated. Each mode correlates to a frequency at with the vibration input into the stand from the engine will be greatly magnified. For the stand the modes were found to be about 375 Hz, 478Hz, 667 Hz, 990 Hz, and 1100 Hz. This means that the stand will not likely experience magnified vibrations from the engine and will thus be relatively stable. Although there will likely be some error in assuming rigid connections, that error is not likely to cause the first mode to drop by 300 Hz.
Mode 1 = 375 Hz

Mode 1 = 375 Hz