From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Notes on investigations into the mechanics of low speed wobble and shimmy, focusing on self-energised oscillations.
| Identifier | ExFiles\Box 170\3\ img028 | |
| Date | 5th June 1935 | |
| JUNE 5, 1935. NOTES ON LOW SPEED WOBBLE AND SHIMMY. We have just finished some investigations on low speed wobble on the 25 Job and Chevrolet Master, which, combined with earlier work on shimmy, begin to offer a fairly consistant picture of the mechanism behind these two phenomena. Ehrlich and Benesi have been figuring on the mathematics of this work, as the job proceeds, and this has greatly assisted in presenting a true picture. We do not have test results of extreme accuracy such as would be needed for a full laboratory investigation, but the general trends are well indicated. Self Energised Oscillations. Both wobble and shimmy are self-energised oscillations, i.e. a working cycle is built up by the parts of the car itself which does not demand for its continuance any periodic external conditions such as regularly spaced bumps on the road, both oscillations can be built up on a smooth road or on smooth drums. These phenomena involve two oscillations of two different parts of the mechanism. These oscillations are necessarily out of phase, but of the same frequency. In practice both oscillations are not far removed from the 'natural' or resonance frequencies of the two parts of the mechanism involved. If the natural frequencies of the two parts are made different from each other, a point is reached suddenly at which the oscillation will not build up. at this point the trouble may be claimed to be cured. in general the requirements for a self-energised oscillation are: 1. an oscillating part of the mechanism, which supplies what we have called the 'controlling' frequency, i.e. if the oscillation is to build up at all, its frequency will be found to be close to the natural frequency of the | ||