Mirror Vibrations

If your mirror was mounted directly to your motor, you would probably see a direct correlation. if you attached it with a rubber mount and extended it away from the motor you would notice one does not vibrate at the same rate. Each time you isolate the mirrors you would get less and less of a direct correlation. Thats why you isolate or place motors on bushings. By the time the engine vibrations meet up with the mirrors through a four point suspension, they are subdued. If they are not mounted correctly you may even get a greater vibration in the mirrors. If the mirrors smooth out when the engine smooths out, your worries are over. If the RPMs increase and the vibrations get worse, there is something definitely wrong.

my engine idling rpm is 650,while i am getting the max. vibrations on mirror near 1100-1250 rpm. Mirrors are mounted on an extended bracket with rubber padding.

What are the considerations involved in designing the rubber pad so that the natural frequency of mirror mounting does not lie in the band frequency of engine vibration?

There are more vibration sources from the car then just a engine. these could be AC pump, cooling fan, gearbox and etc..

The vibration will get worst if any of these sources are the same frequency.

1. The stiffer the mount , the higher the resonant frequency of the mirror assembly, so harder or thinner rubber should raise the frequency. The mount includes everything between the actual mirror and whatever it is mounted to.

2. The greater the distance between mirror and mounting surface, the lower the frequency.

3. The greater the mass of the mirror and its housing, the lower the frequency.

4. The wider the base, the higher the frequency in each direction (x and y, or h and v).

Thus assuming you want to raise the frequency, and need the extended length, you need a stiff yet light mount with a base that has maximum separation both horizontally and vertically. For long mirror mounts, that basically means a tripod.

how will u analyse which mirror is better if u have three kind of mirror and u have the corresponding(x,y,z) data of vibrations with u ????

Mount each one in succession to the same surface, and mount a variable speed motor (maybe a Dremel tool) with a small weight attached off-center, near the mirror. If the surface is somewhat flexible, it should carry the vibrations from the motor to the mirror; otherwise connect a light rod or string between the motor and the mirror. Gradually increase the speed of the motor until the mirror reaches maximum vibration. The mirror with the highest vibration speed wins!

If the housing for the Mirror is magnetic stick some magnets as close to the ends as possible.

If not magnetic use double sided foam tape to add some weights.

As some one said already: More Mass = lower frequcency.

Good Luck!