Rubber servo mounts done right

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With respect to the proper assembly of the brass eyelets to the rubber isolation grommets along with screws for the installation of a servo onto wood rails, or a piece of plywood, the purpose of this brief lesson is to teach the proper way to assemble the rubber isolation grommets within the servo ears and capture same between two surfaces, one a brass eyelet and the other a screw head. Please refer to the photo.


1. Notice the head of the screw and the base of the brass eyelet are about the same size. Basically, if you install the eyelet into the rubber grommet from the top, then once the face of the screw head contacts the broad face of the eyelet, it means there's enough mechanical advantage in the screw threading into hardwood to drive the sharp end of the eyelet deep into the wood if the servo weren't there. The point being you can easily over-tighten the assembly such that the rubber isolator doesn't do its job. Hence, this is NOT how you properly assemble the eyelet and screw.

2. When the eyelet is installed from the bottom, note how the screw bottoms on the sharp edge of the eyelet. This forms a shoulder on both sides to capture the rubber isolator. This is the correct way to install the brass eyelet for two reasons. First, unless you're a gorilla and tighten the screw to the point of deforming the brass eyelet, once it contacts the brass eyelet, it mechanically stops the screw from over-compressing the rubber. Once the screw contacts the rubber, you're done! In practice, there's about 2-thousandths of difference between the thickness of the grommet and the eyelet/screw shoulders (the brass is a little bit shorter than the thickness of the rubber). This is to provide a little bit of tension to help keep the screw from backing out. Further aiding this are the grooves forged into the bottom of our mounting screw such that it snugs against the rubber surface and effectively acts like a lock-washer. Think these screws won't never back out? Just wait because you haven't lived long enough to see it all.

3. Note how the lip (or shoulder) of the brass eyelet sits proud of the rubber surface. This actually keeps the rubber from contacting the wood of the mounting rail. This is important. The rubber mounts are called isolators for a reason - and if they get squashed into contacting the wood - you've defeated their very purpose. While we've tried to make this assembly foolproof I'm reminded of the old saw regarding never underestimating the ingenuity of fools - not that I am calling anyone a fool.

4, 5, and 6. These should be looked at together to grok how they work as an assembly.
To recap, we've learned the eyelet shoulder is about the same diameter as the head of the screw. That the thickness as the rubber isolator is about equal to the throw of the brass eyelet. And that the broad shoulder of the brass eyelet upon contacting the wood has enough area so as to preclude it digging into the wood rail once the screw is tightened until it contacts the sharp edge of the eyelet.

Thus, once the screw comes into contact with the rubber and you tighten it just a smidgen further, the face of the screw head bottoms against the brass eyelet and simultaneously engages the rubber face and presto, the servo will be secured to the wood mounting rails. End result is the rubber isolates the delicate electronics from the vibrations of an off balance propeller, the power impulses of an engine, the effects of flutter, or the harmonics of various vibrations. End of lesson.

In closing, this is an elegant solution that's both inexpensive to execute, and so simple, it borders on pure genius! My hat is off to the nameless engineer who developed this concept. Frankly, times like these that as an engineer make me feel as if I were standing on the shoulders of the engineering giants who preceded me.

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