I wish I could utilise envelopes as effectively as you do, James!
I'd also reached the conclusion that you need to resist rotation whilst still allowing damped displacement in every other plane. I'm certain that the engine mounts in my car are designed along the same lines. Rubber has a handy characteristic that it's stiffer in compression than in shear - so the objective would be to arrange the mounts so that rotation of the motor against its mounts compressed the rubber whilst any other movement sheared it. Industry uses just such a mount, called a Double U Shear Mount (see attached pdf), although they aim to achieve the exact opposite to what we want: they arrange the stiffer axis to resist radial displacement of a motor.
One thing that strikes me is that it should be easier to control unwanted motor movement if the motor is "top mounted" rather than "bottom mounted" (see attached image), simply because there's less mechanical advantage over the mounting points.
Notwithstanding that, I had a little play and came up with an "Anti-vibration Motor Mount (Bottom Mounting)". It's 1.5mm aluminium cut and folded, two identical pieces with 3mm rubber pads glued between the "arms". Assume in the image the motor is rotating anti-clockwise - the wind-up torque will attempt to compress the rubber (stiffest) whereas any other displacement will shear the rubber (softest). Might work... who knows?
I'd also reached the conclusion that you need to resist rotation whilst still allowing damped displacement in every other plane. I'm certain that the engine mounts in my car are designed along the same lines. Rubber has a handy characteristic that it's stiffer in compression than in shear - so the objective would be to arrange the mounts so that rotation of the motor against its mounts compressed the rubber whilst any other movement sheared it. Industry uses just such a mount, called a Double U Shear Mount (see attached pdf), although they aim to achieve the exact opposite to what we want: they arrange the stiffer axis to resist radial displacement of a motor.
One thing that strikes me is that it should be easier to control unwanted motor movement if the motor is "top mounted" rather than "bottom mounted" (see attached image), simply because there's less mechanical advantage over the mounting points.
Notwithstanding that, I had a little play and came up with an "Anti-vibration Motor Mount (Bottom Mounting)". It's 1.5mm aluminium cut and folded, two identical pieces with 3mm rubber pads glued between the "arms". Assume in the image the motor is rotating anti-clockwise - the wind-up torque will attempt to compress the rubber (stiffest) whereas any other displacement will shear the rubber (softest). Might work... who knows?
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