THE STORY BEHIND THE POLY M8 MOTOR MOUNT
For the last 10 years I have been working on my own design PPG. It's a long story but one day I had made a breakthrough of sorts in my design, and it came time to go down to mounting my Black Devil on the new frame to check for clearances. I looked for my mounts and they were in bad shape.
I never really liked the rubber mounts we used. I thought they were too soft and flexed way too much, sometimes I felt they amplified the vibrations.
They also tended to sag after some time. I had seen too many sheer off to expensive and disastrous consequences.
I did some research and discovered they are actually made for sitting on the ground indoors and dampening low RPM motors.
They were never intended for vertical mounting outdoors, or UV exposure! Why has no one questioned them??
I casually started looking at the McMaster-Carr web page and came upon some weld nuts that if welded together with a washer could act as a strong foundation for motor mounts.
I bought a few bags of these parts to see what I could come up with. I started looking into rubber casting with no real good info. Some time later I talked with my girlfriend's 20 year old son, Zak, a world class professional downhill skateboard racer, gear head and tinkerer. At 16 he had started making polyurethane skateboard bushings under
www.venomskate.com and is now the largest producer of skateboard bushings in the country. I ran the idea by him, he said it looked good, and suggested we try making them with polyurethane instead of rubber. They would be stronger, and could be made in colors. COLORS???
After studying up on the properties of polyurethane, I found that is is much more versatile than rubber, handles temperatures from -85º to 200+º and the formula can be varied to make a large variety of durometers for vibration dampening. They are also very UV resistant, much more so than the rubber ones. I looked into this claim and found that race cars, performance vehicles and even high end hot rods use polyurethane in their suspensions. Zak then suggested I weld up some sets, make a mold and the company he worked with could pour several sets in different durometers for testing. A few weeks later I dropped off a box of these welded metal parts, met the shop point-man, and together with Zak we decided on various durometers that they felt would be good as a starting point. Then we added durometers on at both extremes just to be sure.
In spite of the fact that in the PPG world, motor mounts only come in black rubber, we chose some nice colors to distinguish the various densities.
When we got the samples a month later, Zak had scrounged some ancient analog equipment from his grandfather, who ironically used these tools for testing on the original Viking Mars Probe. We rigged up the oscilloscope to measure dampening and vibration, and started the testing.
We narrowed it down to a couple of compounds that was a good compromises between idle and full throttle. After flying both of these sets I felt we had a winner! I was convinced, but what about other pilots? I had the company make a dozen sets in orange, blue and red, sent out eight sets to various pilots and respected industry guys, sold a few and waited. Slowly the feedback started trickling in. Everyone loved them! They said the mounts cut down vibration and even helped with out-of-balance props...very strong, no sagging after a year and they all commented on the cool colors and shape.
Even Alex Varv was complementary after all the tough torture tests he put them through. And if Alex gave me the thumbs up, I felt it was time to take a gamble. I gathered the funds from a couple of video and photo jobs, ordered custom stamped washers cut to my specs, got s big bag of parts, made a jig for welding them and started TIG welding.
After that came time to pour the urethane. Now 120 sets worldwide these mounts are attracting a following. I'm on to the sec on production run and adding more colors to the lineup. I changed thing around and am now making the washers out of Stainless stee for a better look. I'm working on a smaller M-6 mount for the Top 80 as well as mufflers. This is really fun and hopefully I can keep developing more PPG products. I have 3-4 new PPG prototype products that are getting great feedback already.
Hanging on a single engine mount!!! (around 200 Lb of load)
-- Fly safely, Robert Kittilä