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|Frequently Asked Questions:
1. I’m hearing that your soft motor mounts for glow powered motors fail. What’s up with that?
There is a lot of misinformation being spread about our mounts failing (much of it on the internet) so we’ll try and separate “myth from reality”. We have had some mounts fail at the adhesive/rubber/plastic bond line; all of them (that we know of) were assembled prior to June 2005. Many of the mounts that failed, but not all, were prototypes being field tested by various individuals around the country that agreed to provide us with some objective feedback concerning the product and its performance. A limited number of the mounts that failed were production mounts that were purchased directly from us, or from retailers carrying our products.
The problem was with the use of a moisture cure, expanding urethane adhesive. A similar adhesive had been extensively field tested for almost a year with no problems, but we were concerned with the brittleness of the glue after it fully cured. We tested a more flexible urethane adhesive in January 2005 with good results, and decided to switch to it at that time. Unfortunately, when the product was brought to market, it didn’t have enough field test time on it to fully uncover the adhesives deficiency (obviously a mistake on our part).
When those mounts started failing we analyzed the problem, we contacted the major glue manufacturers to get their input and advice, we obtained some glue samples, and then we conducted some pretty extensive lab tests. Based on that information, we switched to using a flexible rubber-toughened cyanoacrylate adhesive, IC-2000, in early June 2005. IC-2000 is much more durable and exhibits far greater peel-strength than any of the other glues we’ve tested. Since switching, there have been NO bond line failures of mounts assembled using IC-2000 reported to us. For those who are interested, here’s an Acrobat.pdf format file of an email communication between ourselves and a customer that has more detailed info: Motor Mount Problem.pdf (40 Kb)
While we have tried to “get the word out” about the problems we had with the early motor mounts using the urethane adhesive, it’s obvious we haven’t reached everyone. We still occasionally receive a report about a mount coming apart and in every case to date it has been a mount assembled prior to June 2005 with the urethane adhesive(s) noted above. And in every case we have replaced the mount with a current one free of charge to the customer, and on an expedited basis. We value our customers and we think this is the least we can do to alleviate their inconvenience.
If you have a mount of ours that you purchased from us, or one of our retailers, prior to June 1st, 2005 that you think may have been assembled with the urethane glue, please do not hesitate to contact us about it. We will exchange it out at no charge to you. If you want to send the mount back we will update the mount and return it to you free of charge. If you’d prefer to swap out the mounting disk yourself (it’s easy to do as the mount was designed to be serviceable), just send us an email indicating when and where you purchased the mount and we’ll send you a replacement disk, free of charge, no questions asked.
If you have a prototype mount that you received from someone who was asked to test it for us, the same offer as above applies. While it should be expected that prototype test products would have some problems (after all, that’s why we test them), we will nonetheless include them in this offer.
2. One of your competitors claims that your mounts are only zero to 15% effective at reducing vibration compared to their 90%. How good is your mount at reducing vibration?
It’s about the same as the other leading competitor’s (OLC) product. We’re not claiming that it’s 90% efficient either, that’s a ridiculous claim that can’t be backed up with any data that would stand up to reasonable engineering scrutiny. Just pick up ANY 2-meter glow powered pattern plane with a soft mount in it, run it up to full throttle, note the vibration, and then try to tell anyone that you honestly believe that 90% of the vibration produced by the motor has been filtered out of the airframe by the motor mount. Back when we flew 60’s in 7 to 8 lb airframes those numbers MIGHT have been achievable, but not today with motors putting out nearly 3x the power and larger airframes that weigh only a few pounds more.
Here’s why we feel their claims are not defendable:
We took some measurements with the E=MC3 we flew the last several years, both before and after we switched from “one of their mounts” initially used, to one of our soft mounts. Nothing else was changed. We used the same motor, the same propeller, the same spinner, the same fuel, the same glow plug, the same everything. The parameter we measured was the amount of battery capacity being used per flight to fly a typical Masters practice sequence of approximately 12 minutes duration, typically ~225 mAh. The number did not change from before with "their soft mount", to after with "our soft mount". We noted this over a number of flights and verified the results each time were relatively consistent from flight to flight.
The OLC quotes a parameter they call Current Drain Reduction (CDR) which is a fancy way of saying that the current being used by the servos/receiver/voltage regulator/etc is reduced by that percentage because of the reduction in vibration in the airframe effected by switching to their product. The OLC’s soft mount used on the E=MC3 in the example above was one in which they claim a 90% CDR. If this were true, using their baseline current assumptions, and assuming their calculations are valid, the battery capacity used for a single flight with a hard mounted motor would be a whopping 1485 mAh! The simple truth is that you can’t equate a reduction in current usage to a quantitative amount of vibration isolation. Such a measurement can only provide trending information as to whether something is better, the same, or worse than a baseline measurement. To claim anything more is just smoke and mirrors.
The effect of motor generated vibration transmitted into an airframe is extremely airframe dependent, having to do with airframe stiffness, the structural resonant bending and torsional frequencies, and the frequency and amplitude of the “forcing function" (in this case the motor/motor mount combination). These effects are extremely difficult to predict with any degree of accuracy without the use of a validated finite-element analysis structural dynamic computer model, or by performing a ground vibration/structural mode interaction test using very sophisticated instrumentation and data acquisition equipment, followed by a thorough engineering analysis. For our applications, one soft mount may work better than another for one airframe, and not as well on a different airframe. To say that one soft mount is always better, on all airframes, is misleading at best. Especially considering the following point.
Both the OLC’s and our motor mounts are fundamentally the SAME. The same overall size, the same general type and amount of rubber compounds, the same general configuration and geometry, the same principals of operation, under the same laws of physics. It would be astounding to think that they’d be very much different in operation or efficiency. They simply aren't.
3. The other leading competitor (OLC) claims in their advertisements that “Many of the [OLC] Mounts designated for use with a nose ring, are performing flawlessly with original isolator rubber even after 5000 flights. There has been no [OLC] Mount failure to date.” Can you make the same claim?
No we can’t (and they really shouldn't be either).
We know of two OLC mount failures involving the rubber mounting disk interface among the current group of pattern flyers in Southern California. In one case the back disk failed where it mounted to the firewall, and in the other case the rubber tore along the slip joint between the front and back disks. To be fair, the OLC may not have known about these failures. But they did occur. There have also been many occurrences of broken beams with OLC’s mount, we had beams break on two of their mounts ourselves when we were using their product. We’ve had our share of problems (see Q#1 above), but we don’t try to hide it, rather we learn from it, and share what we’ve learned with those who are interested in expanding their knowledge base.
The other claim challenges one’s sensibilities. For a single mount to have 5000 flights on it would require it be flown an average of two flights a day, every day, without exception, for nearly seven contiguous years! We’ll leave it to the readers to draw their own conclusions about that.
Let’s be clear about this - we’re not claiming that OLC doesn’t have a good product. They do. We just happen to think that we do too.
4. Do you have a soft motor mount for the YS110, ST2300, or <your favorite motor here>?
Sorry, we don't. All of the motor mounts we currently offer are listed on the website. We may, as time and market demand allows, develop Soft Motor Mounts for these, or additional motors. If we do, they will be listed on the web site at that time.
Another option is to adapt a conventional glass-filled or aluminum motor mount to the Soft Motor Mount Disk shown on our web site. It wouldn’t be a difficult modification as there are attachment holes molded into the face of the disks plus the inside is easily accessible through the center holes in the disks.
5. Why do I have to use a nose ring with your soft motor mount?
The motor mount plate that the motor bolts to is not designed to handle the bending loads placed on it in the pitch axis by maneuvering flight loads when a nose ring is not used. It was optimized for minimal weight and maximum stiffness in the torsional axis and will likely fail if used without some sort of mechanism to support the front end of the motor.
6. When will the Soft Motor with Integral Nose Ring Support be available?
It won’t be integral to the motor mount, but a separate component that mounts directly adjacent to the motor mount and spans the distance between the firewall and the nose ring.
As to when, hopefully soon (we’re still working on it). It’s a difficult problem to solve, trying to come up with a design that works, that’s acceptably light, and inexpensive enough to produce at a reasonable price. What I’ve found is that it’s very difficult to fabricate anything priced for the hobby market using a domestic machine shop. I’m trying very hard to not send this overseas, but that may very well be where it winds up being fabricated.
At this point in time we’re having a handful of prototype supports fabricated domestically for testing to determine if the current concept is feasible. We’ll keep you posted as to how it goes.
7. I keep losing the little white plastic bushings for the Soft Motor Mount. Where can I get some more?
Replacement bushings are now available on our website.
8. Is a soft mount even needed for an electric powered pattern plane?
It depends on your priorities. Granted the vibration environment created by an electric motor is much less hostile to the airframe and equipment than that created by a glow or ignition motor. However, the electric motor/propeller combination does generate harmful vibration and transmits it into the airframe, just at frequencies and amplitudes that are not easily observed with the naked eye. Our philosophy is that if we can provide an inexpensive, quality product that makes the task of mounting the motor easier, and effectively filters the vibration from the airframe, it’s a worthwhile improvement over “hard” mounting the motor.
9. What’s the difference between the rubber bushings for the Standard vs. the Wide Electric Soft Motor Mount?
The soft bushings are ~10 durometer (about like warm bubble gum) and the firm bushings are ~55 durometer (more like a medium pencil eraser). They both filter high frequency, low amplitude vibration well, the main difference being that the softer bushing has a lower cut-off frequency (the frequency were the signal attenuation, in this case vibration isolation, begins to become significant).
10. Can I interchange the rubber bushings for the Standard and Wide Electric Soft Motor Mounts?
Yes, they are dimensionally identical. While we supply the firm bushings as standard equipment with all of our mounts, the soft bushings may used for front mounted in-runner motors such as the Hacker C50 that use a rear support.<p>
The firmer bushings should be used when front mounting an out-runner (Hacker A50, Hacker A60, Axi 5330/F3A) and when aft mounting out-runners (Plettenberg Xtra 30-10, Axi 5330/F3A) to an aft firewall. This is necessary to limit the amount of lateral displacement at the tip of the spinner during maneuvering flight loads to an acceptable amount. We highly recommend the use of a rear motor support brace when front mounting an out-runner (with or without a soft mount) as the structural loads applied to the front of the fuselage without a rear motor support brace can be severe and may result in damage to, or failure of, the fuselage.
UPDATE (5/25/06) - The Hacker A60 motor does not fit the Standard width mounting plate (purple), however it appears that the A50 does. The Wide (gold) electric soft motor mount will fit both the Hacker A50 and Hacker A60 motors but check to be sure it will fit in your airplane if your spinner is smaller than 3.5" diameter.
The Axi 5330/F3A motor should be used with the Wide width mounting plate (gold) as it will not easily fit the Standard (purple) mounting plate.