Although I could rely on finger-flick turnouts, especially since the Walthers Code 83 turnouts have a snap-action on the points, I want to try something different. One of the products in development over at Iowa Scaled Engineering is a 3D printed key switch. Originally intended for the relaunch of our timelock circuit, I wanted to try them as fascia turnout controls. To switch the points, you have to insert a standard key (any key will do) and turn it. The theory goes that this will simulate the locking and unlocking of the switch stand and throwing the points all at once since you have to have the key to make it work.
Anyway, to use the key switch, turnout motors will be required. For some time, I’ve been looking at the MP1 switch motors over at Model Railroad Control Systems.
These are nice, compact, linear motion switch machines that, by themselves, are very quiet. After mocking up a turnout on a piece of foam, along with the MP1 switch machine attached with double-sided foam tape, I noticed a disturbing problem. Noise! It is well known that extruded foam board can be noisy when trains run over it, but I never put together until this moment that a switch machine would also introduce its own noise.
Not content with just accepting the level of noise, I started to do some experiments:
The conclusion (after many more experiments than shown in the video above) was that mass is the key to dampening the vibrations and the resulting noise. The inertia of the large mass prevents the vibrations from the switch motor from getting transferred to the foam and causing the foam to act as a large speaker cone.
Foam tape alone, even though it has some give, is still rigid enough to transfer the vibrations to the foam. Same with rubber. Fellow modeler Matthew Freix suggested a material called Dynamat, used in car audio applications. While it sounded promising, the results were still not as good as a block of metal. The fact was, the square of Dynamat I used was still 10x less mass than the chunk of steel, further supporting the theory that mass is the primary factor:
There were several other helpful comments and suggestions on the Proto-Layouts group over at Groups.io. These are nicely summarized by Seth Neumann in the MP1 Wiring and Control Application Note. My conclusion is that mass is the primary factor in reducing the noise transfer to the foam, and other techniques like silicone adhesive, cork, etc. can provide further incremental benefits. However, I also noticed that once the noise is reduced to a certain level, the improvements become harder to get. I suspect that’s because the noise of the switch machine itself begins to dominate when the foam is no longer the primary path for the vibrations to get turned into sound.
Next, I started looking at different metal pieces I had available. The original piece from a metal angle bracket is on the left (170 grams), an 80/20 aluminum bracket in the middle (168 grams), and a piece of stock steel bar I cut off is shown on the right (138 grams).
All of them had about the same (qualitative) results – i.e. they sounded about the same when pressed against the foam along with the switch machine. The larger aluminum bracket maybe sounded a little better, but it’s hard to say for sure. Perhaps the larger area (or volume?) played a role? I don’t know for sure.
Placing rubber O-rings under any of them made a small, but noticeable, improvement, too. However, attaching the metal to the underside of the foam will need something with adhesive qualities, but the fact that the rubber O-ring improved the noise level is promising if a flexible adhesive is used.
My next step is to try machining a bracket from an aluminum block. I intend to make the bracket with a central hole for the throw bar and two smaller, tapped holes to accept screws that will hold the switch machine to the bracket. Why aluminum, you might ask? Although aluminum is about 3x less dense than steel (meaning you need 3x more material to get the same mass) it is FAR easier to machine (cut, drill, tap) with conventional tools than steel is to work. Since I have the lateral space underneath the layout to accept a larger piece of metal, I’m planning to go the easier route.