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Better Servo Screws
Micro Fasteners to the rescue
Text & photos by Tom Hintz
Posted – 8-20-2014
We all use two kinds of screws with our servos, one type to hold the servo in the plane and the other to hold the servo arm in place. Both of these screw types are always important but when the plane gets bigger the loads on these screws goes up as well.
Servo Mounting Screws
Aeroworks suggests using Micro Fasteners #STW0209 #2 by 9/16” socket head screws. These screws look similar to those that come with most servos except that the threads run all the way to the head. I have worried about how well the standard screws could hold and always “toughened” the screw hole up with thin CA but I would occasionally find that the screws subjected to higher loads occasionally loosened anyway. The full length threads insure that all of the available wood in the mounting area is engaged by full threads. I still apply a bit of thin CA to the threads when installing the Micro Fasteners #STW0209 to maximize the strength of the screw to wood interaction.
Having a socket head also makes installing the Micro Fasteners #STW0209 far easier than the little Phillips head screws packed with most servos. I magnetize my drivers so that between that and the hex head I can use the driver to place the screw more easily in hard to reach places. That means fewer crooked screws that either strip their holes or engage only the edge of the mounting boss.
So what is the cost of so much convenience and peace of mind? I paid $4.90 for 100 screws! That may not last the rest of my life but it will be close. The cost is low enough to me to make not using them simply dumb.
Servo Arm Retention Screws
Here again, the norm is a Phillips head screw that I have been able to round out with surprising ease. During my stint flying RC helicopters I started using socket head screws to hold the servo arms on because I found one of these screws (the Phillips version) missing from a cyclic servo on my 700 AFTER a flight. Since then any servo that I can’t afford to have shed its arm gets a socket head screw. The problem was finding them after I used up the supply discovered in a helicopter parts assortment. Then I saw the note I the Aeroworks 60cc Freestyle Extra 260 QB-L instructions about using the Micro Fasteners #SCM2508 2.5mm by 8mm socket head screws and my problems are solved.
Here again the socket head makes installing these screws way easier, especially when having them stick to the end of the wrench helps reach the servo. Hard to reach or not, the hex head makes installing these screw tightly much easier than the Phillips type screws. Another big point is that I have never stripped a hex head screw in a servo and never had one loosen up. I do use blue Loctite on them and did so with the Phillips style screws but still found a few of them loose after a bunch of flights.
The Micro Fasteners #SCM2508 do cost a little more in part because they are made from a tough alloy steel and it is more complicated to manufacture them. A bag of 20 of these screws cost m $3.25 which I still consider cheap insurance that is just dumb to pass up.
Installing servos and their arms may be a small part of building an airplane (or helicopter) but if the screws hold the servos or their control arms in place fail you can find yourself building a replacement aircraft.
The folks at Micro Fasteners have an impressive selection of fasteners that can make building our aircraft easier and then help prevent a costly failure. I would much rather spend my time at the field flying rather than picking up the pieces. Using quality screws on my servos is a low-cost no-brainer.
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