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The folks at Micro Fasteners make replacement screws that are far better than we normally get. That impressed AeroWorks and me a bunch. Click image to enlarge

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.
While reading the manual for my new Aeroworks 60cc Freestyle Extra 260 QB-L I noticed that they recommended two specific types of aftermarket screws from Micro Fasteners Inc. Because I am installing HiTec HS-7954SH servos capable of producing a bit over 400 inch pounds of torque I wanted to be sure those servos stay put and the servo arms remain firmly attached. The advice from Aeroworks regarding the screws in this review seems like a smart thing to do so I ordered a few bags of each type of screw.

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.

The Micro Fasteners screw is at the top (left) above the normal servo hold down screw. I like the threads going all the way to the head and the socket head design of the Micro Fasteners version way better. Installing them (right) is also a bunch easier to do without stripping the screw as the bottom one in this photo is close to being. Click images to enlarge

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.

Conclusions

The difference in the Micro Fasteners version to the Phillips style is obvious in this photos. (left) It is also very evident when you install the Micro Fasteners version (right) and can tighten it securely without stripping it! Click images to enlarge

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.

Visit the Micro Fasteners web site – Click Here

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