DIY Control Horns and Servo Mounts

Apr 01, 2009 No Comments by

By Jack J. Joseph

I receive at least one unsolicited credit card every month. Usually, I cut them up and throw them in the trash. Ollie Edwards of the Scottsdale, AZ Model Flyers uses the cards to make control horns and servo mounts. They work great on his flat-wing models and probably would be adequate for backyard airplanes of moderate size. Here is the technique Ollie uses to create his custom horns and mounts.

This is a typical control horn and base. The horn is one-inch long and has a base 3/4 in. square. Use those dimensions to draw a horn of any shape you desire. If you already have an adequate store-bought horn, it will save you from designing your own. Draw the base using the dimensions shown. The slot in the center fits over the base of the horn, so be sure to make it the proper length and width.

Lay the paper pattern you designed, or an actual horn, on the credit card and trace around it with a fine-point pen. If the card has been handled, you may have to scrub it with soap and water before the pen will work.

Use the same procedure to draw the bases. Two bases are used with each horn, so the eight bases on a card will accommodate four horns.

Cut the horns and bases from the card. A #11 blade works very well, as does a pair of sharp scissors. Use sandpaper to smooth the edges.

Your custom horn and its bases are now ready for mounting on your airplane’s control surfaces.

Epoxy a base plate to the horn. Set it aside to dry.

Determine where on a control surface you want to place the horn and cut a slit through the foam wide enough so the horn can be inserted. Put a little epoxy on the horn and base plate and slide it in the slot. Next, apply epoxy to another base plate, slip it over the protruding horn on the opposite side of the foam. Snug it tight to the foam’s surface and use a clamp to hold everything in place until the glue dries.

These are the credit card servo mounts. Cut a 3/4 in. strip from the card and mark the center. Measure 1/4 in. on each side of the center mark to create the space between the servos.

Now you can determine the length of your servos and add 1/16 in. to that measurement. For example, Hitec’s HS-81 servos are 1 3/16 in. long. Add 1/16 in. to that measurement and measure that length (1 3/16 in. plus 1/16 in.) outward from each of the 1/4 in. marks. Mark that distance on the card. Most micro servos are about 1/2 in. wide (you might want to measure the servos you plan to use). Measure 1/2 in. from the card’s edge and draw a horizontal line.

You now have two 1 1/4 in. x 1/2 in. rectangles marked on the card. Use a blade or scissors to remove those rectangles. Place the servos in the rectangular openings on the mount and mark and drill 1/16 in. holes for the servo screws. Cut another 3/4 in. strip from the credit card and use the completed mount as a template to carve and drill the second mount for the other side of the foam.

Select the site for the servos on your airplane and use one mount as a template to cut servo holes in the side of the aircraft. Glue a mount to the side of the plane so it surrounds three sides of the newly cut holes. Put a servo in the mount and screw the mounting screws through the servo, card mount and foam until 1/16 in. of the screw protrudes from the foam. Attach the second servo.

Add glue to the remaining mount and place it on the opposite side around the two servos, so its holes lie on the protruding screw tips. Hold the mount in place and tighten the screws. Use a side cutter or file to remove the sharp tips of the four screws that stick out from the mount.

That’s it! No more trips to the hobby shop—you can now make your own horns and mounts!

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