Using Actuators with Micro RC

Written by Joe Malinchak Micro-Flying Column As seen in the May 2017 issue of Model Aviation.

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When it comes to building a micro RC airplane, saving every milligram of weight can make the difference between a great-flying model and a flying brick! Using the lightest components available during construction is one of the best ways to keep weight to a minimum. Fortunately, there are some good options available for receivers, servos, motors, propellers, and other items. Some are custom made by companies such as Micro Flier Radio. You might pay a little more for them, but you’re getting the lightest and best-quality components that you can buy. One model component that I frequently use to save weight is a magnetic actuator. The subject, size, and weight of the model determine which actuator I use. I might even combine the use of actuators with servos. Let’s take a look at the different actuator types and how to best utilize them. The smallest commercially available servo currently on the market weighs in at .515 grams. That’s a lightweight servo and it is a great choice for solid control of a micro RC airplane. However, the servo is still too heavy to use in small projects. That leads us to the only other alternative: using magnetic actuators. Some people avoid using them because of the small wires and basic soldering skills that are required to attach them to a receiver. However, with a little practice and the right tools, soldering them can be a fairly easy task. Three types of actuators are used in our airplanes: a hinge actuator, an in-hinge-type actuator, and an actuator with an arm. Magnetic actuators are made by winding magnet wire into a coil. The wire size and length determine the weight and ohms of the coil. Most actuator receivers on the market specify the ohms required for optimum power and performance. You might not find a perfect match with commercially available actuators, but I have found that most receivers work well within the range of coils that are available. The hinge actuator is probably the easiest to use and mount in an airplane. It features an actuator mounted to one side of a hinge and a magnet mounted to the other. The hinge actuator is typically mounted to a fin and rudder—just as you would glue in a hinge. I normally use UHU Por foam glue to attach my hinge actuators. Plantraco introduced its HingeAct magnetic actuator with the Butterfly Livingroom Flyer airplane many years ago. This model opened up the possibilities of indoor flight to the public and was an instant sensation. I used the Plantraco HingeAct in my design of the Plantraco Classroom Fighter, and still use it today. The in-hinge-type actuator uses the bare actuator coil and a magnet mounted into the control surface. It is the lightest of the actuator types. To mount it in an aircraft, you merely cut a slit the size of the coil and glue the actuator in place with UHU Por or compatible glue. You then have to glue the magnet into the control surface at the position that aligns it with the center of the coil.

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The control surface is hinged in the normal manner so that it moves freely. I cut Blenderm surgical tape into small strips and use them to make my hinges. For more power, I normally use two magnets. I glue the magnets onto a flat piece of carbon-fiber rod or a thin piece of Garolite fiberglass-epoxy laminate purchased from McMaster-Carr. This makes the magnets easy to glue into the control surface and makes it easier to adjust the position of the magnets so that they sit properly inside of the coil. The actuator with an arm features a coil with a magnet and an arm mounted into it. The actuator with an arm is similar to a rotary servo in the fact that you attach a control rod to the arm and run it to a control surface. Actuators with arms have good power for their size. I normally use them on larger micro RC aircraft.

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You can purchase actuators and actuator receivers from several great sources. Micro Flier Radio, Plantraco, and Micron Wings are a few. Actuators are a great way to control your next micro RC project, so give them a try! Sources: Micro Flier Radio (941) 377-9808 www.microflierradio.com Plantraco Microflight (306) 955-1836 www.microflight.com Micron Wings [email protected] www.micronwings.com McMaster-Carr (330) 995-5500 www.mcmaster.com