Motors, batteries and control systems

Model Airplane News, Jun 2001 by Atwood, Tom

world of new gear is now available for micro RC applications: motors, props, batteries, receivers, servos, electronic speed controls, connectors and more. "Plug and play" RC equipment that will be familiar to any RC modeler is offered in every price range.

At one time, electric power was associated with minimal flight times, but that is now history. Across the entire category of park and backyard flyers, power-- on flight times of 10 to 12 minutes (and 15-plus minutes using nickel-metal-hydride [NiMH cells) are quite common. For the really diminutive aircraft that weigh only a few ounces (e.g., those that are typically flown in still air or indoors in gymnasiums), power-on flight times of 4 to 6 minutes are common. And with lithium cells, flight times of an hour or more are easy to achieve.

* Motors. There is an amazing variety of new direct-drive and geared motors that are purpose-designed to power slow flyers. Conventional brush motors range from Speed 400s at the larger end to geared 280 motors and still smaller units such as the very popular GWS motors, the AstroFlight Firefly Micro and European imports such as the WES-Technik DC1717 and DC5-2.4. AstroFlight even offers a diminutive .010 brushless motor. There is a motor in every price range for every application.

Props are offered by a variety of manufacturers for the wealth of direct- and geared-motor systems now being marketed. For a look at some of the latest additions, which include higher-pitch props for park flyers and still smaller props for the smallest RC models, see John Worth's March 2000 "Cloud 9" column, featured in the RC MicroFlight highlights at www.rcmicroflight.com.

* Batteries. The batteries that power micro flyers range from 500 to 600mAh nickel-cadmium (Ni-Cd) and nickel-metal-hydride (NiMH) cells for the larger park flyers down to tiny 50 and 100mAh cells for the smallest "plug and play" backyard and indoor aircraft. Batteries designed for the camera and cell-- phone markets have also been incorporated into the micro RC battery arsenal. Rechargeable and single-- use lithium cells offer extraordinary duration for smaller aircraft. Moreover, a variety of electronic speed controls (ESCs) are now available with battery-eliminator circuits (BEC) that will power both the motor and the onboard RC gear.

The range in battery size simply reflects the power requirements of models of various sizes. Smaller motors flying fully equipped, 3-channel aircraft that weigh less than 9 ounces may draw one tenth the power of larger park flyers--as little as 1/2 to 1 amp while cruising.

Choose the batteries suited to your application, and you'll have no trouble flying your small model for periods of power-on flight that last from several minutes to well over an hour.

Consider the advantages of the tiny 100mAh NiMH cells that debuted in the hobby over the last year. At 3.5 grams each, these cells weigh the same as 50mAh Ni-Cds. Micro RC expert Don Srull charged these NiMH cells at 0.3 amp and found that their performance was very close to that of 110mAh Ni-Cds (see the April 2000 issue of RC MicroFlight). Because they are the same size and weight as 50mAh Ni-Cds, the new 100mAh NiMH cells offer twice the energy density of Ni-Cds.

Lithium cells offer spellbinding performance in the smallest aircraft and come in both rechargeable and "single-use" versions. For details on Tadiran rechargeable lithium-metal cells, see Tom McCann's article in the February 2001 issue of RC MicroFlight. * Radio systems. Hitec and JR are the first of the larger radio companies to develop dedicated systems for the microflight arena. Hitec offers the Focus 3 SS FM system that comes with a 3-channel transmitter with Ni-Cd batteries and a wall charger, two HS-55 microservos and a Feather receiver. This package costs only about $105. Hitec's Feather Flight Pack, which includes four HS-55 servos, a Feather receiver, micro-switch harness, a charging jack and an airborne 270mAh battery, costs only about $70. JR offers its own dedicated system, the J-Line Quattro Lite, which comes with a 4-channel transmitter, JR 610M small receiver and two 241 microservos for $125. For a glimpse of the great many sub-micro radio systems now available, see the "Receiver Survey" included in the RC MicroFlight highlights at www.rcmicroflight.com.

Micro Mustang

Designed by Dave Robelen, the Micro Mustang just might be the ultimate backyard fighter. This diminutive Mustang has an 18-inch wingspan, slightly more than 50 square inches of wing area and weighs only 2.2 ounces. The model can be built from the RC MicroFlight plan using 1/8-, 1/16- and 1/32-inch sheet balsa and is covered with fine-grade tissue on the open areas. The finish on the sheeted sections is spray sealer and clear Krylon paint. The 3-channel model uses Sky Hooks & Rigging's Pro receiver, two WES-Technik servos and an FMA Direct Mini 5 ESC. In the nose is a DC5-2.4 motor using a 4.2:1 gear reduction to turn a 5.2x5.2 prop. The drive battery is a 5-cell, 50mAh Ni-Cd pack that provides about 4 minutes of flying time.