An amazing five-channel microreceiver
John Worth | [email protected]
In the world of micro-flight, RC components are getting smaller and lighter. When they are capable of doing more than many of their larger and heavier counterparts, that draws attention — and that’s how it is with the Micro Invent Minor receiver. Made in Slovakia, it is sold in the United States by Air Midi Micros in Colorado and Bob Selman Designs in Missouri.
The Micro Invent Minor is a five-channel, crystal-controlled receiver available in three frequency ranges: 35, 40, and 72 MHz. It can be used with servos and magnetic actuators (not simultaneously on the same pins). In addition to motor control, it can operate four servos, two magnetic actuators, or two servos and one magnetic actuator merely by the way the devices plug into a clever arrangement of connector pins on the receiver. It controls the motor through a built-in ESC, or the ESC circuit can power an external ESC.
Although capable of operating up to five channels (motor speed plus four control devices), the Minor is so small that it is especially suitable for the smallest and lightest models needing rudder and motor control. It measures only 3/8 x 5/8 inch and weighs less than 1 gram without the crystal. The receiver has a range of at least 300 feet and operates on a single Li-Poly cell. Its basic current consumption is only 6 mA. The battery used in my tests was a high-drain, 130 mAh cell produced by The Atomic Workshops in England.
An earlier edition of the Minor operated with negative-shift transmitters and could handle motors drawing as much as 1 amp continuous (1.6 amp peak). The newer edition, called the Plus, looks identical but works with either positive- or negative-shift transmitters and will handle motors up to 2 amps continuous (2.6 amp peak). The Plus lets the Minor fly larger, heavier models while remaining suitable for the smallest ones. Either version is supplied with vertical or horizontal connector pins.
The MicroBug model
I have the vertical-pin Micro Invent Minor Plus receiver installed in a Jack Dobbins-designed MicroBug. The MicroBug has a 10.5-inch wingspan and weighs 22 grams, with roughly 50 square inches of wing area. It uses a GB04 6 mm motor with a 5.8:1 gear reduction driving a 4-inch Plantraco propeller.
In addition to the built-in ESC, the receiver operates two Micro Invent MCA2 magnetic actuators for rudder and elevator control. These tiny, cube-shaped actuators are approximately 3/8-inch and weigh 3/4 gram each. Their current draw is only 42 mA, and they provide ample power with smooth proportional movement. Microconnectors plug directly into the receiver. Rated suitable for models up to about 30 grams, the actuators sell for about $22 each.
A single 130 mAh, high-discharge Li-Poly battery from The Atomic Workshops provides power. The MicroBug is a delightful little flyer intended mainly for indoor use but suitable for outdoor flying in mild breezes. Construction is light but robust because the wing structure and fuselage tailboom use carbon rod. The tail assembly is 1/32-inch balsa sheet. The receiver, Li-Poly battery, and geared motor are mounted on a 1/2 x 1-3/4 x 1/16-inch plywood pylon. Brass push-pull rods connect the tail control surfaces to the magnetic-actuator control arms. A 1/16-inch plywood stabilizer hangs from the fuselage stick and provides a grip for hand launching.
Micro-Size Toolbox
In keeping with the idea that micro-flight models are compact and easy to carry, it makes sense to use a smaller-than-typical toolbox for carrying model supplies and equipment.
I found a suitable case at a local Wal-Mart that is 12 inches long, 8 1/2 inches wide, and 9 1/2 inches deep. It opens to reveal four trays (3 1/2 x 10 x 1 1/4 inches) and a lower interior well measuring 11 x 8 x 4 inches — just right for my Futaba transmitter to lie inside on a pad of foam rubber.
The all-aluminum case features lockable snap latches and a handle. It is actually a cosmetic organizer sold under the trade name Caboodles, and it cost less than $24. The trays are a good size for carrying an assortment of tools and supplies. The well-made case should last many years and could even serve as a camera case or a beverage or lunch box.
A New Era for RTFs
For approximately two years the micro-flight world has been inundated with a flood of toy-market RTF RC models. Most are low-priced, some are good fliers, and many become a source of components for home-built micro models. This market has introduced many newcomers to RC, and their experiences have generally been positive.
A couple of newer products from established model suppliers have had a dramatic impact on micro-flight activity this year. Although some might still regard these new models as “toys,” they are a class above typical toy-store offerings in quality and performance.
The first was shown at last April’s R/C Expo in Toledo, Ohio; the other was introduced in July on the RC Micro World website. Both became available to customers in August. Horizon Hobby’s ParkZone and Plantraco of Canada provided samples for evaluation. Plantraco’s arrived first — a profile-scale model of the World War II Japanese Zero — followed almost immediately by ParkZone’s scale Cessna 210 Citation.
Both are well designed, well crafted, and perform excellently. Each was ready to fly right out of the box after installing transmitter batteries and charging the airborne Li-Poly battery. From the first hand launch both flew well and coped with gentle outdoor breezes, although they are basically indoor models intended for gymnasium-size flying.
Plantraco’s Zero weighs 4 grams, has a 10-inch wingspan, and features rudder and motor speed control. The ParkZone Cessna is larger, with a 15-inch wingspan, weighs 18 grams, and has motor, rudder, and elevator control. The Cessna uses linear servos for tail controls and has tricycle landing gear for takeoff and landing; the Zero uses a magnetic actuator at its rudder and is designed for hand launching and belly landings.
Both models are well scaled and colored authentically. Largely because they are so light, they have proven crash resistant. After a dozen or so flights each, both still looked like new. Handling is comparable to flying larger, conventional homebuilt aircraft.
Modeler and public reaction has been positive. The Zero receives many favorable comments and costs roughly $88 without the transmitter — a good value for those who already own a Plantraco 900 MHz transmitter. The Cessna, though more expensive, is applauded because it uses 2.4 GHz spread-spectrum technology. It includes the smallest and lightest spread-spectrum system yet, and its price of roughly $150 is a bargain. Being able to fly without concern for others on nearby frequencies is a major advantage, and having that capability in a micro-flight model is impressive.
Micro flight is on the cutting edge of new technology and is rapidly outgrowing the image that smaller and lighter is inferior. It is becoming a significant modeling category: nearly 1,000 people from more than 30 countries subscribe to the online monthly micro-flight resource RC Micro World.
The AMA website has useful micro-flight information, and MA Sport Aviator offers a number of micro-flight articles, including “A Free Guide to Indoor RC Flying,” with many photos and details.
Sources
- Air Midi Micros
(775) 783-8545 www.airmidimicros.com
- Bob Selman Designs
(417) 358-9521 www.bsdmicrocrc.com
- RC Micro World
- AMA (Academy of Model Aeronautics)
- MA Sport Aviator
Transcribed from original scans by AI. Minor OCR errors may remain.
