ElectricFlight I
was fortunate to attended the 2013 NEAT Fair
http://neatfair.org/. De- spite the occasional rain, it was “neat”. The Bergen Flyers Symposium ses-
sions were particularly worthwhile. Indoor flying sessions at the Drainsville High School on Friday evening and Saturday from 1 p.m. on were the high point for me. As usual, the extremes in miniaturization were on display. The Mini Vapor has been discontinued. Why I don’t know; it’s one of the best fliers around. These were available for $30 from several of the vendors. Of course these sold out. The Mini Vapor is quite capable of tow- ing a 20-inch toilet paper streamer. Mini Vapor Combat put twenty or so of these in the air. The winner was the last one down with the longest streamer. Needless to say it was a lot of fun. We also had Mini Vapor races—four heats of five each doing five laps with the winners of each heat in a final round. I ended up try- ing to fly someone else’s Mini Vapor while mine hit the balloon pylon.
One of the more interesting things I saw was the interchangeable power/control mod- ule from Zeke’s
www.parkscalemodels.com for his Wisp series of models. Paul Bradley
www.parmodels.com refined this technique a couple of years ago and flew it in his Comet 25-inch Stinson Reliant SR-7 at KEIF. Sev- eral of the photos in this column come from him. Check out his plans page for more details.
It may appear that the major advantage of using an interchangeable power/control module is being able to fly several models with the same unit. But to me the real ad- vantage is the ease of connecting up the pushrods to the receiver servos in a small fuselage. I have buggered up a micro linear servo or two trying to force the end of a pushrod Z link into the servo tab with limit- ed maneuvering space.
Refer to the magnetic pushrod connectors drawing—1⁄8-inch diameter by 1⁄8-inch thick magnets are used. A length of 1⁄8-inch dowel is drilled through the center axis to fit the
Shrink Sleeve
Magnet Dowel
by stew meyers You can reach Stew Meyers at 8304 Whitman Drive, Bethesda, Maryland 20817, or via e-mail at
stew.meyers@
verizon.net
pushrod. The dowel is glued to the end of the pushrod. A magnet is then glued to the face of the dowel. A length of heat shrink tubing is placed over the magnet/dowel assembly. The tubing is then shrunk. A drop of CA from each side of the assembly helps secure the heat shrink tubing to the assembly. The pushrods can be either music wire or carbon rod. The airframe end of the pushrod is easily installed before the fuselage is closed up or covered. Some method of reten- tion is necessary while the rest of assembly takes place. The Reliant fuselage shows one approach. Similarly, the servo ends need to be restrained if a tray is used. If a hatch is available for access, no retainer is necessary as the short servo pushrods can be easily maneuvered into place.
Let’s look at a little recent history of this interchangeable power/control module con- cept. ItCanFly developed the Snap & Fly R/C 3-in-1 Micro RTF. This featured a 900 MHz four-channel pulse width proportion transmitter and receiver with magnetic ac- tuators, which was very similar to the Plantraco system. Only three channels were used for this system. The receiver, actua- tors, battery and motor were mounted on a Styrofoam control module.
Three airframes—a biplane, canard, and V-tail tractor—had magnets which allowed the control module to snap in place. The pushrods had magnets on their ends which hooked up when the modules were assem- bled. The motors are 7mm direct drive pagers swinging a 2.5-inch prop. These mod- els had a 13–15-inch span and weighed 17– 19 grams, thus they flew a bit fast for com- fortable gym flying. Guillow’s
http://www.guillow.com picked these up and marketed them for a while. Currently they only offer a parts bag with a propeller, motor, motor mount and the base module control linkage rod set for $13. It CanFly also developed a 2.4 GHz light weight Indoor Slow Flying 2-in-1 RTF. These were marketed by Flyzone as “Uber- Lites”. Again a receiver/ power module with actuators is magnetically attached to an air-
frame. The carbon/plastic airframes in this case are mylar covered resembling Vapors. There is also some ancient history. The modular concept appealed to me forty-five years ago. Guillow’s had a line of 18-inch span WWI models. I thought the Fokker
D.VIII would make a nifty micro R/C model. Granted the keel fuselage construction is inefficient for a rectangular fuselage cross section, but this is easy to replace with longeron box construction. The 27 MHz band was available for modelers. Radio con- trol was transitioning from tubes to transis- tors. Finally transistors that would operate at 27 MHz became available at a reasonable cost.
ACE R/C had a range of pulse transmit- ters and small receivers, but none were real- ly miniature enough for the job. Then Howard McEntie persuaded Bill Albin to publish an article in Model Airplane News on his six-gram superregen relayless receiv- er intended to drive escapements or small magnetic actuators, such as Bentert or Adams actuators.
I talked to Bill about this last week. He
was working for a hearing aid manufacturer and had located some mini transistors that were not exorbitant in price, so he designed a micro receiver utilizing them. ACE then kitted the design and I built one. It worked well and had a single end output which means the output was off-on.
The Bentert actuator was single ended with a spring return. An additional bridge was necessary to drive an Adam Actuator which required a plus or minus output to drive the coil both ways. Moreover, the Adams weighed more than the Bentert. I did not want the extra weight and therefore opt- ed for the weaker Bentert, which turned out to be sufficient for the job.
Ni-Cds had established themselves as the lightweight alternative to carbon zinc bat- tery chemistry. However small Ni-Cds were non-existent at that time and S-76 Silver cells seemed the best bet. Again hearing aid
technology. I mounted this all on a sheet of 1⁄32-inch ply that could slide into the model.
PHOTOS: PAUL BRADLEY
Paul Bradley’s drawing of pushrods (above left) with magnet coupling. The Monocoupe equipment tray (above center). It magnetically mounts in the
30
airframe with the battery underneath. Paul Bradley’s Stinson Reliant (above right) showing the air frame pushrods retained by disks.
NOVEMBER 2013
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68