The Ampeer ON-LINE!
May 2006
The Club Newsletter of the Electric Flyers Only, Inc
AMA Charter 2354
Walled Lake, MI, USA
Editor: Ken Myers

Fly the Future - Fly Electric!

     I put the data from the AF site and Fly RC review into Drive Calculator 3 and was surprised at what I saw. I had to revise the data over and over, since NONE of it was worked. I finally came up with the screen capture shown above. I cannot say with certainty that this screen capture actually reflects this motor, but if it does, it can be seen that using the APC 8x6E or larger prop is pushing this motor way past its most efficient operating range of 4 amps to 8 amps.
     Now I had more questions than answers!
     There were some things that I found "interesting" in the data presented in Fly RC. As expected, the 8x6 had the highest volts, lowest amps and highest RPM, but the 9x6 didn't seem to fit into the rest of the data:

     The volts appeared to be too high for the amp draw when compared to the rest of the voltage readings in the Performance Testing data on p. 46.

Graph 1

     I put the Fly RC data into an Excel spreadsheet to see what it would show me about the data. Graph 1 above was arranged by the reported amp draw. It wasn't exactly what I expected to see. I thought that it might be a bit straighter.
     I couldn't believe the efficiency numbers that I was getting, so I decided to start back figuring numbers. I did this for all of the Fly RC data, but will illustrate with the APC 9x6E, as that is a prop that someone might expect to fly on a glow 19 and on this motor. (Of course it would be a glow 9x6.)
     With the reported RPM 9,750, I computed the output watts three different ways after seeing the Drive Calculator 3 output.
     Hyperion Emeter: 9.75^3.2 * 0.129 = 188.5 watts out
     Using Torque via the Electric Motor Handbook by Bob Boucher.
Generator constant (Kv) = 1375
Kt = 1355 / 1375 (Kv) = 0.9854545 (oz.-in./amp)
No Load Current: 0.45 amps
Amps out: 25.3 Ð 0.45 = 24.85 amps
Torque: 0.9854545 * 24.85 = 24.49
Watts out: (24.49 * 2 * Pi * 9750) / 8496.7154 = 176.6 watts out
     RPM / Kv = 9750 / 1375 = 7.09v * 24.85 amps = 176.2 watts out
     Using the above figures the drive efficiency (efficiency of the motor, ESC, connectors and wiring from the ESC to the motor) ranges from a high of 65.4% using the 188.5 watts out to a low of 61.1% using 176.2 watts out.
     That didn't look very efficient to me. I continued to explore what might be going on with the numbers.
     AF states the Rm = 90mOhms. 0.09 * 25.3 amps = 2.277v + 7.09 volts out = 9.367 volts.
     When I checked for the resistance of the Castle Creations Phoenix-35, I ran into the next problem.

Web site

.pdf documentation
(Enough to drive you crazy isn't it!)

     Voltage drop through controller: 0.0045 * 25.3 = 0.114v
     9.367 + 0.114 = 9.48 v into the ESC. Fly RC recorded 11.4v on the Emeter. That is way off!
     I back figured the Rm using the Fly RC data and came up with an average Rm of about 0.165 ohms, almost twice the AF published number.
     0.165 * 25.3 amps = 4.2v + 7.09 volts out = 11.29 volts + 0.114 = 11.4v into the Emeter.
     There are several points that I'm trying to illustrate with this example.
     First, once again, I am pleading with ALL manufacturers to post usable, correct, non-conflicting data on your Web sites!
     When a reviewer makes a statement like the authors of the Fly RC review about efficiency, there should be some "proof" of this in the article.
     Anyone doing "motor testing" using props should provide the following:
     The procedure used
     The equipment used
     The temperature, altitude, and barometric pressure at the time of the testing
     The specific prop, and if an APC E or SF, the prop hub thickness and weight.
     Data to be reported should include:
Two no load measurements including volts, amps and RPM readings using different voltages and only after the motor has been "warmed up."
There should be repeatable data for volts, amps and RPM from three different prop "loads".
The data should be carefully analyzed and spurious data checked again for accuracy and repeatability.
     While it is best if motor testing is done via a dyno, as Mr. Steve Neu does, it can be done with some reasonable accuracy using the parameters and procedures outlined above.
     Lastly, I want to make it perfectly clear that the Astro Flight 19 Direct Drive motor will certainly do the job it was designed for. Even though, in all the examples, it is operating near its recommended maximum current, with its samarium cobalt magnets, it is much more "rugged" than others in its class, and there is no reason to believe it won't prove to be a long lasting, useful motor! Put it in a House of Balsa P-51, use an APC 8x6E prop and a good 3S Li-Po pack and have a ball!

     The January 2006 issue of the Ampeer had a photo of Keith Shaw with his Bantam SRE, a kind of stand off version of a WACO SRE kit-bashed from the SR Batteries (srbatteries.com) Bantam biplane kit.
     Here are the details that Keith gave me:
New tail surfaces
34" span, clipped from the original, with elliptical tips
Radial Cowl
PJS 300 SF motor
APC 9x4.7SF prop
2S1P Kokam 700mAh battery
Castle Creations Phoenix-10 ESC
Weight: 9.2 oz.

     The Radio Aeromodelers of Seattle is hosting the RAMS/PSEMF Electric Fly-In on June 24 and 25. The contest will be held at the RAMS field in Sumner, WA. Take Hwy 167 to 24th St. exit, to West Valley Hwy. It is about 1/4 mile to the RAMS field. The event begins each day at 8:00 a.m. The contact person is Randy Smithhisler at 253.927.4672 or rsmithhisler@paccar.com.

     The following events are scheduled:

     This is the longest running electric event in the country. You are invited to come and watch these incredible aircraft in action in the hands of some of the best radio control pilots in the Pacific Northwest.
     For updated information and a map to the event, check the contest schedule at seattlerams.com.

     To build a hot wire foam-cutting bow I used a scrap 2 x 6 that I cut into 1 x 1 1/2 strips. You could use a 2 x 4 to do the same thing. I wanted a bow that could be used to cut various size parts for aero-modeling, so I designed its cutting width to be adjustable. The adjustable part of the design came about because I didn't have the room to store multiple bows.

     I used 3/8-inch diameter dowel to connect the various parts. Even the bow's pivot uses a dowel. The dowels, used to connect the various sections, are all 2 inches in length. They provide a strong, stable, and removable junction. It is relatively easy to adjust the bow's width by adding or removing an extension.

     The next figure shows a detailed graphic of a dowel junction. These can be combined to give a bow of almost any desired width.

     The most critical fabrication step is in drilling accurate 3/8-inch holes. The holes must all be parallel with the major axis of the beam. I used a drilling jig to ensure all holes were true. Furthermore, I started with a 1/16 inch bit and walked my way up to 3/8 inch using four bits. Otherwise you will loose accuracy and have poor alignment between beams.
     The next two figures show detailed views of the bow's pivot area - located on the left hand side of the bow. These pieces were fabricated by using a table saw with a fence. The saw blade was used as a poor man's dado cutter to cut out the slots - a router table would do the job much more easily.

     The right hand bow handle is detailed below at the dowel junction. It is relatively simple by comparison (see the full bow view at the beginning of the article).

     Above is a figure showing the bow with the rest of the hardware (hooks, spring, and stainless steel wire). As can be seen, I used hooks to attach the spring and the wires. This allows for easy replacement, and the bow's width can be adjusted by changing the lengths of the wires.

     To attach the spring to its neighboring eyehook I used some old copper wire I had lying around -- this is just a piece of scrap romex safety wire.
     I cut the wire to give a reasonable spring tension and then made a loop at each end of the wire and soldered the loops closed.

     The photo shows the completed bow in its narrowest width configuration. You can see the spring being held under tension by the wire with soldered loops. The "extended version" looks the same, just wider.
     Here's a view showing the wooden parts in an exploded view.

     The bow works as expected. In my tests, using a high current DC power supply, I found that thicker stainless wire is needed to cut dense foam. Thicker wire, i.e., smaller gauge, can handle higher currents and is mechanically stronger.
     I had no issue cutting low-density foam with the wire I originally used. However the current had to be held to not much more than five amperes. Anything beyond six amperes and the wire would snap. With higher density foam you need a bit more heat and strength, so a larger diameter cutting wire is called for.
     By the way, the hooks for the cutting wire worked out nicely as attachment points for the power leads. You can easily clip an alligator clip to the shafts of these hooks, and the hooks stay cool even though the cutting wire is quite hot.
     For a more permanent electrical connection you could solder the power leads to the shafts of the hooks and dress the wires away from the hot wire. Anderson Power Poles would work nicely to provide adjustable lengths.
     Here's the bow in its storage configuration. I used one of the bow's hooks to hold the cutting wires, and I used the spring's hook to hold the tensioning wires with loops.

Jim Yuzwalk
March 20, 2006

     The March 2006 EFO meeting was held at Rick Sawicki's house in Commerce Township and was a great night of sharing. Dave Stacer had prepared a really great video of us flying in Rick's basement at the February meeting. Many of you saw a little clip from this video if you checked out the March Ampeer. Thanks Dave, really great and lots of fun.

     Roger Wilfong shared his Astro Flight 035 powered Clancy Lazy Bee. He chose the colors because he likes them, and he also had them on hand. Very nice.

     It turned out to be boat night at the flying club meeting.
     Rick Sawicki shared his Splash 3D Hydro-Plane flying boat. As you can see from the photo, this version is much larger than the more common Miss Hangar One. It is designed by a man named Ben in Jacksonville, FL. The kit contains; CNC cut 6mm Depron construction/3mm cockpit, 4mm carbon spars, .060 carbon control and support rods, 3mm flat carbon bar, Carbon control horns and a CD-rom instruction manual.
     Rick is using most of the recommended power system components listed here, except for the ESC; Hacker A30-28S, Hacker X30 esc, TP 2100 Pro-Lite 3S1P, 3- HS-55 servos 4-6 channel rx and APC 9x6E prop. For more info or to order for $90 the email contact is benrod65@hotmail.com.

     Richard Utkan shared a blue foam version of a flying hydro that he had picked up at swap shop. The plans were printed on the foam. He got a lot of advice as to how to finish it up.

     There was a lot of sharing of ideas by all of the members in attendance. That is the greatest thing about our EFO meetings; they are about model airplanes or related activities!
     Ken Myers demoed the Drive Calculator application beta and showed and shared some of its features, via Rick's TV. (Rick's TV behind Richard - above - is showing stills from the Feb. EFO meeting) Several EFO members are now trying out the application betas as well.
     All of us would like to thank Rick for being a wonderful host all winter long for our meetings, thank you sir!