ElectricFlight E
-36 is this month’s column topic. E- 36 is the National Free Flight So- ciety’s popular electric event. Re- cently the rules have been changed
to take into account the current state of bat- teries and motors (Li-Pos replacing Ni-Cds and brushless motors). To keep things sim- ple no auto surfaces are allowed. The basic motor run is 15 seconds which puts the mod- el at 600 feet or so. Obviously, an electronic timer is desired. While there are several timers on the mar-
ket that will do the job, most are not straight- forward in programing or require disconnect- ing the ESC and DT servo to program. Jim Coffin and Dave Lacey hit me up to come up with a simpler timer, similar to the DT timer I built for Don Srull, and mentioned in this column in the November 2011 issue ofFM. So here is Stone Age’s E-36 timer. The operation of this timer is dead simple:
There are two push buttons and an LED. There are Berg connectors for the ESC and DT servo on the back. The ESC supplies the power to run the timer. In normal operation, power is applied with no buttons pressed and the Ready mode is indicated by a dou- ble flash of the LED. Press PB1 to start the Armed mode indicated by a fast flash. Upon release of PB1, the motor will run at the stored Speed for the stored Run Time. Af- ter the stored DT time delay, the DT servo will function and the timer will enter the in- ert Finished state indicated by a slow flash of the LED. Power must be reapplied to exit this state. Pushing either button while the motor is running will stop the motor and go into the Finished state. If a push button is held down while pow-
er is applied, the timer enters a programing mode. If PB1 is held down, the Run Time is set to the length of time the button is held down. The LED flashes at 1 cps to aid tim- ing, but using a stopwatch is more accurate. Release the button when the desired time has been set. The LED will slow flash indi- cating the task is complete, and you are in the Finished state. Power must be recycled to exit this state. Similarly, if PB2 is held down, the DT time is set. Holding both PB1 and PB2 while applying power restores the default times of a 15-second motor run and 120-second DT delay.
by stew meyers You can reach Stew Meyersat 8304 Whitman Drive, Bethesda, Maryland 20817, or via e-mail at
stew.meyers@
verizon.net
PHOTO: DON DELOACH Don DeLoach (L) with his Super Pearl 202E based on the stock Mini Pearl that Randy Reynolds (R) is
holding. Prototypes are coming in at about 130–140 grams with a 2500 Kv motor and Thunderpower 2S 325 mAh battery. 202 square inches projected area.
If PB2 is pressed during the Ready mode
as indicated by the double flash, the motor will start and the Speed will be set to full bore and then will slowly step down. If the button is released immediately, the default of full speed is retained. Otherwise, hold the button down until the desired speed is reached. Upon release of the button the speed is stored and the timer goes to the Finished state. If you trim the speed too low, simply repeat the process. It will al- ways start out at full bore. Okay, now what power system do you
want to use for the E-36 event? With recent developments in electric power, the power system can be quite a bit lighter than the old brushed motor/Ni-Cd setup, while produc- ing much more power. A brushless motor
with a Kv of 1500 to 2500 rpm/Volt is suit- able. Remember, with motors of similar power capabilities, you can swing a bigger
prop with a motor that has a smaller Kv. You also want to make sure you have a
battery that can supply the current that the motor draws without sagging and an ESC capable of handling the current. It really pays to use a wattmeter or at least an am- meter and voltmeter during setup. You want the battery voltage not to sag below 8 volts over the 15-second motor run. Make sure you don’t over prop the motor beyond the peak power point. The prop will probably be 7 to 8 inches in diameter. Don Srull came up with a nice motor and battery setup from Hobby King, http://www.
hobbyking.com. The Turnigy nano-tech 370 mAh 2S 25~40C Li-Po pack weighs only 27 grams, but does not sag appreciably during the 15-second power run. These nano-tech lithium polymer batteries are built with an Li-Co nano-technology substrate complex greatly improving power transfer making the oxidation/reduction reaction more effi- cient. This helps electrons pass more freely from anode to cathode with less internal impedance.
PHOTOGRAPHY: STEW MEYERS
The power system of Dave Lacey’s E-36 #4 (above). What you don’t see is the ESC above the aluminum hatch and the battery in the pylon between the timer and servo. A loop from the DT hooks over the servo arm. When the arm rotates 90 degrees counterclockwise, it releases. It took a bit of doing to get a folder on the T1804 motor (at right). Dave machined the prop hub from 3 bar stock. The blades are 7–4.
⁄8 56 × 3⁄8 aluminum MARCH 2012
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