Airtek Free Flight Electronics

DT Timer
LED Flasher
DT Timer
Altimax Altimeter
Retrieval Beacons
Finding Models with a Radio Beacon

Simple 1 function low cost DT timer servo controller

DT timer board weights 1.2 grams

Now available is a small DT only timer that can be used on almost any free flight model.  It is powered by a single cell lipo battery and controls any micro RC servo.  Any time up to 20 minutes can be programmed in 30 second increments by using the control button and LED indicator.  The choice of battery and servo is left to the user, but a typical configuration is shown below.

Typical DT system w 2.2g battery & 4g servo, 7.4g total

A typical solution shown is about 7.4g total.  The battery plugs into one end of the timer, and the servo plugs into the other.  Smaller batteries and servos can be used to get the total weight as low as around 4g depending on the application.
When the DT time has expired the servo arm moves about 100 degrees.  The DT line can either be hooked directly onto the servo arm for release, or the servo arm can be used as a cam to release a standard wire release arm.  The system is very flexible and gives the modeler freedom to customize as needed.  For extremely light models a pager motor can be used instead of a servo.  This is the solution I have used for catapult and hand launch gliders.
The timer uses almost no battery energy except for the brief 1 second when the servo is being moved at DT and again for resetting the system.  Therefore a tiny 50mAh lipo battery as shown here will work for hundreds of DTs.  The only battery requirement is that it must provide enough current for the servo being used and must be in the 3 to 5 volt range.  The battery can be left plugged in for an entire day of flying.  At the end of the day the system must be unplugged however as leakage currents will eventually kill the battery.

50mAh lipo battery, 2.2g with connector

Directions for Use:
Plug in the servo and then plug in the battery.  The servo moves to the initial flight position and then the LED blinks to indicate the number of 30 second increments of the programmed time.  For example, 6 blinks would indicate 3 minutes time.  After a 2 second pause the LED blinks 10 times for a 10 second pre-flight countdown or launch window.  After the DT time the servo will move to the DT position and the system goes to sleep taking almost no current from the battery.
The single white control button is used to both start the DT timer and to program the DT time.  Each time the button is quickly pressed the timer begins the entire sequence mentioned above.  If one is waiting to launch with the model ready, this button should be pressed every minute or so to reset the system and prevent the DT from happening, and then of course it should be pressed just before the actual launch.  This is therefore a fail-safe system because it is not possible for the servo to be in the initial position without the timer also counting down towards DT in normal operation.  The idea is to guarantee DT function above all else and to avoid losing the airplane.  An alternate aproach would be to add an ON/OFF switch in the battery wire, or to plug in the battery just before the flight.  However if one fails to turn on the power the model may be lost of course.
The extra 10 second buffer time is intended to both give time to launch the model after the button is pushed and to ensure that the DT happens at least a few seconds after the max time has been achieved in competition.  For example you decide to launch by pushing the button.  You watch the LED flash 6 times which confirms that the timer is running and set for 3 minutes.  You then take about 3 seconds to get in the right position and throw the model.  The model will then DT at about 3 minutes and 7 seconds after the launch.
Setting the DT time:
With the timer running hold down the button for a couple seconds until the LED lights for about a second and then release the button.  The timer will then cause the LED to start blinking.  Count the number of blinks corresponding to the desired DT setting and then press the button again for about a second.  If performed correctly the LED give a quick triple blink for confirmation and then the normal timer sequence will begin again.  For example if a 1 minute DT time is desired do this:  hold the button until the LED lights, release, after 2 blinks press button again and release, LED does triple blink to confirm and system re-starts.  The programmed time will remain in the timer even when the battery is removed so the only time that this programming is needed is when the time is changed.
Test Mode:
A test mode is available to move the servo between the two positions for setting up the model.  Hold the button until the LED lights solid and then continue to hold it down and the servo will move to the DT position.  Press the button again and the servo will move to the initial position and the system re-starts.
Pricing Details:
Servo Timer:  $30
LiPo Battery:  $20  (typically 50 or 60mAh depending on availability)
LiPo Battery charger:  $15  (this is the same charger pictured in the other sections and is the circuit board only - a 6 to 12 volt power source is also required)
Note that the battery and charger are the same as used for both the Altimax and the RDT system.  Batteries are subjuct to availability and may be in the 50 to 90mHa range.  Note that I am NOT in the battery business and am very happy if you buy your own battery elsewhere and you can save money if you do so and wire it yourself.  I use a 3 wire battery plug on all my products and batteries with the positive wire in the middle which means that the battery can be plugged in either direction without harm.  When using another battery plug with the more standard two wires, caution must be used to make sure that the positive wire always connects to the center positive pin of the timer otherwise damage may occur.

Ken Bauer
2306 Turquoise Circle
Chino Hills, CA  91709