Staging Composite Propellant Motors Is Simplified With This Electronics Unit

Launching large two-stage rockets is a unique spectacle that always awe's spectators. With the MiniTimer3 Staging Electronics, you'll be able to launch your big two stage rockets with confidence.

Imagine your big rocket taking off in front of a large crowd. As the booster stage burns out, the top portion coasts away. Everyone's heart stops beating, because the top stage is drifting away on its own. Everyone is thinking, "Oh no, the top section is going to come in ballistic like a lawn dart." Suddenly, while the rocket is hanging mid-air, the top engine roars to life. The model rockets away into the sky, leaving its own distinct and separate smoke column. A wave of applause and cheers erupt from the spectators. Your rocket has just drag-separated and staged on its own with complete success. And it was an awesome sight to see.

Click Here to see a video of a 2-stage rocket that uses this staging timer.

Staging composite-propellant motors is different from staging black-powder motors. The reason has to do with how composite-propellant motors, like the Aerotech single-use and reloadable motors are ignited.

Composite motors need to be fired-off with an igniter that is inserted all the way to the top of the propellant. Because of this, they cannot be staged using the same techniques as those of black-powder propellant motors. Your rocket needs to carry a complete ignition system inside the rocket to fire off the igniter in the upper stage motor.

What controls when the motor fires is the timer circuit, as shown here.

You will also need a small but powerful battery, and an igniter (these are not included). For composite propellant motors, we recommend the First Fire Jr. But this staging controller can also fire off all other types of igniters, like the Quest Q2 igniter. The type of battery you'll need depends on the igniter used. For The Quest Q2 igniter, a 9V alkaline battery works fine. For First Fire Jr. igniters, a NicCad type battery is recommended because it has lower internal resistance.

While it sounds complicated, it really isn't too bad. The MiniTimer3 Staging Electronics is set up to be easy to operate. It is almost as simple as dropping it into the rocket and sending it up in the sky. To be honest, the hardest part is deciding where to stick it in the rocket and how to run the wires to the igniter.

The MiniTimer3 Staging Electronics is a countdown timer circuit with some extra brains that it can tell if everything is OK to fire off the igniter. This built-in level of safety is the reason we sell this particular electronic gizmo.

The brains of the unit automatically detect lift-off of the rocket. Once that occurs, it starts its own internal countdown, and then sends electricity to the igniter to fire off the 2nd stage motor.

For example, you desire to fire the second stage of the rocket when the rocket is three seconds in the air following lift-off. You would set the timer prior to installing it in the rocket, which is simply holding down the little "program" button for a duration of three seconds when you turn it on. Then you put the unit into the rocket and hook up the igniter into the second stage.

When the rocket sits on the pad, the electronic brain's G-sensor (which senses acceleration) is looking for a sustained acceleration of 2.1 G's. If that acceleration threshold it met, it determines the rocket has successfully launched. It's next step is to determine how much time has lapsed since launch, and when the three seconds (for this example) has passed, it sends electricity to the igniter to fire off the second stage. As you can see, it is very simple to use.

Another example of the simplicity is that the same battery that powers the circuitry also supplies the power to fire off the igniter. This eliminates the need to take a second battery onboard the rocket.

Can it be tricked into thinking a launched has occurred?

It is not likely. The threshold of 2.1 G's has to be maintained for 0.5 seconds, which is a long time in rocketry. You would not trigger it by picking up the rocket as it sits on the launch pad, nor by knocking the rocket over accidentally. The G-sensor must be oriented properly (this end up) so that it can't be false-triggered.

But with any rocketry electronics, you should practice common-sense safety procedures. For example, don't power it up by connecting the battery until the rocket is already on the launch pad and everything else is prepped for flight.

The most convenient location is between centering rings of the motor mount as shown to the right. In this configuration it is very simple to run the wires from the staging electronics to the igniter in the motor.

You'll also have to cut an access hole in the side of the rocket so you can get at the electronics to turn it on by hooking up the battery as it sits on the launch pad. The hole is closed prior to launch by putting a hatch cover in place, such as shown on this Aerobee-Hi rocket. The hatch cover can be secured with tape, or with screws.

As you hook this up and "button-up" the rocket by installing the hatch cover, you'll feel just like a technician working on the Space Shuttle. You are in fact doing the same type of procedures that engineers do when launching real rockets.

While the electronics can be mounted anywhere in the rocket, I would advise against putting them in the bottom stage. From a performance standpoint, it makes sense to put them in the bottom so that the top stage is lighter weight. But there is a chance that the stages could come apart at booster stage burnout (called drag separation). If this happens, it will also yank the igniter out of the upper stage motor. That's a guaranteed ballistic recovery which isn't safe.

• Can be used with cluster motors!
  
  
• It is easy to set delay time, and this can be done right at the launch field. The timer is adjustable from 0.6 seconds to over 60 seconds in 0.1 second steps.
  
  
• There is a beeper on the unit. This does three things:

1. Provides igniter continuity check - It beeps when you hook up the igniter, letting you know everything is hooked up properly.
   
   
2. Power-up reporting of current delay time setting - After you set the delay time by holding down the "program" button, the unit will beep back the time so you can confirm everything is set correctly.
   
   
3. Post-flight siren - It makes a siren noise after it is done working. This gives you an audible aid to help you find the rocket after it has landed.

• High accuracy digital time setting is retained in EEPROM memory even with power removed. This means is that once you set the time, it stays in memory forever (or until you set in a new time).
  
  
• Uses secure screw-down terminal blocks for battery and igniter. This means there is no soldering required to hook anything up. All you need is a small screwdriver to attach the wires.
  
  
• Rugged "surface-mount" construction and internal self-diagnostics assure reliability.
  
  
• Backed by PerfectFlite's three year warranty.
  
  
• Can be used for other things too. Use it to fire off ejection charges instead of using the rocket motor's built-in ejection charge.

Operating voltage: 4.8V to 10.5 V (3.0V to 4.8V at half current rating)

Operating current: 1.0 ma no continuity, 3.0 ma with continuity

Maximum firing current: 97.6A for 1 ms, 64.5A for 10 ms, 33.9A for 1 second

Continuity check current: 75 uA/V

Timing range: 0.6 second to over 60 seconds in 0.1 second steps

Timing accuracy: +/- 3% typical

Operating temperature: 0C to 70C

Other Supplies Needed Use This Product (these are NOT included):

• Small screwdriver
  
• Wire to hook up your igniter
  
• Battery (the size/type is dependant on the igniter in the motor. A 9-Volt Alkaline battery works for Quest Q2 igniters. You'll need a 9-Volt Ni-CAD battery for use with First Fire Jr. igniters. Note that Ni-CAD batteries also require a battery-charger too)
  
• Battery Holder or battery terminal. These can be purchased at an electronic supply store such as Radio Shack.
  
• Mounting plate. A stiff piece of thin plywood works well. The size will depend on the type of battery you're using for the flight.
  
• Igniters for the upper stage motor.

Q. Where can I get additional information on electronic staging?

A. Check out Peak-of-Flight Ezine Newsletter #91. You can also download the user's manual for the MiniTimer3 to read more about the operation of the device and to select the proper batteries for your type of igniter.

Q. How long should you set the timer?

A. The minimum time should be the burn duration of the booster stage motor. You can find the burn time of motors on our web site for single-use and reloadable motors. You can also add a little bit of extra time for coasting for a greater visual effect. On your first flight, use no more than one additional second. You don't want the rocket to arc over and fire the top stage horizontally, as that is dangerous. Use the RockSim software to get an idea of the orientation of the rocket when the top stage fires. Make sure to add some wind to your simulation to make things realistic!

Q. What battery should I use for this timer?

A. Please see the operation manual.

Q. Can Copperhead™ Igniters be used with this unit?

A.

While the Staging Electronics shown here can fire off a Copperhead igniter, you shouldn't use them for staging. Copperheads are hard to hook up inside a two-stage rocket. Additionally, they are less reliable than First Fire Jr. igniters. You can use Copperheads in the bottom stage, but not the top one. The Quest Q2G2 igniters are also great for air starting motors.