Control the Ejection of Two Parachutes Electronic Payload Fires Two Ejection Charges to Bring Rockets Down Closer to the Pad

Entacore AIM 3 Altimeter

  • Part Number (PN): 09139
  • Manufactured by: Entacore
  • Product Specs:
  • Size: 2.76" X 0.98" wide " X .59" tall  - Perfect for 29mm tubes! (70mm X 24.9mm X 15mm)
    Altitude Report: Always beeps out last flight in ft or m
    Memory: 6min flight, over 30min total
    Launch Detect: ~200 feet AGL
    Operating Temperature: -40° to 85°C (-40º to 185ºF)
    Weight (w/o Battery): 17.6 grams (0.62oz)
    Altitude Limit: 38,615 ft (11,770 m) MSL
    Battery: 4v to 16v
    Operating Voltage: 3.7V - 12V
    Operating Current: 1.5 ma typical
    Firing Current: 16A max (supplied by battery)
    Warranty: 1 year against manufacturing defects from Entacore.

5 Units in Stock

This is a dual-deployment altimeter and it also records altitude & velocity. Flight data is downloadable to your computer, so you can see the performance of your rocket. Includes a built-in audio beeper for reporting peak altitude.

You Control When the Parachutes are Released

Dual Deployment

Are you tired of chasing your rockets for long distances? Wouldn't it be nice if they didn't drift such a long way and still came down slow enough that they weren't damaged? Then you could fly really big and high-altitude rockets even in wind.

The solution is a dual-event electronic payload that controls when the parachutes are ejected from the rocket.

The concept is simple. Instead of flying a single large parachute to bring the rocket down slowly all the way from apogee, you use two different parachutes.

The rocket ejects a small parachute or streamer at apogee. It falls quickly and doesn't drift very far. When the rocket is closer to the ground, say 500 feet up, it deploys a big chute to slow it to a safe landing velocity. It is a great solution!

Single vs. Dual Deployment

Main Features

Works To Over 38,000 feet!

This unit is meant for nearly all your high power rocket projects, including those really high altitude flights that might otherwise drift miles and miles if you used single-parachute recovery.

Versatile Voltage Requirements Allow Different Weight Strategies!

You can use any power source from 3.7v to 14v (6v+ for igniters) and, this includes small batteries like the A23 if you are using low current ejection charge starters like the Quest Q2G2. (Starters and ejection charges are not included).

User Selectable Main Parachute Deployment Altitude

You determine the altitude you want the main chute to eject. Choose altitudes anywhere between one-meter increments. This programming is done by settings in the Bootloader firmware package (you'll need a PC, not a Mac). We did our test flights using the altimeter out of the box, though, and it works great, deploying the main parachute at 150 meters.

Mach Delay Setting for Supersonic Flights

The mach delay setting is used to prevent premature deployment of the drogue parachute as the rocket makes the transition between subsonic flight and supersonic flight. During this period the pressure surrounding the rocket suddenly increases -- which could be interpreted as a decrease in altitude (see below about how altitude is determined). This condition would cause the altimeter to think the rocket has gone past apogee, and it would fire off the ejection charge to deploy the drogue chute.


Deploying the parachute at mach speeds would be a bad thing. We've seen it.

"Mach delay" prevents firing the deployment charge for a predetermined time (that time period where the rocket is traveling at supersonic speeds). After the time period has elapsed, the device resumes normal operation and samples the air to determine the altitude of the rocket. If your rocket is expected to go supersonic, you must turn this feature on using the Bootloader (see instructions on how to set up the device) for proper deployment to occur.


How do you determine how much "delay time" to use as you are setting up the Mach delay feature? Great question. You perform a rocket flight simulation using the RockSim software. It can show you the interval the rocket is traveling at supersonic speeds. We recommend it for all rocket flights, particularly for complex flights that might use dual deployment.

Apogee Deployment for the Drogue Parachute/Streamer

Firing the first ejection charge at apogee insures that the drogue recovery system is deployed while the rocket is traveling at the slowest possible speed. This minimizes the likelihood of rocket damage due to "zippered" body tubes, over-stressed shock cords, and stripped parachutes. Electronic deployment is preferable to using the engine's built-in timed ejection charge, which can vary from engine to engine. Also, if the rocket weathercocks excessively the time delay in the engine may be too long and deploy the parachute too late, causing a zipper or a shred. Electronic payloads like this one have saved a lot of rockets from an early demise.

Can Also Be Used As Single-Deployment Device

You do not need to configure the altimeter to deploy two parachutes as separate events. You can set it up to just deploy one parachute at apogee. This could be used to provide redundancy to a standard motor ejection charge. If the motor's ejection charge fails to fire at the right time, or if the rocket weathercocks strongly into the wind and the motor ejection would occur too late in the flight, the apogee ejection would "save" the flight. It provides that extra reliability to make sure that your rocket will survive to see another day.

Beeps out the Peak Altitude After The Flight

The AIM USB can also be used as a simple altimeter that can operate up to 38,000 feet above sea level. This altimeter has data storage capability that can be downloaded to a computer.


Working With Data

Entacore Chart

I generated the above chart with Entacore's software after a single-deploy flight at SCORE in Pueblo, site of NARAM-52 in 2010. It's a fairly simple, plain chart that is quick and easy to generate and is pixel-based. In other words, you can't manipulate the data, change colors easily, or display it in a large format without jaggies. While you can't do that, you can export the data from the altimeter as an Excel file, then carefully examine the numbers in Excel. There are columns for Time, ADC, Pressure, Voltage, Altitude MSL, Altitude AGL, Smooth Velocity, and indicators for when the A channel and B channel fire. Each of these parameters is recorded every tenth of a second.

You can then use that data to generate some pretty cool graphics for presentations, marketing, science projects, reports, etc. That's one of the really huge differences between this altimeter and the rest. I created the graph below with the same Excel data I used in the graph above. I imported it into a Freehand graph and then worked out the kinks to get a much better, more professional graph that is vectored instead of pixel-based, so you can even create huge plotter-output graphics with no loss of quality. If you click on the chart below, you can download the PDF file (1.5mb—it has lots of data). You can do the same graph generation and creative stuff in Illustrator and undoubtedly in Corel.

I'm jazzed by the possibilities this altimeter presents. I've just begun to work with it (when I built the chart above I had only flown it twice over a two-week period) and I can't wait to play with the bells and whistles. This is really cool stuff!Chart 2

Additional Features

Hook-up For External On/Off switch

The device has a separate hook-up where you can (recommended) attach a on/off switch (not included with the device). This gives you some extra protection while hooking everything up for flight. Remember, you're getting ready to set up extra black powder to kick out the parachutes, and for safety reasons, you don't want to set off one of those charges prematurely. That's why you don't want to power it up until it is on the pad and ready to launch.

Continuity Of The Starters Reported

When you power up the device, it reports the status on the starter continuity. That way you will know if your rocket is fully ready to launch.

Built-in battery voltmeter

When you first turn it on, the altimeter reports whether current battery voltage is high enough. No more guessing about whether the battery is good or bad and whether it needs to be replaced soon. You'll save money, because you won't be replacing a perfectly good battery.

Mounting holes for increased mounting flexibility

Want to fly multiple altimeters at the same time? Then it makes sense to attach them to a mounting plate inside the rocket. They'll experience the same altitude and you can make an apples-to-apples comparison and get redundant back-up ejection. Note: mounting hardware is not included.

All the components are on one side of the board, so this unit can be positioned right on the board itself, without having to worry about damaging the component pieces.

Even though the altimeter can be mounted firmly in the rocket, it is small enough and lightweight enough that it can also be slipped it into a padded tube for quick installation.


For further information on mounting the device, please see the book Modern High Power Rocketry.


Warranty Information

Entacore will repair/replace your unit if there is any fault in workmanship etc. for a period of 1 year. Please note that we cannot offer guarantees if your unit wasn't well mounted etc.  You can contact Entacore for warranty and troubleshooting.  Don't worry, they respond quickly!

How Does This Dual Event Payload Work?

The Entacore AIM USB payload works by sensing the altitude of the rocket. In simple terms, it is an altimeter. But this one is different, it has more brains and extra hook-ups to to send electricity to two different ejection charges.

As the rocket takes off, this electronic payload calculates the altitude of the rocket. When it senses peak altitude, called apogee, it sends electricity to one of the starters. This starter sets off a small charge of black powder, which pressurizes one section of the rocket and deploys the small parachute, called a drogue chute (rhymes with rogue).

While the drogue chute brings the rocket down quickly, the payload is still sensing the altitude. When it descends to a pre-programmed altitude (which you control), it triggers a second time and ignites another black powder ejection charge which pushes out the main parachute. Since the rocket is now closer to the ground, the wind doesn't have time to push it downrange too far. So it lands gently, but much closer to the launch pad. That means you don't have to walk very far to retrieve your rocket.

Besides controlling the deployment of the two recovery devices, it also records the peak altitude that the rocket reached. So after the flight, you can find out exactly how high your rocket flew. You don't need to carry a separate altimeter in flight, so you save some money!

How Do Altimeters Work - Video Tutorials

Dual Deployment: Part OneSetting Up Dual Deployment Rockets - Part 1

In this first video, we'll explain what dual-deployment (ejecting two separate parachutes) is, and explain how the AIM 3 works and controls the rocket.


Setting up and handling black powder for ejection charges can be dangerous. Be sure to read the precautions in the AIM USB user's manual.  

AIM 3 Tips
  • While you can power the altimeter via a computer's USB port, you cannot fire an igniter with that power. The current for firing igniters comes from the battery source alone because the USB bus can only supply 100 mA under standard conditions. If you use too much current the PC will indicate an over-current on the USB hub and actually switch off the power completely until reboot!
Videos and Tips on Dual Deployment

What is dual deployment? Why would you use it? What kind of equipment do you need? Long-time friend and patron of Apogee Components, Jeff Lane, joins Tim in a series of videos answering these questions on using the Entacore AIM-USB altimeter in your next high power project. While this series directly pertains to the Entacore AIM altimeter, the knowledge is easily translateable to the other dual-deployment altimeters sold by Apogee Components.

Frequently Asked Questions about the Entacore AIM 3 Altimeter
How Altmeters Work
Q:How Do Altimeters Work?
A: The barometric altimeter measures the air pressure surrounding the rocket. Air pressure near the ground is greater than air pressure high in the air (remember, air pressure decreases with altitude, until you reach the vacuum of space, where there is no air pressure). What the unit does is to compare the pressure it senses during flight, to the air pressure on the ground. Using a simple formula, it automatically computes the altitude difference that caused the change in pressure.

How Altimeters Work - A Tutorial
How accurate are altimeters? Which is the best one? These are common questions that are hard to answer, because of the randomness of the atmosphere. This video explains what that means and how it relates to the accuracy of electronic altimeters.

For More Information: See our Peak-Of-Flight Newsletters. Issue #240, Issue #242, and Issue #257

Q:Do you sell any type of ejection charges that could be used with the device on this page?
A: No. The ejection charge is always made from loose black powder. Because black powder is regulated by the government, you have to purchase it from a gun store (one that specializes in muzzle-loading supplies). You also need to be at least 18 years old to use loose black powder in this manner.

Q:Does it matter what elevation the launch field is?
A: The altimeter samples the air on the ground, so it knows the altitude of the ground level. So when you set it to deploy the main chute at 500 feet, it will know that is above ground level. It doesn't matter where you start.

Learn to build the biggest rockets, and get HPR certified.
Q:How easy is it to set up dual-deployment?
A: To be honest, it is not a beginner-level operation. For starters, you have to design your rocket with two separate parachute compartments. This is detailed extensively in the book Modern High Power Rocketry 2. We highly recommend this book if you are new to large rocket or dual deployment techniques.

The mini USB cable is not included, but you may already have one if you have a digital camera.
Q:How do I hook the altimeter up to my computer?
A: You will need a mini-USB cable. It is not included with the altimeter. But it is very common, as this size is often used in digital cameras and cell phones. You probably have one or two already laying around your house.

Q:How does this electronic gizmo compare to other dual-deployment devices?
A: This device uses a single barometric sensor to determine how high the rocket is. The G-Wiz Flight Computer uses both barometric and accelerometer sensors to determine the rocket's altitude and orientation. This provides a bit of extra redundancy, but of course, it also comes with a higher price tag.

Reviews for the Entacore AIM 3 Altimeter
Current Reviews: 4

Random Selected Reviews:

5 of 5 Stars!Alexander Solis -- 03/27/2012
Fun and easy to use. This altimeter is a must have for those wanting simple usage and easy to read information. There is no data transfer kit required and it is a simple plug and play device. 5 out of 5 for its easy use. Highly recommended.

5 of 5 Stars!Andrew Duffy-Peter -- 04/02/2012
This is a great unit for rookie's like myself. Easy to use, easy to get data, nice and small.

5 of 5 Stars!Randy Marek -- 07/14/2013
I have two AIM USB Altimeters, they are great, easy to configure, easy to read the date, no beep counting... it makes it easy. The software works very well, gives a nice graph of the flight. I used one for my TRA Level-2 in my LOC-IV duel deploy. The size makes it easy to install and setup. It flew perfectly and an I a record of the flight. The same day I flew a Aerotech Mustang setup as a duel deploy... not that easy to find a coupler 1.64" ID by 4"... but, built a A-Bay flew, a motor eject drogue chute and a AIM main ejection.... worked perfectly.... So much performance in such a little package!

5 of 5 Stars!Jon Preston -- 07/20/2014
I've logged quite a few flights with the two I have. It is small enough to fit into a Blue Tube 38mm coupler. It is simple, reliable and rugged. Downloading flight data and updating the firmware are user friendly.

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