The AltimeterTwo is a tiny electronic payload that measures the rocket's top speed, as well as the peak altitude that it reaches. It only has one button, so it is very simple to use. Just turn it on, hold down the button to zero it out, attach it to the rocket and launch. When you get it back after the flight, it displays the speed and altitude of the rocket on a little view screen. This makes it great for science fair projects, school groups, rocketry competitions or just plain "bragging rights" when making bets with your friends on the performance of your rockets.
But it actually records more information than just altitude and top speed. It also measures the rocket engine's burn time, the peak boost acceleration, the average boost acceleration, the coast time to apogee, the time from apogee to ejection (if the rocket should arc over), the altitude at ejection, the average descent rate of the recovery device, and the total flight duration (from lift-off to landing). With this information, you can really dial-in on picking the right rocket motor and the launch angle and parachute size for optimum flights.
The AltimeterTwo retains the rugged design, easily-readable LCD, small size, and rechargeability of the AltimeterOne. It difference in that it contains an additional sensor, called a 3-axis accelerometer. This is what allows it to get a very accurate measurement of the rocket's speed, plus allows it to see the different events (such as burnout, and ejection) as they occur during the flight. And you'll have instant access to your flight information, which will make even professional rocket scientists jealous.
After the flight, simply hold down the single button for a few seconds, and when you release it, the AltimeterTwo will cycle through the stored information, one piece at a time until it is all displayed. It is slow enough where you can write it down on the flight log sheet, but fast enough that you won't have to wait around to get the altimeter into the air again for your next launch. Your friends will want to borrow it for their launches too.
The four main reasons are because it displays a vast amount of information on an easy-to-read LCD screen, it is so easy to use, it doesn't require a payload bay like other altimeters, and it is small and lightweight.
1. It displays the information on an LCD screen
The one complaint that people have about other altimeters is that they have to count the number of beeps or flashes. "Was that 8 beeps, or 9?" So they have to wait around for the sequence to begin all over again. Not with the AltimeterTwo. When you pick up your rocket after the launch, you just simply look at the display and see how high it went, as well as the speed, acceleration, flight duration and several other statistics. It is daylight readable, so you can actually see the information in bright sunlight.
2. It is Simple to Use
Besides only having one button, attaching it to your rocket is easy too. There is an attachment point that is built into one end of the AltimeterTwo. Just hook it to the base of the nose cone or to the shock cord (see photo below, but add extra padding). At this point, you can turn it on by pushing the one button, hold it down to reset it to zero, and launch it.
The only other modification you need to do is to make three small holes in the rocket so that the altimeter can sense the atmospheric pressure and record the peak altitude. The holes can be very small. We recommend 1/16-inch diameter, spaced evenly around the rocket. Just make sure that they are just below the shoulder on the nose cone so that they aren't block by the nose cone when it is inserted into the rocket. If you are worried about the holes being fuzzy on the inside of your rocket and possibly closing up, wick some thin CyA glue (super glue) into them and sand off the burs on the inside with some sandpaper.
That's all there is to it. When you fly the rocket, it constantly senses the pressure and records the peak altitude. Note: If your rocket gets caught in a thermal and starts to rise up higher in the air, it will always report back the highest altitude.
3. Doesn't Require a Separate Payload Bay.
It doesn't require a payload bay because it is enclosed in plastic. In fact, this is the first accelerometer based payload created for the hobbyist that has a durable ABS-plastic case to enclose the electronics. That case protects the supersensitive sensor from the spike in heat that is caused by the ejection charge, and from damage of rattling around inside the rocket (however, extra padding is encouraged because it is not indestructible).
Because it doesn't need a payload bay, you'll find yourself wanting to fly it in every rocket you own. And your friends will want to borrow it too, so be sure to get several of them for your range box.
4. Small and Lightweight
The AltimeterTwo is very lightweight at only 9.9 grams. The weight of this thing will hardly affect the performance of the rocket you're trying to measure. It is also physically small and will easily slide into a 24mm diameter tube. So you can use it even for small high-performance rockets like the Apogee Avion or Apogee Apprentice rocket kits. (WARNING! Choking Hazard. Don't put it in your mouth or leave it with small children.)
But it will also fit in large rockets, and can even measure altitude in rockets that travel at supersonic speeds!
As noted in the features section and video below, the AltimeterTwo has two sensors, not just one. First there is a pressure sensor to measure atmospheric pressure, and then there is the three-axis accelerometer to measure acceleration.
The pressure sensor is used to compute the altitude of the rocket above the ground. The sensor that is used on the AltimeterTwo is the same one as use on the AltimeterOne. It is very accurate at sensing pressure differences, which makes it great for model rockets and anything else that flies in the air.
The other sensor, an accelerometer, directly measures acceleration. This is why the AltimeterTwo can display the peak and average acceleration.
But an accelerometer doesn't directly measure speed, like a speedometer in your car. Fortunately, we can compute speed accurately if we know how long the acceleration is acting on the rocket. This is the simple high-school physics equation: For formula is that a change in speed = acceleration multiplied by the time duration that the acceleration is applied. The altimeterTwo can quickly perform this calculation as rocket takes off.
When you turn on the AltimeterTWO, it automatically scrolls through the last flight data. You'll see:
Battery Level - The data first screen you'll see is the percentage of a full battery charge. This lets you know when you'll need to recharge before you can fly it again.
Peak Altitude - This is the highest point in the flight (note: if your parachute catches a thermal, the peak altitude could be higher than the ballistic portion of the launch. It is rare, but it could happen).
Top Speed - This is the highest speed that the rocket reached. It usually occurs right at burnout of the rocket motor.
If the speed of the rocket exceeds the accelerometer's capacity to measure the speed, the speed will be under-reported (lower than the actual speed of the flight). In this case, you'll see the following screen:
Thrust Duration Time – As mentioned above, the AltimeterTwo must make a count of the time that the acceleration is applied to the rocket. This acceleration can only occur while the motor is producing thrust, so the duration of the acceleration is simply the "burn time" of the rocket motor.
Peak Acceleration – This is the highest acceleration sensed by the AltimeterTwo as the rocket takes off. The value is in gee's, or the number of times of the force of gravity. The peak acceleration occurs during the lift-off of the motor, usually very early in the thrust phase of the motor. The acceleration of the rocket at lift-off follows the thrust curve of the rocket engine. High thrust means high acceleration. The number is always displayed in Gs, where one G is 32.2 f/sec2 or 9.81 m/sec2
Average Acceleration – This is the average acceleration in Gs measured from launch until the rocket coasts. Average acceleration is useful for comparing the average thrust of two rocket motors, or to compare the weight and aerodynamic performance of two different rockets during launch.
Coast to Apogee Time – This is the time in seconds from the end of motor burn (when the accelerometer senses engine cut-off) until the highest altitude is recorded (either before or after ejection).
Apogee to Ejection Time – if the rocket should arc over and start descending, this is the time period from the peak of flight (as measured by the pressure sensor), to when the ejection charge fires. This is sensed because the ejection charge create a brief spike in acceleration as the nose cone pops off, so the accelerometer picks this up.
This is actually the time in seconds between the highest altitude recorded and the time that ejection (a 3G shock or greater) is detected. Can be negative if ejection occurs before the rocket reaches its top altitude. If no ejection is detected, this will be zero.
The actual ejection delay (time between motor burnout and the ejection charge firing) can be calculated by adding C2AP and A2EJ, so Actual ejection delay = C2AP + A2EJ
You will discover that the ejection times as given by the manufacturers are really estimates good to within 1-2 seconds. Now you can measure what they ACTUALLY were after each flight.
Ejection Altitude – This is the height above the launch pad at ejection measured using barometric pressure. Can be shown in feet (FT) or meters (M). If no ejection is detected, this will be the same as apogee.
Descent Speed – Once the flight duration is found, the descent speed is found by dividing the ejection altitude by the descent duration (found by subtracting the ejection time from the landing time). This is actually an average descent speed.
Flight Duration – Duration is determined by noting the time at which the descent stops as measured by the pressure sensor. The AltimeterTwo tries to ignore events like the pressure surge from ejection or a sudden rise during descent that could be due to a thermal, or to pressure gusts caused by wind on or near the ground. The pressure sensor is used because it would be difficult for the accelerometer get a true sense of landing; since there could be a lot of jostling of the rocket as the wind rocks it while under parachute, or it could have a very soft touchdown due to a really big parachute.
Apogee and Top Speed: These two figures are automatically shown after each flight. If the top speed is blinking, it means that your rocket may have exceeded the maximum acceleration of the AltimeterTwo at some point during the boost phase, and the speed may be under-reported.
Download This Useful Data Sheet - Use it to write down your flight data so you can store it in a notebook.
3-axis, 24g accelerometer: used to detect launch, acceleration, speed, and ejection. What is an accelerometer? It measures acceleration, which is a change in speed. By measuring acceleration, we can determine the speed of the rocket easily and accurately. What does 24g stand for? For starters, "1g" is the pull of earth's gravity. Therefore, 24g's means it would be like 24 times the pull of earth's gravity. The human body passes out from the stress of around 9 or 10g's, so 24 g's is a lot of pull. The 24g accelerometer tells us the maximum acceleration the sensor can measure (24 times the pull of gravity). What does 3-axis mean? That means it can measure acceleration in three directions at once. For example, it can measure North-South, East-West, and Up-Down all at the same time. Other accelerometer-based payloads for model rockets can only measure one-axis (up-down). By measuring three directions at once, you do not need to orient the payload or even hard-mount it into the rocket. It can dangle from it's hook, and still figure out the speed of the rocket in the "up" direction. It is really smart, which makes it very forgiving in how you mount 100it in your rocket.
- Accurate 19-bit barometric pressure sensor sensitive to altitude changes of less than one foot. This means the altitude reported back by the AltimeterTwo is highly accurate. It was tested in a laboratory vacuum chamber under ideal conditions (Peak-of-Flight Newsletter #283), and was found to be accurate to 99.9999%. That is pretty close to perfect, isn't it?
- Daylight-readable LCD display clearly displays all flight statistics. This means you don't need to plug it into a computer after the launch, you get the results back immediately, on a little display screen. How convenient is that?
- Rechargeable Lithium-Polymer battery lasts for hundreds of launches, no batteries to buy. That saves you money, and is less worry that you may have forgot to bring an extra set of batteries to the launch.
- Recharges in less than 2 hours from any standard USB port, no cable necessary!
- Status of Charge Displayed: Red light charging. Green light equals "done." You'll know exactly when it is ready for flight.
- Samples the atmospheric pressure over 30 times/second, and acceleration at 250 times/second. That is the number of times each second that the computer chip looks for, and records information from the sensors. This sample rate on the accelerometer is very high, which is good. The reason is that it will capture very brief events, like the ejection charge firing to kick out the parachute, or the short burn duration of 1/4A rocket motors, which burns for only 0.25 seconds.
- Stores information on flash memory - That way, you can turn it off and then turn it back on to see what the last flight reading was. Note: It only stores one flight, not multiple flights.
- Power button turns device ON/OFF and RESETs the display between flights. The one-button simplicity makes it the easiest altimeter and speed-measuring device on the planet!
- Automatically powers down to conserve power. That way, you only have to charge it once, and not have to worry about the battery going dead on you during the middle of the launch day.
- Handy tether point allows secure attachment, or independent streamer recovery. This allows you to attach it easily to your rocket, without having to mount it in a payload bay
- Rugged fiberglass and ABS construction to survive the vibrations and shocks of a normal flight. Plus, it is sleek looking and feels solid. That case keeps the grime and residue from launch getting inside to the electronics.
|Features: AltimeterTwo vs. AltimeterOne|
|Peak and Average Acceleration (Gs)||X|
|Motor Burn Time||X|
|Coast to Apogee Time||X|
|Apogee to Ejection Time||X|
|Use in rockets (Projectile Trajectories)||X||X|
|Use in Kites, Birds, Airplanes (Non-Projectile Trajectories)||X|
|Simple Ground-Test Capable||X|
Download the User's Guide (3.68mb pdf)
The AltimeterTWO has one single button that you press and hold to use the different features.
The first time you you press-and-release, it turns the AltimeterTWO on. It will cycle through the data from the last flight it had recorded.
Press and hold the red button down, and you will get to the menu screen. The menu will automatically scroll through a selection of options. Release the red button when you get to the option you desire.
Get Ready to Launch!
To reset the Altimeter for the next flight, press and hold the button until the word "Launch" is shown:
Release at this point to clear the display. The AltimeterTWO will flash the word "Launch" on the display screen, and then toggle between the word "Ready" and the Battery Level screen. You're ready to launch within the next 2 hours.
The Flight History option will display the altitudes from the previous launches stored on the AltimeterOne. The altimeter stores 100 flights, and will scroll through the information from the most recent flight, to the one made first.
If you'd like to switch from English to metric units, press and hold the red button until the display screen looks like this:
The altimeter will automatically convert the current data being shown to the new units without clearing it.
To erase the flight history and reset the device, hold the button until the display looks like this:
The battery screen will disiplay the percentage of battery remaining.
Selecting the Cancel options leaves the menu, and tells the AltimeterOne to do nothing.
Just do a momentary click on the red button. The display will read "Power Off" and then shut itself off.
The best way to test the AltimeterTwo is to simply launch it in a small rocket.
Unfortunately, there really isn't a simpler way to verify it is working like it's sister-product, the AltimeterOne, (with it's simple vacuum test). The reason is that the AltimeterTwo has sophisticated computer software built into it to prevent it from reporting bad data. In other words, the AltimeterTwo is designed to look for specific "rocketry-related-events" and filters out any false triggers.
A trigger is any event that starts the process of recording flight data. There are good triggers, and then there are the bad ones that need to be filtered out. A bad trigger, would be like a gust of wind that hits the rocket while it is sitting on the launch pad. That gust of wind would be registered (felt) by the pressure sensor, and would typically indicate that the rocket is descending (in rocketry, an increase in pressure would be seen as the sensor moving into a thicker part of the atmosphere; i.e., descending downward). These bad triggers have to be ignored while the device looks for "real" events, or "good" triggers.
For example, the "launch-detect trigger" is pretty sophisticated and was specifically designed so that it was not easily tricked. The AltimeterTwo is not only looking for an altitude change (like the altimeterOne), but it is also looking for a sudden increase in acceleration in one direction. While doing that, it has to ignore the normal jostling movements that it would sense if the rocket was being carried to and set up on a launch pad. Even a swing test (putting the rocket on a string and swinging it around your body) is typically not enough to trigger it to start it up. That would create a pull in one direction (one axis), but an oscillating sine-wave acceleration in the other two axes of the sensor. It is smart enough to filter that out as a "false" event.
The AltimeterTwo was designed for ONE set of conditions ONLY – which is the typical flight trajectory of a model rocket. The onboard computer looks for events to happen in a correct sequence, and for the AltimeterTwo, that means it is looking for triggers that feel like a true model rocket trajectory.
This is important to consider when buying the AltimeterTWO. Because it means the AltimeterTwo will NOT work in: model airplanes, kites, falconry, or ballooning. It has only one mission: to record flight data from a model rocket.
The AltimeterTwo is pre-charged and can be used right out of the package when you receive it. You do not need to charge it the first time you turn it on (if the display turns on).
The advanced Lithium Polymer battery in the AltimeterTwo can be recharged in any standard USB port, including those on computers, printers, and other devices.
- Insert the micro USB cord into the slot on the altimeterTWO. Insert the other end into a USB port on your computer or a USB charger.
- The red light will glow if inserted properly. If unit does not glow when inserted follow these steps: Make sure computer is turned on. Most USB ports won't work unless the computer is also powered on. Also, it is possible to power down (disable) a port on your computer. But if you can plug a USB device in and it works, that means that power is okay. For instance, if you plug a USB flash drive in and it works, the port is fine.
- Start of charging: red glow
- Charging complete: green glow
Fully charging the altimeter usually takes about two hours. It does not hurt the battery to leave it in the charger.
NOTE: The AltimeterTWO does not transfer flight data to a computer. The cord is for battery charging only!
User's Guide - Download the user's Manual (click here) PDF format, 568K. Pages are in "print order," so that if you print 2-sided on regular sized paper and then fold and staple they make a book.
- Altitude to 29,500 ft (9000 m) above sea level.
- Capable of supersonic speed measurements.
- Maximum acceleration is from 23G (any orientation) up to 40g (with careful orientation).
- Altitude: nearest foot or nearest meter.
- Speed: nearest 1 MPH (1 KPH)
- Acceleration: nearest 0.1G
- Pressure sampled 25 times/second using 18 bits of precision. Acceleration sampled simultaneously in all three directions at 250 times/second using 15 bits of precision each. Data is NOT downloadable.
- Included rechargeable Lithium Polymer battery (not user-replaceable) recharges in about 2 hours from most USB ports.
- Approx 90ma
- Shuts down after two hours of inactivity
Temperature Compensated: The altimeter uses a temperature sensor (16 bits) for two purposes:
- To compensate for thermal effects in the pressure sensor across its temperature range -- -4°F to 120°F (- 25°C to 49°C)
- To compensate the atmospheric model used to convert true pressure to altitude.
Q. Can this altimeter be used to measure the height and speed of kites, model airplanes, balloons, or birds?
A. No. This altimeter is designed for rockets only. Check out the AltimeterOne for altitude measurements of various airborne implements.
Q. How come the AltimeterTwo does not work with airplanes, kites, balloons, or birds?
A. It has to do with software that controls the unit. We wanted to collect specific information about a rocket's flight, like the rocket motor's burn time. This information does not pertain at all to those other flying objects. But to take this burn-time measurement, the device has to start quickly, so it needs a quick-acting trigger to let the computer know that it needs to start taking measurements. At the same time, it must filter out random disturbances, jitters, and rattling; like the rocket being loaded onto the launch rod. To filter out this random movement so it doesn't get added to the real burn-time of the rocket motor, the computer is looking for a unique and specific event as a trigger to let it know that the rocket is really and truly taking off. Since we are concerned about rockets, we use the initial launch acceleration of the rocket as the trigger.
There is nothing unique that could be used as a triggering-event in the world of model airplanes, kites, balloons, or birds. For those types of things, you would typically use a change in altitude as a triggering event. And that is what the older AltimeterOne uses. And unfortunately, when you're trying to measure burn-time, which happens very quickly in a model rocket, using altitude as a trigger to start recording doesn't work so well. It happens too slow, compared to how fast rocket propellant burns up, which can occur within a few feet for very short-burn rocket motors.
So, to make a long story, short; the reason it doesn't work in other flying devices is the lack of a specific triggering event to let the accelerometers know when to start recording. For those other things, you'll have to find a different solution, such as a radar gun or a GPS recording altimeter (like the TeleMetrum).
If you want just altitude, get the AltimeterOne.
Q. How does the AltimeterTwo trigger to begin recording data?
A. It needs to see a 3-G acceleration for at least 0.2 seconds.
Q. Can the AltimeterTwo be reprogrammed to work in other devices, like model airplanes and quad copters?
A. Sorry. There are other companies that sell those devices. You might perform an internet web search to find those companies. Our passion is model rocketry
Q. Does the AltimeterTwo work in multi-stage flights too?
A. Yes. As long as the delay between stages is short (under 1.5 seconds), the AltimeterTwo will figure out that the rocket is a multi-stage vehicle.
Q. Does this AltimeterTwo store data that can be downloaded to a computer through the USB port?
A. No. The AltimeterTwo USB connector is only to charge the battery. This altimeter stores data which is only displayed on the LCD screen.
Q. Do I have to mount the AltimeterTwo in any particular direction?
A. No, since it has a full 3-axis accelerometer and can sense linear acceleration in any direction. For maximizing range, see the instruction manual or Peak of Flight Newsletter #293.
Q. Why does the speed sometimes flash rapidly when it’s displayed?
A. If an acceleration in any direction is at (or very close to) the AltimeterTwo’s peak capability (24g), it flashes the display to warn you that the speed calculation may be in error. The result is an UNDER-reporting of speed.
Q. Does this altimeter come in bulk pack?
Q. Does this altimeter fire ejection charges?
Q. Is it safe to expose the AltimeterTwo to the corrosive ejection charge gases put out by the rocket motor? Won't the unit get dirty too?
A. Think about this question for a second... When you are prepping a rocket that has flown several times, how often do you say, "look at the base of the nose cone. It is filthy"? NEVER! Why is that? Why doesn't the base of the nose cone get dirty? Why is it so clean? Because there is a lot of stuff between it at the rocket engine: such as a recovery device and wadding. All that protects the base of the nose cone from seeing the heat and the crud of the ejection charge gases. When you put the AltimeterTwo in the rocket, it will also be protected by the parachute and the wadding below it. So it doesn't feel the dirty ejection charge gases. In addition, there is also "clean air" in the tube in front of the rocket engine. This air has to be pushed out first before the dirty ejection charge gases come out of the tube. So you do not need to worry about corrosive ejection charge gases getting to your AltimeterTwo, unless you fail to follow the instructions of using wadding in your model rocket. But if you are still concerned, then you still can put your AltimeterTwo in a payload bay -- it will work there too.
Q. Where can I find out more information about how electronic altimeters work?
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.
The manufacturer warrantees the altimeter to be free of manufacturing defects for one year. If it fails to work right out of the box, return it immediately to Apogee for a replacement.
If you fly it and break it (such as cracking the case or LCD display), we do not warrantee that. It is durable, not indestructible. The ejection of the nose cone off and the parachute out of the rocket is an extremely violent event. The heat is not the problem, it is the whacking around of the parts that can cause damage to the AltimeterTwo. Extra padding wrapped around the outside of the AltimeterTwo can help, but it does not guarantee the survival of the device. If you are unsure or fearful, then for pete's sake, put the AltimeterTwo inside a payload bay. It will work there too.
We can get replacement plastic cases if you crack a case (and the altimeter still operates normally). Call us for details.
For repairs, contact Jolly Logic directly. Due to the inexpensive cost of the altimeter, it is often cheaper to just purchase a new one that to try to repair a broken altimeter. Sorry...
To Be Perfectly Clear...
There is no replacement, exchange, store credit, or refund on this item.
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