Eggtimer Flight Computer User’s Manual Release 1.
Eggtimer Features Altimeter rated to 29,500 ft ASL, resolution to approx 1 ft. Logs data for last 32 flights, “beeps” out maximum altitude of last flight Flight data can be downloaded to a computer using USB interface cable (included) to .
Disclaimers, Legal Stuff, Etc. The Eggtimer is meant to be used for hobby and experimental rocketry purposes. Although hobby rocketry has an admirable safety record, largely due to the efforts of the good people at the National Association of Rocketry (NAR) and the Tripoli Rocketry Association (TRA), rocketry can be dangerous if proper safety precautions are not observed.
Quick How-To Index How to Program Your Eggtimer….14 How to Use the Pre-Programmed Flight Settings…..23 How to Download Flight Info…..29 How to Test Deployment Charges…40 How to Set Up the Eggtimer for Multiple Deployments…..42 How to Set Up the Eggtimer for Airstarts…44 How to Use Servos with the Eggtimer……..35 (#10) How to Pick a Battery for your Eggtimer……………………12 How to Size Pressure Ports…..36 How to Mount Your Eggtimer……33 Beep Code Reference…..
A General Introduction to Flight Computers A flight computer is used to record the flight path of a rocket, and to optionally deploy recovery devices. Typically, you can use it to find out the maximum altitude (apogee) of your rocket, the maximum velocity of the rocket, the maximum acceleration (G forces) on your rocket, and other flight characteristics.
Generally, accelerometers are more accurate for events logged when the rocket is going up, and barometric pressure altimeters are more accurate for events that happen when the rocket is going down. However, since most of the critical events such as ejection tend to occur in the descent phase, an altimeter-based flight computer can do almost everything that a computer with both an altimeter and an accelerometer can do, at much less cost.
Programming is performed using a standard VT100/ANSI serial terminal program, connected to your computer with a USB-serial cable. Since there is no special software required, you can use just about any computer, running Windows, Mac, Linux, or just about anything else you can come up with. Flights can be downloaded to a standard CSV-formatted file, and can be imported into virtually any spreadsheet or data analysis program to produce flight graphs.
wire or other igniters. The Eggtimer is capable of handling up to 30v, so you can ignite even an Aerotech Copperhead igniter with it, assuming you have a strong enough battery (i.e. 14.4v LiPo battery). Channel B Deployment (CHB) - Two solder pads, marked “+” and “-“ for connecting an electric match or other low-to-medium current device. Deployment delay/altitude is programmable. Maximum 8A current, 30 VDC, 60 W.
External Switch/Indicator Options The Eggtimer has several connections for external switches and/or indicators. Power Switch (SW) An external power switch will make it much easier to use the Eggtimer, because you won’t keep having to disconnect the battery, or removing the jumper across the SW terminals.
Reset Switch (RST) When shorted, the Reset terminals put the Eggtimer “on hold”, i.e. resets it so that it does nothing. When it is in reset mode, it draws very little power from the battery, < 2 ma. All outputs are held low, so this is the “safe” mode when multiple deployment systems are used; they cannot be triggered while the Eggtimer is reset.
Indicator Headers – .1”-spaced headers with outputs for the following external indicators: Ready LED – In parallel with the on-board Ready LED. BUZ – In parallel with the on-board buzzer. This must be a pizo element. ALED – Channel A continuity LED BLED – Channel B continuity LED Ready LED (RDY, +/-) This is an external extension of the on-board RDY (yellow) LED.
(www.EggtimerRocketry.com) for details. Similarly you can also use the nice little sounders sold by Adept Rocketry, they make a very distinct sound that’s hard to miss even with other background noise present. ALED/BLED - Deployment Channel LEDs ALED/BLED are designed to provide a visual indicator of deployment channel power and igniter continuity. This lets you know immediately after connecting the igniter and powering up the channel if something isn’t right.
3) How much room you have for a battery – If you have a 3”, 4 pound I-powered rocket you probably have plenty of room for a 250 maH 3.6v NiMH battery, and don’t care so much about a few extra grams. Not so true if you’re flying it in a BT-55 “D”-powered rocket… 4) How much the battery costs – Rechargeable LiPo batteries are nice, but you may need a special charger for them. NiMH or plain old alkaline batteries are heavier, but they cost a whole lot less to use. Non-rechargeable Lithium cells (i.e.
2) Balance your model with the batteries in place. AAA and NiMH batteries are fairly heavy, as are some of the larger Lithium batteries such as a CR123. Alkaline 9V batteries are VERY heavy, almost 50 grams (nearly 2 oz!) You should always weigh your rocket and determine the CG with the intended flight battery in place. We strongly recommend using a program such as RocSim or Open Rocket to determine the flight path of your rocket with the intended payload configuration (batteries, sled, etc.) and motor.
Before you try flying your Eggtimer, we recommend that you play around with the programming screens on your workbench, until you are comfortable with it. You can’t hurt anything, and if you totally mess up the memory you can always do a Master Reset to clear out all of your experimental values. To get to the Eggtimer menu screen, be sure that the power on the Eggtimer is OFF.
Note: When you first get your Eggtimer, the flight memory is NOT initialized. Please see Appendix A for instructions on how to clear the flight memory by performing a Master Reset. You will need to do this before you can program or fly the Eggtimer, or unpredictable results may follow! Field Descriptions: A Launch Detect Altitude <50-500 by 50> Also called LDA, this sets the altitude Above Ground Level (AGL) that the Eggtimer uses to detect that a valid flight is in progress.
B Burn/Coast Samp/sec. <4,5,8,10,15,20,25,33 <4,5,8,10,15,20,25,33> ,33> This selects the number of samples per second that are written to the flight memory during the Burn and Coast portions of the flight, which begins at Launch Detect and ends at nose-over. This value is also used for the pre-launch sampling which occurs prior to Launch Detect, while the rocket is either sitting on the pad or is approaching LDA. Values are 4,5,10, 15, 20, 25, and 33 samples per second.
will be 100 ms. You cannot change this setting, it is automatically populated when you change the Bur/Coast Sample rate. C Descent Samples/sec. <1,2,4,5 1,2,4,5, 2,4,5,10> 10> This selects the number of samples per second that are written to flight memory after nose-over is detected, until the rocket lands and sampling ends. Values are 1,2, 4, 5, and 10 samples per second. Nose-over is defined as one second after apogee, the maximum altitude.
500 ms. You cannot change this setting, it is automatically populated when you change the Descent Sample rate. D E F F Main Enable (0-Off, 1-IGN, 2-Servo CCW, 3-Servo CW) Main Altitude <100-2000 by 100, 0 @ Apogee> Main On-Time <1-9, 0-Cont.> {only if Main Enable =1} Servo PWM <0-9> {only if Main Enable = 2 or 3} This setting controls the Main (Channel A) deployment channel. When set to “0”, the channel is turned off, so the other settings don’t matter.
G CHB Enable (0-Off, 1-IGN, 2-Servo CCW, 3-Servo CW, 4-Airstart) H CHB On-Time <1-9, 0-Cont.> {only if CHB Enable =1 or 4} H Servo PWM <0-9> {only if CHB Enable = 2 or 3} This setting controls the Channel B deployment channel. When set to “0”, the channel is turned off, so the other settings don’t matter. When set to 1-3, the deployment channel turns on at noseover, 1 second after apogee. If this setting is 2 or 3, the deployment channel sends out pulses that can control standard analog hobby servos.
since aerodynamic effects may compromise the accuracy of the pressure-derived altitude reading. Zeroes in these fields means that CHB didn’t fire, either because it wasn’t enabled or because the conditions to fire CHB weren’t met (i.e. Airstart Delay expired after Nose-Over). I Burn Timer <1-20> The Burn Timer is used to indicate to the Eggtimer what the burn time of your motor is.
Also note that if you set the Airstart Delay too long (way too long...) and it expires AFTER Nose-Over is detected, the CHB channel will not fire. This is a safety feature, so you don’t shoot off the second stage while it’s pointing downward.
Pre-Programmed Flight Profiles The Eggtimer has 8 pre-programmed flight profiles, in addition to the programming screen. These are designed so that if you are out in the field and you want to set it up with a fairly standard flight profile you can do it without having to use a computer. They are accessed by holding the button down while the Eggtimer is beeping during the programming phase.
Flying Your Eggtimer Once you’ve programmed your Eggtimer, you are ready for a flight.
Take the rocket off the rod/rail, open up the payload bay, disconnect all batteries, and fix the failed condition. Then, you can start all over having hopefully learned one more thing to check in the future… You can see that if you’re doing multiple deployments, it’s a lot more involved than just stuffing some wadding and the parachute into the tube, popping in the motor, and hooking up the igniter.
The beep codes are: Number of Beeps 1 2 3 4 5 Problem Battery Low ( < 2.
really high value (over 15°). If the pressure ports in your payload bay aren’t sized properly, this can introduce an error, particularly if they’re too big and you have two of them opposite each other (you’ll get a crossflow through the payload bay which makes the pressure readings very noisy). Finally, differences in the processor’s timing may introduce errors, although the readings are taking at relatively precise intervals so it’s going to be very small.
broken shock cord or a zippered tube. It also means that you really don’t know that you’ve reached apogee until after you’ve been there because you can’t define apogee as when the altitude change reaches zero, because velocity won’t be the same as altitude change if you have a horizontal velocity component. Accordingly, the Eggtimer fires the drogue parachute at Nose-Over, which we define as one second past apogee (highest recorded altitude).
Once you’ve noted the maximum altitude so you can brag about it to your friends, you should turn off the Eggtimer as follows: Turn ON the Reset switch; this hold the Eggtimer Turn OFF the deployment batteries Turn OFF the Eggtimer Gather your rocket up and take it back to your work table, get a can/mug/bottle of your favorite beverage, then you are ready to download the data.
Downloading Flight Data The Eggtimer records your last 32 flights into its flight memory, reporting three types of data: - Flight Settings – All of the settings on the Flight Settings menu (or the Presets, if you used one) Summary Data – Stuff like apogee, length of flight, maximum velocity, etc.
After you hit the letter for the flight, you will be prompted to hit the button to start the download. At this point, you should go into your terminal program and select the appropriate option for dumping the text to a file. Since the summary data and the detail data are dumped in two separate operations, you can save them separately by simply closing the buffer after dumping the summary data, then opening it again for the detail data. We recommend that you use a file name like “Flight 2012-08-26 No1.
Altitude Nose-Over:1214 Time@ Nose-Over:8375 Altitude Main Trigger:298 Time@ Main Trigger: 75100 As you can see from this data, the rocket got to 1215 feet, had a maximum velocity of 289 feet/sec. To dump the detail data, press the button again… you will see something like this. T,Alt,V 0,0,-24.00 125,2,16.00 250,5,24.00 375,12,56.00 500,20,64.00 625,31,88.00 750,48,136.00 875,64,128.00 1000,85,168.00 1125,105,160.00 1250,128,184.00 1375,159,248.00 1500,187,224.00 1625,216,232.00 1750,248,256.
You can clearly see that the rocket hits peak altitude at about 10 seconds, and maximum velocity at about 3 seconds. Note that the velocity graph is jaggedy compared to the altitude graph; this is due to the aforementioned issues with deriving velocity from barometric pressure. The important thing is that you can see clearly where the velocity peaks then drops sharply; this is where the motor burned out and aero drag immediately started to slow the rocket.
Building Your Rocket to Use the Eggtimer Mounting In order to use your Eggtimer with a rocket, it will need to be properly mounted and secured. The Eggtimer is designed to be used with just about any rocket with a 1.35” dia. (BT-55) or larger payload bay, so any rocket that will take an egg will easily take the Eggtimer. However, there is some preparation that will be need to be done to secure it properly.
Two AAA batteries (or AAAA if you can find them) work very well, however the holders can be a problem because they are usually spring loaded and can come loose in flight. We do not recommend using AAA batteries unless the body tube is large enough to mount them horizontally, so that the G forces of launch and deceleration cannot make the batteries shift and lose contact.
5) 12v “A23” batteries work well for firing low-current igniters (i.e. Quest Q2G2’s), but they don’t have a lot of capacity so they’re not going to be able to fire very many times before they will need to be replaced. 9v batteries are heavy (almost 50 grams) but they will fire a Q2G2 igniter several dozen times before you need to worry about replacing them.
“-“ outputs of the deployment channel. If you leave out the resistor, the servo will not work, because the resistor pulls the control line down to ground while the channel is turned off. The Black lead of the servo will go the the “-“ lead of the deployment battery, and the Red lead of the servo will go to the “+” lead of the deployment battery. Note that most servos will run fine on a 3.7v Li-Po cell, a 3.6v NiMh pack, and any battery up to 6V.
For example, a small 5” payload bay 1.5” inches in diameter (inside of a BT-60 coupler…) 1) Length of Payload Bay in inches: 5 2) Diameter of body tube: 1.5 3) Square of #2 2.25 4) Multiply #1 and #3 11.25 5) Divide by 1500 .0075 6) Take the square root: .0866 We’ll multiply this by 32 to get the size of the drill in 1/32nds, it’s 2.77/32” so we should be fine with a 3/32 drill bit.
Appendix A – Special Functions There are some special functions that are accessed from the Flight Settings screen that are not on the menu. In general, you will probably not need to use these functions very often, if at all, but you need to be aware of them in case you do. Master Reset A master reset completely clears all flight memory, and resets the flight settings to the defaults.
Support staff to debug problems that you may encounter, but you can also use it to save all of the flight data prior to a Master Reset if you choose. To dump the memory, hold the Button down while the power is off or the Eggtimer is in reset mode, and continue to hold it down as you turn on the Eggtimer or release the reset. After about 10 seconds you will hear a long beep, acknowledging the Monitory mode, and you will see a “MON>” prompt on the screen.
Appendix B – Deployment Channel Testing You can perform a pyro deployment test on your igniter channels using the Monitor mode. This allows you to make sure that the battery and the igniter that you are going to be using for deployment and/or airstarts are compatible, before actually flying them. SAFETY WARNING: ALWAYS TEST IGNITERS OUTDOORS, WITH A SUITABLE DISTANCE BETWEEN YOU AND THE IGNITER (AT LEAST 5 FEET). If the igniter has a lot of pyrogen, i.e.
Appendix C - Sample Flight Settings Low-to-Medium Power Non-Deployment Example These settings will work fine for a small D-size rocket, or most E-G rockets. If the rocket is heavy, you might want to take the Burn/Coast sample rate down a notch, to 5. Eggtimer Build_1.45 A B C D E F G H I J K 100 8 125 2 500 0 300 2 0 2 1 0 0 O Flight Settings T:23.50 LDA <50-500 by 50> P:97804.00 Burn/Coast Samp/sec: <4,5,8,10,15,20,25,33> A:975.
Higher Power Multiple Deployment (Using motor’s ejection) This example is for a much higher powered rocket, using the motor’s ejection charge to fire the drogue near apogee. Since the projected altitude is likely to be higher than a lower powered rocket, you will most likely want to have the second deployment occur at about 800’, higher than what you had set it for the mid-power example. Eggtimer Build_1.45 A B C D E F G H I J K 200 20 50 2 500 1 800 2 0 2 3 0 0 O Flight Settings T:23.
Water Rocket Servo Deployment Example These settings will work for a 2 litre or larger water rocket using a micro servo to trigger a parachute after apogee. Water rocketry is an art all to itself, if you haven’t looked at it lately do a little Google’ing… you’ll be amazed what they’re doing. The Eggtimer is the only flight computer that will modulate servos without any extra electronics.
Appendix D - Setting Up Your Eggtimer for Airstarts Channel B can be used to fire airstart igniters, however with airstarts you have to take extra safety precautions due to the consequences of an motor being accidentally fired on the pad. The Eggtimer requires three separate events, in order, for the igniter to be fired in Airstart mode: 1) The Breakwire must have been tripped. This actually happens on the pad right after liftoff, but it doesn’t get checked until the Airstart Timer expires.
It is STRONGLY recommended that you use a good quality switch for the deployment battery, and that you shunt the igniter until immediately prior to launch, releasing it right before you start the Eggtimer’s flight sequence by releasing the Reset switch. The sequence at the pad should be: 1) Connect your booster igniter 2) Turn on the Eggtimer, with the Reset switch enabled 3) Turn on the Deployment Battery 4) Release the Igniter Shunt 5) And approx.
bring that stage down, it should be timed to pop right around the first stage’s projected apogee. You may have to model the first stage’s flight separately from the second stage to determine this value, but it will usually be a few seconds after second stage ignition because the added drag will slow the first stage rather quickly.
Appendix E - Specifications Pressure Sensor: Type Bosch BMP-85/180, accuracy rated to approx. 9000 m (29,500 ft) Accuracy Approx 1m (3 ft) throughout rated pressure range Precision Approx ½ m (1.
