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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.  All you need is a 39 ohm ¼ 
watt resistor across the deployment channel outputs to provide continuity and pull the servo’s 
control input to ground when the channel isn’t firing. 
 
You will want a very low LDA, 50’ should work.  10 samples per second should be appropriate, 
and 2 samples/sec for descent.  We set the main channel to deploy at nose-over, with the servo’s 
PWM at 6; this will give us pulse widths of 800ms and 2400ms lock-to-lock, which should make 
almost any servo go full range.  The rocket is obviously not going anywhere near mach speeds, 
so we’ll set the Burn Timer  to the minimum value, 1. 
 

 
Eggtimer Build_1.48b              Flight Settings 
                                                                T:23.50 
    A    50    LDA <50-500 by 50>                               P:97804.00 
    B    10    Ascent Samp/sec: <4,5,8,10,15,20,25,33>          A:975.39 
         100   Interval (ms)                                    Main:0 
    C    2     Descent Samples/sec <1,2,4,5,10>                 CHB:0 
         500   Interval (ms)                                    Batt:3.12 
    D    2     Main Mode <0-Off, 1-Igniter, 2-Servo CCW, 3-Servo CW> 
    E    0     Main Altitude <100-2000 by 50, 0 @ Apogee> 
    F    6     Servo PWM <0-9> 
    G    0     CHB Mode <0-Off, 1-Igniter, 2-Servo CCW, 3-Servo CW, 
                         4-Airstart, 5-Airstart w/o Breakwire,6-Delay> 
    H    2     CHB ON-Time <1-9,0-Cont.> 
    I    2000  Burn Timer <100-20000 ms by 100> 
    J    0     Airstart/Delay <0-9900 ms by 100> 
    K    0     Airstart Min Velocity <0-700 by 50> 
    L    0     Telemetry 
 
 
    O          Comments:    H20 rocket servo 
        
      
              Options: Esc, A-O, ?

            

 
 
 
 
 

 
 
 

Содержание Eggtimer

Страница 1: ...1 Eggtimer Flight Computer User s Manual Release 1 48b Board RevC 2013 Eggtimer Rocketry All Rights Reserved...

Страница 2: ...d Drogue Airstart Supports two stage multiple deployment flights using motor ejection for booster recovery and second stage drogue deployment Three logic level outputs triggered at nose over Main depl...

Страница 3: ...g list so we can figure out what went wrong so it doesn t happen again If your Eggtimer does not work properly after assembly take a deep breath get out the magnifying glass and a good light and see i...

Страница 4: ...to Set Up the Eggtimer for Multiple Deployments 47 How to Set Up the Eggtimer for Airstarts 50 How to Use Servos with the Eggtimer 41 10 Wire Options for your Eggtimer 13 How to Pick a Battery for you...

Страница 5: ...fairly reasonable accuracy You can in theory use one to determine acceleration but slight errors tend to be multiplied resulting in much larger errors Since they read barometric pressure which depends...

Страница 6: ...rockets typically from D to G power or Level 1 and 2 HPR rockets using H through K power The Main Channel A deployment channel is programmable so that it may be triggered at apogee or at a fixed alti...

Страница 7: ...your Eggtimer Although the Eggtimer seems relatively simple you will want to familiarize yourself with it BEFORE you install it in a rocket and certainly before you try flying it Battery 3V Two solder...

Страница 8: ...on the same battery i e they re both either servos or both igniters then you can jumper the BCHA and BCHB terminals together to and to AUX1 Output The AUX1 output turns ON V for two seconds at nose ov...

Страница 9: ...pin FTDI compatible standard header connector for connecting the USB serial data cable for programming and downloading data and also for connecting a telemetry device such as an RF serial transmitter...

Страница 10: ...to at least twice the G forces that you are likely to see a 1 Radio Shack special isn t going to cut it spend a few bucks and get a high quality switch You can also use a push on push off type switch...

Страница 11: ...Remove Before Flight ribbon on the end of the plug and you re ready to go simply pull the plug out when you re ready to launch to start the Eggtimer flight sequence You can also use the same rotary s...

Страница 12: ...to the terminal If you are using an external LED in a holder with leads the red wire should be connected to the terminal and the black wire should be connected to the terminal We recommend using an ul...

Страница 13: ...to have the wires directly soldered to the board This allows you to choose whatever method of terminating the connections you want barrier strips solder directly to the switches etc We ve found that s...

Страница 14: ...ity batteries will have to be replaced or recharged more often than larger batteries which is the trade off for the smaller size 3 How much room you have for a battery If you have a 3 4 pound I powere...

Страница 15: ...is designed to be used as a quick check to see if your battery MAY be getting low It is not a substitute for checking the battery with a DVM it does not have the accuracy that you re going to get with...

Страница 16: ...d doing a Paste into a text editor such as Notepad If you do not already have a suitable terminal program or you need the USB Serial driver for the cable go to www eggtimerrocketry com click on the Li...

Страница 17: ...your keyboard exits the screen and saves the flight settings you will hear a long beep that confirms the save and then the Eggtimer will halt both lights will blink continuously The key allows you to...

Страница 18: ...ading If it s a windy day or if the sun is starting to come up or set then the temperature will change more quickly and the base altitude reading may be thrown off if the rocket sits on the pad for to...

Страница 19: ...ful not set the sample rate too high Besides wasting memory the noise due to variations in air pressure will be proportionately higher for smaller interval sizes If you choose too high a sample rate y...

Страница 20: ...this up and you will either waste a lot of memory or you will run out of memory A sampling rate of 2 samples sec is adequate for most flights In fact if you re going over 5 000 feet then you should pr...

Страница 21: ...on is controlled by the Servo PWM value each tick changes the servo pulse width nominally 1 5 ms at center by 100 microseconds in each direction so the total possible range of servo pulse width is 5 t...

Страница 22: ...it also requires that the Breakwire must have been tripped as well See Appendix D for more information on airstarts WE STRONGLY RECOMMEND THAT YOU RUN A SOFTWARE SIMULATION ON ANY AIRSTART CONFIGURAT...

Страница 23: ...rm an airstart ignition on Channel B and is also used to start Delay timer if CHB is in Delay mode The burn timer starts from the last pre LDA sample 5 ft AGL and expires after the selected time has e...

Страница 24: ...at if you set the Airstart Delay too long way too long and it expires AFTER Low Speed detect or Nose Over is detected the CHB channel will not fire This is a safety feature so you don t ignite the sec...

Страница 25: ...is insures that you re going to get a continuous data stream that you can use to help find your rocket on the ground We ve all wandered around deserts cow pastures or farm furrows for a few hours look...

Страница 26: ...u reset the processor after the Ready signal begins to sound all of the settings including the Comments will be carried over to the next flight If you want to change the Comments you will need to go i...

Страница 27: ...ht profiles look like this Profile No LDA Ascent Samples Sec Main Channel CHB Channel 1 100 10 Off Off 2 200 20 Off Off 3 100 10 Nose Over Off 4 200 20 Nose Over Off 5 200 10 500 Nose Over 6 200 20 50...

Страница 28: ...long with showing them that your rocket is flightworthy of course At the Pad DOUBLE CHECK that the Reset switch is ON so that the Eggtimer will be put on hold when you turn on the power Connect the fl...

Страница 29: ...nline Google is great for finding them We also recommend that you get a copy of the book Modern High Power Rocketry it s full of good information too and subscribing to a forum like The Rocket Forum w...

Страница 30: ...nels status If for some reason you need to disconnect the deployment power we STRONGLY recommend that you also Reset or power off the Eggtimer so that you do not end up launching with the deployment p...

Страница 31: ...the pressure readings The smoothed readings produce a much gentler velocity profile which allows it to be used to obtain reasonably accurate velocity samples If the velocity reaches 500 ft sec it is a...

Страница 32: ...n time altitude and therefore are completely independent of the recording process The recorded deployment altitude and time ARE dependent on the recording process however so you may not get an accurat...

Страница 33: ...ou 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 puts the Eggtimer in hold state Turn OFF the deploym...

Страница 34: ...pad until right before your launch slot To enter the Flight Display screen hit the key at the Flight Settings screen You will see something that looks like this Eggtimer Build 1 48b Saved Flight Summ...

Страница 35: ...e really like this rocket it s an easy hack and it s cheap so if you wreck it you re not out much The rocket s weight was just over 3N ready to fly we used an Aerotech 24mm 24 40 RMS F24 7 reload no d...

Страница 36: ...help you figure it out The status codes are 0 Flight Not Started in programming or pre Ready mode 1 Waiting for LDA 2 LDA reached 3 Not used 4 Airstarted on CHB if selected 5 Mach Lockout expired 100...

Страница 37: ...le you can open it with the data analysis program of your choice For example if you import it into Excel you can graph Time vs Alt and Time vs Velocity See our web site www eggtimerrocketry com for st...

Страница 38: ...u 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 You can also see where the drogue ejection charge...

Страница 39: ...sled moving around in the payload bay during flight Mount the Eggtimer with at least two preferably four 4 40 screws and nylon spacers and use nylon washers on the top of the board if you are using m...

Страница 40: ...l If you are going to use the motor s ejection charge to fire the drogue and the motor has a fixed delay time i e one that you cannot drill out to adjust it might be a good idea to do this before you...

Страница 41: ...o increase this time by a second or so to give the nichrome extra time to heat up If the igniter fires and does not melt through however it s going to keep drawing current from the battery while it s...

Страница 42: ...y If you make the ports too large then crossflow air currents can disturb the airflow and your readings will be very noisy during the boost and coast phases when the rocket is moving at high speed The...

Страница 43: ...are 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 Make sure that you use a good sharp drill bit you do not want an...

Страница 44: ...2 CHB Enable 0 off CHB ON Time 2 Burn Timer 2000 Airstart Delay 0 Airstart Min Velocity 0 Telemetry 0 off To perform a Master Reset hold the Ctrl and Y keys down together at the Flight Settings screen...

Страница 45: ...ress within memory 0 65534 by two s High Byte Byte value of first byte Low Byte Byte value of second byte Integer value Value of integer two s complement if negative Servo Set Reset If you have set th...

Страница 46: ...n Hit the M key and you will hear a continuous warning beep Press the Button and the Main igniter channel will fire for the programmed amount of time To test the CHB B deployment channel enter the mon...

Страница 47: ...n deployment example Options Esc A O Low Medium Power Multiple Deployment Example Using Motor s Ejection If you add multiple deployment to the example above you probably don t need to change the sampl...

Страница 48: ...n Timer 100 20000 ms by 100 J 0 Airstart Delay 0 9900 ms by 100 K 0 Airstart Min Velocity 0 700 by 50 L 0 Telemetry O Comments HPR w motor ejection Options Esc A O High Power Full Multiple Deployment...

Страница 49: ...nel to deploy at nose over with the servo s PWM at 6 this will give us pulse widths of 800ms and 2400ms lock to lock which should make almost any servo go full range The rocket is obviously not going...

Страница 50: ...make Check the CG and the weight carefully against your simulation What you are looking for is the LDA and first stage burnout time and altitude You will use these to figure out the LDA Burn Timer and...

Страница 51: ...Shortly before the flight release the Reset switch 6 Assuming that self test passes and you get the Flight Ready tone you re ready to launch If you get an error and you cannot start the flight the pow...

Страница 52: ...oximately 2 6 seconds and that we want a 1 second delay after burnout before firing the second stage If we know that our igniter will take about 5 to ignite the second stage motor the actual delay fro...

Страница 53: ...ry Type I2C Serial EEPROM Size 64KB 512 Kb Deployment Voltage 3v 60v Current 8A max 60 W Isolation 3000V opto isolator Duration 1 9 seconds or continuous Output On or pulse width modulated output for...

Страница 54: ...Mode Beep Beep after power up until the beep code matching the flight profile that you want to use is beeped out Release the button you will hear a long Beep followed by a repeat of the Beep Code then...

Страница 55: ...ent Samples sec 1 2 4 5 10 CHB 0 1000 Interval ms Batt 3 12 D 1 Main Enable 0 Off 1 IGN 2 Servo CCW 3 Servo CW E 500 Main Altitude 100 2000 by 50 0 Apogee F 2 Main ON Time 1 9 0 Cont G 1 CHB Enable 0...

Страница 56: ...mputer as a TXT file The Eggtimer is now ready to download the Flight Detail data To download the Flight Detail data Open the capture buffer in your terminal program see your terminal emulator s docum...

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