2nd Stage Ignition Logic and Electronics Setup

Hi all,

This is my first post on the rocketry forum and so please let me know if I posted this in the wrong place and I will repost it where it is more appropriate. I am working with a small team of newbies when it comes to High-Power Rocketry and we are trying to figure out how to setup the electronics for the upper avionics in a 2-stage rocket (L motors, ~10k AGL). The upper avionics will need to control 2nd stage separation, 2nd stage ignition, payload deployment, drogue deployment (at apogee with payload but in different compartments), and main deployment.

Here is what we have:
Arduino Mega
Xbee Pro S2B
Venus GPS with SMA connector /w Ceramic Antennae
x2 Raven Altimeters (one with bad sensors but good terminals)
1 Missile Works Altimeter
9-axis IMU from Sparkfun - LSM9DS0
Voltage Converter board 3.3V to 5V
Some transistors

Logic and method we are thinking of employing for 2nd stage separation:
1. Using one of the Raven's to detect launch then delaying separation based on a delay timed to burn time of the booster.

Logic and method we are thinking of employing for 2nd stage ignition:
1.Delay .5 seconds after separation charge
2.Check to make sure booster has separated. We are thinking of doing this via a continuity check but not sure how to employ that method. Suggestions would be helpful or suggest another method.
3. Use an Arduino and an Inertial Measuring Unit (IMU) to determine whether the rocket is more than 10 degrees off the Z-axis. The arduino will be connected to a both the continuity check and a wire that leads to a transistor (gate) which opens and closes the 4th channel signal coming from the raven for 2nd stage ignition. If either the continuity check or the Z-axis logic does not pass, the gate on the transistor will be closed. If they both pass, the gate will be open and the signal from the Raven will pass through and ignite the 2nd stage. We are very sure how to program and connect all of this logic and I guess importantly if this is a good way to do it. Any explanations, suggestions, or thoughts would be helpful!

Payload, Drogue, and Main deployment we have figured out and redundant with a Raven and another altimeter.


Thanks for your help everyone!

Welcome to the forum. This sounds like a very ambitious project for a group of newbies. Does anyone in your group have any experience if Rocketry? Do you have a mentor that can assist you? Unless you have some sort of certifications you will not be able to get an L motor. There are numerous threads about 2 stage and air starts. Ironically it is easier to Google search and look for results that are in TRF, than it is to search directly inside the Forum. Good luck and be safe.

Yes, we have a certified mentor and have the motors. Just not a lot of experience with avionics and airstarts. What posts would you recommend I peruse?

Thanks!

here is just a very simple google search. the first result will be TRF. look at the bottom of it and it says more results , click that and it will show all the the threads related to your search. the key i have found it the url being in the google search to filter the other stuff not in the forum. there are more power users on the forum that will add many solutions for you. try the search string below and see what i mean.

all of this without the quotes "air start www.rocketryforum.com" will result in the links below (the hyperlinks below didn't work with my copy and paste)

Airstart Timers - The Rocketry Forum
www.rocketryforum.com/showthread.php?...Airstar...
The Rocketry Forum
May 16, 2015 - 6 posts - ‎3 authors
What are peoples opinions regarding brand of airstart timers? Perfectflite Timer4, Adept ST236 or Missle Works PET2+? Need something that ...
Thread: Saturn V Airstart Two-Stage Rocket Ideas? 1 post Apr 24, 2015
Thread: Air Start fun with the Klingberg Rocket Wing 7 posts Dec 23, 2014
Thread: Help Programming the RRC3 - for HP 2 stage ... 5 posts Oct 28, 2013
Thread: Dealing with airstart igniters 18 posts Feb 19, 2012
More results from www.rocketryforum.com

To address your specific question, you can use the Raven to light your second stage with the following logic:

- Time < X
- Altitude > Y
- Pressure decreasing
- After burnout 1

The altitude Y is the altitude where you want the ignitor to fire. The time X is selected to be a second or so after you expect the rocket to reach altitude Y. The logic is that if you reach the selected altitude reasonably close to when you expect to, the rocket must be traveling upward about as planned.

I have three other suggestions for you. First, do the suggested research. You will find a tremendous amount of misinformation on this topic. That just means that you have to dig deeper to figure out what is actually the best path. But don't believe everything you read on the first pass.

Second, light the sustainer with the Raven, connected to the igniter using a shunt, and keep all of the other electronics you mentioned out of the firing circuit. The circuit that lights a sustainer needs to be as simple and safe as possible. It is not the place to be inserting home-made electronics, no matter how confident you are that you can do it safely. You do not need to use tilt detection if you use the altitude check with the Raven (per the approach above). If you want to use tilt detection, than use a commercial unit, such as from Altus Metrum, where the tilt measurement circuitry has been designed for use in rockets.

Third, do your first flight with a booster motor only to verify that all of the systems work as planned. You can test everything - electronics, sequences, the separation and recovery systems, etc., without the risks associated with having that sustainer motor installed.

Jim

^ for sure. Jim is the man if he says it listen.

Jim!

Thank you for your thoughtful reply! If you don't mind I have some questions and counterpoints.

1. How can we accurately tell how high the rocket will actually go? I am worried about relying on software to predict an altitude and then risking having altitude Y be too large and not firing the 2nd stage, or being too small and firing it before first stage separation/ burnout. We use Openrocket for design and simulations.
2. Do you know where I can find a diagram for an airstart that takes into account a shunt? I searched for "shunt" at home depot and a local electronics store online and nothing is coming up. Do they go by another name or is there a specific low cost model you would recommend? I read that they operated similar to a diode.
3. Unfortunately our budget does not permit multiple full scale tests and so doing a test with only the booster would not test our 2nd stage ignition logic or system during flight. Other than that I like your idea.
4. Unfortunately our budget does not permit the purchase of a TeleMetrum or TeleMega. Those certainly appear to be great products and we would undoubtedly purchase a TeleMega or 2 if we had the capital. Hopefully next year!


Thanks again for your help as it is highly appreciated over here!

-Noel

Closest you could get for a test rig might be to use a vacuum chamber. Run a test with the altimeter to see how long and how high you get within X number of seconds or mins, repeat it several times to see if the data is repeatable, the altimeter needs to be logging obviously. If you can get the same or very near same result each time, you have a "flight profile" for a theoretical flight. Now you can test your ignition to see if it works based on the "test flights" you just did. This will allow you to learn if your method of programming the Altimeter are going to work. I only way I can think of to achieve a time to altitude profile similar to your rocket would be experimenting with a vacuum resevoir that could pull a vacuum on the chamber very quickly. This method would also allow you to test with out actually firing the rocket, just lighting up some LEDs instead of igniters.

Next you get to test fly the real thing with information based on simulations and experience gained from individuals like Jim . I could be way off too

npuldon said:

Jim!

Thank you for your thoughtful reply! If you don't mind I have some questions and counterpoints.

1. How can we accurately tell how high the rocket will actually go? I am worried about relying on software to predict an altitude and then risking having altitude Y be too large and not firing the 2nd stage, or being too small and firing it before first stage separation/ burnout. We use Openrocket for design and simulations.

Click to expand...

Part of doing two stage flights is learning how to simulate them. I use Rocksim and not Openrocket, but my belief is that if you do a reasonable job of putting in the rocket characteristics, that you can get a simulation that's close enough for setting up the program. As an alternative to the program I provided before, you can also use a trigger such as burnout 1 plus a delay, say 2 seconds, and then altitude > X. In this case, if you thought the altitude would be 3000 at motor burnout + 2 seconds, you might set altitude > 2500 as your margin. This approach relies a little less on the simulation results, but still ensures that the rocket is away from you when the sustainer lights.

npuldon said:

2. Do you know where I can find a diagram for an airstart that takes into account a shunt? I searched for "shunt" at home depot and a local electronics store online and nothing is coming up. Do they go by another name or is there a specific low cost model you would recommend? I read that they operated similar to a diode.

Click to expand...

A shunt means basically a short circuit from the altimeter outputs through a switch. When the shunt is closed, if the altimeter accidently fires, the shunt prevents current from going to the igniter. You open the shunt as the last thing you do before leaving the pad. The secret to a shunt is to keep the wires short to minimize the resistance of the shunt part of the circuit. On my sustainers that use shunts, I typically use both a shunt and an additional switch that opens the circuit to the ematch. I just finished wiring up a board that way.

npuldon said:

3. Unfortunately our budget does not permit multiple full scale tests and so doing a test with only the booster would not test our 2nd stage ignition logic or system during flight. Other than that I like your idea.

Click to expand...

My suggestion was to include both the booster and the sustainer for the flight, but only have a booster motor. That is, the sustainer is there, but there's no motor. So, you launch in a two-stage configuration, which tests your interstage coupler, you fire your separation charge, you fire your igniter ematch except there's no sustainer motor, and then everything has to recover. You do the flight and analyze your data, such as how well did you simulate the flight, was everything sequenced correctly, etc. You will learn a lot doing this. I assume I can't talk you into doing what you really should do to prepare for a flight like this, which is several years of HP experience and working your way up, so I'm suggesting the booster motor only test flight as an accelerated but relatively safe and relatively inexpensive pathway. Do this to prove you know what you're doing, and then fly as a two-stage.

npuldon said:

4. Unfortunately our budget does not permit the purchase of a TeleMetrum or TeleMega. Those certainly appear to be great products and we would undoubtedly purchase a TeleMega or 2 if we had the capital. Hopefully next year!


Thanks again for your help as it is highly appreciated over here!

-Noel

Click to expand...

Well, you only need those if you want tilt control over ignition. My opinion is that an altitude check is for the purpose of safety while a tilt check is for protecting the waiver. I have tilt checks in my rockets, but I also use the altitude check for that reason.

Jim

Jim,

Your iteration of the "booster-only" test flight makes more sense to me now and I think you have several valid points. I will discuss it with the team and see if we can go the route you suggest.

Thanks again for your thorough replies.

Cheers

-Noel

npuldon said:

Jim,

Your iteration of the "booster-only" test flight makes more sense to me now and I think you have several valid points. I will discuss it with the team and see if we can go the route you suggest.

Thanks again for your thorough replies.

Cheers

-Noel

Click to expand...

Just as an FYI, I'm currently testing a stabilization system for a multi stage rocket. I have a two-stage test rocket which has the stabilization unit between the first and second stages. The idea is that it will launch, separate the booster, and provide guidance while attached to the bottom of the second stage. Then, it will separate just before the sustainer lights. I'm testing the concept with a booster-only test flight before a high altitude flight this fall - to prove that it works as I say it will. I'm not asking you to do anything that I wouldn't do myself.

Jim

Jim for the booster only flight (which is a great idea) it seems to me more accurate atlitidude data would be collected if the sustainer motor is installed just not lit. The ematch (iginiter) for the sustainer could be put in the tube with the parachute for the sustainer. I'm just curious about why not include the susteainer motor which has an impact on altitude becuase of it's weight. The reason I ask is I have some students working on a 2 stage and we will be testing later this summer.

amarillo_rocket said:

Jim for the booster only flight (which is a great idea) it seems to me more accurate atlitidude data would be collected if the sustainer motor is installed just not lit. The ematch (iginiter) for the sustainer could be put in the tube with the parachute for the sustainer. I'm just curious about why not include the susteainer motor which has an impact on altitude becuase of it's weight. The reason I ask is I have some students working on a 2 stage and we will be testing later this summer.

Click to expand...

The main objective of the flight would be to get data on the staging and safety aspects rather than the altitude (which you could simulate with or without a sustainer motor). Having said that, on my flight, I'm flying the motor case with a long piece of all thread to better simulate the weight distribution. One downside of not having the reload installed is that the rocket might be less stable without the motor installed. This has to be checked, although the CG is often around the location where the sustainer motor would be, so not much effect on stability. It might also be possible to do the test flight on a smaller motor and save a few bucks.

Jim

Jim, could you put the motor casing in, seal the end, and fill it with sand or something to simulate the load?

markkoelsch said:

Jim, could you put the motor casing in, seal the end, and fill it with sand or something to simulate the load?

Click to expand...

Yeah, you could do something like that.

At a minimum, the OP probably needs to close of the lower end of the sustainer so that a separation charge would simulate the condition that would be there during an actual flight (i.e., you don't want to have to pressurize a large cavity in the sustainer if that's not what will actually be present). Beyond that, it's just whatever is required for a specific rocket/flight. For my stabilization flight, I need enough weight in the sustainer motor location to move the CG ahead of my canards. Otherwise, they would be turning the wrong way during the boost.

Jim

I just completed a similar project for myself. Creating your own Arduino based 2-stage flight computer is a heck of a lot of work. It definitely can be done, but takes a lot of testing and perseverance. If you don't have the time or expertise, then I second Jim's recommendation about using the Raven to light the second stage.

In the 6-months it took to complete this project, I built 2 failed prototypes, 22 versions of code, re-wrote 4 sensor drivers, and had a 3rd degree burn from a soldering iron. In the end, the product turned out great and it successfully flew twice at NSL 2016. Maybe I'll start a thread about it.

Below are the specs I was able to achieve, and attached are the plots from one of the NSL flights.

Tilt-angle inhibit of 2nd stage event
Minimum altitude inhibit of 2nd stage event
Mach immune events
Acceleration based apogee event (Barometric backup)
Barometric based main deploy event
Acceleration based separation event
350Hz 3-axis digital 24G accelerometer data logging
350Hz 3-axis analog 200G accelerometer data logging
350Hz 3-axis digital 2000dps gyroscope data logging
350Hz of integrated pitch, yaw, roll, velocity, and altitude
350Hz of 13 different flight events
20Hz of digital barometric data logging
Optional Apogee delay
Audible Continuity reporting at startup
Audible Post-flight status report
Separate files for each flight
Optional test mode for bench testing
User defined delays for apogee, separation and staging
User defined altitude inhibit, tilt-angle inhibit, and 5 other flight parameters
Safety override of user defined parameters