Programming a Raven 3 for sustainer?

Can anyone please either point me at an existing thread, or show/tell me how to program a Raven 3 for use in the sustainer of a 2 stage Wildman Darkstar Jr?

My configuration is running an Eggtimer Quark in the booster for simple apogee/main (main with cable cutter) duties.

The Raven 3 in the sustainer will light the sustainer motor, and handle apogee/main deployment. I've not configured this before and given there's a large opportunity to create mayhem, I figure I should ask those with experience for advice.

Thank you @Ethan

matthew said:

Thank you @Ethan

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There is an alternative method that Jim mentions further down
https://www.rocketryforum.com/threa...ic-and-electronics-setup.125997/#post-1463054
But i need think about this one, as I think the delay is applied once ALL other criteria are met, so it will wait until motor burnout and alt > X before the delay starts, so the post should read In this case, if you thought the altitude would be 3000 at motor burnout, you might set altitude > 2500 as your margin.
I

Ethan said:

There is an alternative method that Jim mentions further down
https://www.rocketryforum.com/threa...ic-and-electronics-setup.125997/#post-1463054
But i need think about this one, as I think the delay is applied once ALL other criteria are met, so it will wait until motor burnout and alt > X before the delay starts, so the post should read In this case, if you thought the altitude would be 3000 at motor burnout, you might set altitude > 2500 as your margin.
I

Click to expand...

You are correct. I actually made this mistake on a flight (the mistake being that the altitude criteria occurs after the burnout, so you are not really setting burnout +2). I did this on a three stage flight where it was easier (I thought) to trigger off of the second burnout. The 3rd stage was moving pretty slow at ignition! With the setup of the Raven screen, it is easy to incorrectly conclude that the delay is associated with the burnout. The second method you linked to shouldn't be used.

Jim

JimJarvis50 said:

You are correct. I actually made this mistake on a flight (the mistake being that the altitude criteria occurs after the burnout, so you are not really setting burnout +2). I did this on a three stage flight where it was easier (I thought) to trigger off of the second burnout. The 3rd stage was moving pretty slow at ignition! With the setup of the Raven screen, it is easy to incorrectly conclude that the delay is associated with the burnout. The second method you linked to shouldn't be used.

Jim

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Copy that. I only picked this up because I've had my fair share of programming fun as well (an especially good one recently) so this stuff gives me the willies.
Your original post should probably be a sticky.

For the purpose of lighting the sustainer can the raven be set altitude>x and a velocity <x ?

Hybrid33 said:

For the purpose of lighting the sustainer can the raven be set altitude>x and a velocity <x ?

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Using these values only wouldn't be a good idea. It would be possible to just creep above the altitude x while arcing over at a low velocity. There needs to be a time criteria - altitude x at T< y. Also, since many Ravens (through Raven 3's?) have inaccurate accelerometers, you should be very careful how you use any accelerometer-derived results. Best is to check your Raven for accelerometer issues as a starting point.

Jim

Forgot to mention that a Tiltometer 2 would be used in line

Very Helpful Thank You !!!

JimJarvis50 said:

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.

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OK, so may I please request a sanity check to make sure I have understood?

I have included screenshots of my Raven config and a zoomed plot of my booster burnout time and altitude.

Using an AT J500G in the booster which has a 1.4s burn time, it appears that the rocket will reach 125m (410ft) at burnout. I have configured my Raven 3 to use the 3rd channel to light the sustainer with Time < 2.4s, and Altitude > 100m (328ft).

Are the Time and Altitude parameters reasonable or should I tighten them up a bit?

matthew said:

OK, so may I please request a sanity check to make sure I have understood?

I have included screenshots of my Raven config and a zoomed plot of my booster burnout time and altitude.

Using an AT J500G in the booster which has a 1.4s burn time, it appears that the rocket will reach 125m (410ft) at burnout. I have configured my Raven 3 to use the 3rd channel to light the sustainer with Time < 2.4s, and Altitude > 100m (328ft).

Are the Time and Altitude parameters reasonable or should I tighten them up a bit?

View attachment 378455 View attachment 378456

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I think we have a little work to do yet. With the settings you are using, the igniter will fire when the rocket reaches 100m - not good since the booster motor will be under thrust.

Here are the steps to use. First, decide where you want the igniter to fire. For your example, let's assume you want to fire the igniter at 2 seconds (the motor will come up to pressure very shortly after that). At 2 seconds, the expected altitude is 200m. So, you might program A>200m (the altitude where you want it to light based on your simulation) and T<2.5 seconds. You expect to get to 200m at 2.0 seconds, so 2.5 seconds is your margin for error. You could go a little less than 2.5 seconds, but I would use 2.5 seconds.

I can't tell from the plot what your velocity would be through this part of the flight, but I would typically use a little longer delay between staging. That is, I might choose to light the sustainer maybe 3 seconds into the flight to give a little coast time, but it depends on your velocity and what you want the flight to do. The process of determining the Raven settings would be the same.

Also, watch out for setting the Raven altitude. I think it has to be in multiples of 32 feet. Your intention of 328 feet became 320 feet in the Raven program.

Jim

Since "After burnout 1" is checked on that channel, that will hold the firing until the instant of burnout when all criteria become true (assuming it has reach 320 ft in < 1.4 seconds, and pressure is decreasing)

Might be worth posting the entire sim file (or at least the full view of velocity and altitude vs. time)

Ethan said:

Since "After burnout 1" is checked on that channel, that will hold the firing until the instant of burnout ...

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Yes, good point. I would still recommend a little time between burnout and lighting the sustainer, as detected burnout does not mean the motor has stopped burning (trust me on this one).

Jim