Discussions

Rocket application

Posted by Kraig Krumm on March 16, 2010 at 6:12am

Hi All,

I am working with Steve Eves who last year launched a 36' tall scale Saturn V rocket and in so doing, set a record for the largest model rocket ever launched and safely recovered. Having accomplished that he has now set out to build a 1/10 scale Saturn 1b with two stages. What he needs, and what I am researching is a method to determine whether the second stage is at or near a vertical attitude before the second stage engines are ignited. I have been palying with a Parallax Javelin board and a Sparkfun two axis rate gyro, but as you have probably already guessed, a rate gyro in this application is useless. So, I am currently looking at the 9dof Razor IMU and would welcome input on the best way to go about accomplishing my task. We basically need a go or no go signal if the vehical is off of local vertical by more than 10 degrees or so. Any input would be appreciated. Remember that at first stage burn out, the vehical will be experiencing zero G flight. Thanks!!

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Replies

Kevin Baxter March 14, 2011 at 11:14pm

Test, test, test before you risk it all. The vibrations are your biggest problem. Send up whatever your avionics on a small rocket with higher g’s and a higher dynamic than the big scale model will achieve.

Check out 2 our weekends ago: http://www.garvspace.com/2011/P-18A_FT-1/P-18A_FT-1.htm

Kevin Baxter

President Friends of Amateur Rocketry, Inc.

P-18A_sRLV_Flight_Test_1
Ron Jacobs June 9, 2010 at 4:31pm

How is this project going?
automatik March 16, 2010 at 11:50pm

Kraig,
see these for more info:

Comment1

Comment2

Rocket post
Developer

Doug Weibel March 16, 2010 at 5:02pm

Think through the IMU approach. We use accelerometers to correct the gyro drift, Gravity will be much smaller than linear acceleration in your case making measurement of the gravity vector difficult. Accelerometers are also prone to vibration issues, and the gyros can be as well. I think it may be very difficult to have any gyro drift correction during the burn. You should look for gyros which will not have vibration issues and which will be stable enough to rely on for the time span of the burn without drift correction. You may need to characterize the thermal characteristics of the gyros and compensate for the temperature dropping too.
Mike Bakula March 16, 2010 at 2:44pm

This is an application where thermopiles should shine -- VFR conditions, insensitive to vibration and acceleration, and lightweight.
Petr Hubacek March 16, 2010 at 2:31pm

when you have zero G, any of mems can be used, they get no comparision to the G they need. I would recomend you clasical mechanical gyro that can guide you through the whole flight...but no one sells it I think...
Diarmuid Wrenne March 16, 2010 at 12:08pm

Hi,
Have you any info on the vibrations experienced in the previous flight? Is it possible to steer the second stage after first stage burnout. I'd have a look at trying to use a camera based system (maybe in conjunction with the solid state IMU). That said, the rocket requirements are very different from an IMU for a UAV.

For a rocket, flight time is very short, accuracy needed is likely to be substantially higher, accelerations are much higher, weigh constraints are negligible in comparison, you can't rely on flight mechanics (dihedral, etc) to stabilise flight.

Since flight time would be in seconds, would you maybe use a conventional gyro. http://gyroscope.com/d.asp?product=GIMBALS

It would be very interesting to compare an SS IMU and the conventional gyro

Regards
Diarmuid
3D Robotics

Chris Anderson March 16, 2010 at 6:53am

The Sparkfun 9Dof is actually overkill, since you don't need the magnetometer. ArduIMU+ will do what you need out of the box (you won't need to use the GPS, because you don't care about yaw). The only thing is that I don't know how many Gs those sensors can handle (they're the same ones as the Sparkfun board).