Class C rocket launches today
JonOxer
I'm planning to do a couple of launches of Marco's class C rocket from
3:30pm this afternoon from the trotting track at this location in
South Croydon, Victoria:
http://maps.google.com.au/maps?ll=-37.810471,145.277731
If anyone is local and interested in attending you're welcome to turn
up, but to be on the safe side perhaps let me know first (SMS to 04
3851 6600) in case it turns out the park is being used for something
or we have to cancel for some reason.
I have the rocket loaded up with an accelerometer connected to an
Arduino and a radio transmitter so we can try logging G force during
the launch and flight.
Regards,
Jonathan Oxer
Jonathan Oxer
Hackerspace groups, since there are people interested from both groups
and there seems to be a lot of crossover anyway)
On Sat, 2009-05-02 at 19:20 +1000, Shaun Moss wrote:
> How'd it go?
The launches worked really well, but I don't think the accelerometer
data is going to mean anything much at all. I learned a very important
lesson: always, always, always put an absolute timestamp in with the
data, even if there's a relative one in there! The code running on the
Arduino in the rocket pumped out values looking like this:
562047|326|328|395
562204|322|330|393
562361|327|327|397
562516|317|335|604
562673|325|331|590
562830|328|330|514
562985|328|331|506
563142|328|331|500
563298|328|329|501
where the columns are:
1: Time in milliseconds since the Arduino booted
2: X force
3: Y force
4: Z force
That segment is from around the time of the second launch, with the Z
value stable at around 394 while the rocket was stationary then jumping
to 604 and falling to 500 over the next 800ms.
Which brings me to the second lesson learned: comms failed right at that
point, less than 1 second after launch. So the el cheapo 433MHz modules
from Jaycar just didn't manage to do the job.
I have a pair of 60mW XBee modules here that should be good for 1Km+
range, so for next time the 433 modules are out and XBee is in.
Rohan and Marc both came along and brought their kids, and Rohan wielded
a video camera while Marc took some still shots. I saw one of Marc's
shots and it was stunning: a shot of the rocket about 2m above the
launch stand with a trail of smoke, and the laptop sitting on the grass
in the foreground. It looked like a magazine cover shot, very cool.
The extra mass in the nosecone didn't seem to hinder the launches at
all, but because I used C6-7 motors with a 2 second separation delay
there was a heart-stopping moment when it reached apogee, turned over,
and started coming straight down *really* fast before the charge fired
and the chute deployed. On the second launch I thought the separation
had failed because it descended a very long way before it fired, so the
final lesson for the day was to use motors with a smaller separation
delay when working with a larger payload mass.
I'll post a follow-up when I've had a chance to look at the data a bit
more, and hopefully generate a couple of graphs.
Finally, thanks to Rohan and Marc for coming along! I know Andy wanted
to come but had other commitments, but there'll be other opportunities.
Regards,
--
Jonathan Oxer
Ph +61 4 3851 6600
Geek My Ride (www.geekmyride.org)
Lunar Numbat (www.lunarnumbat.org)
Practical Arduino (www.practicalarduino.com)
Paul Schulz
Can you please upload the program and the output?
Cheers,
Paul
MarcoOstini
Brilliant News! I've noticed that the weather in Melbourne has not
been ideal for rocket launches in the past week or so, so it's great
news that you managed a few launches.
How many launches did you fit in, two?
> The launches worked really well, but I don't think the accelerometer
> data is going to mean anything much at all. I learned a very important
> lesson: always, always, always put an absolute timestamp in with the
> data, even if there's a relative one in there!
and to store it in the wiki or dotproject.
> I have a pair of 60mW XBee modules here that should be good for 1Km+
> range, so for next time the 433 modules are out and XBee is in.
> Rohan and Marc both came along and brought their kids, and Rohan wielded
> a video camera while Marc took some still shots. I saw one of Marc's
> shots and it was stunning: a shot of the rocket about 2m above the
> launch stand with a trail of smoke, and the laptop sitting on the grass
> in the foreground. It looked like a magazine cover shot, very cool.
would be good to have the images in or linked from a LN blog post.
> The extra mass in the nosecone didn't seem to hinder the launches at
> all, but because I used C6-7 motors with a 2 second separation delay
> there was a heart-stopping moment when it reached apogee, turned over,
> and started coming straight down *really* fast before the charge fired
> and the chute deployed. On the second launch I thought the separation
> had failed because it descended a very long way before it fired, so the
> final lesson for the day was to use motors with a smaller separation
> delay when working with a larger payload mass.
huh ;)
> I'll post a follow-up when I've had a chance to look at the data a bit
> more, and hopefully generate a couple of graphs.
> Finally, thanks to Rohan and Marc for coming along! I know Andy wanted
> to come but had other commitments, but there'll be other opportunities.
too, just the small matter of distance kept me away.
As always, lovely work Jon, with some very useful knowledge gleaned
for the next series of launches, as well as Andy's work on the Class
G. I'll record this in dotProject. It would be good to have all the
launch data in a common LN repository.
Cheers,
Marco
JonOxer
I've put up a blog post about the launches with some of Marc's pics,
including the stunning one of the moment of launch. That one really
does deserve to be on a magazine cover!
http://jon.oxer.com.au/blog/id/330
Regards,
Jon
MarcoOstini
Thank you kindly for the LN blog post and the detail in the LN wiki.
Much appreciated.
Cheers,
Marco
Roy
thread
from the C-class launch.
The numbers for the X and Y axes come out with means and sigmas of
X: 325.4 +/- 3.7 units
Y: 330.2 +/- 2.3 units
Presumably the X and Y axes lie in a plane approximately parallel to
the earth's surface and Z is pretty much perpendicular to it.
I suppose formally Z is along the "long axis" of the rocket so I'm
basically assuming the rocket is standing upright at launch
(I can remember lighting firework rockets as a kid in Melbourne
when that wasn't the case at all....)
Anyway, taking X and Y together we get 327.8 +/- 3.9 units.
Looking at the Z axis, the couple of samples before launch
show values around 394 units. If this difference (394 - 328)
is due to gravitational acceleration, then a rough calibration
is that 1 unit corresponds to 0.15 m/s**2 or 0.015g
(g being 9.8 m/s**2 here).
After the engine lit, the value of 604 implies that the rocket
was experiencing 4.1g at this time.
What I don't understand is the magnitude of the errors here,
though. An rms of 3.9 units corresponds to an rms of
0.6 m/s**2 (0.06g). The datasheet for this device
(http://www.sparkfun.com/datasheets/IC/LIS3LV02DQ.pdf)
lists a typical resolution of 0.001g in "2g mode", which
presumably would be something like 0.003g in "6g mode".
This whole analysis is based on very little data, but
it suggests that these data might be an order of magnitude
noisier than the device specification (0.06g vs 0.003g).
Hmmm.....
--Roy
Roy
you pushed the red button? I suspect the rms noises will be
lower in X and Y when the unit is quietly sitting at 1.0000g.
Thanks!
--Roy