| Using a Rabbit Isn't Rocket Science…Or is it? |
The Amateur Spaceflight Association (ASA) of Houston, Texas has a mission:
Promote space-related activities in such a manner that safely challenges
the technical limits of amateur space flight. Breaking the world
record for amateur rocket altitude would help accomplish this goal, but
the ASA needs more than a bottle of liquid oxygen, a book of matches and
a really long ruler. Given a payload of opportunity, Nicolaus Radford,
Chief Avionics Engineer for ASA went ballistic with the RCM2300 Microprocessor
Core Module.
"I got into Rabbit about 3 ½ years ago, basically just looking
for an embedded processor that would fit the form factor and capability
I was after. I came across the Rabbit Semiconductor web site, bought one,
and haven't looked back since." From there, Radford described ASA's
most recent rocket endeavor with Rabbit power. "The rocket that we
launched was about 18.5 ft. in length and 9 inches in diameter. It pulled
about 8.5 G's on takeoff, broke the sound barrier, and flew up to about
12000 ft. The rocket had video, telemetry, GPS, full dynamical analysis
of the rocket, all real-time," stated Radford. "What we were
having to do on the rocket was measure all these vehicle parameters including
acceleration, velocity, pressure, and position. We built a custom data
acquisition board that had all the components on it. We were using the
Rabbit and an I2C bus to read and store data in the Rabbit's Flash. At
the same time, the Rabbit was also serially interfacing to a terminal
node controller and a GPS unit on 2 serial ports. The Rabbit would run
out on the I2C bus and read all these different sensors around the rocket
and then it would format the data and send it to the terminal node controller,
which would then format the data for packet radio and send it down on
a HAM radio frequency. Intermittent to this were GPS readings being sent
via our telemetry band to the ground as well."
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[The costate construct] was just phenomenally easy to use.
—
Nicolaus Radford, Chief Avionics Engineer
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Concerning the ease of designing, programming, and communicating with
the RCM2300: "The communications bus was an I2C protocol. We absolutely
loved it! It was very simple to string up multiple I2C controllers and
talk to them to get all the data back. It was great because on a long
rocket you have sensors in the nose cone and the body, and it was nice
to interface with these sensors with 2 wires instead of a string of wires.
We used 2 of the 4 serial ports on the Rabbit to interface to a terminal
node controller, which interfaced to a HAM radio. We also interfaced to
a GPS receiver. When you look at how small the RCM2300 is compared to
what it does, I don't think there is anything on the market that can beat
it. You've got 40 I/O pins, 4 serial ports, Flash memory to store data-you
don't need any external interface to it to run our system except the core
module. The size space savings is just tremendous for the capability.
And it has got relatively low power consumption-110 mA at 5 V is pretty
small!"
In regards to the usage of software in the project, critical components
of Dynamic C helped Radford get to the launch pad. "We probably could
not have done the project in the timeframe and ease that we did if we
didn't have the costate construct. It was just phenomenally easy to use.
It basically simulates a multi-threaded environment with hardly any overhead
what so ever. The way Dynamic C time-slices and the way the event control
is setup is just amazing. If you were to try to write out and code out
to simulate a multi-thread yourself, you would be bogged down in months
of coding. I don't think as a programmer I could make a better utilization
of processing time than what the Rabbit did using the costatement. And
I have yet to see this anywhere else."
The bottom line for development time, ease, and risk reduction is what
Rabbit customers have voiced as the most important factors for design
wins. Radford elaborated on his own experience: "Our development
time to completely get the system the way we wanted it was eight months.
Had we not had the development kit and protoboard to easily interface
the programming pins of the Rabbit, had we used some other processor where
we would continuously have to fabricate our own ways to interface to the
processor, it wouldn't have been nearly as fast. It was really nice that
the pins were broken out to individual headers on the protoboard-that
made development tremendously easy. The ready-to-go protoboard surface
mount pads helped significantly as well. My best guess is that our development
time would have been twice as long if we hadn't gotten these benefits
in the development kit."
During flight, the rocket performed perfectly. It wasn't until the way
down that ASA had a scare in the form of a failed main parachute. "Upon
landing, our data told us that we took 61 G's on impact. Even though the
backup parachute successfully protected the entire rocket, it was pretty
impressive that the Rabbit withstood the shock." Radford laughed.
So what is in store for the ASA in the future? Radford explains, "[This
launch] is all in preparation for a space shot we are going to be attempting
early next year of a 40 ft. liquid motor vehicle. It will enter space,
reach 400,000 ft. and return. We'll have many Rabbits on that flight."
Radford continued, "Our next design where we actually have throttle
control ability, the Rabbit will be used as a motor controller. We'll
have multiple Rabbits; one of which will be used for liquid motor throttling
and data acquisition of the liquid motor. We will also use the Rabbit
to analyze power usage and to turn things on and off as they are needed
to conserve power."
"We have also already started a product spin-off from our main vehicle
system. It's a data acquisition system aimed toward the high-powered rocketry
community. The rocketry community is all about size: how small can you
get it? The first thing that struck us about the RCM2300 was how small
it was for what it did. That was extremely important to us because we
did not have a lot of space to work with. The benefit over say, a PIC
processor, was that the Rabbit has all the extra overhead, the Flash memory
interfaces that you need to add onto a PIC and 3 times the processing
power. We believe that the Rabbit will give us a product we can take to
market that will be superior to anything currently available for a data
acquisition system in high-powered rocketry applications."
For more information on ASA, visit: www.asa-houston.org
Submit your design application
success story to press@rabbitsemiconductor.com
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