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Using a Rabbit isn’t rocket science… or is it? FLY FLY Run, Rabbit, Run Remember the RABBIT RCM2100 microprocessor module we introduced to SILICON CHIP readers back in October 2001? Seems lately its brother, the RCM2300, has been soaring to new heights . . . T he 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 box of matches and a really long ruler. Given a payload of opportunity, Nicolaus Radford, Chief Avionics Engineer for ASA, went ballistic with the Rabbit RCM2300 Microprocessor Core Module. “I got into Rabbit about 3½ years ago, basically just looking for an 38  Silicon Chip 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,” he said. The ASA’s most recent rocket launch was about 5.6m in length and 230mm in diameter. It pulled about 8.5G on takeoff, broke the sound barrier and flew up to about 3500m. The rocket had video, telemetry, GPS and full dynamical analysis of the rocket, all in real time. To measure all vehicle parameters, including acceleration, velocity, pressure and position, they built a custom data acquisition board that had all the components on it. It used the Rabbit and an I2C bus to read and store data in the Rabbit’s flash memory. At the same time, the Rabbit was also serially interfacing to a terminal node controller and a GPS unit on two serial ports. The Rabbit ran on the I2C bus and read all the different sensors around the rocket, then formatted the data and sent it to the terminal node controller. This in turn formatted the data for packet radio and transmitted it on an amateur radio frequency. GPS readings were also being sent via a telemetry band to the ground. According to Radford, 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 two wires instead of a string of wires. We used two of the four serial ports on the Rabbit to interface to a terminal node controller, which interfaced to an amateur 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 siliconchip.com.au Getting an 18.5ft rocket ready for launch is not quite as simple as placing it in a large bottle and lighting a long wick! Some idea of the size of the craft can be gleaned from these two photos, courtesy of ASA. on the market that can beat it. You’ve got 40 I/O pins, four 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 and space saving is just tremendous for the capability. And it has got relatively low power consumption –110mA at 5V is pretty small!” 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 whatsoever. The way Dynamic C time-slices and the way the event control is set up 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 utilisation of processing time than what the Rabbit did using the costatement. And I have yet to see this anywhere else.” The development time to completely get the system up and running 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 Front view of the payload/electronics section of the rocket (red section at top). siliconchip.com.au 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 readyto-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 on the way down that ASA had a scare in the form of a failed main parachute. Upon landing, their data told revealed a 61G impact. Even though the backup parachute successfully protected the entire rocket, it was pretty impressive that the Rabbit withstood the shock. Commercial spin-off There has already been a product spin-off from the project: 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 Rabbit will enable a product which can be taken to market that will be superior to anything currently available for a data acquisition system in high-powered rocketry applications. The first thing that struck the ASA designers was how small the RCM2300 was for what it did. That was extremely important because there was not a lot of space to work with. The benefit over say, a PIC processor, is that the Rabbit not only has three times the processing power but also has all the extra overhead and the flash memory interfaces that need to be added onto a PIC. So what is in store for ASA? The launch described here is in preparation for a space shot to be attempted early next year, using a 12m liquid motor vehicle. It will enter space, reach 120km and return. There will be many Rabbits on that flight. With the design calling for throttle control ability, one Rabbit will be used for liquid motor throttling and data acquisition of the liquid motor; another to analyse power usage and to turn things on and off as they are needed to conserve power. For more information on ASA, visit: www.asa-houston.org Dominion Electronics are the Australian distributor for all Rabbit products. Ph 9906 6988. Watching the data coming back to earth, courtesy of the Rabbit and an amateur radio link. Photos: ASA. May 2004  39