The first ATV flight was a premature ejection while the rocket was under boost at over 300 mph and passing through 1200 feet......if you ever wanted to see what it would be like to jump out of a plane without a parachute here is your chance!
Telemetry:
Nike-Smoke flights have housed a R-DAS Classic board, GPS/active antenna, and telemetry transmitter inside the nose cone. Previous Terrier-Sandhawk flights utilized a R-DAS Classic board and a telemetry transmitter housed inside a much smaller nose cone. The basic R-DAS and and telemetry system were first flight tested in a 4 inch rocket, that report is here. Below is a photo of the R-DAS electronics payload for the Nike-Smoke flights:
The GPS active antenna is mounted perpendicular to the support board, the board has a rectangular hole so the antenna projects to either side. Immediately below is the coiled coaxial cable, it is threaded through two holes.
Below the coax is a Radio Shack 1600 mA NiMH 9.6 volt RC car battery (23-331B), which will power the payload for about 3 hours of continuous run time. The battery has a connector on it, the opposing connector is used to connect the battery to the main board. To charge, the battery is disconnected from the R-DAS power leads and hooked up to a battery charger with the appropriate opposite connector. Connectors are available from Radio Shack.
Below the battery is the GPS board, connected via a long ribbon bus cable to the classic board. The last board is the telemetry transmitter and inverted V antenna.
Note: there is a lot of room in the Smoke nose cone, so the electronics were spread out and placed on just one side of the board. This configuration could have been "tighter" had both sides of the board been used. The ribbon cable is longer than it needs to be, we didn't want to fabricate a new one so we used a previously made cable that is long enough to wrap around both sides of the Terrier-Sandhawk board.
The inverted V transmit antenna is made out of 1/8 inch piano wire, cut to the appropriate length for 1/4 wave at the 433.92 MHz transmit frequency (roughly 6.5 - 6.75 in), and soldered to lugs. (Note: although not required, for best power transfer the antenna elements should be trimmed to the lowest SWR using a meter. The low cost 70cm band MFJ 219-B is available from MFJ Enterprises for about $100) These lugs are anchored to the electronics support board with nylon screws and nylon wing nuts (so its easy to tighten the coax and elements together, the orientation of the nylon wing nuts doesn't electrically effect the antenna) and connected to a short run of 50 ohm coaxial cable. The antenna end of the cable has the same size lugs as the antenna elements, the other end of the cable is soldered to the underside of the transmitter board where the SMA connector pins protrude. The antenna elements project through small holes drilled above the nose cone shoulder. A key switch in the nose cone baseplate is used to control power to the unit.
Terrier-Sandhawk nosecone mounting board and antenna element. Foil was used to help shield the GPS receiver on the other side of the board from transmitter RF. Holes in the top were used to wind the active antenna coax around to take up the slack (coax was also shielded inside foil). We never were able to get the GPS and the telemetry transmitter to work together in the very tight Terrier-Sandhawk nose cone area probably due to harmonics from the transmitter getting into the active antenna and overwhelming the very weak GPS signal. We found through experimentation that the GPS would get a lock if we had about 6 inches more spacing between the GPS antenna and the inverted V telemetry antenna. For applications other than in a small nose cone or very small payload bay, both systems should coexist with little problem.
Telemetry is received via a turnstile antenna (see construction details on the telemetry flight test page). A short run of 50 ohm coax is soldered to the bottom of the receiver SMA connector. An "old" 486 desktop PC powered by a large UPS and the cars's electrical system recorded and displayed the received information for the first flights because my two laptops, an IBM and Toshiba, put out too much RF noise and interfered with telemetry reception. The December 15, 2002 flight used a Dell laptop which didn't effect telemetry reception unless the receiver was set directly on top of the keyboard.
The received telemetry information is passed via a FRS walkie-talkie and relayed directly over the PA system to the crowd. This can be heard on the ground video. The system has performed very will on all flights and is a real "crowd pleaser" in addition to providing live information about the status of the flight.
RDAS telemetry lessons learned so far:
1 - For live telemetry display, make sure you set the graph scale to be greater than the maximum expected altitude of the flight. If you forget to do this the altitude curve will hit the top of the graph.
2 - If you are going to read out real time performance for the crowd via a walkie talkie or or microphone, first set the display to the graph mode. This way it will be easier to read out peak acceleration, after motor burn out switch to the data screen and read the altitude data as it scrolls by. Its easier to read the altitude numbers this way rather than trying to interpolate them from the graph while it builds, although watching the graph build in real time is definitely "cool".
3 - If using downlinked GPS, switch to the 3D mode after apogee to watch the rocket return to the ground and the effects of the wind. Practice rotating and changing the aspect angle of the 3D display prior to flight.
4 - This transmit and receive configuration is confirmed good now on two flights for at least two miles line of sight, for the most part received signal quality at apogee shows very close to 100%. My guess is the inverted V & turnstile configuration is probably OK on ascent to at least 15,000 feet. If the stock whips are used the range will be a lot less. Carefully soldering 50 ohm coax to the SMA pins projecting through the bottom of the TX & RX circuit boards seems to work OK for connecting the antenna coax at both the transmitter and receiver end, so removing the SMA connectors is not required.
5 - Range of the telemetry transmitter when laying in a farm field for direction location is about 1/2 mile using a 6 element yagi hooked up to a low sensitivity 20 year old scanner. If using a ham walkie-talkie with a decent receiver the range with a similar antenna is probably on the order of a mile or more. Once the signal is acquired its easy to walk right to the transmitter, the last flight we couldn't see the nose cone and parachute until we were maybe 100 feet away because they were in about 2 feet of growth.
ATV:
The ATV system was located in the mid section of the Sandhawk, above the altimeter compartment and below the main parachute compartment. This has not been tried yet in the Smoke project. The system power consumption at 13 volts is approximately one watt. See the short article at http://www.vahpr.com/atv/atv.html for general details of the transmit and receive system used on previous flight tests with J-415 motors and 4" air frame rockets (the receive antenna for the telemetry and ATV are the same design and construction). For best power transfer a SWR meter should be used to trim the antenna elements, see comments in the telemetry system.
The ATV system test flights used a camera that looked directly sideways, and were recorded to a VCR. The video was later converted to .mpg1 files and some quality was lost in the process.
The Terrier-Sandhawk ATV system uses a different support board configuration then the test payload, and the camera is mounted internally to the body tube instead of the support board. Received video is recorded on a 4 head VCR powered by an inverter, and is also recorded directly to a laptop via a Dazzle USB external .mpg box at 3 megabits per second. The ATV video posted to Jerry's site and this site utilized the real time .mpg file instead of a VHS tape conversion. "Instant replays" for the crowd were displayed on a 12 inch color TV connected to the VCR and on the laptop LCD screen.
A first surface mirror angled at approximately 40 degrees inside a shroud is used to provide the downward looking video. For the first Terrier-Sandhawk flight a system was configured to eject the shroud by using an igniter to burn the three monofilament lines which secured the shroud to the body tube, unfortunately or unfortunately (depending on how you look at it) the igniter didn't function and the shroud stayed on through the entire flight instead of deploying 10 seconds after liftoff. The view looking down all the way to apogee is good so for the second flight we hard mounted the shroud and removed the ejection system.
ATV lessons learned so far:
1 - It takes a lot more power due to the bandwidth required to transmit video. You can see the signal quality decline as the rocket climbs to apogee, 12Kft is probably about the limit for this system without boosting the TX power or increasing antenna gain. For the next flight we may install a low noise amplifier on the ATV receive antenna to see if that works without introducing a lot more noise into the signal. If that doesn't work, we will go to some sort of gain antenna, but those will probably require tracking of the rocket. The turnstile design is nice because of its very broad arc of reception, the cost of course is less gain. The last option will be to boost the TX power, this costs in terms of power consumption and increased battery weight. Also, we are somewhat concerned with keeping the RF field down because at higher power levels it might influence altimeter functioning.
2 - The extra TV power makes for a great long range location beacon. Although its not possible to receive video once the rocket lands, its easy to DF the TV transmitter when its on the ground at a range of easily several miles by tuning to the center frequency of the signal and listening to the sync buzz. Between the TV transmitter for long range acquisition and the telemetry transmitter for short range precision location (close in the TV signal is so strong it can swamp the radio connected to a yagi, and so elements have to be removed or a attenuator used) it makes it pretty easy to locate a high altitude rocket landing spot.
This site will be updated with the results of future flights.