Mike McCarty's ATV project
Mirror mount details. Mirror is a 1.5" square first surface mirror from Edmund Scientific. Mount was shaped out of balsa block and epoxied to BT. Mirror angle and position was figured out through trial and error. Best mirror angle turned out to be around 50 degs. mirror was affixed to mount with double sided tape.
Picture of circularly polarized receive antenna. This idea was taken from Tom O'Hara's ATV application notes at PC Electronics. The original plan shows using 2x2 lumber and hardware cloth for a reflector. I felt that was overkill and built the variation of it shown above. A camera tripod normally has a 1/4" bolt for mounting equipment so I cut a reflector out of aluminum and drilled a 1/4" hole. I installed a 1/4-20 brass insert into the bottom of a 7/8" dowel to accept the mounting bolt. I cut flats onto the other end of the dowel and affixed the 3/16" copper tubing elements to the dowel with #2 wood screws. The phasing line and matching section were then made as the app note describes.
Tweaking transmit and receive equipment the day of the launch Sept 16, 2000.
Assembling rocket as Denzil looks on.
Final pose before the moment of truth.
Forgot ladder to arm altimeter.
Liftoff on a J-570 motor.
And Now The Rest of the Story:
When I arrived at the site the morning of 16 Sept, I fired up the generator and the TV and VCR. I turned on the transmitter and nothing happened, no video at all. I checked the battery pack voltage and noticed it was dropping quickly like there was a heavy load on it. I checked the current draw and measured 3 amps (.6 is normal). I disconnected all the devices and started hooking them up one by one. With the camera and the transmitter drawing .4 amps and good video on the screen I called it good and decided not to use the GPS and video overlay, I'd have to find the short later. We prepped the rocket and launched it on a J-350 to around 3,000 feet. It went straight up and slightly away from us. Drogue charge fired on cue and the rocket came down in a flat spin with tubular nylon connecting the sections. Around 500' the main charge fired and the Rocketman R7C parachute inflated instantly setting it down nicely around 1200' out. Denzil and I walked out and recovered the rocket. When we got back I did a quick playback of the video and saw we had perfect coverage the whole time.
I found that the lower Black Sky rail button was missing from the airframe. We assumed it pulled out as it came off the rail. I dressed the hole with CA and installed another button. We then prepped and launched on a J-570. This time the rocket jinked as it came off the rail and headed North at a 45 deg angle. It reached around 4,000 feet about 3/4 of a mile north of us before the drogue fired. Again it descended in kind of a flat spin, but each section seemed to tumble as it came down this time. At 500' we had another perfect main chute deployment that set it down ever so nicely.
After recovery we noted that the lower rail button was missing again and one of the antenna dipole elements was missing. The elements were friction fit into matching brass tubes in the frame and we suspected that the shock cord pulled it out after drogue ejection.
At home I reviewed the tape and found the recorded video to be extremely dark, almost a black screen. After finding the remote and figuring out the on-screen menus I was able to turn up the brightness until the video looked normal. I realized that in trying to get the transmitter working at the site I had fiddled with the brightness on the 5" portable TV I was using, partially because the transmitter wasn't working well to begin with and partially because of the bright sky that was washing out the screen. After I got the transmitter working again I adjusted the video level on the input to the transmitter for best picture. The end result was the brightness on the monitor was set very high and video level on the transmitter was set very low.
The video of the first launch showed a perfect boost and then the drogue charge firing. After the drogue fired the booster was spinning extremely fast on it's axis while the two sections orbited each other. I got dizzy just watching the video. Next time I'll try a small drogue chute to stabilize things on descent. I didn't have a decent chute to use so I just split the airframe. After the main fired things settled down and we lost the signal as it touched down. The signal is only good for line off sight coverage at 1.5 watts. The whole flight had P5 (perfect) coverage even during the violent descent, no nulls in the signal at all.
The second flight showed P5 video on the boost until the drogue charge fired. At this point the booster started tumbling/spinning violently and I could see the nylon strap connecting the sections wrapping around the booster and pulling off many times during the descent. This must have been what stripped half the antenna. With the one element missing there were distinct nulls to P3 as the booster spun and tumbled. After the main fired and things stabilized we had P4 video until it touched down.
One last comment. There were concerns that RF from the transmitter might lock up the CPU on the Black Sky Altacc that fired the ejection charges. I had the Altacc mounted in a payload bay 2 feet away from the bay the transmitter and antennas were mounted in. I did not shield the Altacc or do anything special. I did not shield the transmitter either because I felt it was useless to shield a transmitter that had an antenna radiating from the same bay anyways. I would NOT do this with the transmitter and the deployment avionics in the same bay! If anyone is building a similar package be sure to take appropriate precautions that the RF doesn't interfere with any avionics on board.
All in all I felt the two launches went extremely well. There are small things to address before next time, like video levels and rail button placement, but I didn't need a shovel to recover it and the video was just an extra bonus. The whole project took me 3 weeks from start to finish, but I had numerous days off of work to build and I know ATV and electronics quite well. I've been tinkering with ATV and GPS and video overlay for around 5 years now and wrote a tech article for a magazine a few years back on how to put together this same package for other uses. This is just the first time I had ever tried putting it in a rocket.
-Mike McCarty firstname.lastname@example.org