Panoramic image created from a Vidroc flight. Note the booster ejecting the parachute on the right
Getting Started in Video Rocketry
(originally published in Sport Rocketry Magazine)
by Jamie Clay
Some of us who've been around since color TV was a novelty no doubt remember the debut of the Estes Cineroc movie camera that would fly atop a 2 stage Omega booster. This was THE payload to fly back then (and is quite the collector's item now). It required the "large" Estes D13 engines to push it hundreds of feet into the sky.
The film footage gave us a pilot's view of the launch, staging and recovery; the next best thing to actually being in there. The down side of this system was it required a Super 8mm projector (or hand viewer), special film cartridges, custom processing and, of course, patience while you waited for the developed film to return in the mail. And that was all contingent on having a successful flight to begin with -- but the end result was SO worth it. I remember studying every frame of that first flight, to the point that I actually wore out sprockets on a few of the frames.
Flash forward to now. 8mm film pretty much relegated to use by collectors, film students and Cinerocs have been out of production for almost 30 years. Even if you do pick one up on Ebay (for $150 plus), you better plan on loading the cartridges and film processing "by hand". No small task, especially for the weekend hobbyist. Then, after all that, you still don't have the sound from the rocket. What to do? Enter Video Rocketry.
Video Rocketry has been around for some time, but until recently it cost hundreds of dollars and required building a rocket large enough to carry a full video camcorder aloft. Also, to launch a rocket of that size usually required you to get at least a Level 2 certification. On top of all this, you risked losing the camcorder if things don't go as planned during the flight.
Luckily, recent developments in low-cost consumer electronics have opened up the possibilities to anyone looking to capture that view from above. All you need to do is choose what system is right for you. It really comes down to your budget and flying field, but without a doubt it has become much easier for you to build and fly your own Vidroc (Video Rocket).
The two types of Vidroc systems are downlink and onboard capture. Downlink involves transmitting the video signal back down to a receiver on the ground where you record it to a Camcorder or VCR. Onboard capture used to mean the "flying camcorder" approach, but recently, small digital video capture devices have become available that reduce the size and weight to an affordable range. The biggest limitation of this system is the frame rate, usually about 1/3 that of a downlink system.
Onboard Capture System
The Digital Movie Creator camcorder by Intel is just under $100.00. All the video (320 x 240 @12 fps) is stored in onboard memory and downloaded to a computer via a USB port once you've recovered the rocket. As of this writing the Intel system is the only one that provides onboard capture video worthy of comparing to the results of the Cineroc or a downlink system. Yes, I've looked at the small "pen" digital video cameras, but they pale in comparison. Currently the biggest drawbacks to using this system are its shape and weight and, if you suffer from a power failure, all the footage is lost. Also, if you want to fly it more than once when out at the launch field, you'll need a laptop with a USB port.
The Movie Creator is so efficiently built (to hold up to the abuse of young hands) that it doesn't lend itself well to a lot of modification. However, I was able to trim about three ounces off the total weight by removing the housing. I also had to refit it with a single 9 volt battery as the four AAA batteries would always lose contact and delete the footage before it could be downloaded to the computer.
Images from Vidroc Eye using Intel's Digital Movie Creator
For less than $100.00, you can purchase a wireless 2.4GHz video system that will transmit video and audio back to the ground for recording. Several companies sell a suitable downlink system -- X10's XCam (www.X10.com), Spy Eagle's SpyCam (www.SpyEagle.com), Plantraco's Color ATV and RF-Video.com, to name a few.
One of the most common questions that I get asked is "The manufacturer says this system only has a 100' range, how are you getting more?" The simple answer is the manufacturer has underestimated the range because most folks will use it in a household and encounter obstacles to the signal (such as walls.) When flown in a model rocket you have the best possible unobstructed line of site and if all goes well you can get about 1300' from the stock antennas (but the signal is just borderline at that point).
I've installed the XCam into everything from a C6-3 powered Egglofter to my Level 1 certification rocket. It's best suited for a rocket and motor combination that will send it up no higher than 800' with the stock antennas.
Choosing a rocket: Because the resulting system is so small and light (under 4 oz total), there are about as many ways to mount this in a rocket as you can think of. If you want to use a commercially available kit, consider any of the Estes BT-80 tube rockets, like the Fat boy or Big Daddy. The nose cone has TONS of room and the antenna is easy to mount in the correct position. I should mention that the Vidroc 1 design wasn't specifically designed for Vidroc usage, it was just what I had already built when I first tested this system.
Prepping the XCam: Because for most model rocketry purposes weight is an issue, you need to strip the 2.4GHz video system of all unnecessary plastic, being cautious not to pull wires from the circuitry. You'll find you can easily do the task with a Phillips head screw driver, razor knife and a pair of diagonal cutters. Once you have that done, take the time to note what color wires go where -- take pictures, draw diagrams -- just be sure to document their locations. Trust me (and if you DO forget to make diagrams, I have them on my website).
Powering the XCam: This minor task is actually one of the more challenging aspects of this project. Most small 2.4GHz video systems say they run from a "12 volt" power supply. In reality, 12 volts is the voltage under load, but the supplied power needs to be between 20 and 28 volts. Finding 24 volts that are light enough to fly in a small rocket wasn't that easy. After experimenting with a number of battery configurations, I found that DUAL A23 12volt batteries (in series) will power the camera for a good 5 minutes, which is much longer than most flights last.
Another option is to find a compact DC-DC power converter to increase the output voltage from a standard 9volt battery to 20 volts. This is a few ounces heavier than the dual A23s, but it will keep the camera powered up for a good 15 to 20 minutes, making the launch a little less rushed.
If you're using the dual A23 powered system, you'll want to always fly with fresh batteries. I've tried to get two flights out of a pack and have been very disappointed with the results. They'll run about $3.50 a pair at most of the *Mart stores. I have used the old ones for testing purposes but once they're drained below 10 volts, the only thing they're good for is altimeter duty.
If you go with a toggle switch to activate your Vidroc, you should consider taping the switch in the off position until you load it onto the pad. This will prevent accidental activation that will take life off your batteries.
Wiring the XCam: I prefer to use plugs between components as it makes it easier to test-mount the components in the payload section. When you do solder the connections make sure to insulate any exposed wires with either electrical tape or heat shrink tubing.
Most local electronics shops have small plugs that will work and while you're there pick up some spare color-coded wire and a micro switch. You may need extra wire (I did) to give you more flexibility in your installation, and the micro switch allows you to power-off the camera until ready for flight. I've also used micro plugs and jacks where the jack, when inserted, turns off the power supply. This makes it a little harder to accidentally activate the camera.
Mounting the electronics: To make it easy to install and secure the electronics (and to offer a layer of cushioning), I've come to use a soft sticky putty, like DAP "Fun-Tak". It gives you the opportunity to trial-fit all the components, align the camera's view angle, and to easily remove everything in the event you need to make changes (or repairs) to your system.
Another design issue you need to address is how the batteries are secured. For example, if you mount the battery holder perpendicular to the ground, at launch the weight of the batteries will compress the spring holding it in and cause a brief power loss. It's best to mount the batteries parallel to the launch G forces, but if you can't, be sure to put some sort of removable putty into the springs to prevent them from collapsing.
The antenna(s): These systems use a flat "patch" antenna that has a directional beam (or cone). Because of this, the antenna becomes an important consideration when designing your rocket.
This directional cone emanates from the front and back planes of the antenna. Once the rocket gets farther away, you need to keep the (ground) receiver's antenna pointing towards the rocket's antenna or you will experience signal loss. The best solution to this is to align the rocket's antenna perpendicular to the length of the rocket (parallel with the ground) and to have the receiver's antenna as close to the launcher as possible.
Replacing the stock transmitter antenna with a Dipole or Ground Plane antenna tends to make it easier to fit into smaller spaces, but in my tests both designs have reduced the signal range considerably.
If you have the money (another $100 or so), replacing the receiver's antenna with a high gain antenna will significantly improve the range of your system.
Positioning the camera: There are two classic methods: looking directly down or looking directly out to a mirror angled to reflect the view down "Cineroc style". Because the camera is so small, the amount of shroud you need for it is about the same as for a mirror capable of reflecting the image. I've found a 1/2" square mirror (usually found at arts and craft stores) covers the FOV (field of vision) of the standard camera lens nicely, but if your wireless system is using a wide angle lens, you'll have to mount it looking directly down. The size of mirror you would need to reflect the wide angle view is a bit too large for smaller rockets.
I should mention that you can also have the camera look directly out (without the mirror), but it's not as exciting as seeing the launch plume billow as the ground pulls away, plus if your rocket spins (and most do) the footage often isn't as interesting.
Ground Support: With a downlink system, you'll need a video recording device on the ground. The easiest method is to use a standard Camcorder hooked up to the output of the 2.4GHz receiver. Most camcorders have RCA video jacks that allow you to feed in an external video signal. With this, you can also monitor the flight in real time via any method the Camcorder provides. Other ways to record the flight include a battery powered VCR/TV or a laptop with video capture tools.
The XCam 2.4GHz receiver needs 12 volts just like the camera, so you need to either power it from batteries you bring to the launch site or via your car (if it's parked that close). I picked up a small, contained rechargeable 12 volt lead acid battery and it works great.
One key thing to always remember is to activate the recording function before you launch. One time (in my haste to launch a new system) I forgot this obvious step. Unfortunately that rocket crashed. The beauty of flying wireless video is that even if the rocket CATOs or crashes, you still get footage (as long as the VCR is recording).
You should organize a ground crew as you'll need someone to activate the camera, verify signal to the camcorder/tape deck and possibly track the rocket with the receiver's antenna.
Usually the same person that's verifying the signal can do the tracking. If you're flying a smaller Vidroc with maybe a C or D engine, you may not need to worry about tracking the flight with the receiver, but you'll find you can improve the signal if you keep it pointed at the rocket during recovery. When tracking, think of the antenna as being the base of a flashlight cone, and as best as you can, you want to keep it pointed at the rocket. If you can monitor the flight from the recording device, you can use that to verify that you're on target.
3...2...1...LAUNCH. <rewind> <play> and watch it again!!!
What's next? While it's fun to watch the footage on your TV, it becomes more interesting to digitize it into a media format that can be played frame by frame on your computer. There are a jillion ways to accomplish this, so the next best step would be to join the Vidroc email list and simply ask what the latest techniques are.
Various pictures from the article
Images from Vidroc 3 using XCam downlink system
More images from Vidroc 3 using XCam downlink system
Images from Vidroc 5 using XCam downlink system.