Ever want to create those Star Wars type effects? The rock solid video, you will remember, is because the model was stationary, and the camera moved. When played back, the model appears to be moving, smoothly. A camera dolly can be used for all types of special effects, or interesting camera angles. The finished "dolly" uses a standard tripod receiver, so any camera with a 1/4" tripod adapter hole can be used. And we show a quick and dirty modification, so you can even use your smart phone.
We will also build our own motor control circuit, so the MicroController will not have to power the motors that move the camera dolly. One 9v powers the Parallax Homework Board, and (4) AA batteries power the dolly itself. So when we call the pin, pin 2 in our case, we will only be "connecting or closing the ground wire" to send the (4) AA batteries' power to the Camera Dolly Motors. If that sounds confusing, it will make sense as we work on the circuit.
In summary, the focus of this Instructable, will be on the motor control circuit, the three or four lines of program code, and mounting the camera.
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Step 1: The Camera Dolly Base
Many different bases can be utilized, and this is the least important part of this Instructable. We used a 4 DC motor robot chassis, but you could even convert that old R/C car with a little hacking. You will notice in the picture, we added a small bread board, and a battery pack, again (4) AA. This chassis had red and black wires, we plugged all the red wires into the left of the bread board, and all the black into the right. Now apply power and make sure all the wheels turn the same direction. We had to reverse the leads of one motor, to have it turn like the others. In summary, when you complete this step, you will have a chassis that moves in one direction when powered up.
Step 2: Mounting the Micro Controller and Tripod Receiver
My robot platform, had a second plexiglass level, so I mounted the Micro Controller, to it. So in this step, mount your Controller. I actually used a couple of dabs of hot glue, because I wanted to be able to retrieve the controller when not in use for some other project. Couple of screws will accomplish the same thing. Grab an old tripod, and remove the "receiver", look for a pin and use a punch to carefully drive it out. Drill holes for 3/16" screws, about 3/8in each side of center. This will keep the screws close to center, as shown in the picture, to make sure the camera will engage. I used long sheet metal screws, and adjusted the receiver somewhat level using nuts and washers, which you can see in the third picture. The camera piece is hollow. Your project should now look like the picture on the far right, Micro Controller and Tripod Receiver secure.
Step 3: Building the Motor Controller Circuit
First, why a Motor Controller Circuit? The Parallax Homework Board, is a noble piece of equipment, built for noble purposes. Controlling stuff. Turning a motor on and off, or in this case 4 motors on and off, we want to use more common equipment. We could use a relay, or I chose a large transistor. Besides, applying this principle, we can learn to control much larger loads than a Micro Controller can handle. And then we reserve the Micro Controller to do all the complex stuff, like wishing you Happy Birthday with blinking LED lights while at the same time performing complex mathematical calculations for who knows what purpose. Make sense?
Electrical engineers, please comment on the following. I chose to use a large TIP3055 transistor, about 2 bucks, which actually has a 5v emitter base voltage, so the Homework Board cannot produce enough power off pinP0 through pin 15 to harm the transistor, and that eliminates the need for a resister between the pin and the transistor. You probably should install a diode to protect the Homework Board, but the function of a Camera Dolly is short run times. 2-3 seconds usually. So I chose not to install one at this time. Anyway, if I broke any Electronic Engineer Protocols, let me know, but it works great.
A close look at the picture, I connected PIN 2 (my choice) to the Base of the Transistor (pin designation 1 on the transistor). The AA battery pack, we run + wire to one side of the breadboard on the chassis. The - wire on the battery pack goes to Transistor Pin 3 (Emitter). A jumper wire goes from Pin 3 (Emitter) to Vss (ground on the board of education). Going back to the breadboard on the motors, we take the ground wire (remember we hooked the + pole of the motors to the AA battery pack), we take that remaining motor wire and run it up to Transistor Pin 2 (Collector). This is much easier to do than say, but essentially, when we energize the transistor in our program, it takes what was an open ground, and closes it. Like the black ground wire is cut, and we reconnect it, only using the transistor rather than scissors :) I will add a schematic, to help clarify the above scenario. We chose only to run the motor in one direction, that is usually the role of a camera dolly. A second transistor circuit, and we can easily reverse the motors (you can see two wires left loose at the rear of the dolly, which we can employ to reverse the motor direction if necessary, calling on Pin3 let's say.
Step 4: The Program
Now the embarrassing part. Anyone can write this program. Lets think about some basics before we look at why the program was so simple. Studying movies, as an armchair videographer, I once dissected the entire Star Wars Film. What do I mean. It occurred to me that Star Wars was really a slide show, a collection of very short clips. What I did, I timed each scene in the entire movie (boring or what). I count a scene as no camera movement. There are several pans, which I did not "time", but the overwhelming majority of the film are very short clips. How short? Going from memory, 90% of the clips were 1 second long or shorter! Some 5% were 2-3 seconds long, and 5% were longer than 3 seconds. If I recall correctly, the longest scene was 5 seconds. Again there are several pans. like the moisture evaporator pan which might be 6 or 7 seconds long. Try just timing a few scenes in the next action movie you see, we have very short attention spans, I guess, and they have to keep it coming to keep our interest.
So action videos, the action scenes are a collection of very short clips. Or it gets real boring really fast. So we programmed our camera dolly to move forward 1.5 seconds (about 3 feet)
When you plug in the battery, the motors run one cycle (1.5 sec). When ready to film, start the camera and press the small green button on the homework board and the program executes, moving the dolly forward 1.5 sec. Congratulations, you shot your first scene. You did remember to set up your model, didn't you?
Step 5: Bill of Materials
I built this Dolly with stuff laying around, so be creative. But here is my Bill Of Material
1. Microcontroller with 9v battery holder, http://www.parallax.com/product/555-28188
2. Robot base, not exactly what I had, but includes battery pack.
3. Small bread board for connecting motor wires
4. Old tripod receiver
5. (4) AA battery holder
6. Radio Shack TIP3055 transistor
7. Extra 22g wire
8. (2) 9v battery clips Radio Shack 270-0326 for cell phone holder
Step 6: Smart Phone Clip
Because of the nature of filming a small model, for that task it is hard to beat a smart phone for this camera dolly application. So without becoming an instructable in itself, we screwed two 9v battery clips to a piece of aluminum 5 3/4 " long. In the center we drilled a 1/4" hole. Screw the tripod camera base, onto a 1/4" x 1 1/2" barrel nut. Secure the aluminum cross piece with a 1/4" machine screw and lock nut. Snap the assembly into the camera dolly. Get your shot ready, then turn on the video recording of the smart phone, put the phone horizontally into the clips, and press the green button on the Homework Board. You create 1.5 seconds of rock solid motion for that alien space ship you are filming. There are tons of Youtube videos on setting up a white background, or green for those chroma shots (replacing the green with a background of the Martian landscape for instance).
Have fun with that new movie creation! Check out our website under construction; www.dronelasertagacademy.com
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