As part of “the creepy box” project, which I’ve now decided to call “Boxie the Creepster”, I needed to control a couple LED lights with a RC helicopter remote control. These lights would go inside a ping-pong ball and form light-up “eyes” of some kind. These LEDs did a good job of evenly lighting the ping-pong balls for a creepy effect. Additionally, I made the eyes move back and forth. I’ll go over that as well. Here’s a video of “Boxie” in action with eyes that are able to change color:
The helicopter controller that I had available had four channels, two of which controlled servos, two controlled “normal” DC motors. I used one of the servos to move the eyes and both of the Motor outputs to control the color of the eyes. Originally I was thinking about using one of the motors to actually spin the box around, but that’s on the back burner for now.
The first part of this post is how I got the LEDs working with the “motor” output from my RC helicopter controller. After poking around with a voltmeter, the top voltage that the controller put out was around 8VDC. LEDs can’t generally be hooked directly into your voltage source as they will burn themselves out. The solution is to use a resistor as a voltage divider so that some portion of the voltage is taken up in the resistor while some goes to the LED. It’s not that hard to calculate, but if you’re lazy, “ledcalc.com” is a pretty good resource.
I put these LEDs in series as shown to the right. The red wire goes to positive, through the 270 Ohm resistor, through one led and then the other and then back to the power supply ground. On LEDs, the long lead is the anode or side that needs to be hooked up to the positive leg of the circuit. Reverse these and you won’t get any light. These Red LEDs are hooked up to one motor control output.
The other output I hooked up in a similar fashion to green LEDs. The resistor values are different (180 Ohm) as all color LEDs have different ratings. Since both motors can be controlled independently (sort of, the tail speed is somewhat tied to the main rotor), one is able to change the color of the eyes as the situation dictates.
Once these LEDs are inserted into each of the eyes, you’ve got a great glowing effect. After coloring in the middle of the eyes with a blue marker, it really made the movement of the eyes pop.
As for making the eyes move, I used one of the servos linked together as shown below to make both eyes move in unison. 4-40 threaded rod was used to link everything together with ball joints.
Originally, I used a screw only through the bottom of the ping-pong ball, but as can be seen in the video here, the eyes tend to wobble around instead of moving left or right. The frame in between the balls and the servo helped align things some, but what finally fixed things somewhat was putting a nail all the way through the balls. This acted as a central axis and kept things from wobbling so much.
One thing I plan to do is cut the ball linkages and move them closer to the “eyes.” This should make the eyes rotate further as it will reduce the distance from the linkage connection point to the central axis. Also, a longer servo horn would help, so maybe I’ll look into that. I’ve used Servocity.com for servos, horns, and other stuff like that, so they might be worth a look.
The final thing that you may be wondering is, “how was the Ping-Pong ball cut?” Yes, it is a difficult thing to cut a ping pong ball with a drill or drill press without the correct fixturing. Fortunately, I’d developed something to help me drill golf balls for another project, and by using a smaller hole saw (1 1/2″), I easily made another fixture for this situation.
*Post updated 5/30/2011
And finally, for no reason, here is a picture of “Tom Servo”, a robot from Mystery Science Theater 3000 next to an ad which you may or may not want to click on.
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