BrianZ

Hey all, I finished building my 2.4GHz circuit board for controlling Power Functions motors and servos with a hobby RC transmitter. It turned out as well as I hoped, giving full proportial speed control, all 7 servo positions on either side of 0 degrees, and the servo snaps back to center, just like you would expect it to when you let go of the steering wheel. You can drive two motors, or two servos, or one of each. It fits in a 4x6 stud area, 3 bricks tall. If I used a shorter voltage regulator I could have gotten it down to 2 bricks tall, so not much bigger than the IR receiver. I posted my bill of materials, the PCB etching art, and the microcontroller program on my blog so that anybody with basic electronics skills can build their own. There's also pictures of the process and a video of the final product. Here's the link: http://brianzawesome...ions-radio.html I have wanted to have radio controlled LEGO cars since I was a little kid, and now I can. I have also wanted to document a project on the internet for a while too, so I'm pretty pumped on both counts. Brian Z

I just wanted to post an update on my LEGO radio controlled system progress. I built a working circuit, and now I have full proportional control over 2 motors at a time. The servo still has just 7 postions on each side though, but I can't help that yet. I have designed and etched a printed circuit board and I have it drilled. Tonight I hope to populate the board and solder the the components, and have a test. The whole circuit fits in less than a 4x6 stud space, and just a hair more than 2 bricks tall. I think I can make it shorter on a future revsion too. When it's finished and tested I'll post a full schematic, parts list, and pcb design for easy do-it-yourself LEGO radio controlled fun.

I am currently working on a brick to replace the IR receiver, which will accept 2.4GHz hobby radio controlled signals. Here is how it's going to work. I am going to de-case a HobbyKing 3 channel RC receiver and use that to accept the signals. It is very small when it is de-cased. I am also going to build a circuit board that will translate the hobby servo signals being output from the radio receiver into pulse width modulation signals identical to the output of the Lego infrared receiver. The chip that is going to do that job is a Picaxe 14M2, which costs $4. This is a programmable microcontroller that uses the BASIC computer language, which is the only programming language I know. I am going to use the PULSEIN command on two pins to measure the length of the RC pulses, which normally tells the servos what position to go to. Then, the Picaxe will do a little formula to translate that signal into the pulse width modulation signal. The Picaxe can only output about 10 milliamps though, which is barely enough to light an LED, so I am going to amplify the PWM signals through an H-bridge motor driver chip, the SN754410. This can drive 2 motors, and costs $2.35. However this H bridge chip can only output 1 amp per motor, so that's not going to be enough for the XL motor at stall. I may stack another SN754410 right on top of the other one and get 2 amp output. My circuit board will also have a 5 volt voltage regulator on it for powering the Picaxe and RC receiver. At this point I plan on sticking with the standard Lego battery holders, motors, and servo, so my connections to the battery box and motors will be from cut-up lego extension wires stuck to the top of the brick I encase this in. The final size should be about 1" x 1.5" x 2 bricks tall. I expect to be finished by the end of Janurary, and I plan on documenting the entire project so anybody can easily build it. I really wish Futaba or somebody would build servo cases, RC receivers, battery holders, and motor housings with Lego connections. I feel like there is a lot of potential here, but the Power Functions infrared system just sucks for controlling cars. Brian Z