Lego RCX

[MattK]

Does anyone know how to amplify the signal from a Lego RCX?

[Brant Bowen]

It's been a while, but i do think i remember there being a switch in the bottom front of the transmitter that adjusted between a short distance and a long distance signal, and i remember the long distance going quite far, or do you want it longer than that?

[kmcclary]

Originally posted by MattK
Does anyone know how to amplify the signal from a Lego RCX?

IF by that you mean "can you amplify the RCX motor outputs for higher current motors", the answer is YES.

As a group project, we at my local (adult) robotics club have just designed and tested a CHEAP optoisolated MOSFET H-bridge RCX "motor amplifier" circuit. It allows us to use a vanilla RCX and an external power supply to drive FIRST kit motors at something like up to 40A and 24V without breaking a sweat via their LEGO motor outputs. You simply use the standard LEGO motor commands. If there's demand I can easily scale the circuit up for more current.

We're in the "running breadboard" stage now. Works great! We just ran some Globe Gearmotors off of it at 24V at our last meeting. It draws virtually nothing from the RCX batteries, but because it's optoisolated we still plan to add a simple voltage regulator to power the RCX from the bot's main motor battery.

Later this fall, after deciding on a few form factors, we'll create a PCB to mass produce amplifiers for the "base" configuration.

Once the PCB is made, I'm sure our team will be happy to sell the Motor Drivers in kit form to other teams (or individuals) as a fundraiser, for anyone that wants to turn RCX bricks and spare kit motors (or discarded kid's jeeps) into some awesome "Super Sized Mindstorm" machines.

One big decision yet is the configuration... An RCX handles up to three motors. Should we go with one, two, or three motor channels per PCB? (We're leaning toward a "breakaway" board right now. Snap off however many channels you wish.) Should we include an RCX power supply on the same PCB to power the brick off the motor's battery?

BTW, we're designing a set of Motor Drivers to facilitate an off season contest that may involve autonomous FP kid's jeeps. We intend to inexpensively support driving kit motors from RCX bricks, PICs, Basic Stamps, or other CPU of your choice, so if THIS MD isn't to your liking, we'll soon have others to choose from. (More on that later.)

Is this RCX Motor Driver what you're looking for?

What's a reasonable price point for a one channel RCX motor driver of these specs? How about a three channel RCX high current Motor Driver including a built in brick PS?

- Keith