Corky'z Robotz

Sometimes you feel like a nut, sometimes a bolt

Here's a little robot I built, mostly from "junk box" parts. (all right, the BASIC STAMP isn't junk, but I got one a while back to mess with, and it was just waiting around for another project). It kind of looks like a mutant toy from "Toy Story". It is remotely controlled by an ordinary TV remote.It can move forward and reverse, and turn in either direction. Its head can turn independantly, and LED eyes turned on and off. And it can beep, buzz, and play a little tune. All by remote control.

If you prefer to buy all the stuff to build the robot, the cost would be around $100. See the parts list below.

There are several interesting innovations here that I would like to share with the world. The main chassis is made from a sheet of plastic I had, about 3 by 5 inches. Or you could use wood, metal, foamcore, or whatever. Everything is stuck together with double stick foam tape and rubber bands.

I used wheels from a cheap Lego set, and also stuck on the little guy from the same set for esthetics. I got a doll head from a craft shop and poked out its eyes and installed LEDs. A drawer knob is used for the front skid. I run a TV fixit shop, and one of the things we fix is satellite dishes. The big dishes (not the little DBS jobs) use a device called a polarotor, which is in fact a model RC servo, so I had a few kicking around. I saved bad ones when I replaced one (because it looked too good to throw away) and later realized the wisdom in doing so. Often, the electronics inside a servo will fail (surge, improper hookup, etc.) but the motor is OK. So open it up, remove the circuit board, and bring out the motor leads. Also remove the feedback pot and the stop which prevents the output shaft from turning all the way around. Presto! A nice little gear motor. I use two of these for the drive wheels. Another (functional) servo turns the head.
If you don't have any defective servos, an alternative (cheaper than chopping up new servos) would be to use Mondotronics' dual gear motor. I haven't seen one yet, but it looks like it would do the job for the drive wheels at only $15.

Since I removed the electronics from the wheel servos, I needed something to drive the motors. Usually, a circuit called an H bridge is used to give forward/reverse control. They are not complicated, but wiring one from scratch is a pain. There are special ICs designed to do the job, but those are a little hard to find. Or you can buy a kit, but those are kind of pricey. I discovered an IC, available at Radio Shack for less than $2.00 which does the job with only a single external resistor. The shack also has cheap pre-etched proto-boards which can hold two of these ICs to contol both wheels. So what is this miracle chip? It's a 556, the dual version of the famous 555 timer. Timer, you say? Yes, but I'm not using it as such. The important part is the pull-up/pull-down drivers which can source or sink about 300 mA. The motor is connected to two outputs, and if one is driven high, the motor runs in one direction. Drive the other one high, the motor reverses. Drive neither (or both) and it stops. See schematic for details. The resistor sets the input threshold to about 2 volts so that a cmos output (from a Stamp, or whatever) will switch the outputs. The value depends on what the drive (motor) voltage is, and how many threshold pins are connected.

Power for the motors comes from 4 AA cells. The H bridges can handle higher voltages but I stuck with 6 volts to stay compatable with the head servo. The stamp runs from a separate 9 volt battery.

The next part is the remote receiver. I got mine out of a dead vcr, but they can be purchased new from Radio Shack for a few bucks. It connects to 5 volts, ground, and a Stamp pin. The stamp is able (BARELY) to decode signals from a TV remote control.

I bought a universal remote control by ONE FOR ALL for about $10, batteries included. The unit I bought has the channel and volume keys arranged like a cursor keys. Perfect for steering. There is also a second cursor-like pad in the vcr section. I programmed the remote to transmit Sony codes, both in the TV and vcr modes. I use the Sony codes for two reasons: they are standardized and virtually all universal remotes have them, and they are relatively easy to decode. I wired a piezo beeper to a Stamp pin, and 2 LED "eyes" (through a resistor) to another.

Let's see... two pins output per H bridge times two motors, an output pin each for the head servo, LED eyes, and the beeper. And an input pin from the IR receiver. Eight pins. That does it! And the program uses just about all the available program memory in the Stamp. (How much are the Stamp 2s going for? Hmmm...) Well, it's a lot of fun for something made out of junk, and pretty amazing what one can do within the limitations of the Stamp 1.

OOPS! If you downloaded the schematic before August 25, 1997, the pins to the stamp are numbered backwards. The current schematic is correct.

View Schematic Diagram
View BASIC program
Click here for info on using Stamp and Sony IR remotes
Parts List

STAMP	$34	DigiKey
Wheel Motors	$15	Mondotronics
Servo	$15	hobby shop
Remote	$10	WalMart
Wheels from Lego set	$4	WalMart
Skid (furtiture knob)	$2	hardware store
Base (scrap wood, plastic, etc.)	free
556 (2)	$3.18	Radio Shack
Resistors (3)	$.98	Radio Shack
Caps (2)	$.98	Radio Shack
LED's (2)	$.99	Radio Shack
IR Receiver	$3.59	Radio Shack
Piezo Speaker	$1.49	Radio Shack
Head	$1	craft shop
Battery holder	$1.39	Radio Shack
Battery Snaps	$1.39	Radio Shack
16 pin Sockets	$.99	Radio Shack
Batteries	$5
Circuit board	$1.49	Radio Shack
Double stick foam tape, rubber bands, hot glue, etc.	free	Look in your junk drawer!
Stamp programming package	free	download from Parallax