Get a CPU that is easy to use and can be in-circuit programmed. Having to take your 'bot apart to reprogram is a real pain in the rear. I have played with different kinds of PICs, 8051 variants, and have lately become attached to the 68HC11. Specifically the CPU_1A1 from PMB. It has 32k of RAM,128k of Flash, programs through the serial port and only costs about $34.50 . The 6811 itself is widely used in the hobby robotics community. There are numerous web sites with info on hardware, programming, free compilers and examples. My favorite is SBASIC by Karl Lunt and the PFE IDE to go with it. If you decide to go this way, drop me a line and I'll give you some hints on how to set up the IDE and SBASIC for the 'F1 variant used on the CPU_1A1.

Lately I have started using the AVR microcontrollers from Atmel, mostly the ATMega163 and ATMega128. These have 32k or 128k of flash, are in system programmable and you can get gcc (a free c-compiler) from AVR Freaks.

Find some good, surplus rechargeable batteries. Unless you have a source of free alkalines, batteries can become a large portion of your 'bots budget. At $10 for 8 AA's this can add up fast. A buddy and I went in on 25 each of these 7.4V 1350mAh Li-ion batteries for $2 each. With another $9 for three chargers I spent $59 and will never need another 'bot battery again. The small 'bots I build should run for about 4-6 hours AT FULL SPEED from one of these batteries. Even longer under normal stop and go usage.

Alternatively, try the rechargeable Lipo's from Bishop Power Products.

Places to try for surplus rechargeable batteries are All Electronics, Alltronics, Electronics Goldmine, and HSC.

 

Build an easy to use TTL to RS232 adapter. Nothing helps debug a 'bot faster than to be able to ask it what's going on. SBASIC has the good old PRINT statement that can be liberally sprinkled through a program during development to trace execution.

The adapter I show here is a MAX3221 single chip converter housed in a standard DB9 shell. On the other end is a 4 conductor RJ11 connector like you'll see on a phone. The 'bot sends power through the outer two wires to supply the converter chip, and data passes on the inner two wires. With another RJ11 jack on the robot, just wire up +5V, GND, TX and RX and <click> you can speak with your robot through Hyperterminal on any Windows PC, or from QBASIC on a DOS machine.

Get a couple of cheap hobby servos and some wheels at your local hobby store, Budget Robotics or Servo City. Modify them, and if you have a 6811 or AVR you can have a moving bot in about 10 lines of code.

 

Motors for robots WILL need to be geared down in some way or another. I have been happy with the motors that I got from Macintosh floppy disk drives. You can power them with an L293 IC.

The most important tip is to BUILD SOMETHING and PLAY WITH IT. You will find that after you have a few quick weekend robot projects under your belt, the larger projects will be MUCH easier. You will have a better idea of what sensors you will need, what kind of wheels work, how much room everything will need on the chassis, etc.

Don't be afraid to use double sided sticky tape and hot glue. A $1.99 hot glue gun can be your best friend. I delayed my entry into hobby robotics by over a year because I kept telling myself  "I'm not going to use hot glue, I'll design it right and machine everything. It will look professional." It didn't look like anything because I never got anywhere. Now I bang out a new design like Rolie Polie Olie in about three weekends