And Then Some by Joe Tuffts

And then some, is constructed from parts I got from two 
disabled Power Wheels Jeeps. The control system is based on a
Direct Logic Dl05 plc and a 4 channel Futaba fm radio. 
ATS has the abillity to record and replay the radio commands given
it. So you can develop driving patterns and watch as the 
robot seems to act on it's own.

It has four independantly driven gear motors (pictures shown 
as two wheel drive) and uses tank style steering. Speed
control was cost prohibitive so I simply mounted limit switchs 
to radio controled servor motors to give the plc the
directional inputs. 

Functions:
Radio Remote Control
Run pattern play back
Heavy pay load capability (75 lbs appox)

Parts:
CPU- Direct Logic DL05 PLC
Two 6 vdc gel cell batteries
Two Futaba 3003 servo motors
Four SPDT limit switches
Drive gear motors from two Power Wheels Jeeps.
Four Additional heavy current rated output relays 

Problems:
Output current to motors was more than the DL05 built in relays 
could handle, had to add additional output relays. ON or
Off tank style steering (no speed control) is jerky and a little 
hard to control at first, but it did get us up and
running very cheaply.

Cost:
Have $55 into used PW cars and around $10 into the limit switches. 
The rest of the stuff I scrapped out from old control panels.

just getting started on a web site but you cantake a look at 

Web site:
http://www.torchlake.com/robots

Email: ROBOTS@TORCHLAKE.COM