Ellen, sorry for the late reply but I've been busy and it's been hard to
keep up here... Dan and I kind of started at the same time and compared many
notes here in this forum. Please check the archives for the subject line
beginning with "PIC Robot Update" for more info on my current efforts.

   I started with a RadioShack R/C car and the first problem I encountered
was the gear ratio as Dan has mentioned. That, and the mechanical `slop'
in the gears. While they do have a tank model, I had a racing car...

   It's important to define what you want your robot to do. In my case, I
wanted a technology `test-bed' to try a variety of sensors. It was to be
confined to roaming rooms in my house. Going into this, I realized I wanted
a dual drive so I can basically turn in small spaces. I thought a about
using treads but cat hairs on the carpet would have been a problem. Since I
already had this RS car, and it only had rear wheel drive and front wheel
steering, I thought I would experiment with motor control and a basic bumper
switch. The turning radius was about 2ft... After wasting way too much time
analyzing the RC car's receiver and `crude' H-Bridge, I designed my own
motor driver and interface. While this worked well, there was still a
problem with a high speed motor and low-torque gears. I tried several
combinations of PWM frequency and duty cycle but it was not really what I
was looking for. However, I did manage to add bumper switches and it was
able to climb around the thick-braided carpets in my house. Overall, it
was good experience.

   They do have a tank model and someone else mentioned Tower Hobbies for
more expensive vehicles with a low gear ratio, but I strongly suggest taking
a hard look at doing it from scratch. Tamiya makes an excellent series of
gear boxes that are normally used in a lot of the R/C models and toys that
you see. I ended up using their Worm Gear Box HE. It cost around $10.

   My current `bot' uses a dual drive Tamiya Worm Gear Box HE. with front
wheel drive and a castor wheel with bearings in the rear. It's built on a
9x6" aluminum base with a similar upper deck. So far, I've got a rather
fancy power management scheme that supplies the dual Tamiya motors, the CPU,
and the sensors. There are front bumper `whiskers' and IR sensors that look
left and right. I've been testing the Vector 2X Compass on a wooden platform
to eliminate stray fields. I expect to integrate that with the bot this
month. I'll be adding ultrasonic ranging, mounted on a standard RC servo to
build-up an acoustical description of the environment. I'm also looking at
light and sound sensors. I also have VoiceDirect364 which I have already
interface to a PIC but want to add to this project. Since I made good use of
the lower deck for motor control, power supplies, and the CPU, I have plenty
of room on the upper deck. BTW, my little bot is controlled by a 16F877 so
far but I may add a Lattice CPLD to expand the capability.

   - Tom

Ellen Spertus wrote:
>Has anyone adapted motorized toy cars to be controlled by a PIC or other
>microcontroller?  I'd welcome any pointers.

Dan Michaels wrote:
>Also, Tom Handley did it - and he may be lurking around about piclist
>somewheres. I think a major problem Tom found is that the basic off the
>shelf RC toy car runs a little too fast to make a good robot, and has
>to be geared down substantially.


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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