Young Noob wanting to start Hobby

Having actually converted an RC car, I'd recommend you try a simpler
project first. RC cars have a number of things that make them more
difficult to automate:
* The motors draw very high current, so you need to either buy
   expensive drivers or be clever about how you re-use the
   existing drive transistors (I did the latter).
* The motors tend to have a heavy magnetic detente - they "pulse"
   strongly, jumping between preferred positions when you turn them.
   That means you need to ramp up to above 50% before they start at
   all, then they take off like a rocket.
* The gearing is far too high.
* You need axle or drive-motor speed sensing to get around the
   previous issues. It's pretty hard to fit mechanically. I somehow
   found room inside the gear casing for a slotted wheel and photo-
   sensor, but I think I was lucky.
* Then you need some fancy programming to make the motor do what
   you want. PID control is the minimum, but the high starting current
   means you must modify the basic PID approach.

On the plus side, if you can find the interfaces between the receiver,
the decoder, and the motor drivers, you can hack in to make an RF
link from remote to your controller, while the controller drives
the car - pretty cool! I even fitted a connector with a "null modem"
plug that converts the car back to normal remote operation.


I used the MC68HC11 - get a flash-based micro instead. If you want
to write direct to the hardware (C or assembler rather than Basic
or Forth), an AVR is probably the best compromise. I like the MSP430
too, but you're more likely to need interface chips for drive and
level conversion. Some people like PICs or 8051's, but I can't
explain that except to say I think it's mostly nostalgia (ducks:-).


$10 gets you an MSP430 USB dongle *and* a decent little controller
chip, compiler etc, at the moment, see comp.lang.embedded for the
clues. Well worthwhile to learn embedded programming this way
before you start wiring other things to it and blowing things up.
Then have a play with hooking up an L293D motor driver chip to some
smaller motors and you'll be off and away in no time. Google for
the Miniboard schematic to see how to hook these up - but check
logic voltage levels if you go MSP430, they're not 5V like the 'HC11.

Clifford Heath.

I'm not sure what your objectives are, but I am working on a project that is
intended to create a working robotics platform for $500 or less. It uses
mostly stuff you either have lying around, can buy cheap, or find on the
road side on trash day.

http://www.linuxpcrobot.org

It isn't built on a race car, exactly, it is built on extruded aluminum
bolted together, with the axle and motors of a kids toy. IF you can find
these things, the only thing you need to buy is the electronics.

Like I said, I'm not sure what you are trying to build, but I hope it helps.

I really like this linuxpcrobot thing.
I've got a complete spare system here with a 27gig harddrive already
set up with gentoo linux.
All I need is the wireless ethernet card (so I can ssh the bot) some
batteries, and that vellman board (along with a wiring terminal)

Any more instructions for that robot though?
Basically, if I do this linuxpcrobot.. I need some assistance in
setting up the motors.
Or... I could put my lawnmowers engine on it and use a servo to
controlthe throttle......
But I think rechargeable batteries would be better in the house :p

You'll need a DC to DC power supply for the computer main board. You can
find those on the internet.

You'll need a PS/2 ball mouse. It HAS to be either PS/2 or RS-232, a USB
mouse connected to the USB port will not work because the USB HID interface
protocol differs from the PS/2/RS-232 and once the mouse realizes it is
connected via USB port, it uses the USB HID protocol.

The mouse issue is a mixed blessing. On one hand, it does free up USB
bandwidth for other things, but it does require an additional bus interface
in electrical terms as well as software.

No instructions, per se' but source code and some pictures.


Well, I'm always willing to put out some pointers. My feeling is that I
would like this to become more of a community sort of site where people,
through trial and error, post tips.

Like I said, the site was developed to show that a real working platform can
be created for less than $500, out of common parts, using a single tool
chain. (gcc, make, etc.)


You could do that, but you'd need two lawnmower engines each driving a
wheel. I'm not sure that the throttle response of the motors would lend
themselves to operate in this fashion, but, well, there you go. :-)


I'm pretty sure.

Well, I have a machine sitting here with 512 memory and a 27gig
harddrive. Gentoo can be installed almost immediately (spring break in
3 days woohoo). Uhm, I've been looking around and I'm having trouble
finding an ATX 12vdc power supply. Once I get that I have the entire
computer system done.
I have plenty of PS/2 mice sitting around, so...

I need:
1. 12vdc atx power supply.......................................$?
2. 9v-18v dc to dc 5v 3a converter ?what for?...........$?
3. 9v-18v dc to dc 12v 1.5a converter ?what for?......$?
4. Velleman K8055 I/O board..................................$44
5. wireless
card.....................................................$35
6. Two motors........................................................$?
7. Custom dual motor amplifier ? explain...................$?
everything else is packed nicely into a little box to my right... :)
Any websites that can be suggested would be great for that 12vdc power
supply..

Thank you for all of this advice :-D

I got one off eBay a couple of months ago. I think it was about $45?
Here's the site that sells the one I got: http://www.short-circuit.com/

Pogo had a good link.


These two converters are not necessary for the base system but may be
necessary if you intend to build additional hardware.



I suggest looking at second-hand stores and bargain basement sorts of places
for a kids ride around toys. That's what I used.


That's actually the sticking point. There are "lots" of motor amplifier
systems available in kit form. Google for 12v h-bridge motor or find a
schematic on-line or in a book.

Right now, I have basically two components in a box. A dual pulse width
modulator and a dual motor driver circuit. It is something I built 15 years
ago and all I have is a hand written schematic. There are several
remarkable things about this fact: (1) I have retained the schematic on
paper. (amazing) (2) There are no component values written down (A sure
sign I was just hacking it together) (3) When I blew up some power
transistors I was able to FIND replacements.


I found this:
http://www.kitsrus.com/pdf/k166.pdf

It is kind of similar to the circuit that I have, well, actually, pretty
different, but it should work for the most part. I would add a bridge
rectifier across the motor output, and *AT* the motor, add a .1 uf ceramic
cap to kill the big spikes. I would also add a big electrolytic and a 0.1uf
ceramic cap at the transistor power transistor power input.

Anyway, remove the "P1" potentiometer and connect it to the analog out of
the velleman board.


Someday, when I get some time, I should like to put my motor control circuit
on line, however, I sort of like the velleman board, it has PWM output
already. I could use it as well as a couple of the digital output bits for
direction. The only problem is that the PWM is 22KHZ The motor would
probably has too much inductance to ever build enough current to move. I'd
probably also have to design an L/C filter to smooth out the power to the
motor.