Hey everyone, I've been looking around on the internet for programmable hardware to convert my RC Car into an autonomous robot, but due to a limited budget I can't afford to buy the wrong thing. I'm not quite sure of everything I need. I need a card I can program (In any language, I'm always willing to learn) preferably with a serial cable (extra hardware for programming chips would be costly?). Other than the card, do I need anything else? (of course sensors, but thats later).
I need at least two I/O ports, one for steering and one for throttle. Something with about 6-8 I/O ports would be nice for expansion..
But anyways, I'm not even sure I know what I'm talking about :-D Any advice at all, links, starter kits, anything would be helpful.
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.
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.
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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 $500, out of common parts, using a single tool chain. (gcc, make, etc.)
You could do that, but you'd need two lawnmower engines each driving a wheel. I'm not sure that the throttle response of the motors would lend themselves to operate in this fashion, but, well, there you go. :-)
Well, I have a machine sitting here with 512 memory and a 27gig harddrive. Gentoo can be installed almost immediately (spring break in
3 days woohoo). Uhm, I've been looking around and I'm having trouble finding an ATX 12vdc power supply. Once I get that I have the entire computer system done. I have plenty of PS/2 mice sitting around, so...
I need:
12vdc atx power supply.......................................$?
9v-18v dc to dc 5v 3a converter ?what for?...........$?
9v-18v dc to dc 12v 1.5a converter ?what for?......$?
Two motors........................................................$?
Custom dual motor amplifier ? explain...................$? 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..
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:
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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.
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