Subject:
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Off-road mobile robot
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 11 Feb 2007 11:43:17 GMT
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Viewed:
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3406 times
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For original web site, go to: http://robot.proof.cz
I’ve decided to build a mobile robot in the first week after my summer
examination period in the 4th year at the university. I’d finished all exams
quite early and I got bored soon doing nothing. My field was technical
cybernetics so I thought I might learn something new and have some fun. Among
others, I really wanted to practise soldering and this was a great opportunity.
So I did some research on the Net (meaning Goole ;)) and found HandyBoard. It
can do exactly what I need and it’s very simple to program. HandyBoard runs
special system called Interactive C which allows you to connect to the
microcontroller through the serial interface and execute C-language commands in
real-time right on the board. It’s incredible! Simply connect your robot to a
computer and using one simple command it’s possible to control all motors, read
inputs, send data to outputs, control display and more. It works almost like a
normal unix shell. I was impressed.
Many people asked me about cost of this toy. Well, it was almost $0. I’m not
kidding you :) I had to buy the printed circuit board, but it’s extremely cheap
and the quality is excellent, it’s really worth buy. Don’t waste your time and
money trying to make the PCB on your own. So that was PCB, now all the
electronic parts. I got them for free as samples from different manufacturers.
Just register on sites like Texas Instruments and others. They will send you
almost anything you want for free using UPS, I couldn’t believe it :)
Now let’s have a look at some specs and I’ll describe the construction itself
below...
Visit original web page at http://robot.proof.cz
Microcontroller:
- 2 MHz microprocessor Motorola 68HC11.
- 32 kB RAM, battery backed.
- Drives up to 4 DC motors. I’ve changed the two L293D circuits with four
- Two motor outputs can be used to
- 16 x 2 LCD display. * Two fully programmable
- 7 analog and 9
- 9.6V NiCd
- A 38kHz infra
- 8 pin powered serial connector interface
- Easily expandable using the
Wheelframe:
- I’ll describe the wheelframe later on. I don’t really know exact technical
Electronics:
In the beginning of July 2004 I decided to use Handyboard to control the robot.
However, the biggest challenge was getting all the electronic parts. I couldn’t
find some parts with exactly the same parameters as stated in the HandyBoard
documentation, but it’s life... Fortunately it was easy to find list of
equivalent parts so I managed to buy everything.
Originally I wanted to make the printed circuit board (PCB) by myself, but I
realized that its drawing was only available as a set of GIF images and redraw
them to the computer would have taken me at least a week or two I quickly
decided to order over the Internet from a manufacturer in California. It turned
out that it was much cheaper than if I let it manufacture here in Czech
Republic. And I must say that its quality was really perfect. Non-soldering
mack, metalic holes, printing on top, simply wonderful.
After about three days (I couldn’t find a resistance net with 10 pins) I had
finished the main PCB as well as the interface board. Everything went smooth.
Mechanical construction
My biggest problem was where to find a suitable wheelframe. It’s not that easy
to make at home so I went out looking for something I could use. Finally I found
a flea fair where people were selling anything you can imagine. At one stall
they had broken RC offroad car without the controller. I got it for less then
$10 which was quite good concerning it has two-speed gear, independently
supported wheels, suspension and a ballance gear unit.
Only steering design was so stupid... There was a small geared DC motor but
almost no information about the actual position of the wheels. It worked with
only five states:
- left end
- somewhere on the left
- middle
- somewhere on the right
- right end
Isn’t it great? :) It was sufficient for basic steering and having fun with the
car, but not for computer controlled steering. So I dove into the steering
system first. The ideal solution would be to use a servo motor which can turn
exactly to requested position. But I didn’t know what type to use that time and
it was quite expensive considering that this project was extremely low-cost.
Moreover, I was facing this during weekend and had no chance to buy any servo.
But I realized that there was a (Piher) potentiometer on my desk which could do
the trick. I was quite lucky because it perfectly worked with analog inputs on
the HandyBoard. The solution is simple, I just fixed the potentiometer on the
steering motor’s axle and connected it with one analog input. There was then
value in range of 0-255, but because of the different range of the trimmer I got
only 25 usable values. But it’s still much better than only 5 states as before.
You can find lots of links and pictures at http://robot.proof.cz
  
  
  
  
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