A (VERY) Simple "Robot" (if we can call it that.)
April 3, 2012
One of our members ask how he could build a robot but lacked parts, money, soldering iron and so on.
I decided I would try to come up with the simplest way a small "robot" car could be done without all those things.
He said he had an old car he could use, and that he had some motors and wires.
Without a soldering iron connections can be made by twisting wires together. It is not a good way, but will work for a little while. If your robot stops working check that the wires have not come loose.
The only things I had to add in the line of "parts" were a couple capacitors and a resistor. Since how well this will work depends highly on what DC motors you have and the resistances and current they need, you will have to play around with the values of the capacitors and the resistor.
I can tell you that the capacitors will be in the thousands of microfarads (also known as μFd, mfd, and uf). The bigger the better.
The resistor should be as high as possible and still let the motor 2 turn and move the robot. If the ohms value is too big the motor won't turn. You will probably find that somewhere between 10 ohms and 270 ohms will work. The higher this resistor is but still turns the motor, the better the whole thing will work.
The principle is this. When you hook up the batteries, the capacitor across motor 2 will charge up through the resistor. as soon as the capacitor charge is high enough, the motor will start and the car will go forward. It will continue forward until it hits something with the front bumper.
The bumper is made to act like a SPDT (single-pole-double-throw) switch. It will swing away from the top contact, and motor 2 will run out of power and stop. the bumper should contact the lower piece of metal making contact with the wire going to motor 1. Battery power will go to motor 1's capacitor. Since there is no resistor, it should charge quickly. By the time motor 2 stops turning, motor 1 will have enough charge in its capacitor and start. The instant it backs away from the obstacle, the battery contact is broken and it will only turn as long as there is still charge in its capacitor.
The bumper will swing back to normal position and make contact with the wire hooked to the resistor tied to motor 2. Motor 2 will not start immediately because its capacitor has to charge through the resistor. By the time it is charged enough for motor 2 to run, motor 1 should have stopped turning, and the robot should be backed away a little ways from the obstacle.
Now normally the robot would just start forward again and end up going back and forth, but that is where the left front wheel comes into the picture. A thin piece of metal attached to the car chassis is set to stop the tire from turning in reverse, although it can turn in the forward direction. When motor 1 is turning the right front tire and pushing the car backwards, the left front tire is locked up, forcing the car to turn some.
When motor 2 does come on, the car should be backed from the obstacle (at least slightly) and turned (at least slightly). It may rock back and forth several times but should eventually find a path away from the obstacle, and so it can continue on.
** CLICK THE PICTURE FOR A BIGGER VERSION.**
If you needed a simple on/off switch,you might make it like this: http://www.beam-wiki.org/wiki/Making_a_Touch_Sensor
BUT for this little robo-car to work properly, you need a switch that will connect to two different motors depending on whether it is pushed or not. I am doing that by fixing the bumper piece so it will swing back and forth.
It may be hard to get the bumper to switch right. Make sure the part of the bumper that moves does not have to swing too far from one contact to the other. The more carefully you make it, the better it will work.
ADDED 15APR2012: The bumper may not make good contact with the top contact with normal gravity. Add a rubber band (or a small spring if you have one) from the top of the bumper to a screw put into the car's frame. This will pull back on the top of the bumper to help it make good contact to go forward. (the motor labelled #2).
Wondering how to get something to build the robot car on?
Stiff cardboard might work for a little while, but will get bent and wrinkled too easily, -maybe before you are even finished building the robot. So, here is something else you could use that is pretty strong.
Most people have old CDs or DVDs lying about. If you do, then try those. They work great but do NOT use GOOD discs. They are light weight and strong for their size.
The big problem with old CDs is that they are brittle. They can break easily. Here is a way around that. If you laminate them; that means, put two of them together with a flexible material glued in between, a lot of the brittleness disappears.
I like to use a rubbery glue like "contact adhesive". Spread it around good, so your finished result is solid and won't come apart. Once the contact adhesive gets tacky, squish your CD sandwich together. Maybe lay something heavy on it til it is dry. Once it is dried, it will give you a good but light chassis material.
Latest addition was rewording to make it easier to understand for the young robot experimenter. (At least I hope so.)