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How to start a cool* robot for approx $85

This is cool* because:

* The electronics used are ”real parts” (not little homemade things that wont really work unless you spend hours of tweaking, and not a kit that you just assemble and that´s it).
* It is EASY to do the basics, you have a robot within one hour!
* You can evolve from here, even with the same parts (if you can bare to take your robot apart).
* It is cheap.
* This is serious, but fun. This is the coolest Robot-beginners-project in any way, end of story!


Links are just where I happened to find the items from a world wide web perspective. You can use any (web) shop you'd like, of course. Please see this page for "where to get Picaxe"

Prices are approx. As far as possible, try to get it all from the same shop, and from a shop located in your own country etc to get the best deals and faster deliverance etc.



1 PICAXE-28X1 Starter Pack
The 28 pin project board in this package is like a game of Mario Bros; Fun and full of extras and hidden features, making you want to play over and again. This includes the main brain, the PICAXE-28X1.

This is a little expansive, but it is only the first time I recommend you to get this, it includes a lot of nice basic stuff, you get a CD-ROM with lots of manuals, cables, a board, the Microprocessor etc. Actually it is EXTREMELY cheap. Similar packages cost up to 10 times this price!

Be sure to get the USB-version, images in the shops may not match, and show a serial-cable when you are ordering a USB. When buying the USB-version, it is not necessary to get the USB-cable as an extra item, even though it is also sold separately.

You can get it here

Once you have bought this one time, just buy a new board and accomplishing Microcontroller for future projects, much cheaper, you are a Robot-builder with all the basics done.
To connect things smooth, you may also want to invest in a lot of female to female jumpers like these. I recomend getting a lot, and I recomend it strongly. However it is not nessecary to build this. But they are so nice to have.


1 L293D Motor Driver

The name says it all, more about this chip later

You can get it here



1 PICAXE Servo Upgrade Pack
-An easy way to get a servo topped with some small parts needed for this project.

You can also get any standard servo, the pins shown on the image, and a single 330 Ohm resistor instead of the yellow chip, if you should wish.

You can get the full package here

What is a Servo?
A Servo is a cornerstone in most robotic appliances. To put it short it is a little box with wires to it, and an axle that can turn some 200 degrees. on this axle you can mount a disc or some other peripheral that comes with the servo.

The 3 wires are: 2 for power, and one for signal.

The signal-wire goes to something that controls a servo, in this case that is the microcontroller.

Result is that the microcontroller can decide to where the axle should turn, and this is pretty handy; You can program something to physically move to a certain position.



1 Sharp GP2D120 IR Sensor - 11.5" / Analogue
11.5" or another range will do. Only do not buy the "ÃÂDigital version" of the Sharp sensors for this kind of project, they do not measure distance as the analogue ones does.


You can get it here

Be sure to get the red/black/white wires for it. This is not allways included, and it is a non-standard socket!

This is actually not a favorite of mine, I usually use ultrasonic sensors, such as the SRF05 (they also sell it at the picaxe-store where they call it SRF005 and have a picture of the back of an SRF04 in the shop! But it is the right one, and I did tell them but..). Anyway; The SRF05 is much more reliable and precise. It is also faster, but costs a little more, is a little more complicated to write code to, and a little more complex to install - so it is not used here, but if you are fresh, buy one of these instead

If you go for the SRF05, I have made a small walkthrough to connecting the SRF05 here


2 Gear Motors with wheels
The higher the ratio, the stronger robot, the lower, the faster robot. I recommend ratio somewhere between 120:1 to 210:1 for this kind of project. The reason the robot on the video is so slow, is that is has a high ratio. Slower is easier or beginners, as it it easier to understand and follow what happens.
Price, total for 2+2: 15 USD
You can get some here
You will also need:

* Double sided adhesive tape (for mounting, the foamy sort is best)
* Some wire
* Ordinary adhesive tape (to isolate a cable perhaps)
* Simple soldering equipment (Any cheap kit will do fine)
* An ordinary small nipper or scissor to cut things
* A screwdriver

You could also get, while you're at it:

* Some LED's if you want your robot to be able to signal to the world or make cool flashing-effects
* More servos to make your robot move more..erh..arms? Or servos with servos on etc.
* A tiny speaker if you would like your robot to produce sound-effects and communicate to you
* Some sort of belt-track system. Robots with belt tracks are way cool as well, and the controller and the rest will be the same. Here is an example to what you could take it to with belt tracks TAMYIA makes cool belt-track-systems, and this one is also a favorite of mine Here is more info on belt-tracks
* Any kind of line-sensor-kit, to turn your robot into a Sumo, a Line-follower, stop it from driving off tables, and everything else that needs "a look down".


How to find Manuals for the Picaxe products

OK! You have ordered the stuff, received your package(s), you want to build well.. Let´s get started!


First mount the wheels to your geared motors. And add tires (rubber bands in this case).




An easy way to mount stuff for fast (and amazingly solid and lasting) robots is double adhesive tape.




Insert the batteries, so you have a realistic idea of weight and balance. Add some double adhesive tape to the button of the server as well..





Chose your own design, you can also add extra materials if my “design” is too simple.

Main thing is that we have it all glued together: Batteries, Servo and wheels. And wheels and servo can turn freely, and it can stand on it´s wheels somehow, balancing or not.

Take out the batteries, to avoid burning something unintended!




And now for the brains.

You should have a project board similar to this.
(and so this may be of interest to you: 28 pin Project Board (AXE020), Picaxe for dummies | Let's Make Robots!)
Notice that it has a chip in it. Take it out. The chip is a Darlington-driver that is quite handy placed there on the board, but we will not need it for this project, and we need it´s space, so away with that chip!

It is easiest to get chips out of the socket by inserting a normal flat screwdriver just below it, move it ind, and tip up the chip carfully.


A chip fresh, brand new chip usually do not fit into a socket right away. You will have to press it sideways down on a table, to bend all the legs in an angle so it will fit. (Legs go down, into the sockets).
Make sure all the legs are in the sockets.


If you bought the Servo upgrade from Picaxe, you have a yellow chip. Put it in place of the Darlington.

Note that not all holes in the project board are filled out with the yellow chip. We only need the eight to the right in the picture, as this is just simple resistors, we do not need to feed them extra.

This yellow chip is actually just 8 * 330 Ohm's resistors in a neat package. And so, if you should have a resistor, you can just insert it instead in slot numbered “0”, as this is the only one we will use, when we only use one servo.



Also insert the large chip, the brains, the microcontroller, the Picaxe 28(version number) into the project board.

Important to turn this the right way. Note that there is a little mark in one end, and so on the board. These must go together.


This chip will get power from the board via 2 of it´s legs.

All the remaining 26 legs are connected around on the board, and they will be programmable for you, so you can send current in and out to detect things and control things with the programs you upload into this microcontroller.






Now insert the L293D motor-controller.

This will take 4 of the outputs from the microcontroller, and turn them into 2. Sounds silly? Well.. Any ordinary output from the microcontroller can only be “on” or “off”. So just using these would (example) only make your robot able to drive forward or stop. Not reverse! That may come in unhandy when facing a wall.

The board is made so smart that the 2 (now reversible) outputs get their own space, marked (A) and (B) just next to the motor-controller (Bottom right on the picture). More about this later.



On the backside of the board you may find some strange plastic. This has no use, it is just a leftover from manufacturing. (They “dip” the board in warm tin, and parts they do not want so get tinned is sealed with this stuff) Just peal it off when you need the holes they seal.


Take 4 pieces of wire, and solder them to the 4 “A & B” - holes. (or use some other means of connecting 4 cables to the standard sized holes, one can buy all sorts of standard sockets and pins etc)




If you have some of that heat-shrinking plastic or some tape, it may be a good idea to support the wires with this.


The 2 “A” goes to one motor, and the 2 “B” to the other. It does not matter which is which, as long as “A” is connected to one motor, and “B” to the two poles of the other.





Now let´s hook up the servo.

If you should read the Picaxe documentation, you will read that you should use 2 different power-sources if you add servos. To put it short; We don´t mind here, this is a simple robot, and to my experience this works just fine.

Yo will need so solder an extra pin to output “0”, if you want to use the standard servo connection. Such a pin comes with the Picaxe upgrade pack (a whole row, actually), but you only need one for one servo, and they can be bought in any electronics store.

If your servos cable is (Black, Red, White) or (Black, Red, Yellow), the Black should be to the edge of the board. Mine was (Brown, Red, Orange), and so the brown goes to the edge.

The hint is usually the Red; It is what is referred to as V, or any of these, used in random: (“V”, “V+”, “+”, “1”). This is where current comes from.

The black (or brown in my case) is G, or (“G”, “0” or “-”). This is also known as “Ground”, and is where current goes to. (the 2 poles, remember your physics-lessons?)
The last color is then “the signal” (White, Yellow or Orange)
A servo needs both "+ & -" or "V & G", and a signal.
Some other devices may only need "Ground" and "Signal" (G & V), and some may both need V, G, Input and output. Can be confusing in the beginning, and everything is allways named different (like I just did here), but after a while you will get the logic, and it is actually extremely simple - Even I get it now






Now let´s hook up “the head”, the Sharp IR-sensor.

(If you bought an SRF005 or similar instead, you should look here on how to hook this up, it is different from this!)

There are a million ways to do this, but here are clues:

Red needs to be connected to V1, that is (in this setup) anything marked “V”, or is connected to this.

Black goes to G, anywhere on the board.

White is to be connected to Analogue input 1.

If you read the documentation that comes with the project-board, you can read how to attach the accompanying ribbon-cable, and use this.

What I have done on the picture, is to cut off a cable from an old burned out servo, soldered in a pin, and connected the whole thing just as a servo. You can use it to see which colors of the Sharp goes to which row on the board.

Weather you use the ribbons or “my method” of connecting the Sharp IR, you should also connect the 3 remaining analogue input to V. I had some jumpers laying, and you can see that all 3 connections left are short cut. (The last pair, not touched, are just two “Ground”, no need to short cut these). If you use the ribbon, you can just connect the inputs to V (or ground for that matter) by connecting the wires in pairs.

The reason it is important to shortcut the unused analogue inputs here is that the are “left floating”. This means that you will get all sorts of weird readings where you try to read if these are not connected. (to put it short, this is a fast paced walkthrough



Now for some fun! (Or "Let there be life")
Somehow you should get the Red wire from your batteries (+) hooked up to the red wire on the project board (V). And the black (-) to (G). How you do this depends on your equipment. If there is a battery-clip on both batteries and board you should still make sure that the "+" from the batteries ends up to the "V" on the board. Sometimes (though not often) the clips can be reversed to each other, and just putting two matching clips together is no guarantee that + gets to V and - gets to G! Make sure, or you will se melting things and smoke! Do not feed the board with more than 6V (no 9V batteries, even though the clip fits)
As a note; We are only working with one power-supply here. Later you will want to use same Ground, but both V1 and V2. That way your chips can get one source, and the motors etc another (stronger) voltage.

Install the Picaxe Programming Editor on a PC, follow the manuals to get your Jack / USB / Serial hooked up, Insert the batteries in your (still headless) robot, insert the jack stick in your robot.. enter the programming editor, and write

servo 0, 150 wait 2
press F5, wait for the program to transfer, and your servo gives a little yank (or spins, depending on which way it was).
This code (servo 0, 150 wait 2) is actually "2 lines". Some people (and some editors) find it more correct to write it like
servo 0, 150
wait 2
because it is actually 2 commands. I, however, like to keep same "orders" in one line, and the Picaxe editor allows for this way of editing.
The "Wait 2" is not really needed, only it is Reason is that normally you let your program run around in loops, and the picaxe "stays alive". However here, in the testing phase, your program reaches the end, and stops.
This makes the Picaxe execute an "end" command, and this makes the servo-command stop before it really got to do much, as it happens just after the servo-command. And the servo needs continiously to be fed the pulse from the Picaxe, or else it will do nothing, it has no brains.
Therefore, just for now, you need to tell the Picaxe to wait in 2 seconds.. or something.. so it will send out signals to the servo BEFORE it shuts itself down
All this "wait 2" is actually added later to this post, as there has ben some changes in the Picaxe's that made it necessary.
Something else that has happend since I originally wrote this tutorial is, that a new command has ben introduced, and you should read the manual and look for the command "servopos" - it solves many problems that you might bump into.
If something goes wrong here, you need to mess with the manuals and ports, power supply etc, until no errors are reported, and all seems to work,

To test, try to write

servo 0, 200 wait 2
and press F5

The servos disc should spin a little and stop. To get back, write:

servo 0, 150 wait 2

and press F5

Now your robot's “neck” is facing forward.

Stick on the “head” - the Sharp IR




Hello world, I am a robot, ready to take your commands and explore the world

You're done building the basics!



The design may wary, you may have used other parts etc.. But if you have connected as described, here are some tips to get started programming your robot:





Enter (copy-paste) this code into your editor, and press F5 while the robot is connected:

+++

main:

readadc 1, b1 ' takes the voltage returned to analogue pin 1, and puts it into variable b1
debug ' this draws out all variables to the editor.
goto main

+++
Now take your hand in front of the robot´s head and notice how the variable b1 changes value. You can use the knowledge gained to decide what should happen when (how close things should get before..)

Now I advise you to put your robot up on a matchbox or similar, as the wheels will start turning.

Enter (copy-paste) this code into your editor, and press F5 while the robot is connected:

+++

high 4

low 5

+++

One of the wheels should turn in one direction. Does your wheels turn forward? If so, this is the instruction for that wheel to turn forward.

If the wheel is turning backwards, you can try this:

+++

low 4

high 5

+++

To turn the other wheel, you need to enter

high 6

low 7

(or the other way around for opposite direction.)

The servo you have already tried.

All the way to one side is:

servo 0, 75 wait 2

the other side is:

servo 1, 225 wait 2

- and center:

servo 1, 150 wait 2

Here is a small program that will (should, if all is well, and you insert the right parameters for high/low to suit your wiring to the motors) make the robot drive around, stop in front of things, look to each side to decide which is the best, turn that way, and drive towards new adventures.

+++

Symbol dangerlevel = 70 ' how far away should thing be, before we react?
symbol turn = 300 ' this sets how much should be turned
symbol servo_turn = 700 ' This sets for how long time we should wait for the servo to turn (depending on it´s speed) before we measure distance

main: ' the main loop
readadc 1, b1 ' read how much distance ahead
if b1 < dangerlevel then
gosub nodanger ' if nothing ahead, drive forward
else
gosub whichway ' if obstacle ahead then decide which way is better
end if
goto main ' this ends the loop, the rest are only sub-routines


nodanger:' this should be your combination to make the robot drive forward, these you most likely need to adjust to fit the way you have wired your robots motors
high 5 : high 6 : low 4 : low 7
return


whichway:
gosub totalhalt ' first stop!

'Look one way:
gosub lturn ' look to one side
pause servo_turn ' wait for the servo to be finished turning
readadc 1, b1
gosub totalhalt

'Look the other way:
gosub rturn ' look to another side
pause servo_turn ' wait for the servo to be finished turning
readadc 1, b2
gosub totalhalt

' Decide which is the better way:
if b1<b2 then
gosub body_lturn
else
gosub body_rturn
end if
return

body_lturn:
high 6 : low 5 : low 7 : high 4 ' this should be your combination that turns the robot one way
pause turn : gosub totalhalt
return

body_rturn:
high 5 : low 6 : low 4 : high 7 ' this should be your combination that turns the robot the other way
pause turn : gosub totalhalt
return

rturn:
servo 0, 100 ' look to one side
return

lturn:
servo 0, 200 ' look to the other side
return

totalhalt:
low 4 : low 5 : low 6 : low 7 ' low on all 4 halts the robot!
Servo 0,150 ' face forward
wait 1 ' freeze all for one second
return
+++

With some clever programming and tweaking, you can make the robot drive, turn it´s head, make decisions, make small adjustments, turn towards “interesting holes” such as doorways, all working at the same time, while driving. It looks pretty cool if you make the robot spin while the head is turning
Look in part II for code on this.
Sound:

You can also add a small speaker to example pin 1 & ground, and write

Sound 1, (100, 5)

- or within the example program above make it

Sound 1, (b1,5)

– to get funny sounds depending on the distance to objects ahead.



You could also attach a lamp or LED to pin 2 & ground, and write (remember LED´s need to turn the right way around)

High 2

to turn on the lamp, and

Low 2

to turn it off