# Create a Logo Turtle -- Winter Challenge

Back in the dim days of computers, there was (*) a language called Logo. In Logo you can draw shapes and patterns by giving the drawing tool commands. In Logo, the tool is called a “turtle” and you give it commands like:

[INDENT]Forward 100
Right 90
Forward 100
Right 90
Forward 100
Right 90
Forward 100
[/INDENT]
And the turtle would draw a square.

I’d like to build a physical turtle to make drawings on paper. I thought I’d ask the forum “Hey if you had to create a turtle how would you do it?” since there seems to be a lot of talented designers looking for problems to solve.

Requirements:
Turtle will run on a flat surface like a floor or a large table.
Turtle will draw on newsprint.
Turtle has a felt tip marker in the exact center.
Turtle needs to turn on the exact center axis.
Movement needs to be exact. In the above example the two endpoints of the square should be touching. It becomes harder when the drawing is of a 24 point star.

Software commands: These would come in from the serial port so the robot would read in the command and do what it’s told.

FORWARD x move forward x amount
FD x
BACK x move backwards x amount
BK x
RIGHT d turn to the right d degrees. (90 is a right turn, 180 is a 1/2 turn)
RT d
LEFT d turn to the left d degrees.
LT d
So a RT 90 and LT 270 have the turtle facing the same way

How far, how fast?
I’m going to say about 16 ticks to the inch. So if you say FD 64, the turtle will move forward 4 inches. Turtles in real life don’t move very fast, so this turtle does not need to speed around. On the other hand, if it takes 10 minutes to draw a 12" square people will get bored. On the other, other hand if your 12" square is lopsided or has big gaps then that won’t work either.

Bonus Requirements:
Be able to lift the pen up and down so the turtle can move without drawing a line.
Be able to change pen colors.

Software for bonus requirements:
PENUP Lift the pen up
PENDOWN Put the pen down
SETC c Pick c colored pen.

Other information
There is lots of information about Logo and Logo turtles, Google is your friend. Newsprint comes in rolls from either your local newspaper, ask them for the end rolls, or from the craft store. Because it’s wide (36") and long it makes it a good medium to draw larger pictures on.

Saying “was a language” is a little off, since Logo is in use today. Logo had it’s roots in the very early days of computing, it was developed in 1966-1967. So it pre-dates “C” by 5 years and Java by almost 30 years. Logo is more powerful than just pushing a turtle around, but it’s unlikely you’ll see any business systems developed it it. It was designed to help teach students programming.

Anyway post your ideas, comments and design ideas!

I’d use a holonomic drive train. It would be very easy to use, and it wouldn’t even have to turn.

vex isn’t very accurate. i’m not sure if it’s the best system to use.

You can make it accurate by using a gear ratio to lower the speed.

but the axle wobble and the gear lash makes it inaccurate. and don’t get me started on the sensors.

Well… It could work. Just get a stronger axle, metal gears, and a very accurate accelerometer. I doubt this would be very, very, very accurate but it would at least give something “presentable”. I would rather use a setup like the keyboard robot in the gallery. One bar would move side to side, while a box holding the the two other motors and a pen would slide across it. Then, the robot would just push down the pen and draw.

Is this legal for your competition?

The idea is to be able to put paper on the table and then place the robot on the paper. It should be mobile rather than a carriage / head assembly.

Someone said the Vex components are not accurate. The issue around the design challenge is how can they be made more accurate?

hmm…maybe use ball bearing instead of the bearing blocks? and different gears?

or you can use a REALLY BIG sheet of paper
and a REALLY FAT sharpie
so the screwups due to sensors, axle slop, ect wouldn’t affect it that much

I would use stepper motors since they are more accurate and used in plotters and printers and also research 'Odometry" and “Dead Recogning” related information to control the turle robot.

I think that Optical Encoders would increase accuracy greatly.

See my previous posts, (Look for “Cricket LOGO Interpreter” in thread, Vex Projects that I am working on…) and Post #3 in thread,Vex On-Line Controller Code v2.x, ROAD MAP .

Stepper Motors would be a great idea, but the Vex Controller does not support them directly. I have been working with some Easy Drivers connected to some Stepper Motors for an Underwater Robot, and they seem to be quite functional.

I used this program in elementary school for math class O__O

I feel so old, knowing that this is.

And clearly, it’s quite an old thread… just saw this a good 20 months or so later.

I was thinking tank treads with shaft encoders: slow and steady.

For pen lift and color change I was thinking of a turret system mounted on slide rails or a scissor lift.