Let's Make Robots!

CD Turtle


Goal:  Make a robot that draws and takes some of the same commands as KTurtle.  Eventually this robot will draw using a marker through the hole of the CD.

 I like to try to find the cheapest possible way to make things. Here's the list of materials so far:


Item: Price

2 HXT900 Servos: $3.65each= $7.30

discarded CD: $0.00

discarded RC airplane wheels: $0.00


Grand total: $7.30


Planned additions:

ATmega8: ~4.00

754410 quad half-H: ~1.50

5V 1A linear regulator: ~0.47

7.4V 900mAh Lipo: ~8.00 (be VERY careful with lipos. They can burst into flame if abused.  Many hobbyists have had fires from handling lipos improperly.)


I think the total cost of this project can be kept under $25 with some careful scrounging.


UPDATE----- 8/12/2008




I hooked up the electronics without mounting them in the bot, just to check things out.  I'm glad I did, since I found that my voltage regulator (LM2931, just because I had it handy) heated up quite a bit and the voltage dropped to three volts when the motors are both running!  Other than that things seem to be working okay.

 As soon as some of the LM2940 regulators come in from Digikey I'll be up and running!  Thanks for the suggestion in your comment, Krumlink.


UPDATE-----  8/15/2008

Woohoo!  It drives, it draws, it needs more work!




At first I tried to use the LM2940 for both the motors and the AVR, but it had some weird problems, even with a 100uF cap between VCC and GND on the AVR.  I kept the LM2940 for the motors, and used a LM2931 for the AVR.  Much better now!

 It drives around and draws, but it needs some work.  The pen is a snug fit in the tube, so it can't slide up and down easily.  Since the wheels are slightly out of round, the pen draws only when the robot is in the lower part of each revolution of the wheels.  I'll fix it by making a larger tube so the pen's weight can keep it in contact with the paper.


Here's the list of components so far:

2 HXT900 Servos: $3.65each= $7.30

discarded CD: $0.00

discarded RC airplane wheels: $0.00

ATmega8: ~4.00

754410 quad half-H: ~1.50

LM2940: ~1.50

LM2931: ~.75

 2x 100uF cap

2x 1/4w resistors

5 pin connector for programmer

part of a ball point pen to slide on

7.4V 900mAh Lipo: ~8.00

small breadboard: 3.95

Grand total: $27

Slightly over my $25 estimate, but still not too bad.


The next big thing will be writing some code so that it can draw complicated shapes!

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This looks real good i planed to use a CD to make a robot but i changed my idea this is real cool.

Thanks for the comment!  I thought I was probably not the first to think of a CD.


What made you change to a different material?

Well hmmmm i changed to wood because it could be bigger if you look at my robot its on here some where you can see its quite big!, i needed it to be quite big as im using bread boards to do my circuitry because i dont have a soldering iron nor can use one :). I love your idea tho and once ive finished the code for mine i may build one just like yours but with a different perpouse.

I see what you mean.  It may turn out to be tricky to cram everything into the space allowed by a CD.

Massive flash-back, my friend.

I was working with logo right about the time 400k floppys were the big thing! Thats single density, single side! Man, that was fun stuff. 

Logo really is a lot of fun.  It's a great way for non-programmers (like me) to get a taste of programming.
lego is alright i used to play with it alot as a young kid i can remember always wanting the robot kits and could never get any, so instead now im a little older ive just baught other parts and dont use lego anymore apart from small bits n bobs.
You will need a higher voltage input if it is the regular 7805.

Oh, thanks for the heads up.

I see on pg 3 of the 7805 data sheet that the dropout voltage is 2 volts at 1A, and I plan to draw much less than one A, so I think the dropout voltage will be slightly less in this application.  7.4V nominal lipo is about 8.3V fresh off the charger, and I won't run it below 7V.

I think this will work out okay, but I see I may have to switch to a LDO regulator if there is trouble.

If you are to use a LDO, use a LM2940. It can run to 5.4VDC with minimal oscilliation without capacitors. With capacitors it is perfect. I am using a charge pump on ARES to boost the voltage from 4.8VDC max to 5VDC. I have yet to select the correct charge pump.