Boy Scout’s Robotics Merit Badge – A Low-Cost ‘Bot

Here is an idea, which may help with anyone wanting to offer a class for Boy Scouts to work on earning their Robotics Merit Badge ( advancementandawards/meritbadges/mb-robo.aspx):

A few years ago, a guy named Steve from the ChiBots Mailing List ( asked for help in setting up a robotics class for kids.  The catch was that he was limited to a budget of only $8.00 per kid.  This is awfully low for a ‘bot for each kid in the class, however it did get me thinking about an extremely low-cost ‘bot for classes on robotics.  You can see the reply that I sent to him to help with his class at:

With all the interest in the new Boy Scout’s Robotics Merit Badge, I have revisited that low-cost ‘bot and have updated it with today’s prices:

Here is the updated parts list – notice that some of the parts have been replaced because they are no longer available, and most of the ones that are available have higher prices:

Desc Jameco P/N


Price For 1 Total Price
24 MHZ PDIP IND TEMP 5.0V Atmel ATTiny13 765345


$2.29 $21.90
IC, 74LS244, Octal TRI-STATE Buffers, As A Motor Driver 1341966


$0.65 $5.50
Dual General-Purpose IC PC Board (Use Radio Shack product) 276-159 (R/S Part #)


$2.19 $21.90
SOCKET,IC,8 PIN,1-390261-2,
.300″,DUAL,LADDER,P/B,TIN (10)


$1.30 / 10 $1.30
SOCKET,IC,20 PIN, .300″ (10) 526221


$1.60 / 10 $1.60
MOTOR,DC,1.5-3.0 V,0.17A 154915


$2.50 / 2 $21.80


$0.29 $2.60


$0.29 $2.50
CAP, RADIAL, 10%, 10μF,  29891


$0.60 / 10 $1.20
BASCOM AVR (Trial Version) N/A


$0.00 $0.00


$11.71 $80.30

Total price per ‘bot (in quantities of 10) = $8.03 + Shipping & Handling

You must order 10 ‘bots at a time to get these prices.  The original price for 1 “kit” was $7.50+S/H and with inflation has only gone up to $11.71, still extremely respectable.  There are a couple of items which loose their quantity discount with 1 kit, and the IC sockets and .01uF caps only come in quantities of 10 (the original price of $9.94 price for a single ‘bot included extra IC sockets and capacitors).  Wiring for connecting the components can be about a foot of old cat-5 per kid, they will get enough wire to totally hook up their bots with that little bit.

Here is a simple schematic for a ‘bot which can maneuver and even sense it’s surroundings.

The Schematic - Use the capacitors in the parts list for bypass caps across the +V and Gnd of the two ICs.


You will use both PB0 and PB1 together to drive the left motor (PB0 high and PB1 low to turn the motor one way and PB0 low and PB1 high to turn the motor the opposite way.)  Likewise, you will also use PB2 and PB3 together to drive the right motor.

With the small size of the Tiny13, you only have one remaining pin for sensors.  A trick that I came across long ago is that you can use a R/2R resistor ladder combined with the A/D input on PB4 to allow up to 4 bump sensors (theoretically you can get more, but four is about the limit due to the tolerances of resistors)  You will need to play with the numbers that your A/D input provides for each button press.

You can use the A/D capabilities of the Tiny13 to read up to four seperate digital inputs.


If you do not need your bot’s motors to be reversible, you can drop two of the motor control outputs and use them for other inputs or outputs (perhaps an LED for looks?)  Some or all of the four pushbutton switches could be replaced with photo sensors to provide the ability to program in light sensing (phototrope –, such as a photophobe [light avoider] or photovore [light follower]) or maybe two of the sensors facing down to allow a simple line-follower.  In spite of the simplicity of this robot, you can actually do some pretty cool things.

To this kit, you will need to add something like 2 round rubber pencil erasers, 2 short pieces of hot-glue sticks or just dip the motor shafts in a liquid rubber stuff to use as the wheels/tires, and then somehow mount the motors angled down so that the wheels touch the ground (see the Cybugs wheels at: for further information about that – I’m not related to JCM, just like their ideas).  You will also need at least 1 programmer to download the programs into the ’13.  Eddy Wright has USB ( and Parallel Port ( programmers for under $15.00; I have been a friend of Eddy’s for years and he has great deals – especially for stuff that I do not carry in my store 😉

This is the best that I could think of and give each kid a ‘bot of their own.  And, really you need more for anything beyond the most basic (however, this can do things like the TableTop contest from Chibots –  You can fashion bumper switches out of paper clips, and other junk can be interfaced (tell the kids that they get a reward for bringing in electronic junk – maybe a certificate or candy or something).  That will get you at least some LEDs and maybe some other stuff that can be useful in your CBs (cheap bots).

Go to the BSA’s Scouting Store and pick up a copy of the Merit Badge Pamphlet (BSA Supply No.: 35972 –  It has a lot of good information for helping kids to learn about robotics.

Also, I am nearing completion of my new ULC-Bot (Ultra Low-Cost Bot) and will be putting this up in my store soon (I need to complete the experiments in the manual.)  This will include a complete introduction text with step-by-step instructions to get a beginner up and running.  My target price is about $25.00 to $30.00, and it looks like I may be able to meet that goal.  Check back for updates on the ULC-Bot.

And now, the small print: Be aware that this is still just an IDEA.  I have not actually breadboarded this circuit yet.  That said, I do have over thirty years of computer/electronics design experience and this should work.  I will breadboard this sometime pretty soon and write up some more material for the project.  In the mean time, I would appreciate hearing from anyone who takes this idea and runs with it…  How did the class go?  Was everyone able to get their ‘bot running?  How long did it take? (I’m thinking a whole day class, or maybe two.)   Most importantly, how did the kids like the class and their robot?