How to Freeform the Bicore ( BEAM Robotics )




About: I am a French Canadian that loves robots and embedded electronics. I work on all kinds of cool projects, like a high-power electric push scooter controlled with an Arduino. Please visit my website for more ...
This instructable is part of the one motor walker.

The bicore or suspended bicore is the name given to a little circuit created by Mark Tilden. He is the founder of BEAM robotics. BEAM robotics is an acronym for Biology, Electronics, Aesthetics, and Mechanics.

quote from Wiki

"Probably the most utilized Nv Net topology in BEAM, the Bicore consists of two neurons placed in a loop that alternates current to the output. Input into the loop is given in the form of changing the resistance in each separate Neuron, which changes the rate at which the Neuron discharges, affecting the pace at which the loop oscilates."

WOW my head! Let me reformulate that for you.

The bicore is a oscillating circuit. In our case, it will oscillate a motor, like the wiper on your car.
The motor will go back and forth, back and forth when power is apply.

Look at this video to understand:

This instructable was a Flash animation for my BEAM website. You simply follow these instructions.


Step 1: The Bicore Freeform

Many thanks to Ian Bernstein from

Step 2: How to Freeform the Bicore ( BEAM Robotics )

the parts

I recommend the 74AC240

the AC version.

It give more power for the motor.

The resistor in this circuit will change the oscillation. Bigger resitor make the oscillation long.
You see both (R)

it equals to this


You connect the resistor between the tow (R)
From pin2 to pin17

You will find all these part at

They have everything and there are very friendly!

Step 3: How to Freeform the Bicore ( BEAM Robotics )

Step 4: How to Freeform the Bicore ( BEAM Robotics )

Step 5: How to Freeform the Bicore ( BEAM Robotics )

Step 6: How to Freeform the Bicore ( BEAM Robotics )

Step 7: How to Freeform the Bicore ( BEAM Robotics )

Step 8: How to Freeform the Bicore ( BEAM Robotics )

Step 9: How to Freeform the Bicore ( BEAM Robotics )

Step 10: How to Freeform the Bicore ( BEAM Robotics )

Step 11: How to Freeform the Bicore ( BEAM Robotics )

Step 12: How to Freeform the Bicore ( BEAM Robotics )



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    43 Discussions


    4 years ago

    100% nothings wrong checked it many times


    I Have followed the steps one by one and managed to make it BUT , when i connect it to 5v all i can see is that my motor is vibrating like crazy and after measuring the voltage across the motor i discovered it was less than a volt.....

    I Used the 74HC240 , With the 22nF Capacitors and a 1/4 100k resistor , my motor is a dc one from a cd player . . . . I Am utterly confused, any help please ?

    3 replies

    oh boy oh boy! It's been a very long time I did not touch a bicore!

    are you sure those are 22nF?
    are you sure that is a 100k resistor?
    is the motor able to spin easilly with a 5V battery?

    If you change from 100k to 1Meg resistor, this will tell how long it turn on one side then the other side. On a servo motor it turn clockwise for 1/2 a second and anti clockwire for 1/2 second

    if you have a small resistor, that mean that it would oscillate really fast..
    maybe that is why you hear the vibration but it might just be the motor spinning clockwire then anti clockwire REALLY fast.

    try a different resistor,

    measuting the motor voltage could and could not be usefull.
    I guest that if the oscillation is slow, you might actually see for example 5Volts for 1/2 second then -5Volts for 1/2 seconds.

    if that does not work, disconnect everything and star again.
    try on breaboard. try other small motor.

    oh yeah... the HC240 is not that powerfull... you need the AC that can provide more current per pins. Yeah HC = 35mA per output

    the AC = 75mA

    you have 3 buffer/output on the bicore, that mean
    35mA * 3 = 105mA
    75mA * 3 = 225mA

    Now it depends on how much current your motor is. If it's brand new and not recycle it can be low, under 100mA otherwise if it's more then it could not work since the chip will protect itself or fail.

    good luck!


    Reply 4 years ago

    Well , I don't know I am starting to feel dumb , I made the whole thing again only to get the same humming motor , the difference is when I push the motor it starts moving indefinitely to one direction , for the love of god I can't find a AC version


    7 years ago on Introduction

    hi. im wondering if the capacitor value is essential? can i use a 0.1 microfarad ceramic cap instead of 0.22??


    7 years ago on Step 12

    no programming or software?


    8 years ago on Step 9

    If i am using a 9v battery which Chip should I use instead of 74AC240.


    8 years ago on Step 11

    hey guys.
    i got the ic 74hct240.
    What i was wondering is that does this ic require any sort of programming or is it pre programed..


    8 years ago on Step 2

    Hello Sir, Can I use 'SN74LS240N' instead of 74HCT240. I am unable get this IC . Please tell sir,I really want to do this project. Also is their any application of '74HC14B1' IC in BEAM Robotics.


    Reply 8 years ago on Step 8

    you got it wrong, that is pin 3 and 4, the chip is upside down. It connected like that because that is the way to make the bicore work. Look up the schematic of the bicore.

    I have constructed the bicore circuit. Now I have modify the servo. However I want to know why the servo was chosen over a simple DC motor. And what is the drive current and the sink current of the circuit?

    2 replies

    simple DC motor does not have a gear box, that mean no power to make the robot walk. Each inverter from the smith trigger can deliver 24mA. I think we have 3 gates so that mean 72mA for one direction, then 72mA for the other direction. A total of 144mA . That is the 74AC240 chip from fairchild. It could change depending of the manufacturer.

    I don't understand. So what if it doesn't have a gearbox. Can I not just glue a circular piece of plastic to the shaft of the motor which will do the same thing as the servo horn and then glue the gear which has been cut in half to that plastic piece?
    Also, if I'm using the servo I don't have to remove the plastic tab right? And is 6V input to the terminal okay? Because it says 5V in the bicore tutorial.


    8 years ago on Step 9

    I have made my BICORE.But it is not working.Does the difference in motor cause that.I live in India so can be?the poblem is-it's taking only one round and stoping,don't know why?I have a 9V battery so can that be the problem.i have many questions to ask so please don't be annoid.Please.

    2 replies

    Reply 8 years ago on Introduction

    Hello, I believe the 74AC240 can only handle 6v max so chances are you've blown the chip. With my playing around with freeforming ive found it usefull to freeform an IC holder as that way any damaged ICs can easily be replaced.


    Reply 8 years ago on Introduction page 2 absolute max rating is 7V, the recommended is 2 to 6V


    8 years ago on Step 9

    Hello again,Jerome i have another problem-i have a resistor of some other colour so that could be the prob?only two colours are matching.