Let's Make Robots!

"Moooo" Rare Swiss Cow Project has begun

Following on from the Laser Experiments i have decided to attach it to some kind of walking Robot.

I am now a avid fan of Theo Jansen -  after rik brought him to light in his Blog.

So far i have Prototyped two pairs of "Theo" legs using "MindStorms" as an experimental base.

It worked better than i could have imagined - these legs go like a Cow on its way to the milking parlour.........

Only problem now is what  medium shall i use to make the final version.....

.....and how the blasers will i get it to turn - may have to run it off 4 motors and double up on the number of legs.

First stage is to replace the Lego Mindstoms with something more exciting..... Wood.


This worked well ..... however after looking closely it suddenly dawned on me

that there are two fixed triangles in the arrangement .....dduuhhhh,

( it puzzled me to rik why you coloured those bits in green )






so i simplified the mechanism with well yes 2 triangles........and 2 flexible squares.

I used the Hypothenus as the fixed link static anchor points (yellow motor and wood spar)





The motor is a geared motor courtesy of "OddBot"

Using some PolyMorph i was able to quickly construct a crank arm,

with PolyMorph it is so easy to tweak the orientation and length, 

giving a super smooth gliding effect....

Second Crank arm made and the yellow motors changed to GM2s for lower speed and higher torque.

Also at long last it has four Legs - and the arduino with motor controller driving them.







 Made 2 extra legs and for more torque installed two GM2 motors





 Syncronising the Legs :-

I had a problem with the missmatch of the legs - ie she would not walk straight with equal power going to each motor.

So i installed 2 QRD1114s, one pointing at a flat region with painted line on each motor drive shaft.

So both motors send a sync pulse every revolution - if these occur at the same time then all is well and the leg motion keeps a straight line.

When there is a difference between the arrival of the two sync signals a control action is made - stop one motor (slave) and wait for other motor (master) to catch up- then restart slave motor - back into sync and cruising straight again.


I have a number of other strategies - all based off the QRD1114s which will unfold.........any other ideas greatly welcome.

 Time for some cosmetic surgery - Swiss Cow gets Her "Beauty Treatment"

Using first a Cardboard Template

i crafted the PM with some "Skinning" techniques.

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Gareth's picture

Here is my first exact setup.........well not exactly exact .... i was unable to attain the A=38 measurement......

...... What i have done is to calculate the Hypotenus ie ²⁄((38²)+(7.8²))      A = 38.79 (equalling the distance between the two fixed pivots). When you attach the crank arm and spin the motor the linkages crash into each other. (ie the triangles clash together)


It only works when you use thin linkage struts ...... so i have extended this A value to avoid clashing.

What you see above is a second version 1.5 X  bigger but the same problem happens with the clashing....

Edit :- I should have paid more attention to the way you scooped the wood on your version rik...thanks

rik's picture

"Scooping" the wood? You probably refer to the nice curves in my pieces. They are sometimes functional. Like when the curves in Pat and Pes (the triangles) fit into each other but still leave enough space to drill a big hole.

Here is an SVG with all the shapes. It uses Theo's numbers x 2.0 . It is a digitization of my latest prototype. I intended to use Ponoko.com for laser cutting many parts, but the shipping from New Zealand is outrageously expensive.


I thought I already posted this, but all I can find is a photograph of an older prototype.

Gareth's picture

Wow this baby would win the Beauty competition with all her Curves.

That is amazing work rik - will have to get out my coping saw to attempt this one - my band saw has a 1cm blade :-(

I will have to print it out and see which curves i can apply to get back my A=38 ratio back..

With so many cnc machines on LMR at the moment we will be able to cut these "in house" - will have to experiment with pulsing a 1Amp current though my laser. 

rik's picture

The distance between € and $ is given in two measurements because Theo wants A to be parallel to the ground. By applying Pythagoras to A and L, like you did, you are not changing anything substantial in the proportions of linkage lengths. All you did is rotate the whole assembly a bit around € (or $, whatever).

Your new A' now runs approximately 12 degrees = atan(7.8/38) from horizontal according to the original design. That means (still all in theory) that your creature will be lifting and lowering its weight a little bit with every step.

Gareth's picture

Woooo - the holy secret is out - thats amazing - thanks rik - goes to show that lego cant quite reach the accuracy.

Here is my set up ..... unfortunately i am unable to get the best settings (lack of swiss cheese holes)

i havent worked out the magic lego numbers yet ......liable to change.....i will see what happens when i tune to your diagram

the 17mm is the crankshaft measurement


rik's picture
If only you could stretch a lego piece to the exact required length. Isn't that stuff thermoplastic as well?
OddBot's picture

Thanks to Gareth's direct link I finally got to watch a video on a new post. Lately I can't even get a proxy to work. You guys have no idea how much difference video makes to the LMR experience.

Nice legs Gareth, makes me miss my old "lego technical". As for the question of what to make the legs out of, I'm surprised you had to ask.


Squash it between two sheets of tempered glass to get a nice flat sheet. Print your design on a laser printer and iron it onto the polymorph sheet like I did with the caterpillar. All instructions are in my walkthrough.

Gareth's picture

 My first version will be out of wood just to get the mechanics working......

However i have used some amazing PolyMorph to make a crank arm for driving the Theo Legs.

Do you recognise the Motor............... yes being put to good use.....


yellow one is  the motor?


what is this crank mec hanism can you please explain me 

Gareth's picture

Yes the Yellow object is the motor.........

.... however it needs to be a far bit stronger as the "Yellow one" is slipping its clutch (ie there is a mechanism inside the motors gear box that slips if it comes under excess load  - to stop motor stall)

The crank mechanism is a simple peice of PolyMorph shaped over and secured to the motor shaft - is that what you mean....