Let's Make Robots!

Theo Jansen style robot leg: prototypes #8 and #9, I suppose

My Theo Jansen Leg is finally starting to become something reproducible. Every step in in this arduous journey has been aimed at reproduction. No robot needs just one leg. And also, I wanted to share my design with anyone who fancies a walking Strandbeest robot.


Update 25 feb 2009: New video demonstrating the first powered test. Maybe that should read overpowered test...

(The ugly green screens are an editing artifact. Imagine beatiful fades.)


tj-pt7-parts-strijklicht.jpg

As explained in the video (?), I decided against the hybrid design of my previous model (with the vertical parts in the bones). It was too bulky and introducing pivots or hinges through a piece of 3.6 mm plywood on end just was not practical. Pivots are a headache as it is.

So the decision was made to produce the entire leg from layers of plywood on top of each other. I needed four layers (not counting layer zero: the robots flank). I always stuck with the ideal of pretty design. Nice curves and blunt points. A little bit like skeletal bones and a little bit like wooden hour pieces. Here is a step by step build up of prototype #7 (which still functions as the set of mother templates; I never glued them together).

tj-pt7-stack-compo.jpg

The dimensions that really matter to the functionality, Theo Jansen's "magic numbers", were maintained throughout the process. That's why I can say this latest instalment is equal to prototype #5. Here is an image of my drawing with the numbers.

tj-magic-numbers.jpg

The designations are mine except for letters A-M. Those are by the original artist. The numbering of different prototypes has become quite blurry with several late night mistakes and all the different redoes and mods to individual parts. At one point I had recreated the entire "fibula" part because the holes were drilled askew. Then I continued testing with the old, crooked, part. Several frustrating days later, I rediscovered the remade part and an awful lot of swearing was nullified all of a sudden.

So I retake control over my project by simply announcing (more to myself than any one else) that this one (the one in the video anyway) is number eight. Still need to update my templates though...

I discovered very late in the process that resistance in the joints does matter a lot. I had reasoned that each link (bone) provides sufficient leverage to overcome a little friction between pieces of plywood pressed together by nut and bolt. I were wrong!

tj-pt7-180degr.jpg

When the crank is in this position (which I call 180 degrees), all the narrow bones in the middle are folded together. The projected lever is at a minimum now. The friction in pivots X and Y is very significant in this phase of the cycle. When I loosened the nuts almost, to the point where they were no longer pressing any wood, the clunky action finally disappeared. Almost completely.

I also discovered how sensitive the design is for little inaccuracies in fabrication. When a pivot hole were drilled half a millimetre out of its proper position, the parts would touch each other when in motion. Sometimes to the point where they could no longer complete the whole revolution. Especially at 180 degrees, as shown here. The reason for this is also the very function of the four bar linkage (which there are two of in this leg). It serves to amplify the motion of the crank. 

The crank has a diameter of 60 mm. The leg has a horizontal reach of 120 mm. That is an amplification by factor 2.

The next version will hopefully benefit from all these lessons. And then, I will truly have a set of golden templates from which I can cut and assemble a full set of legs. Four or six, that remains to be seen. And I might publish my templates as a CNC design on Ponoko.com. To have cut by CNC laser just makes it so much cooler. And more expensive... Oh well, I deserve it.

Rik


This is a continuation from here. More Theo Jansen on LMR here. Brass shenanigans here. Music by Doe Maar and Candy Dulfer

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Brilliant video that #9. I thought you were vid-tricking me with the speed until you showed up in the picture giving the thumbs up.
Posted new video in old blog. Figured it could use a bump...
I've been meaning to ask, how did you get the video to appear at the bottom of this post? Sorry for the off topic question :/

Not all LMR/Drupal pages are the same. The format differs with content type.

Some feature the embedding of videos at the top (robots), others down below.

Never exactly where you need it 8-(

Bugger! I was hoping there was an editor I could use.

I just received a personal message from a new LMR member "4volt". It contains useful info, so I took the liberty of reposting it here:


"rik,

I have also been researching and developing a jansen leg, here's some intresting and useful links i've found over the last few days:

This link is for the demo of a phisics engine that happens to have an animated jansen leg walker in it. I took the time to measure the lengths of the 12 numbers there, and it turns out they are slightly flexable so not useable with solid materials.
http://www.cove.org/ape/demo2.htm

You've probably seen this photo already, it's a good shot of the jansen leg from jansen's workshop, i've also measued this one and i'm going to try my first prototype on it's 12 numbers.
http://www.strandbeest.com/mGallery/index.php?s=y&id=ypenburg__board&p=2&view=file

This link is for a jansen walker built with VEX robotic parts at the receint toy fair, I suspect some of the parts are custom:
http://i.gizmodo.com/photogallery/vexwalker/1007065989?viewSize=thumb800x800

I have been tracking the diffrent varations of the 12 numbers i've found in a spreadsheet (including yours), if you are intrested in seeing it let me know.

Jeremy"


Well Jeremy,

Welcome to the club. Feel free to post this kind of material straight here on the website for everyone to enjoy. This is first of all an information sharing site. Hope you don't mind me taking the liberty of publishing an otherwise private message.

The APE Physics Engine was new to me. Thanks for that link: went straight into my bookmark folder named

inspiration
Wooden tank thread vehicle
YouTube - Pixar light and heavy
JANSEN - KLANN LINKAGE COMPARISON
http://www.cove.org/ape/demo2.htm
theo_jansen.shtml

I notice that many simulations and copies have the drive shaft level with the main hinge. This will rotate the leg (compared to Jansen's design) and shorten the floor touching phase of the cycle.

Rik

Rik,

 I was very intrested to see the  JANSEN - KLANN LINKAGE COMPARISON link, the Klann linkage is very unique.

 Jeremy

So, I am preoccupied. Deal!

How about replacing plywood with PCB? Could I solder my brass pivots directly on the copper clad side? Would this can of worms ever bottom out?

 

sparkfunartshow_cc.jpg

Via Makezine (if you can get in).

wow...   amazing!

I see you have been very busy  :-)

Great work. Nice rant. Great choice for the music finale.

I'm dying to see a "strandbeest" with a picaxe controling it.