Let's Make Robots!

Theo Jansen legs - possible applications

Here is an open invote to all of you to join yet another Shoutbox debate. Oddbot and I are both thinking of ways to mount a vehicle, or creature, on Theo Jansen legs. (use the search box)

Most creatures living on the 'net have two sets of three legs. Each set on a side. In the front and in the back. Many creatures I saw even double up on the legs: six in front, six in the rear. All connected to the same crankshaft in the center of the creature.

See the original Transporter or  Animaris Rhinoceros

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At best a TJ-leg touches ground 50% of the crank's revolution (or 180 degrees of the cycle). The foot is air borne the other half of the time. Probably a bit longer. So for a set of legs to replace a wheel, it needs at least two legs. A stable vehicle needs three points of contact. So either give the creature four sets (Transporter) or plenty of legs on opposite sides of the vehicle.

Oddbot poses the question of steering the vehicle. Tank style steering (stopping one thread, powering the other) seems somewhat inelegant for this beautiful piece of art.

I plan to build a "shoe box with legs flush against the sides". But to be honest, steerability has not entered my design plans yet. Mostly because I plan to make it (eventually) a towed vehicle. Maybe I should drop Mr Jansen a line. My version probably will be much lighter to pull...

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Those sort of toothed belt/pulleys are perfect for robots and very strong. They are used a lot in inkjet printers and even some 4WD RC cars. You can buy some small ones at hobby shops for that reason. I am using a similar belt system for my low cost industrial robot because they have far less play (less unwanted movement) than gears.

Rik,

Here is an alternate idea for steering a jansen walker:

Insead of having two legs per drive wheel facing opposite directions, put them both facing the same direction on each side of the drive wheel. Then mount them to the front and back of the robot instead of the sides. It would look like a crab walking sideways.

For steering, add a pivot point in the center, like some big trucks have.

For powered movement, the back legs could be unpowered, and be "dragged" along.

For unpowered movement the natural force of pulling the front section would force the machine to pivot in the center.

Pivot Idea

http://www.4volt.com/lj/other/PivotIdea.png

I am considering the option of making a creature with a "wasp waist". And I am very much aware of the option to put the leg assemblies on front and rear of the vehicle.

Note: I use both terms "vehicle" end "creature" as if it were the same thing. I reserve the word "robot" for everyone else's stuff. Stuff that has brains, rather than "exists in brains" only.

But, as your diagram clearly illustrates, it leaves very little room for the actual creature. Where would I put the battery, motor or even payload?

I like the idea very much and I'm sure Oddbot is also considering something along these lines. Thanks for joining this discussion. Don't be modest. Jump in. Please.

And feel free to provide bigger pictures. I love'm.

Your right the main drawback is a lack of space to mount or carry things, it seems like most designs have the legs to the side, or don't have any payload area.

With the pivot design you could maximize the payload area by overlapping your base pate with the rear module's swivel area, but there's still not a ton of space.

You could also put the payload above the legs, with more more smaller legs. That would leave you with supporting the platform from the pivot and front shoulder mount. The back legs would kind of trail around under the back of the platform and there would also be considerable downward strain on the pivot joint.

For my design I'll be putting the legs to the side, it seems like anything but that makes the design complicated fast. Also, my bot will probably be pretty small, so simplicity will be wise in that case. But I do see your point with the elegance of the solution, it does leave something to be desired. I think it might be the lesser of two evils.

As a side note, some day I would love to repourpose a wheelchair with big flat jansen legs off to the side. Imgine seeing someone riding around on that next to a segway, that would be pretty cool.

Ok I have to ask for the record since the guys with the prettiest diagrams are here.

What software do you use for your drawings ?

Rik?

OddBot?

Interesting article Rik, although I'll have to re-read the discussion a couple times (leg bone connected to the knee bone ...)

I used Visio for my SpeakJet diagrams - the first and only ones I've made so far. It's a bit cumbersome, but would get easier as you tailor the library of pre-defined symbols.

Inkscape.org because ponoko.com supports it and because it is free (and gratis too).

I think Oddbot uses some presentation app that he even uses for his electo schematics. can speak for himself.

[root@home]# yum --install opensource !
I use Corel Draw
Wow! Rik does pretty diagrams. Better than mine :D