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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tj-biped_svg.c125.87 KB
tj-hexapod-sidelegs_svg.c53.78 KB
tj-multipods-frontrearlegs.svg_.c85.71 KB
tj-sidelegs-arrangement.svg_.c262.02 KB

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I need the practise in Inkscape, so I can digitize my (very) analog templates into ponoko designs. Will update the latest one as attached svg file. Just needed to tweak the filename extension (remove .c).
I love svg, but no-one seems to use it and Adobe has stopped supporting the free browser plug-in in favour of one of its other paid-for products :(
What is SVG???
SVG is a device independant vector graphics standard. It was designed to be an extension of HTML so you could embed a drawing into a web page. Never quite got critical mass.
Thanks for reducing my ignorance :D

 


tj-biped.png


The point of this silly drawing is to present a common nomenclature: words we can all use.

In dark brown: the drive train. The $ axle is the shaft that is driven by a motor. The € axle is fixed to the chassis. The leg parts rotate around it. This is the vehicle's weight bearing point.

In this  example, the starboard crank has a 180 degree phase difference from the port side crank. The $ axle is divided, but could easily be one and the same.

When looking at the green (starboard) side, a clockwise rotation of the shaft will also make the foot rotate clockwise. When point M (where the rods connect with the crank) is in any position between noon and six (afternoon), the foot touches the ground. During the night (six until midnight) the foot is lifted.

This creature will not walk. It will have it's tummy scraping the dirt while hopping from one foot to another.

 

Man, these lessons are time consuming and brain warping. But I'm getting closer!

tj-hexapod-sidelegs.png

This is a picture I have had in my mind since dont-know-when. Does it make any sense?

They are very time consuming. I know ;-)

When a number of legs must replace a wheel, it's important to coordinate the timing of the steps.

This first example has three feet on the left (port side) touching ground, then three in the air, then three on the ground again and finally three more on the ground. I only drew the cranks for the first six legs. You can imagine the remaining ones.

You can see how the stages of the legs are "phasing" through the constellation. Compare Animaris Ondula.

tj-dodecapod-inline-movesleft2right.png

 

This example has the "wave" rolling inwards from the outsides. Note: this could have one long crank shaft.

tj-dodecapod-inline-movesinwards.png

 

This last one could get away (...) with only six legs. By better spreading the touching and the swinging feet across the width of the vehicle. Sould it still need another set in the rear of the vehicle? The foot placement seems pretty well distributed back to front as well.

 tj-hexapod-inline-alternates.png

 I suppose it would tip over. In the indicated position, all three touching feet are aligned. It would fall on the right side of its face...

 

I had also considered using rollers @ 45 degrees for feet and having two cams driven by two motors. When both cams spin in the same direction, the legs would move as if a single cam was used and it wold move normally. When the cams work in opposite directions, the bot rotates or moves forward/backward depending on the roller configuration. Here's a simplistic diagram looking down on the robot.

Theo_crab_1.jpg