cosmodog walks2

COSMODOG
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Technical details:

Size: 30 X 29 X 16 cm

Weight: 740g

Number of motors: 3 X 9 volt (One power-motor)

Controls: Control Centre from Lego Set 8094

Number of parts: approx. 600

Functions: Walking Turning the head Raising and lowering the head Turning the ears Waging the tail


How everything started:

Initially (1996) I was only thinking about constructing a robot that was able to walk. As two-legged walking mechanisms
are difficult to realize, I decided to go for a dog. The first Cosmodog still looked rather crude.
It didn't have knee joints which would have provided it with a more real gait, and its body was a bit clumsy.
The movable ears and the wagging tail were added later, too, when Cosmodog already looked the way it does now.




The problem with balance:

The walking function has worked fairly well. The only problem was that the head holds a motor to make its rotation
possible. This shifts the centre of gravity of the dog very much to the top and to the front to an extent that
in the beginning Cosmodog wasn't able to walk properly. It was just shuffling around. But as I wanted to keep the
cute look of the big head that was able to turn, I had no choice but to reduce weight in general, and in particular
at the head. That‘s the reason why Cosmodog is so sparsely covered. On top of that I moved the positioning of the
head more and more to the back which also provided it with a curious expression.



The head:

Even if it doesn't look that way, the head was - apart from the walking function the most tricky bit to realize.
As I mentioned before, I had to cut down on bricks to reduce the weight. I did this by among other things
making the head (and eventually the whole dog) two units slimmer. Therefore the area around the motor is extremely
condensed. I have used literally every square millimetre. The fact that I did find space for the turning ears
(along with eyebrows) after all is due more to chance than to intention.



The drive:

Apart from the power-motor, which transfers its power via two chains to the four legs, I have used belt-drives.
This guarantees a high transmission ratio and a smooth running. One of the two motors drives via two eccentrics
- simultaneously the nodding of the head, the waggling of the ears and the wagging of the tail. The other one is
located in the head and turns it by pushing itself off from the big gear rim. As far as the walking function is
concerned, only a power motor seemed to make sense, because due to the inbuilt step down ratio I was able to
economise on weight (and space) once again. The initial idea to use a belt-drive here as well was abandoned pretty
soon because the belts didn't last very long and began to slip through after a short time. The forces active at this
particular spot are simply to strong. Also, the two motors located in the body of the dog were gradually moved towards
the rear in order to transfer the centre of gravity further to the back.



The story of the missing pieces:

At the end of 2003 Cosmodog was more or less finished. What was and partly still is missing were yellow bricks.
Therefore I contacted LEGO service in England via e-mail and asked for their help in finding the right pieces.
Much to my surprise I received, after sending them a list of the required pieces, seven of the missing pieces
free of charge. I didn't have to pay for postage nor for the bricks themselves. This was an altogether pleasant
experience! What I'm still looking for as you can see on the pictures are the bricks for the ears and the
lateral covering. But I'm sure I'm going to find them eventually.



The walking function:

There is certainly a technical term for the way in which the joints of Cosmodog are constructed. But as I'm not an
engineer I can only describe amateurishly what I've done. In the first versions of the dog the legs were still
inflexible and were driven directly by a big cogwheel with forty teeth. A bit like the wheels of a steam engine
but on stilts. Of course this made the gait very stiff. By trial and error I finally got the idea of introducing
a knee joint and placing the eccentric there. This not only makes Cosmodog look more natural, but also gives it a
smoother walk. Furthermore it takes smaller steps now and thus I could simplify the step down ratio once again.

Fabian

Category:

Entertainment

Tags:

• lego
• dog
• robot
• hund
• chien
• technic
• cosmodog
• walker
• dogs
• technik
• power
• funktions
• moc

[455329]

wow walks very good !! nice doggie !!

[soccertapes]

0:12 - 0:14 is gonna give me nightmares

[DJLrunie]

@meeee4568 i can see that it is run by an rcx 9v motor

[meeee4568]

what is it run by power functions, creater motor, or nxt

[ruudriessen]

great, i love the idea

[LordRacklo]

cute, very cute (the face is a bit ugly)

[legolarsi123]

pluto the dog to mickey mouse is evil.i,m scared.

[burf2000]

very cool mate, do you mind if i copy it?

[twisterfield651]

It will take over the world.

[mabrekl]

to real!!!!