Building a biped: Fixing the reset and control issues

After building the first two models and starting work on
the third model my building efforts where starting to look
like a true development program.

While experimenting with model 2 I decided that I should
reduce the complexity of the next bot to make it more
controllable.

I did not use any rotation sensors, I only used touch sensors.

The touch sensors gave me big problems, it turns out that
they work perfect when you press them at a straight angle
but when the angle is not close enough to 90 degrees they
don´t always work. To fix the problem I replaced the touch
sensors with reflective tiles and light sensors.

A single NXT brick, three sensor multipexers and three
motor multiplexers where used to control the robot.
The software was written in NXC.

Controlling this robot proved difficult. Because I replaced
the touch sensors with light sensors and used them in
combination with multiplexers they where slow to read.
Before reading a sensor value from the multiplexer you have
to give it some time to stabilize the power. This takes
about 50ms. That does not sound like a lot but the multiplexer
has 4 ports. To read all ports takes 200ms which means
you can only read your sensor values 5 times a second...
Way too slow!

Mechanically model 3 was a step down from the previous models
it was too weak to stand on one leg and the motors moved very
slow.

While experimenting with this robot I found out a simple trick
which makes it easier to shift the weight of the robot. If
the feet of the robot are angled in a way that the robot always
leans to the left or right side then the robot can select a
side to shift the weight to.



Next time: Putting it all together

Qrio... unbelievable:

Building a biped: Another year, another robot

With the experience of the first robot I knew that the
most important thing was to make the robot light and strong
enough to allow it to stand on one leg.

The first robot (model 1) had six degrees of freedom in each
leg. I decided that I could do with four.

The new model used power functions motors combined with
RCX rotation sensors. The robot was controlled with three
NXT bricks which was not enough to control all functions
but it did allow me to experiment with the legs.

The primary goal, building a robot which could stand on
one leg was achieved.

Unfortunately by solving one problem I ran into another
problem. When you control a motor you have to know the
exact angle of the axis. To do this you have to put
the robot in a starting position of which all angles
are known. From there you can move the axis relative to
the start position.



Next time: Fixing the reset and control issues...

Here´s something fantastic...
Stuff like this used to be science fiction:

Trying to build a biped robot

Last week Chris invited me to contribute to Tinkernology,
and here it is... your reading my first post.

Every year I build one large LEGO model. My last model
which wasn't a robot was a Startrek model. (if you're
interested you can find it here)

About four years ago I started looking for a new building
challenge. It had to be something technical, with lots
of electric components.

What could be considered almost impossible to build?
I decided to build a biped robot...

The first goal was to just try and see how far
I would come. After studying videos and images of Hondas
Asimo robot I started building.

I used the old 9v motors combined with the RCX
rotation sensors. After working on the robot for about six
months it was finished, it had 22 degrees of freedom.

When the robot was finished it was clear that my construction
would not be able to walk. The legs could move but the robot
was too heavy to stand on one leg.

Another problem was the complexity of controlling the robot.
Because of the large number of motors and sensors I needed
eight RCX bricks to control it. It was just not practical.



So... the robot was finished, was looking pretty good but
could not walk. What should I do now, look for something
else to build? Or would it be possible to improve my design?

Next time: Another year, another robot...

The masters showing how it's done:

HiTechnic Sensor Multiplexer Review Part 1

I just got the Sensor Multiplexer from HiTechnic the other day. I haven’t even plugged in a cord yet, but I wanted to share a few initial thoughts.

The first thing I noticed is that it is slightly bigger than I imagined. No big deal, I just imagined it to be a little smaller. It’s about 2 ¼ inches square and about 1 inch high or 7 studs square by 3 studs high. It is built to standard Lego dimensions so it will easily fit into your mounting.

HiTechnic carefully avoided infringing upon the Lego stud design my making all the protrusions and the distance between them one stud wide so a standard beam fits between them. You cannot snap the SMUX into your project so it must be captured between regular elements.

The second thing I noticed is that it has an external power source of a 9 volt battery box. There is a rather small red and black wire about six inches long connecting the battery box to the SMUX. I didn’t realize it required an external source because I was using the Touch SMUX as a reference which does not have the battery box requirement and I guess I didn’t look closely at the picture on the HiTechnic web site.

There is an indicator light on the battery box which has some functions related to the state of the SMUX and I will get into that more when I start to program it. There is a small on/off switch to turn the SMUX on during operation. You must use a small screwdriver to install the battery.

The battery box isn’t built to Lego dimensions, which makes mounting a little more cumbersome, but not overly difficult. The best way to mount is right now is probably using a couple of rubber bands and strapping it to other Lego elements. Personally, I wish that the battery box was incorporated into the SMUX. That way all the mounting could be done at the same time and I wouldn’t have to worry about breaking the small wires connecting the two during construction.

The distance between the ports on the SMUX are just wide enough for a beam to fit between them, but it is tight.