Tuesday, July 6, 2010

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

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

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.

LegoAsimo model 3

Next time: Putting it all together

Qrio... unbelievable:

No comments:

Post a Comment