Sunday, January 24, 2010

Little walking robots

After seeing this robot by Pololu I suddenly found myself inspired to try and make a small walking robot. This post doesn't result in a finished robot, but it (hopefully) will act as a overview of starting points for small walking robots.

Initial idea
I wanted to make a 6 leg robot (for stability) using the smallest motors/gearboxes I could find. I was thinking of a design similar to this one where the middle pair of legs pivoted around an axis between the back and the front of the robot. I was thinking of using a cam mounted on the end of a pager motor to rock the tilt the leg back and forward - this was my starting point.

(Yes, this is my first model in SketchUp)

First effort
Soldering some paper-clips together led to the creation of the following disaster (AA battery for scale):


This initial prototype suffered from two major problems; it was almost impossible to tune the legs accuratly and the page motor had nowhere near enough torque to lift the leg.

The cam
The problem with the cam was that it was too abrupt in its transition from low to high for the low-torque motor to rotate. I set about fixing this with a small file with the following result.

The lower half of the cam is the original size, the top-half is the smaller profile.

The modified cam mounted on the pager motor

The chassis
The chassis was redesigned to be simpler, stronger and more accurate - this time using a stripboard as the base. This is the result:

Under construction

Posing for the camera

Results
Well, the modification to the chassis certainly worked. The legs were significantly easier to tune. On the other hand the same problem still exists for the motor. The cam is too large and generates too much friction where it connects with the top of the leg.

The next step will be to increase the motor size and to add gearing - probably with one of these from Solarbotics. This should allow me to up-size the cam to allow greater leg movement. From here I can work on the forward and backwards movement of the legs.

Conclusion
Whilst hardly a stunning success, this mini project was a great chance to learn how to fabricate on a small scale and I will try to keep posting about it as it progresses.

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