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Sunday, October 18, 2009

Robot Experimental Walk Cycle First Attempt

This weekend I finally hat the time to mess around with the robot some more and I managed to get it to walk. It still isn't as smooth as I would like but it does walk! I'll start this blog entry with a couple videos of it doing it's thing.

From the video you can see it stumble along the floor on a piece of rubber mat that I set on the carpet. The rubber gives it's 'feet' some traction because it was getting hung up in the carpet, and /or slipping and sliding on the hardwood floor. I suppose the obvious solution would be to put rubber tips on the feet but the rubber mat was easier for now. The legs and feet are made from 0.17" diameter carbon fiber tube and there is no traction on wood and the ends of the tube get caught in the carpet. A long term solution will be to put some rubber or other type of material on the ends of the tube.

The walk cycle that the legs are running through is just a pattern that is repeating and a rather rapid rate. I found that running it slow is actually more unstable than at a faster rate. A couple of things that I am going to play with are the speed that the servos are running and the center of gravity. Changing the speed will be a software change and lowering the center of gravity will mean cutting the legs shorter. I could lower it by adding some weight to the robot base underneath the robot but the increase in overall weight would strain the servos too much.

What follows is a detail of the leg motions that I am using right now to make it move and a picture to help explain it. The rectangle at the top is showing the top view of the robot with each leg location 1 through 4. The bottom rectangle shows a side view with some colored arrow boxes. The letters in the boxes indicate locations of the feet relative to the base of the robot.

So if you look at the colored box on the right it's showing the feet positions of legs 1 and 4, and the colored box on the left is showing the feet positions of legs 2 and 3. As you can see from the box moving a foot from position 'a' to position 'b' is raising the foot up. Moving from 'b' to 'c' is moving the foot away from the base  while it's up off the floor, and moving from 'c' to 'd' is setting the foot down at a distance from the base.

Additionally there are some colored arrows in the boxes that indicate the order in which the feet are moving through these positions. The blue arrows indicate motion that a foot is doing all by itself and the orange arrows show the motion that all the feet do together at the same time. Here is what is happening to make the robot walk with all the legs (feet) starting at the 'a' positions:

Move Leg 1 from 'a' to 'b' to 'c' to 'd'
Move Leg 4 from 'a' to 'b' to 'c' to 'd'
Move all the legs together:
     Legs 1 and 4 move to their 'a' positions while legs 2 and 3 move to their 'd' positions
Move Leg 2 from 'd' to 'c' to 'b' to 'a'
Move Leg 3 from 'd' to 'c' to 'b' to 'a'

At the end of the above motions all the legs are back to their 'a' positions and the robot has moved about 1.5" forward. Right now that is all it can do but that is enough for now. Each of the legs also has a Turn servo that isn't being used yet. I want to get the walking forward part completely figured out and smooth, then I'll work on walking backwards and hopefully turning  after that.

Anyone interested in the Python code I wrote to make this work let me know and I'll post it.


  1. Hey I was wondering how do you get functions and different applications for python to open. Also nice robot.

    Thanks for checking out my blog and the compliment. I'm not sure what your question is regarding Python but here is what I did. For windows you can download the Python installer and it will load all the necessary stuff. The IDLE interface lets you write programs but any text editor that is "pure" text will work (no formatting etc...).
    There is a command line interface as well to type in commands.
    Check out the online documentation for Python, there is ton's of it.
    For the robot I used a pololu controller for the servos and a USB driver that comes with it.
    Let me know if you have any trouble or questions, I'll be happy to help if I can.
    I'm not a software guy but I manage ;-)
    - Otto