View Full Version : Cire's Simple Biped

05-30-2011, 11:41 PM
Also posted on my new blog: http://cirerobotics.blogspot.com/2011/05/simple-biped.html

KISS - Keep It Simple Stupid. This is a good principle to follow when designing robots. Usually there is a well defined goal for a robotics project, so why make things more complicated? Alright, maybe we all want to make our projects really cool, and add extra bells and whistles in order to make it cooler. This new biped is not meant to do that though - it is meant to be a very robust biped that can carry a high payload. Once that is achieved it may become the platform for a competitive mech for http://www.mech-warfare.com/ 2012.

The robot features legs with 2 DOF each, with a 4-bar linkage on each DOF to maintain a level foot in any position. This eliminates the need for additional servo's. 2DOF is all that is required to make a leg move into any position in the plane of the leg. Turning is achieved by moving the legs in opposite directions from each other - similar to how a tank steers. This means that the feet must be able to slide on the surface it is walking on. The robot also must have a way to maintain balance when a leg is lifted. Traditionally bipeds will tilt their body weight using hip and ankle servo. In order to maintain balance, one of two methods will be used - either overlapping feet or a "tail" that moves to change the center of mass to be over the supporting foot as it walks.

These are the first generation of legs, designed to be made out of sheet metal.

http://img828.imageshack.us/img828/5024/bipedlegs.png (http://img828.imageshack.us/img828/5024/bipedlegs.png)

In order to get things moving quickly though, I decided to print out the first prototype legs using my Makerbot 3d printer. This makes a quick way to test out the design and see how it acts, and to bring more insight into the walking motion.

http://2.bp.blogspot.com/-KCRnZTq6iq8/TeRpvQMuODI/AAAAAAAAAAs/FW4PVcTFZMw/s320/100_0581.JPG (http://2.bp.blogspot.com/-KCRnZTq6iq8/TeRpvQMuODI/AAAAAAAAAAs/FW4PVcTFZMw/s1600/100_0581.JPG)

A basic walking gait was created using Pypose ( http://code.google.com/p/arbotix/wiki/PyPose ). As you can see from the video, the legs drag when they return to the front, causing the robot to rotate back and forth as it walks forward. This is because biped does not have a way to balance itself yet, and when the leg lifts for the return step of the gait, the robot just tips. Once the overlapping feet, or balancing tail is implemented, it should walk a lot straighter and faster.

YouTube - ‪Robot Does The Shuffle‬‏

~ Cire

06-01-2011, 02:55 AM
Hey, looks promising! I think there is a potential to save a lot of weight by using this mechanism as it eliminates the need for as many DOF. I saw this video a few months ago which impressed me with its simple design as most bipeds seem over-complex for what they actually achieve.


06-04-2011, 08:07 PM
That's a pretty cool Dino Chench, I was considering doing that, but i came up with another way to shift the weight using just the legs.

In order to walk better I changed the orientation of the legs to be facing away from each other on the biped. This allows it to use its leg motion to move its center of gravity, rather then a tail or a mass on a slider. Having this leg layout eliminates the ability to turn though, so I added a hip rotation servo to each leg. This turns it into a 6dof robot, and greatly increases its ability to walk and turn.

This video shows about an hours worth of gait development, the side strafing isn't exactly how i was thinking it would be like, but it works really well the way it is now.

YouTube - ‪Strafing Robot‬‏

Unfortunately I will soon be abandoning this project to work on an RX based biped instead, returning these servo's to Immortal. I do believe that this kind of leg setup would allow for a low cost competitive biped in mech warfare, which has not been done yet. This project has proven that this leg setup can be very effective, and I may use my RX servo's to build something similar.

06-05-2011, 08:17 AM

He is really good, but also really creepy the way he moves around. Especially on his turning motions.

Nice job my friend.

06-05-2011, 01:24 PM
I really like this design. I think with a little work you could make this a fairly capable mech...though a little funny looking. :-)

06-05-2011, 01:56 PM
Thanks guys, it does look unique, i agree :D. It can actually stand in the same orientation as it does in the shuffle mode, and appear to be a normal humanoid.

06-05-2011, 03:45 PM
You say unique, we said creepy and funny looking.

06-05-2011, 07:40 PM
I think it is a clever idea. Then again, working with an RX 'bot is a valid enough reason to move on from this project.