Darwin Op Inspired Mech

I have been working on a new biped (Tychus) for 2 months now. The short term goals for this robot are to have a robust walking gait that can change speeds and a mech warfare payload. Long term goals I am not sure of yet, but may include vision processing, aesthetics, and perhaps even a "running" robot.  


Specs:
Actuators: 21 DOF, 16 RX-28, 5 RX-24F
Processing: 1.6Ghz Fit-PC2I
Board: Arbotix 2
Sensors: Accelerometer and Gyro for dynamic balancing
Camera: USB Webcam Weaponry: 1 Chain-gun, 1 Chainsaw
Framework: Mostly custom designed Aluminum frames/brackets, legs inspired by Darwin OP
Armor: 3d printed shells or Sheet metal armor.
Battery: 4s 2100mAh Thunderpower LiPo
Height: 16" Weight: 7 lbs / 3.2KG


Here is a render of Darwin as it was designed when i sent the parts to get cut.

The design uses all 2mm thick 5052 Aluminum, to reduce manufacturing costs. The entire robot is cut with a laser from a few square feet of material. Here is a photo of the brackets as cut by Fox Valley Metal Tech .

From there I bent them to my design, unfortunitly my brake is at its limit with this thickness which made bending some of the brackets fairly challenging. In the end everything fits though!

Walking is one of the most challenging parts about of bipedal robot, so i began working on that portion first. Eventually I plan on using the fit pc and a arbotix 2 to generate the walking gait, but to get things moving I wrote a spreadsheet that generates a series of poses that can be copied into Roboplus Motion (Robotis software) to test different gait strategies and parameters. The spreadsheet can modify the body shifting distance, leg lifting height, step length, body position, and servo offsets all in seconds, and takes about 30 seconds to copy into the software to try out the effects of the new motion.

After about a week of frustrating tuning, I decided to add rubber soles to the feet of the robot so the feet would no longer slide. In my past experiences with quads, sliding feet help keep the servo's from overheating. In my bipeds case though, this is not true because theoretically the feet do not slide on the floor at all, even when turning. Adding the rubber to the feet instantly gave Tychus a stable walking gait without any further tuning to the walk.

~ Cire

2DOF Quad

Last weekend was the Kansas City Maker Fair where there was a pretty big robotics display, which included a Mech Warfare arena called "Atlantean Robotica". The arena was very well done, with a Jungle theme. Immortal managed to take home the gold, although its performance degraded during the competition because the servo gears on the femur joint are starting to fail due to the weight of the robot. In order to combat this for next year, I have decided to retire Immortal and rebuild a new quad for next years mech warfare.


The new design will utilize a very robust 2dof leg setup and inverse kinematics. The leg geometry allows the robot to stand straight without any load on the motors, making it very efficient relative to Immortals 4dof design. The main disadvantage of 2dof compared to 3dof is that depending on how you walk, either the feet need to slip or the body will bounce up and down. This can be minimized with longer coxa and femur lengths, although with reduced mechanical advantage. Below is a video of the proof of concept prototype i made. It has the capability of walking at about 250mm/s with fairly good stability:






Videos from the maker fair Mech Warfare competition can be seen here:
http://mike-ibioloid.blogspot.com/2011/06/atlantean-robotica-videos-from-kc-maker.html

Simple Biped Walking

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.



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.

Simple Biped

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.

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.

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.

 

New Blog!

Hello everyone!

I have created this blog to keep track of my progress on current robotics related projects.

In addition to this blog, you can visit my YouTube for videos and my website for project overviews:
YouTube: http://www.youtube.com/cirerobotics
Website: https://sites.google.com/site/cirerobotics/

~ Cire