After waiting for what seemed like an eternity my servos finally arrived in the post!! This has enabled me to put my Quad back together and start working on the gait programming. Here is a quick video to show what I’ve done so far.

Creep Gait

So in the video you can see the robot creeping forward. This type of gait is pretty much the same as what your cat does when it’s creeping up on something … slowly moving one leg at a time while making a stable tripod with the other three legs. I found Oricom Technologies NICO project a really useful resource whilst researching suitable walking patterns for my quad. There is a ton of really useful stuff but most of all the timing diagrams came in really handy. In order to implement the timing I wrote some code to produce trapezoidal curves over the course of a set period of ticks to produce the ‘y’ value for leg lift and ‘z’ value for travel:

        while (tick < period) {
            if (tick >= this.a && tick < this.b) {
                double AX = this.b - this.a;
                double BX = this.amplitude;
                double AB = Math.sqrt((AX * AX) + (BX * BX));
                double angle = Math.asin(BX / AB);
                y = Math.tan(angle) * (tick - a);
            } else if (tick >= this.b && tick < this.c) {
                y = this.amplitude;
            } else if (tick >= this.c && tick < this.d) {
                double CX = this.amplitude;
                double DX = this.c - this.d;
                double CD = Math.sqrt((CX * CX) + (DX * DX));
                double angle = Math.asin( CX / CD);
                y = Math.tan(angle) * (d - tick);
            } else {
                y = 0;
            }
            yield(y);
            tick++;
        }

... where 'a' is the start of the rise, 'b' is the maximum, 'c' is the fall of the rise and 'd' is the end of the rise.

I then used Inverse Kinematics to position the feet where they fall on the timing diagram. I based the IK on the algorithm described on the Learn About Robots website - but had to modify it so it would work in 3D. My next task will be to incorporate the body physics into the IK routine which will allow for tilt and twist (as per the original Phoenix hexapod code). This will be essential as I plan to invest in a gyro/accelerometer for balance compensation at some stage in the future.

Light & Sound

I'm using a small piezo speaker controlled by my arduino for the amazing sound effects! So far there is a few beeps when the robot finishes the setup routine and a repeated beep when it encounters an obstacle. I was also sent a free RGB LED from the good folk at oomlout.co.uk which is responsible for making the robots colourful expressions.

Sensors

The only sensor I have at the moment is a Sharp Infra Red detector. This generates a voltage representing the proximity to an obstacle within a range of about 10-30 cm. I'm not doing anything exciting when an obstacle is encountered at the moment aside from stopping the robot in his tracks and flashing the LED purple. I could perhaps sweep the sensor left to right and decide which way to turn to avoid the object - but I think I plan to use sonar for general obstacle avoidance instead. The IR sensor could then be used to detect any sudden drops in front of me or if the robot has somehow left the floor (ie - stairs or picking it up).

The small body footprint of the initial design was causing me problems -- namely the coxa joints were too close together limiting servo movement. I’ve decided to use a piece of trusty meccano to serve as a new body until I can afford to get a custom aluminium body cut for me.

With a larger body I now have room to mount the electronics more effectively and there is also spare room for adding funky stuff such as sensors, head etc in the future.

There is also enough room to mount the battery pack beneath the body using a thick cable tie. This allows me to shift the battery pack forward and back allowing fine adjustment to the center of gravity.

I’ve managed to hack an old fat XBOX controller to use as my new control mechanism. This is a temporary solution until I can afford a blue-tooth receiver. I’ve done this by re-wiring the controller -- using the six wires in the default cable -- one for each of the analog pot data lines (LS horz/vert, RS horz/vert) the other two for power and ground.

Unfortunately, 2 of the 12 cheap Tower-Pro servos have burnt out -- limiting what I can do in terms of development of the gait and body movement. I’ve decided to invest in the superior quality Hi-Tec HS 645MG heavy duty metal gear servos. However, these come at a price so will probably purchase 4 at a time over the next year.

This is a quick video to show progress on my Quadruped Q-P1. My SES chassis arrived today Spent a few hours figuring out the best configuration and went ahead and built it up. Just added the servos and electronics to the chassis and this video demostrates the first power on test with some up and down movement and a drunken walk …

As you can see there’s still lots to do -- but I’m happy that it’s most definitely a robot now!

To do:

• Calibrate software with measurements and angles.
• Develop a better control system.
• Implement the rest of the body movement routines -- pitch, roll etc.
• Tidy up robot -- wires, electronics etc.
• Try to figure out a smooth walking gate -- a slow creep would be nice.
• Add some sensors
• Go autonomous!!!

I will post more when I accomplish some of the things on the list -- together with more comprehensive notes and hopefully some sourcecode to share. Not sure when I’m going to find the time over the next few weeks to do much of this as I’m wrapping up ready for a big move down south. But any comments are most welcome -- just use the contact link and drop me a line …

Short video showing the first part of my project to build an autonomous Quadruped robot. I converted the Phoenix Hexapod code to work with the Arduino development board and SSC-32 servo controller from LynxMotion. Only electronics and servos so far …

The following links provide further information about the kit I’m using in this video:

• Arduino Dev Board
• LynxMotion SSC 32 Servo Controller

I’m also waiting for a custom chassis built using LynxMotion SES aluminium brackets and leg pieces to arrive in the post. When it arrives, the next part of this project is to build it up into a robot and see what happens when I switch it on!