Arduino Quadruped Robot

Latest Hexapod: https://www.instructables.com/id/Arduino-Mega-Hexa...

This is my first robot that relies on calculations to position the servos vs. relying on pre-programmed sequences. I chose a quadruped to help keep the cost down.

Build Time 8 weeks
Weight 2 Pounds 14 Oz.
Dimensions 8 inches, 8 inches, 7 inches (L:W:H)
Run Time 15-30 minutes
Programing Language Arduino IDE
Control Method Blue-tooth Remote
Cost ~$540.00

Powersource: LiPo

1x 7.4V 1650Mah 2S LipPo

I am powering everything using a 2S LIPO & Turnigy 15A UBEC (Ultimate battery elimination circuit). I love the UBEC and will definitely be the regulator of choice for future robot projects.

Locomotion:

The body's roll, pitch & yaw are calculated using a rotation matrix. That in turn feeds into the Inverse Kinematics equations that position the legs. I am using a ripple gait for walking although I am still fine tuning that portion of the code. A few modes exists, 1: Body Translation/Body Position 2:Walking Mode 3:Accelerometer Mode. The first two modes are pretty self explanatory; accelerometer mode takes the x-axis & y-axis from the accelerometer, maps the values to (-20, 20), then use those values as the body's pitch & roll respectively. This allows the robot to stay level on uneven surfaces.

It has been some time since I have been enrolled in a math class. I also don't believe in re-inviting the wheel; I used the rotation matrix & inverse kinematics from NUKE (Nearly Universal Kinematic Engine). I am not using the micro-controller is was designed for so I could not use their python tools to generate the code I borrowed from. Instead they had an already completed sketch for a quad which is what I modeled my program after. A big thanks to the people that put that tool together, it was true to its name! Also big thanks to "tom_chang79" his discussion, "Let's Discuss Kinematics, Shall We?" was very helpful. Thanks, & thanks for your email responses!

I have built a blue-tooth remote control which has worked great so far. As I continue to progress I intend to build more functionality into my remote and robot. I found some 3-funtion joysticks at servo city that will replace the parallax joysticks I have now.

Here is the link to the ideal joysticks from servocity:
http://www.servocity.com/html/3_function_joystick...

Controller/CPU: Arduino MegaMini 2560, Lynxmotion SSC-32

The Arduino Mega handles all of the computation along with taking input from the accelerometer & blue-tooth. Once all the calculations are complete it sends the appropriate commands to the SSC-32 servo sequencer. I love the SSC-32 it is super great!

Sensors

Triple Axis Accelerometer (ADXL335)

When I started off I thought that I would need a 3-axis gyroscope in addition to the accelerometer. My thought was that I would need to mesh the data together using a Kalman filter. I have worked with IMU's (Inertial measurement unit) in the past and needed to use directional cosine matrix's to mesh the accelerometer, gyroscope and compass readings together. This creates very stable orientation data and outputs a single yaw, pitch & roll that doesn't drift. In the end I was able to get the data I needed from just the accelerometer. This is good thing, I would most likely need another MCU to process all that data.

Actuators

I am using HS-422 servo's; I have been very impressed with all the HITEC Servos. At some point I will replace the HS-422 servos with HS-465MG servos which have more torque and metal gears instead of composite.