Well... actually it was not mine but
from my university, but I used for my master thesis and I showed him how to
move from scratch.
The details on the mathematical
calculations and code implemented is detailed on my thesis. You can find it
here (it´s in Spanish).
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| Bioloid robot with a BeagleBone Black board on the chest. |
Usually Bioloid humanoid robots are
controlled by Robotis proprietary controller (a microcontroller board) and
their proprietary software. On that system, basic moves are already being done
and you just have to program the high level instructions you want, like:
"Robot, go get me some coffee", well maybe not so high level but you
have basic moves like "walk forward" or "turn right" already
programed. The idea at the university research center (AI2) was to replace that
controller and use an embedded system instead, specifically a BeagleBone Black.
By using an embedded system on future Bioloid projects, we could use the
benefits of this type of system like true parallelism in processes, extended
computation capacity and easy integration with cameras and IMUs. But before
this, the guts of the system had to be done, and here I come...
My thesis objective was to develop
the Locomotion libraries (in an API) for the robot to move, that is creating
from scratch all the movements on the robot in order to have some high order
instructions like the proprietary software have.
 |
| That's me with my robot. |
The first thing I did is that I used
the code created for a single robotic arm (see previous post) and used for the
two arms in the robot. For the legs to move I programmed the kinematic
equations that describe the movement of the foot using hip as a reference and
the equations that describe the hip movement using foot as a reference. The
reason to have 2 sets of equations for the legs is that for example walking is
divided in two main phases: foot on ground (here you move the hip) and foot on
air (here you move the foot). Likewise I created two linear trajectories
generators, one for the foot and one for the hip. Both were generate movements
in straight lines since it´s important to control on every moment were the foot
and hip is, and avoid this way any possible unstable position.
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| Matlab simulation of the legs as kinematics chains. |
This time for the communications
from the BeagleBone Black to the servos (Dynamixel bus) I used an USB2Dynamixel
device. The low level drivers for the BeagleBone Black to send the Dynamixel
data frames was created by David Cisternes as a generic API for communications
on a Dynamixel bus.
Next task was to create those high
level movements everybody loves, so for example for a movement "one step
forward" I divided the movement into 7 different segments: lean sideway,
lift foot, low loft, move hip forward and sideway, lift back foot, low back
foot, return to normal position. Then I created the trajectories for all the limbs
during each segment. This duty required a lot of trial and error correction to
reach a stable movement.
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| Robot during one the segments of "one step forward" movement. |
I called this high level movements
as "behaviors" in order to be used on a state machine that ruled the
robot logic. The robot would move between behaviors based on the input from sensors,
in my case the ones implemented on the smart foot (see previous post). Finally
the robot was able to climb or descend stairs (not big ones, it was a small
robot after all!), walk forward and make small turns to the right or left.
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| Robot climbing one step of a stair |
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| Robot descending the same step of the stair |
The code used on the BeagleBone
Black and my thesis are on my GitHub web:
https://github.com/jcbrenes/Bioloid-Locomotion-API
