Over the last months, I redesigned some parts of the robot (see Figure 1), mainly:
- The Pelvic and the brackets “linked to the Pelvic” are made with aluminum. Initially the Pelvic and related brackets were made of resin, but because of the torque exerted by the servos and the weight of the robot, they bent which lead to difference in terms of angles (Pelvic in Sagittal plane to be precise) between the simulator and the real robot. The use of aluminum solved the problem
- The lower part of the leg and the foot in order to change the distribution of weight.
This new design contributed significantly to the creation of a “stable” walking gait.
Figure 1: The actual robot
The picture below focus on the foot, the passive articulation of the heel and active articulation of the forefoot.
Figure 2: Articulated foot
The gait cycle I have implemented is “hardcoded”, i.e. it consists in a list of couple (position, speed) which are triggered at a specific time frame. First a simulator (see Figure 3), taking into account the kinematic of the robot, computes the angular position of each limb for the different phases of the gait.
Figure 3: Snapshot of the simulator. the simulator provides views of the robot in the saggital, horizontal and frontal planes and on the upper right side a view of foot movements in the horizontal plane
The output is list of “angular position profiles”. These profiles are then used by another piece of software (see Figure 4&5) that will compute a list of angular positions and associated angular velocity in order to create a sequence of commands that will be sent to the servos. It is able to compute the angular velocity because the duration of each phases is given in the parameters list as well.
Figure 4: Snapshoot of the software which computes the sequences of pos/speed for all actuators.
The picture below focuses on aone actuator:
Figure 5: Focus on one profile - original profile - segmentation and computation of pos&speed
By trials and errors I was able to find a stable gait.
I choose this “trials and errors” methodology in order to understand how the gait is really working, how the different parts of the body interact, how to coordinate the different movements and finally how the dynamic plays here. This is not the easiest way because it is a very frustrating compute/test/failure loop but at the end I come up with a quite stable gait and more important, a good (better) idea about how a dynamic walking gait looks like. But here in order to move forward, i.e. implement a dynamic walking gait, I will have to look for people and/or partnership with universities because my skills in math are not efficient enough.
Besides looking for the Graal, I mean a dynamic walking gait, my next goals are
- Implement a “turn gait” – the interesting thing to understand here is whether the lateralization phase is easier or more difficult than the straight walking gait to implement or not;
- Explore the stride length and its implication in the lateralization phase;
- Connect the different sensors and gyro in order to collect data and see how it looks like. What can we do with them?