By Juan Gonzalez-Gomez, Ivan Gonzalez, Francisco Gomez-Arribas and Eduardo Boemo

Computer Engineering School, Universidad Autonoma de Madrid (Spain)
E-mail: Juan.Gonzalez@uam.es

Evaluation of a Locomotion Algorithm for Worm-like Robots on FPGA-embedded processors

Abstract

In this paper, a locomotion algorithm designed for an eight modules worm-like robot has been successfully tested on three different FPGA-embedded processors: MicroBlaze, PowerPC and LEON2. The locomotion of worm-like robots, composed of a chain of equal linked modules, is achieved by means of wave propagation that traverse the body of the worm. The time the robot needs to generate a new motion wave, also known as the gait recalculation time, is the key to achieve an autonomous robot with real-time reactions. Algorithm execution time for four different architectures, as a function of the total number of articulations of the robot, are presented. The results show that a huge improvement of the gait recalculation time can be achieved by using a float point unit. The performance achieved using the LEON2 with FPU is 40 times better than LEON2 without FPU, using only 6% of additional resources.

1

4

Implementation on FPGA

Target

architectures

Processor

Frequency

FPGA

1

2

3

4a

4b

LEON

LEON + FPU

MicroBlaze

PowerPC

25Mhz

50Mhz

100Mhz

Virtex XC2000E

Virtex II Pro

Processor

Slices

BRAM

MicroBlaze

LEON

LEON + Meiko FPU

1321

4883

6064

(6%)

(25%)

(31%)

74

43

40

(46%)

(26%)

(25%)

Architectures used for the evaluation of the algorithm

Synthesis results:

Algorithm execution time

Normalized results supposing a 50Mhz system clock frequency

Conclusions and future work

5

The locomotion algorithm for worm-like robots locomotion has been tested on four different architectures

The gait reconfiguration time (GRT) can be drastically improved by means of the use of and FPU unit

A 25 Mhz LEON2 with an Meiko FPU is almost one order of magnitude faster than a PowerPC working at 100Mhz

When not low GRT is required, the use of the MicroBlaze is a good solution.

It saves about the 75% of the area, leaving this percentage free for the implementation of new hardware cores

For further work, the architecture chosen is the LEON2 + FPU.

The locomotion on 2D problem (2D) has to be solved.

The same algorithm will be used but using two waves: one for the joints in the plane parallel to the ground and the other for the joints in the perpendicular plane.

The final locomotion will be generated as a composition of the two waves

“Cube Revolutions”: the worm-like robot

2

It is composed of 8 similar linked Y1 modules

The modules are connected in the same orientation

The robot only can move forward or backward

The electronic and power supply are located off-board

One degree of freedom

Made of plastic

Actuated by a servo

Can be connected in two configurations:

Y1 MODULES

Locomotion Algorithm

3

Step 3: Fitting the worm to the wave again

Step 2:

Shifting of the wave

Step 1: Fitting the worm to the wave

The problem to solve is the generation of a sequence that allows the robot to move forward or backward

The shape of the robot at instant ti is described by the angular position vector

The sequence of movement is characterized by a Matrix, which rows are the angular position vectors at different instants.

The locomotion algorithm calculates this matrix, based on the propagation of waves along the body of the robot

The algorithm operates as follows:

Step 1: The articulation's angles are calculated so that the worm fits the wave.

Step 2: The wave is shifted

Step 3: The worm is fitted to the wave again

Steps 2 and 3 are repeated until the wave has moved a distance equal to the wavelength

Angular position vector

PowerPoint Presentation

Erik Watzeels

2004-02-12T12:43:28