DEVELOPMENT OF THE CONNECTED CRAWLER ROBOT

FOR ROUGH TERRAIN

Realization of the Autonomous Motions

Sho Yokota, Yasuhiro Ohyama, Hiroshi Hashimoto and Jin-Hua She

School of Bionics, Tokyo University of Technology, 1404-1 Katakuramachi Hachioji, Tokyo, Japan

Kuniaki Kawabata

RIKEN, 2-1 Hirosawa Wako, Saitama, Japan

Pierre Blazevic

Institut des Sciences et Techniques des Yvelines, 7 rue Jean Hoet, Mantes, France

Hisato Kobayashi

Faculty of Eng., Hosei University, 2-17-1 Fujimi Chiyodaku, Tokyo, Japan

Keywords:

Crawler, Rough terrain, Step climbing, Autonomous motion, Connected crawler.

Abstract:

The purpose of this paper is to develop a rough terrain mobile system. Our mobile system adopts the connected

crawler mechanism. It had 3 connected stages with the motor-driven crawler tracks on each side. RC-servo

motors were used for driving joints between the stages. This system also has a high mobility. In this paper,

we showed the mechanical features, and proposed the operation strategies for autonomous motions. We have

also made veriﬁcation experiment of proposed operation strategy. For this veriﬁcation, we did 2 types of

experiment. One was that the robot passes over bumps with different heihgts. The other was stairs ascending.

Both experiments had a great success. There were remarkable points in these experiments. These experiments

showed that the robot can pass over the different height and different structual obstacles by using only (same)

strategy. Moreover the sensors which realize proposed strategy were very simple, and the number of sensor

was very small. Therefore it can be concluded that proposed strategy has extremely high usefulness.

1 INTRODUCTION

Since there is a great meaning to use crawler mecha-

nisms as a mobile function on rough terrain, the con-

struction machineries, the tanks, and a lot of rough

terrain mobile robots adopt a crawler mechanism. Es-

pecially many rescue robots use the crawler mech-

anisms. Because, in general, crawler mechanisms

can obtain big impulsion on rough terrain than the

leg mechanism and the wheel mechanisms. On the

contrary, it also has weak points as a poor stability

in complex geographical features. And the mobil-

ity on the area such as stairs is inferior to that of the

leg(Hirose, 2000).

Therefore, a lot of researches have tried to supple-

ment with these weak points. The main theme com-

mon to those researches is to improve the mobility

performance on rough terrain. Generally the variable

crawler structure is adopted as an approach for this

main theme. In order to realize this transformation,

many research proposed connected crawler mecha-

nisms which crawler stages were connected by active

joints. Lee et al (Lee, 2003) designs two stages one

active joint type resucue robot that uses tow triangu-

lar crawlers, and shows the high mobility by the com-

parison of climb-able step height between proposed

mechanism and a usual one track type. ”Souryu-

III” (Takayama, 2004) is the connected crawler robots

of 3 stages 2 joints type for resuce operations, and

it shows high mobility by some basic experiments

such as climbing up a step and passing over a gap.

”MOIRA”(Osuka, 2003) is also rescue robot which

is 4 stages 3 joints type connected crawler. As men-

tioned above, the mobility performance was improved

by using connected crawler mechanisms.

Although we can see such research, there are no

robots which can move autonomously. The one of the

most important reason to introducing rescue robots

to disaster places is to automate a sufferer search-

ing in place of the manpower searching. If many

396

Yokota S., Ohyama Y., Hashimoto H., She J., Kawabata K., Blazevic P. and Kobayashi H. (2007).

DEVELOPMENT OF THE CONNECTED CRAWLER ROBOT FOR ROUGH TERRAIN - Realization of the Autonomous Motions.

In Proceedings of the Four th International Conference on Informatics in Control, Automation and Robotics, pages 396-401

DOI: 10.5220/0001624203960401

 SciTePress

rescue robots can search sufferers automatically, it is

enable to search wider and faster than conventional

manpower searching, that brings early detections of

sufferers. However current rescue robots don’t real-

ize the autonomous operations, therefore that has not

achieved above mentioned important reason of intro-

ducing robots to disaster places.

Thus this research proposes a rough terrain mobile

robot which can realize autonomous motion in disas-

ter places. Especially, this paper proposes operation

strategies for passing over obstacles autonomously, as

well as constructing of connected crawler robot as the

ﬁrst step of this research.

Also this paper is organized as follows. Chap-

ter 2 introduces the outline of our prototype robot.

This mobile robot consists of 3 connected stages with

the motor-driven crawler tracks on each side. RC-

servo motors were used for driving joints between the

stages. Chapter 3 presents operation strategies. Chap-

ter 4 addresses the veriﬁcation experiments. This ex-

perimental results will show that the proposed opera-

tion strategies can be adapted to various shape of ter-

rain. Chapter 5 describes the conclusions and future

works.

2 THE PROTOTYPE

This chapter shows the outline of the prototype.

The mobile function of our prototype adopts crawler

mechanisms. Because The crawler mechanism shows

the high mobile ability on various terrains; moreover

it is simple mechanism and easy to control. But con-

ventional single track mechanism has also mobility

limitations; the limitation is determined by attacking

angle, radius of sprockets, and length of crawler. In

order to improve its mobility, we add some active

joints to conventional crawler tracks, namely that is

connected crawler mechanisms.

2.1 Mechanical Structure

Our mobile mechanism has 3 connected stages with

the motor-driven crawler tracks on each side(Fig. 1).

The features of the proposed mechanism are as fol-

lows.

• This mechanism has high mobility to passing over

the obstacles.

• It can adjust the size of the robot.

• It can adjust the attack angle.

• It can minimize the grounding area.

Table. 1 also shows the speciﬁcations.

Figure 1: The overview of Connected crawler robot.

Table 1: Speciﬁcations of the test model.

Length(maximum) 354.0[mm]

Length(minimum) 118.0[mm]

Width 125[mm]

Mass 0.608[kg]

Radius of the sprockets 20.0[mm]

RC-servo motors are used for driving joints be-

tween the stages. The left and right crawlers are

driven by 2 DC motors independently, while the 3

crawlers on each side are driven by a motor simul-

taneously (Fig.2). The output of each motor is trans-

mitted to the sprockets of the three crawlers through

several gears.

2.2 Control Structure

We adopt a hierarchical control structure by installing

an intelligent servo driver to each actuator. We con-

nect each of them to the master contoll unit by UART

serial line. The parts marked by red line in Figure 3

are servo drivers. Each servo driver consists of one

Figure 2: The driving system.

DEVELOPMENT OF THE CONNECTED CRAWLER ROBOT FOR ROUGH TERRAIN - Realization of the

Autonomous Motions

397

Figure 3: The overview of the servo unit.

Table 2: Communication data format.

1 byte 2 byte 3 byte

Data 1 Data 2 Check Sum

7 6 5 4 3 2 1 0

0∼254 Data1|Data2

Mode=0∼2 ID=0∼3

microcontroller (PIC16F873) and 2 DC motor drivers

(TA8440H). One microcontroller is installed to con-

trol the two RC-servo units for the joint control, where

RC-servo is controlled only by PWM signal.

Figure 4 shows the control structure of this sys-

tem. The master unit is equipped with several sen-

sors which are increnometers, PSD distance sensor

and photo reﬂector. The usage of these sensors will be

shown in Chapter 3. Master unit culclates high level

task (setting trajectory, sensing environment, etc), and

servo driver works for low level tasks. The master

unit processes the high level task, and derive the data

to low level task (crawler velocity, joint angel and so

on), and send them to the servo drivers. After receiv-

ing these data, the servo drivers control their motor

by conventional feedback control low. Table 2 shows

the communications data formats. The command sent

by master unit consists of 3 bytes. First byte indicates

mode ID and motor ID. The mode ID distinguishes

3 kinds of control modes: position control, velocity

control and compliance control. The motor ID is used

for selecting motor to control. Second byte shows the

data depends on control modes (crawler velocity, joint

angle). The third byte is checksum.

3 OPERATION STRATEGIES

A rough terrain such as disaster places has various

shapes. Hence, it is difﬁcult to derive each au-

tonomous motion relative to each shape. But it can

Figure 4: The control system.

Figure 5: Proposed operation strategies.

be assumed that these shapes are consisted of many

bumps. Therefore, in this paper, we set the envi-

ronment to one bump, and consider about the oper-

ation strategies to climb up this one bump. Because

the climbing bump ability is important as one of the

most fundamental mobility index (Inoh, 2005), in ad-

dition climbing bump experiment is adopted by many

researches as an evaluation experiment for mobilities.

The proposed operation sterategies has 7 steps (Fig-

ure 5). It is low level operations(tasks), namely it is

not high level operations such as path planning etc. In

this paper we assume that the trajectory of the robot is

already given. Therefore the proposed operation deals

with how the robot can pass over the obstacles. Fol-

lowing sections will show the details of each steps.

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398

Center Stage

Front Stage

Rear Stage

Joint

Figure 6: The deﬁnition of the parameters.

Figure 7: The PSD distance sensor.

Figure 6 is the diﬁnition of the parameters. Here θ

is the orientation of the center stage. θ

and θ

are

the 1st and 2nd joint angle related to the θ

. Our pro-

posed operation sterategies can work by using only 3

very simple sensors.

3.1 First Step

First, the robot goes forward until detecting the wall.

If the robot faces the wall, then robot stops moving.

PSD distance sensor which is attached to the 1st stage

is used for detecting the wall (Figure 7). The informa-

tion of the PSD sensor is managed by the main con-

troller (Figure 4).

3.2 Second Step

In this step, 1st joint are driven to detect θ

ref

. θ

ref

is the 1st joint angle when the tangent of front stage

meets the edge of the bump (Figure 8).

Figure 8: The deﬁnition of θ

ref

Inclinometers

Figure 9: Inclinometers for detecting θ

3.3 Third Step

In third step, 2nd joint is driven while the robot goes

forward. The purpose of this step is to get the trac-

tion forces by keeping a grounding of rear stage. If

the robot goes forward without driving 2nd joint, then

robot could not get enough traction forces due to the

lift of rear stage. In order to keep the grounding of

rear stage, 2nd joint angle should be set to angle of

center stage, namely the 2nd joint is driven in the fol-

lowing condition.

= θ

Here, the inclinometers which are attached to the cen-

ter stage are used to detect the angle of the center

stage (Figure 9).

3.4 Fourth Step

In this step, 1st joint angle is set to 0 rad, 2nd joint is

driven to let the angle between rear stage and ground

be right angle. At this moment, the robot continues

moving. There are two purpose in this step. One is to

obtain the traction forces, that is the role of 1st joint

motion. The other is to lift up the robot as high as

possible, that is the purpose of 2nd joint motion. 2nd

joint angle is determined by following condition. By

this condition, rear stage can always stand with keep-

ing right angle to the ground.

− θ

DEVELOPMENT OF THE CONNECTED CRAWLER ROBOT FOR ROUGH TERRAIN - Realization of the

Autonomous Motions

399

Figure 10: The situation of climbing up a bump.

Figure 11: Contact detection device.

The trigger to shift third step to fourth step is the θ

ref

In the third step, when the orientation of center stage

is equal to θ

ref

, operation step is shifted.

3.5 Fifth Step

The robot goes forward with keeping above men-

tioned conditions. When the center of gravity of the

robot is in the right side of the bump edge, then the

clock wise moment is generated around the edge, the

robot can climb a bump. Figure 10 shows the situation

of this case.

3.6 Sixth and Seventh Step

At the end, 2nd joint angle is set to the initial position,

not to interfere robot’s moving. The trigger for this

motion is contact between bump and rear stage. The

photoreﬂector is adopted to detect this contact. This

photoreﬂector is attached to root and bottom of the

rear stage (Figure 11).

By above steps, climibing a bump is completed.

4 EXPERIMENTS

In order to conﬁrm proposed operation strategies, ver-

iﬁcation experiments are conducted. We prepare two

kinds of experiments. One is that the robot passes

over two bumps with different height. The other is

stairs ascending. There are remarkable points in these

experiments. These experiment veriﬁes whether the

robot can pass over the different height and different

structures obstacles by using only proposed strategies.

Moreover the sensors which realize proposed strate-

gies is very simple, and the number of sensor is very

small. Therefore if these experiments success, it can

be concluded that proposed strategies has extremely

high usefulness.

4.1 Passing Over the Different Hight

Bumps

In this chapter, the robot passes over the different

height bumps. The heights of bumps are 150 mm and

40 mm. The experimental environment is indoor, and

robot goes only forward, does not rotate and reverse.

We made the experiment by implementing proposed

strategies to main controller.

The result is shown in Figure 12. This Figure

shows that the robot can pass over the different hight

bumps autonomously.

4.2 Stairs Ascending

Next experiment is stairs ascending. The height be-

tween stairs is 150 mm, that is conventional stairs.

The implemented software to main controller is the

same as experiment in 4.1, namely we do not add any

modiﬁcation, that is completely same. Then we con-

ducted the experiment.

The result is Figure 13. From this Figure, it

is turned out that the robot could ascend stairs au-

tonomously with driving joints.

5 CONCLUSIONS

The purpose of this research is to develop a rough ter-

rain mobile robot which can realize autonomous mo-

tion in disaster places. Especially, this paper proposed

autnomous operation strategy for passing over ob-

stacles, as well as constructing of connected crawler

robot as the ﬁrst step of this research. The connected

crawler robot consisted of 3 crawler stages with ac-

tive joints. The operation strategies was proposed in

Chapter 3. This operation strategies was consisted

ICINCO 2007 - International Conference on Informatics in Control, Automation and Robotics

400

Figure 12: The experimental results of passing over bumps.

of 7 steps, and it needed only 3 simple sensor which

were PSD distance sensor, inclinometers and photore-

ﬂectors. We have also made veriﬁcation experiment

of proposed operation strategy. For this veriﬁcation,

we did 2 types of experiments. One was that the robot

passes over bumps with different heights. The other

was stairs ascending.

Both experiments had a great success. There were

remarkable points in these experiments. These exper-

iments showed that the robot can pass over the dif-

ferent height and different structual obstacles by us-

ing only (same) strategy. Moreover the sensors which

realize proposed strategy were very simple, and the

number of sensor was very small. Therefore it can be

concluded that proposed strategy has extremely high

usefulness.

Future works: Proposed method was veriﬁed by

two experiments. In addition, we are going to verify

proposed method by many different types of experi-

ments. Moreover, this paper derived the autonomous

motion empirically. Therefore we have to analyze

motions of the passing over the obstacles as next step.

Figure 13: The experimental results of stairs ascending.

Furthermore we have to compare empirical results

and analytical results.

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Inoh, T. (2005). Mobility of the irregular terrain for resucue

robots. In 10th Robotics symposia. pp 39-44.

Lee, C. (2003). Double -track mobile robot for haz-

ardous environment applications. Advanced Robotics,

Tokyo, vol. 17, no. 5, pp 447-495, 2003 edition.

Osuka, K. (2003). Development of mobile inspection robot

for rescue activities:moira. In Proceedings of the 2003

IEEE/RSJ Intl. Conference on Intelligent Robots and

Systems. IEEE.

Takayama, T. (2004). Development of connected crawler

vehicle souryu-iii for rescue application. In Proc. of

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Autonomous Motions

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