An approach to build simplified semi-autonomous Mars Rover Nazmus Sakib', Zayed Ahmed2 ,ArafFarayez3, Md. Hasanul Kabir4 Department of Computer Science and Engineering, Islamic University of Technology (!UT) Gazipur, Bangladesh Email:
[email protected] [email protected] [email protected] [email protected] Abstract-This paper represents a simplified approach to build and operate Martian Rover in order to carry out complex tasks. The robot IUT Mars Rover, had been successfully tested on simulated Martian terrain at European Rover Challenge
2015,
Poland organized by European Space Foundation. It is built on popular simplified rocker bogie suspension system, a robotic arm, sensors integrated with interactive applications. The research work
is
mostly
focused
on
vision
and
enhancement
of
computational efficiency. The wirelessly controlled mars rover is also capable of autonomous ride with GPS and has RGB-D camera for smooth control and depth sensing. In this paper we will discuss the overall design mechanism and the technologies used along with the operating algorithms for different rover functionalities.
Index Terms-mars rover; autonomous navigation; RGB Depth; ofJline map, mobile robot I.
INTRODUCTION
Planetary exploration is one of the major topics in research nowadays. These research contributed not only the aspects of space technology but also inspired solving many problems related to earth. Mobile robot is a vital key to carry out mission in adverse planetary surface and carry out experiment or data collection. The type of missions where human activities are limited, wheel based locomotion equipped with multiple sensors, controls can help us on a greater level. Different types of competitions like University Rover Challenge (URC), United Kingdom Rover Challenge (UKRC), and European Rover Challenge (ERC) create pseudo mars like terrain and invite students, researchers across the world to test their own built technologies and ideas. In this paper we are providing insight into the technological aspects of our designed rover, our own built software for control, vision and autonomous navigation. H.
kinematic modeling for traversing on rough surface [2]. Traction control on rough surface is one the most critical phenomenon in this field. Different scientists have derived mathematical relation in order to ensure maximum traction force with the terrain geometry reckoning wheel ground contact angle [3]. Lindemann and Chris delineated performance criteria and testing of mars rovers like spirit and opportunity [5]. Optimization of different performance matrix like hardware manipulation as well as structural design, on rough terrain had been analyzed by Thomas Thueer. [6] .The rover Rocky 7 by Ohm and Ivlev [7] describes the overall hardware and software solution including vision based navigation. The Russian Rover Marsokhod [8] cover the design procedures with stereovision for autonomous mobility. M.Maurette's [9] work on autonomous navigation depicts the fact of rover's daily traversal capability mostly on crossing critical terrain. 1II.
SYSTEM ARCHITECTURE
Our rover follows a simplified version of rocker-bogie mechanism with six wheels driven by gear motors with triple rocker system consists of two frontal rockers and a rear rocker. The chassis serves as a mounting point for rocker arm, electric box, and robotic arm. The arm has 6 degree of freedom and a replaceable grabber for accomplishing various task like astronaut assisting, equipment servicing, soil collection etc. The rover weighting 39 Kg is mobile and can be controlled from
RELATED WORKS
Inspiration for space exploration made its path long before in the past. Different works have been done by various scientist and space organizations. After the exploration of the moon, people put their interest on mars. Small rover "Sojoumer" conducted scientific experiments for 83 Sols (Mars Days) and took hundreds of photographs [1]. This successful mission encouraged the scientists and NASA to continue the Mars exploration with new rovers. M. Tarokhl and Hung gave the
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Fig.
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J. CAD
design of the JUT Mars Rover
800m distant. It has 3 cameras for VISIon and navigation. Rover is controlled via computer application and is capable of autonomous ride with pre-loaded co-ordinates. IV.
ROVER MECHANICS
A. Body and suspension Each side of the body contains equal number of wheels ensuring the uniform load distribution all over the body. At the back side a spring suspension system is used to absorb shock, assuring the maximum traction force which enhanced the traversing capability on the rough terrain. The body frame of the rover is made up of light hollow aluminum bar which is totally rigid and can withstand the impact load. In the chassis, There are four horizontal and two vertical bar joined with one another using L clamp with nuts and bolts. The dimension of the rover is 150*110*45 cm. This height of the rover ensures lower center of gravity which will assist during inclination. Electrical box which is attached with two centrifugal fan of 1000 RPM can withstand temperature up to 45 degree centigrade. CFD analysis of the fluid flow and contour temp rise is provided in the fig 3. Rocker arm is analyzed, the upper hole's boundary condition is taken as simply supported and reaction force 200 N is applied in the lower two holes Fig. 2(a).
... N
....... ..
...
_v
B. Wheel Wheel rims are made of aluminum covered with Styrene Butadiene, natural rubber, zinc and different types of additives to increase traction and reduce friction between ground and tire. The diameter of the wheel is 26 cm. The rubber has chevron like zigzag pattern as Fig. 2(b) to assist in locomotion in rough terrain and overcome impedance created by large rocks. FEM analysis was done before manufacturing, giving force 200 N and torque 300 Nm. The results are shown in Fig.2(c). Another type of bicycle-wheel with less width is also tested which consumed less power. But due to less width traction area with the ground is reduced. It is analyzed by giving 200 N point force and 160 Nm torque at the center shown in Fig. 2(d).
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, ,...... '..,...
..... y30. 201#1 " .... '" .... (I '� ... .. •• .
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"",,,,,' •• 201. 0 ':HO. "". _ .......... .
Fig. 3. FEM analysis of excavator bucket, Fluid flow and temperature contour of electronic box
V.
ROVER ARM
The main parts of our robotic arm are comprised of base with 360 degree rotation by means of DC gear motor, arm elbow and wrist. The base is basically a spur gear assembly which provides the precise movement of the arm. Two 12 inches actuators are placed, providing the up down movement of arm and elbow respectively. Wrist is attached with two 12kg DC servo motor for providing flexible rotation as well as linear motion of the grabber with a four bar linkage. The gripper and excavator buckets are modular and hence easily replaceable. In the bucket sharp teeth edges with an optimal angle and spacing between teeth is provided for maximum efficiency [12]. The gripper has a worm gear assembly driven by a servo motor [13]. Bucket is made up of aluminum. In Fig. 3(a) ANSYS software shows maximum deformation when 150N force is applied which is under permissible limit. VI.
ELECTRONICS
(m)
.l
The circuits are either ready-made or self-made housed in an insulated electric box. The motor controllers are placed at the peripheral region of the box with heat sink and cooling fans. There are 8 Lithium Polymer Batteries (4 cell, 16.2 volts & 2200mAh). Of them 6 are used to power up the motors, 1 for actuator & motors of the robotic hand and I for router. LiPo battery is used for its lightweight, reliability & small space consumption. The rover can run for approx. 35 minutes with full charge. For low voltage modules (servo, sensors etc.) Buck converter (LM2596S) is used to get 12V, 9.6V, 5V and 3.3V.
Fig. 2. FEM analysis of rocker ann and wheel
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Bas@Station
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Conttolll'l'
Fig. 4. Software architecture and communication design
The rover has 69.Scm brushed DC motors, each having 270 KgF-cm torque, 150 rpm, encoder & helical gear system. SRC SM-S431SR continuous rotation servo having stall torque of IS.4kg.cm & speed of 0.14 sec/60 degrees is used for the hand wrist. One 12kg.cm servo is used for the two fingers of hand. SM-S8166M, twin bearing hybrid geared servo capable of carrying 33kg weight is used for the hand base. Two Pololu LACTlOP 12V linear actuators which can provide positional feedback are used for robotic hand. It has 2S.4cm stroke. It has no load current of SOOmA & full load current of 3A with 20: 1 reduction gear box giving it a dynamic load rating of SOkg. 6 lBT_2 H-Bridge motor controllers are used. It contains two chips (BTS7960) with input voltage rating is 6-27V & maximum current rating of 43A. The H-Bridge driver, thermally protected by a large heat sink, is controlled by PWM signals generated & controlled by MCU. Ubox Neo 6M-0-00l is used for positional updates. Accelerometer MPU-60S0 and a HMCS883L magnetometer are used for assisting in blind traversal task. There are sensors for measurement of pH, humidity, air pressure, moisture, temperature along with Voltage Sensor SEN-OO101 to detect voltage within range 0-30. VII.
COMMUNICATION
For communication we have used 802.11 b/g/n network following the FCC standard. We connected the base station over 2.4 GHz 1000Mbps Wi-Fi router as access point with a 12 dBi Ornni-directional antenna. On the rover side S4Mbps High Gain (4dBi) Wireless USB Adapter was used for better wireless networking, showed in Fig. 4. For reliable data transmission User Datagram Protocol (UDP) was implemented in the controlling applications. The designed network supported control and video streaming up to 700m with operating frequency of 2.412-2.472 GHz. VIII.
Fig. 5. Offline Map
B. OjJline Map The offline map in Fig.S is created with the satellite image of the operating terrain and each pixel is mapped to a co-ordinate using 2d geometric equations. The app needs calibration with 3 realistic data before use. The map window also assists user with live feedback of GPS, magnetic, accelerometer and sensor data sent from the rover. IX.
ROVER VISION AND CONTROL
The rover has 3 cameras: on the top for surveillance, on the arm and another (Kinect Xbox 360) at the frontal part of chassis for depth sensing and depth perception of the terrain immediately before the rover. The acquired raw depth image is converted in to 3d spatial coordinate with the methodology discussed in [10] using the formula following the equations. Xi,j
=
Yi,j
=
V �) 5 ( i -�) d -
*
* *
(Ut + MinD)
(1)
(Ut + MinD)
(2)
The pixel co-ordinate [X Y] has to be converted into linear length with respect to the depth value Z. So mid of the depth image is taken as (0,0) then the left side has negative length in X axis and right side has positive and for Y the upper part is positive and lower part is negative. In the resolution of w x h the scale factor S .0021 and minimum active distance of =
ROVER SOFTWARE
A. Software Architecture The rovers operating software is divided into 3 major parts: (1) Main Controller, (2) Rover controller and (3) Peripheral Controller. The main controller running on a notebook computer is responsible for remote controlling and monitoring the status from the base station. The rover controller runs on a small netbook computer housed inside the rover. It receives commands from the base station and also sends back the sensor readings, GPS position and other necessary parameters. Another important task of rover controller is to extract necessary commands and forward it to Peripheral Controller over COM port. The peripheral Controller is responsible for executing commands for motors and actuators of the arm.
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Fig. 6. Acquired Depth Image and corresponding ROB image with colored visual assistance
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Kinect MinD 10 are taken with trial and error basis. Based on the new spatial co-ordinates if the rover has a clearance of enough space to move forward then a green rectangular box or otherwise a red box is displayed in the live video feed (Fig. 6). The depth points immediately before the rover within a proximity is marked with red dots. The special co-ordinates are calculated on the netbook on rover and the calculated values are sent to base station app.
XI.
=
X.
AUTONOMOUS NAVIGATION
The rover has a simple autonomous navigation feature with obstacle avoidance. Algorithm 1 demonstrate the overall process detailed in following section: Algorithm 1 Autonomous Navigation
1. visit_coordinates +- LoadLocationsToVisit( ) 2. for each next-destination in visit-coordinates 3. while distance between current�osition, next-destination < thresh-min-dis 4. if obstacle( ) true then obstacle_avoid_sequence( ) 5. 6. end if error +- deviation angle between current_head and 7. target_head if error < thresh_deviation _angle then 8. 9. adjust_rover_direction( ) go to step 3 10. 11. end if 12. Rover_Movement_PID( error ) =
13.
end while
XII.
CONCLUSION
Our approach of building mars rover and its application follows simpler procedures yet solves the critical problems. Although the low cost mobile rover was designed to participate and solve the challenges of ERC 2015 yet the proposed solution and system design can successfully be used in multivariate applications e.g. environmental dataset collector robot, human assistant robot, surveillance robot etc. REFERENCES [I]
B.Vilcox, T.Nguyen, Sojoumer on Mars and Lessons Leamed for Future Planetary Rovers, ICES, 1997
[2]
Tarokh, Mahmoud, et al. "K inematic modeling of a high mobility Mars rover." Robotics and Automation, 1999 . Proceedings. 1999 IEEE International Conference on. Vol. 2. IEEE, 1999 .
[3]
Thianwiboon, Mongkol, and Viboon Sangveraphunsiri. "Traction control of a rocker- bogie field mobile robot." Thammasat Int. J. Sc. Tech 10.4 (2005).
[ 4]
Lindemann, Randel A., and Chris J. Voorhees. "Mars Exploration Rover mobility assembly design, test and performance." Systems, Man and Cybernetics, 2005 IEEE International Conference on. Vol. I. IEEE, 2005.
[5]
Thueer, Thomas, et al."Performance comparison of rough-terrain robots simulation and hardware.",Journal of Field Robotics 2 4.3(2007):251-271 .
[6]
T. Ohm and R. Ivlev , "Rocky 7 : a next generation Mars rover prototype". Advanced Robotics, volll , n0 4, pp. 3 41-358 , 1996
[7]
M. Lamboley, C. Proy , L. Rastel , T. Nguyen Trong , a. Zashchirinski , Buslaiev, " Marsokhod: Autonomous Navigation Tests on a Mars- Like Terrain", Autonomous Robots, 2 , 3 45-351 (1995) , K1uwer Academic Publishers, Boston. Manufactured in The Netherlands.
[8]
M. maurette , "Mars Rover Autonomous Navigation" , Autonomous Robots 1 4 , 199-208,2003 K1uwer Academic Publishers. Manufactured in The Netherlands.
[9]
Kamarulzaman Kamarudin , Syed Muhammad Mamduh et al. "Method to Convert K inect's 3D Depth Data to a 2D Map for Indoor SLAM ", 2013 IEEE 9'h Intemational Colloquium on Sigmal Processingand its Applications , 8-10 Mac. 2013 , Kuala Lumpur , Malaysia.
14. end for
In the above algorithm the rover attempts to traverse each of the supplied co-ordinates one after another. If the rover reaches the destination within a minimum threshold distance it goes for the next destination. The rover calculates error as the deviation in angle between its current heading and next destination with the help of magnetometer. If the deviation is more than a threshold angle it tilts either left or right to adjust its heading by calling adjustJover_direction function. The calculated error is passed into a PID controller [11] which generates appropriate motor offset to run the rover in linear path. During traversal if the rover senses any obstacle it calls obstacle_avoid_sequenceO, a pre-calibrated function with definite steps. The steps include the rover to move backward by a threshold distance, turning right as long as no obstacle before. Then it goes forward by another threshold distance and the function returns back.
OBSERVATION AND EXPERIMENTS
In Different types of variable terrain tilt surface, rover mobility test has been carried out. The rover was successfully able to run smoothly, traversing two types of terrain one with soft sand medium obstacle with height of 6 cm and another by a very rough and muddy surface along with tilt angle varied from 15 to 22 degree. However, it gives us the chance to look at the limitations of our design. Our robotic hand can easily grab any object, weighing maximum 1.2 kg. It can collect 200 gm. of sand at a time. In ERC our rover picked up a 150 gm. stone. It can perform astronaut assisting task efficiently as well. For the mobility of the hand it can easily pick up any assisting tool like screw driver, electric plug etc. Besides it can successfully rotate valves and turn switches on-off. The autonomous navigation works fine except the deadlock U shaped obstacle.
[10] Sellers, David. "An overview of proportional plus integral plus derivative control and suggestions for its successful application and implementation. [11] Maciejewski, J., A. Jarzybowski, and W. Tr�mpczynski. "Study on the efficiency of the digging process using the model of excavator bucket." Joumal of Terramechanics 40 .4(2003): 221-233 . [12] Coules, Russell G. "Gripper force sensor/controller for robotic arm." U.S. Patent No. 4,600,357 . 15 Jul. 1986 Fig. 7 . Rover testing in pseudo Mars Terrain, ERC 15
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