The Design of a Rugged, Low-Cost, Man-PackableUrban Search and Rescue Robotic SystemThomas J. Mathew,

Greig Knox and W. K. FongRobotics and Agents Research Lab

Department of Mechanical EngineeringUniversity of Cape TownCape Town, South Africa

Email: thomas@mathew.co.za

Tracy Booysen

Robotics and Agents Research LabDepartment of Mechanical Engineering

University of Cape TownCape Town, South Africa

Email: tracy.booysen@uct.ac.za

Stephen Marais

University of JohannesburgJohannesburg, South Africa

Email: stephentmarais@gmail.com

Abstract—Requirements of robotic systems for Urban Searchand Rescue vary according to the disaster, and a number ofsystems have been developed to meet these needs. However ithas been identified that there is a need for a general purpose,first response rescue robot. Such a robot would be small, rugged,equipped with a basic general-purpose sensor payload, and beeasily transported. This paper outlines the design of a Low Cost,Man-Packable, Rugged Rescue Robotic System intended to meetthis need. It discusses the requirements and implementation ofthe system currently being developed by the Robotics and AgentsResearch Lab at the University of Cape Town.

Index Terms—Design Engineering, Earthquakes, Tsunami,Terrorism, Reconnaissance, Inspection, Nondestructive testing,Mobile robots, Ergonomics, Identification of persons, Remotelyoperated vehicles,

I. INTRODUCTION

The attractiveness of robots for disaster rescue stems fromtheir potential to “extend the sense of the responders into theinterior of the rubble or through hazardous material” [1]. Theirincreased expendability over dogs or human workers alsomakes them ideal, especially for initial surveillance of danger-ous areas. The first documented case where robotic systemswere used to assist the rescue operation was in the aftermath ofthe 2001 terrorist attack on the World Trade Center [2]. Whileno actual survivors were recovered, it served as a platformto highlight the possibilities for the use of robotic systemsin Urban Search And Rescue (USAR). The knowledge fromthis rescue operation along with subsequent robot-assistedUSAR operations has highlighted some of the difficulties andshortcomings of the currently available systems. The majordifficulty for a USAR operation is the challenging and highlyvaried nature of disaster environments, and although a numberof solutions have been proposed and developed in the past,none have been cheap and reliable enough to infiltrate all areasof USAR. In a companion paper [3], a review of the disasterswhere rescue robots were used was made. This highlighted thechallenges faced by rescue workers in incorporating robots intotheir teams, and in particular raised concerns about the existinglarger and more sophisticated systems. Following this, a reviewof commercially available robotic systems, such as the ReconScout [4] [5] and the IRobot FirstLook [6] was conducted.

While these systems can fulfil the man-packable and throwablerequirements, they are far from low-cost solutions. From thisresearch, the need for a small, affordable General Purpose,First Response Rescue Robot was shown.

In order to address this need, a rugged, low-cost, man-packable robotic platform is being developed, which could beused as a primary investigative tool in any disaster scenario.It follows Jacoff’s recommendation that “the entire roboticsystem and required tool can be carried by a single operator”[1], can be deployed by throwing or dropping up to 3 metres,and is cheap enough such that the robotic platform can beconsidered to be disposable or expendable. Based on currentresearch, this is benchmarked at US $500. This is low-costenough that one or more robots could be present in each rescueteam and fire department and that they could be used withoutsignificant concern for losing a robot. This would ensure thatrescue operations could commence without the need to waitfor more complex and specialized robots to arrive on scene.

II. SYSTEM OVERVIEW AND DEPLOYMENT STRATEGY

The system described in this paper was designed with theobjective of fulfilling the requirements of a man packable,throwable, tether-less rescue robotic system. The robotic sys-tem is comprised of two main subsystems. The first subsystemis a wearable operator station, comprised of a transportationdevice and user interface. The second subsystem is the roboticplatform, seen in Figure 1, which is mobile, throwable andis used to explore the disaster environment. The tether-lessinteraction between these two subsystems can be seen inFigure 2.

Having multiple rescuers carry a single robot, in disasterzones, is very cumbersome. The optimal ratio of rescue work-ers to robots, for both transport and operation, is 1:1 [2]. Thetransportation harness is attached to a tactical vest, creatinga man-portable system with the desired ratio. In additionto transporting the robotic platform, the harness also housesthe in-field charging station, the communication and controlmodules for the user interface. The in-field charging systemincreases the operational range and efficiency of the systemby charging the robotic platform after each deployment.

Fig. 1. Drawing of a prototype robotic platform

Fig. 2. Diagram of system data flow

Deployment of the robot is designed to be as easy aspossible, with the operator removing the robotic platformfrom the vest and throwing or dropping the platform into theinspection environment. The tail which is attached to the robotcan be used as a handle to ease carrying and assist in throwing.On impact, the large wheels (seen in Figure 1) absorb themajority of the energy of the impact, protecting the payloadlocated inside. The design of the platform allows for a varietyof specialised sensor payloads to be fitted. The first iterationof the robotic system includes two payloads, the first of whichwill incorporate minimum sensing requirements as defined byMurphy [7] and completes the low cost configuration of thesystem. A more advanced and expensive payload will be thebase for further higher-function sensor designs.

Due to the hazardous nature of rescue environments, thereis a reasonable chance for a rescue robot not returning safelyto the operator. To avoid the huge financial risk and operatorstress of losing a robot, this system was designed to beexpendable. However, since the operator remains in a placeof relative safety the operator station was not designed to beexpendable. Each operator station can be used with multiplerobots should any become lost or damaged or should differentrobots with different sensor payloads be needed. Despite thenon-expendability of the operator station, the complete systemremains significantly more affordable than any commercially-available alternatives. The specification of the proposed system

are summarized by Table I. As the operator station is thepoint of human-robot interaction, we begin by describing thissubsystem.

TABLE ISUMMARY OF SYSTEM SPECIFICATION

Robotic PlatformSpecification Value

Operational Time 1 hour 10 min

Sensors Temperature, Audio, Vision

Illumination LED 200 Lumen

Communication Range (Indoor) 30m

Weight 1.6 Kg

Dimensions 298 x 396 x 223 mm

Drop Height 3m

Operator StationPlatform Charge Cycles 2

Human : Robot ratio 1:1

III. OPERATOR STATION

A. User Interface and Data Fusion

During the setup and initial phases of a rescue operation,operators may not sleep for 48 hours and work in 12 hourshifts [2]. Operator fatigue becomes a significant issue andshould be accounted for in the design of the operator station.The operator may be wearing gloves, and the interface willbe exposed to the hazards and rigours of an urban searchand rescue operation. This indicates the need for a simpleand rugged operator interface. The simplicity of the operatorinterface should extend to the training time as long trainingtimes will significantly reduce the efficacy of a first responsesystem. To maintain the 1:1 human/robot ratio, the interfaceshould be hand-held. Taking all of these considerations intoaccount the the rugged hand-held controller seen in Figure 3was designed.

Fig. 3. The Hand-held Controller

The controller circuitry is enclosed in an ergonomicallydesigned HDPE shell and includes a joystick for basic robotnavigation, four buttons to provide auxiliary functions and

a 3.5” LCD screen for the display of sensor data. Selectedsensory data is overlaid onto the incoming camera feed tobe displayed on the LCD. Alternatively, should viewing theLCD screen not be viable due to environmental factors suchas glare or dust, the video feed and sensor data can be viewedvia a set of FatShark Dominator FPV goggles included withthe pack. In order to reduce the weight and damage risk of thehand-held user interface, all data processing circuitry is locatedinside the transportation harness. User inputs and data to bedisplayed on the LCD screen is communicated via a tetherbetween interface and the harness where the data is processedusing an ARM Cortex-M4 STM32F407 microcontroller. Thetether also serves to prevent the controller from being droppedand/or lost.

The position of the joystick is translated into motor com-mands which are transmitted to the robotic platform. The fourbuttons allow modification of the sensory data displayed onthe on-screen display. This simple user interface with minimaluser inputs reduces the complexity of operational commandsand thus reduces training time. A Maxim MAX7456 on-screendisplay chip overlays sensory data received from the platformand the controller provides the operator with their GPS loca-tion using an uBlox Neo-7M. Additionally, the controller unitmonitors the operator station power systems and charging ofthe robotic platform during transport.

B. Transportation Harness Design

The transportation harness has multiple functions; it car-ries the robot and the hand-held controller and houses thecomputational circuitry of the communications system andcontroller. A modular design segregates each of the fourfunctional modules into their own respective compartment.These modules include, the on-board charging system, themain processing unit, the power management and the wirelesstransmission. The system is designed to be weatherproof whilestill allowing the operator easy access to system controls anddata logging. The axles of the robotic platform are held byslots in the harness which allow for quick deployment; theseare seen in Figure 4. The transportation harness is primarilymachined from HDPE due to its large strength to density ratio,providing ruggedness at a light weight.

The harness has been integrated onto a Crossdraw tacticalvest (shown in Figure 5) which enables the system to beworn by the operator. A high resting position of the systemdistributes the bulk of the weight between the operator’sshoulder blades, letting it rest directly on the hips.

IV. THE ROBOTIC PLATFORM

A. Platform Design

For ease of manufacture and to reduce costs associated withmechanical complexity, the body is designed such that thestructural chassis, supports for fastening internal components,and an outer ’skin’ are combined into single integrated parts.As such, the bulk of the mechanical design is represented bythe top, bottom and front pieces of this shell (shown as anexploded assembly in Figure 6). The front panel is designed

Fig. 4. Transportation Harness (top) & Transportation Harness with RoboticPlatform inserted (bottom)

Fig. 5. Crossdraw Vest with Carrier Pack Back View (left) & Front View(right)

to support the sensors, cameras and other electronics that couldbe carried by this robotic platform and as such is removableand customisable to specific needs. Two small aluminiumheat-sinks are recessed into the shells to allow heat frominternal electronics, (RF transmitters and the motor controllercircuitry) to dissipate to the environment. All the mountingsurfaces incorporate a clearance for a rubber gasket, sealingthe inner workings of the robot from water, dust, and othercontaminants.

Two DC motors with built-in reduction gearboxes are di-rectly coupled to the wheels. To absorb any forces that are not

taken up by the wheels themselves, the motors are completelyencased in dense impact-absorbing expanded polyethylenefoam, which allows a small amount of movement in anydirection.

Fig. 6. Exploded view of robot platform shell assembly

The battery, communication and motor control modules arelocated at the rear of the platform. In order to reduce the cost ofthe interchangeable sensor payloads, and to ensure reliabilityof the platform, these are fixed components and are used forall payload configurations. The sensor payload is positioned atthe front of the platform in a T-shape to maximise the frontalarea on which sensors can be placed.

Fig. 7. The Internal Structure of the Robotic Platform

The robot platform is equipped with enough control cir-cuitry so as to be self-sufficient. All that it requires is powerfrom the battery and a serial data stream of instructions in apre-defined data packet format. In return it provides feedbackon temperature and current consumption of the system. This isachieved with two Freescale MC33926 H-bridge drivers anda low-cost MSP430 microcontroller which manages commu-nications between the controllers and other sub-systems.

Although it is envisaged that the final product can be mass-produced by injection moulding, a first iteration of theseparts have been manufactured by CNC milling at the UCTMechanical Engineering Workshop.

The mechanical design also incorporates a ’tail’ whichserves three purposes: firstly, to provide reaction torque to thebody of the robot when it is attempting to surmount obstacles;secondly, to aerodynamically control the falling of the robotsuch that it lands in a controlled fashion, face-first, on bothwheels; and thirdly as a handle to throw the robot in thestyle of an Olympic hammer-throw, increasing its deploymentdistance. Prototyping has shown that even a small ’dart’ tailcan have a dramatic effect on the falling orientation of smallrobots whilst in free-fall. This tail is designed to, consideringthe size of the wheels, leave the robot at a resting positionsuch that the primary camera’s field of view allows optimalvisibility of its surroundings.

B. Wheels and Shock AbsorptionThe design of impact-absorbing wheels is, broadly speaking,

not a well-documented field. Most prior designs are intendedto absorb very small deflections such as those usually expe-rienced by automotive suspension systems, and as such areonly of peripheral interest to the challenge at hand. Manyother designs are not in the public domain as they are ofa proprietary commercial or military nature. As such, thisaspect of the design has relied heavily on an empirical testingmethodology.

In the interest of using materials that are both low-costand easily workable for testing purposes, the wheels are two-dimensional structures laser-cut and laminated from sheetsof expanded polyethylene foam. An existing drop tester righas been re-purposed to drop a mass representative of thefinished robot, and it is instrumented with a high-G, high-bandwidth piezo accelerometer. Additionally, a high-speedcamera captures video at 10 000 frames per second, enablingimage processing techniques to be used to corroborate theaccelerometer data. Images from this testing can be seen inFigure 8.

Fig. 8. High-speed photography showing prototype wheels under drop testing

Wheels of varying densities and geometry were affixedto the mass and dropped from varying heights to determinethe shock absorption capabilities of each wheel. The easeof manufacture of these wheels allows for rapid prototypingand affordable iterative design, with each wheel improvingon the rapidly-obtained results of the previous iteration. Thisinvestigation is currently ongoing; Figure 9 shows some ofthe wheel designs considered. At present the best wheels arelowering the impact acceleration to as little as 90G, well withinthe target of 250G, but a better-optimised design will trade offsome of this cushioning for decreased deflection so as not torisk the suspension bottoming out.

Fig. 9. Examples of some prototype wheel designs

C. Sensor Payload

One of the major downfalls of many existing systems is thatadditional sensors are attached externally. This increases thebulkiness of the robot and reduces its deployment options, asthe sensors are no longer protected. In order to circumvent thisissue, the system was designed to incorporate interchangeablesensor payloads internally. The first generation prototype hastwo sensor payloads; one has an aggressively minimalisticdesign in order to reduce cost and operator training time. Thesecond has increased capability which will allow for futureaddition of higher level data processing and additional sensors.

The minimum sensor requirement for an inspection classrobotic system includes a colour optical camera, lighting,environmental temperature sensor and a microphone [7], [8].This will allow the operator to inspect the environment usingboth sight and sound. Additionally, as the robotic platform canoperate either way up, it is necessary to know the orientationof the robot so as to invert the video feed and motor controlappropriately. A magnetometer and accelerometer providethe system with a 6-degree-of-freedom IMU, adding to thefunctionality of the platform with minimal additional cost andpower consumption. The sensor integration and communica-tions with the operator and platform itself are managed by aTexas Instruments MSP430 microcontroller which is both lowcost and low power, but is limited in its expandability andprocessing power if further sensors or data fusion are required.

The second sensor payload will allow for a higher levelprocess such as image processing, proposed as future work.This system is controlled by an ARM Cortex-M4 STM32F407microcontroller, and incorporates the capabilities of the min-imum requirement sensor payload, with added expandability.There are additional power and communication ports availablefor additional sensors - for example, the FLIR Quark thermalcamera and a 9-degree-of-freedom IMU are currently beingused.

V. DATA COMMUNICATION

To reduce the bandwidth requirement, the communicationsbetween operator control station and the robotic platform havebeen spilt across two different frequencies. The commandsand sensor data are transmitted using the Texas InstrumentsCC110L, a low-cost transceiver operating in the 433 MHz

frequency range, while video and audio is transmitted usinga 1.3 GHz transmitter receiver pair originally designed forhobbyist drones. As high data loss can be expected due tothe likely prevalence of RF-blocking concrete and steel inan USAR environment, CRC checks are applied to the datapackets, to enable detection of corrupted packets. This haslead to a zero packet loss in current tests. Motor commandsare separated out by the microcontroller in the sensor payload,which then exchanges information directly via wire link to theplatform’s dedicated controller.

VI. POWER MANAGEMENT

Research into previous USAR operations has found thatthe average operation time of a robot, before returning to theoperator, was 6.44 minutes [2]. However, at the point wherea victim has been identified, the robotic platform becomesthe means of communication with the victim, who will takeon average 4 hours to excavate [2]. Therefore both the fulloperational and active standby modes need to be considered,which can be defined as;

Full Operational ModeMotors operating at 75% of maximum capacity, LEDillumination at 80% of maximum power and all sen-sory and communication systems fully operational.

Active Standby ModeLED illumination at 10% of maximum power, fullcommunication, optical camera, and microphone op-erational.

TABLE IIOPERATIONAL MODE POWER CONSUMPTIONS

Operational Mode Power Consumption (W)Full Operation 37.5

Active Standby 6

The data in Table II is calculated from tests of our prototype.Assuming 4 minutes of full operation before identifying avictim and a 5 hour excavation time [9], a 2200mAh 4SLithium Polymer battery could be selected. However to allowfor future sensor payload power requirements and a safetymargin, a 3000mAh battery was selected.

The operator station is required to be battery powered, toallow deployment of the robotic platform from any locationin the disaster environment. As suggested by Barnes [10],field charging has been incorporated in the system allowingfor two charge cycles of the robotic platform. The powerfor this in-field charging is provided by a large 8000mAhLithium-Ion battery contained in the transportation harness.The control station’s battery is also able to be charged whilethe robotic system is in storage, using a separate power supply.This allows for both batteries to always be fully charged oncerequired for an operation. Due to the risks [11] associated withlithium batteries, considerable efforts have been undertakento protect the operator in the event of a battery malfunction.A battery protection board is included on the transportation

harness, disconnecting the 8000mAh battery from the rest ofthe system should any battery faults occur, such as cell over-voltage, under-voltage, or over-temperature. This also providescell-balancing functionality.

In the platform, a two-tier battery protection system hasbeen implemented. The primary battery protection is per-formed by a state-of-charge IC. When an over-voltage or over-current event is detected, the battery is disconnected from thesystem using two MOSFETs. The system can be softwarereset once the event has passed. Should the primary batteryprotection fail, the secondary battery protection IC opens ahigh current path, limited to 60A, which is used to blow a 10Afuse disconnecting the battery and the system permanently.This is a destructive last-resort mechanism; once activated,both the battery protection system and the fuse need to bereplaced. The batteries are also mechanically protected frompiercing or other damage by their strategic placement withinthe housings of the platform and control station.

VII. COST BREAKDOWN

Based on the recommendations outlined in the companionpaper [3], the combined robotic platform and basic sensorpayload are designed to be expendable. As such, this costis benchmarked at USD $500. The operator control stationis more expensive, although the combined system is still,orders of magnitude cheaper than the competitors [12], [13].A detailed cost breakdown is shown in Table III.

TABLE IIICOST BREAKDOWN BY SUBSYSTEM

Sub-system Production cost(Estimated USD)

Operator Control Station Total: $1100

HDPE mountings $350

Battery and Electronics $650

Tactical Vest $100

Robotic Platform Total: $445

Motors & Control Circuitry $200

Power System $70

Communication System $55

HDPE shell $100

Wheels and Tail $20

Basic Sensor Payload Total: $40

VIII. CONCLUSION

Our development thus far has shown that it is possible,within the financial limitations of keeping the robot expend-ably cheap, to build a suitable general-purpose, first-responserobotic rescue system. Although some sub-systems are stillunder development, the work thus far shows a reliable proof-of-concept. The platform is simple enough to be affordablyreplaced, and rugged enough to withstand deployment bythrowing. The operator control station provides a safe and easymethod of transporting, charging, and controlling the robotduring rescue operations, and requires only one operator per

robot. Sensor payloads are basic but effective and have thecapacity to be extended in future work.

IX. FUTURE WORK

The full integration and testing of the current system has notbeen completed and hence will be the focus of the future work.Critically, testing of the system in a real world environment -either an actual disaster or a simulated environment - willprovide invaluable information. This will guide the futuresteps of development and highlight specific target areas forimprovement.

A variety of areas for further development have been noted.For example, detailed FEM simulations could be valuablein optimising the designed geometries of the wheels andshell components in terms of increased strength or reducedmass/cost. Following the advice of Murphy and Casper [2],real-time image processing could be implemented to allow forthe detection of objects associated with victims such as bodyparts, watches and glasses.

Although this robot is presently configured to be tether-less,certain rescue scenarios may benefit from the use of a tether.To mitigate the know disadvantages of tether use [2], [3], sometether management system could be developed.

REFERENCES

[1] A. Jacoff, “Search and rescue robotics,” in Springer Handbook ofRobotics. Springer, 2008, pp. 1151–1173.

[2] J. Casper and R. Murphy, “Human-robot interactions during the robot-assisted urban search and rescue response at the world trade center,”Systems, Man, and Cybernetics, Part B: . . . , vol. 33, no. 3, pp. 367–85,2003.

[3] The Case for a General Purpose, First Response Rescue Robot, 2014.[4] Recon Robotics, “Recon Robotics - Throwbot XT with Audio.”

[Online]. Available: http://www.reconrobotics.com/products/ThrowbotXT audio.cfm

[5] ——, “Recon Scout XL Specification Sheet,” 2013. [On-line]. Available: http://www.recon-scout.com/pdfs/ReconRoboticsReconScout XL 4-13-v106.pdf

[6] iRobot Corporation, “iRobot FirstLook Specifica-tions,” Tech. Rep., 2012. [Online]. Avail-able: http://www.irobot.com/us/robots/defense/firstlook/∼/media/Files/Robots/Defense/FirstLook/iRobot-110-FirstLook-Specs.ashx

[7] R. Murphy, J. Casper, J. Hyams, M. Micire, and B. Minten, “Mobilityand sensing demands in usar,” in Industrial Electronics Society, 2000.IECON 2000. 26th Annual Confjerence of the IEEE, vol. 1. IEEE,2000, pp. 138–142.

[8] R. Murphy, J. Blitch, and J. Casper, “Urban Search and Rescue EventsReality and Competition,” vol. 23, no. 1, pp. 37–42, 2002.

[9] United States Fire Administration and National Fire Association, RescueSystems I, 1993.

[10] M. Barnes, H. Everett, and P. Rudakevych, “Throwbot: Design consid-erations for a man-portable throwable robot,” in Defense and Security.International Society for Optics and Photonics, 2005, pp. 511–520.

[11] L. Xiao, X. Ai, Y. Cao, and H. Yang, “Electrochemical behavior ofbiphenyl as polymerizable additive for overcharge protection of lithiumion batteries,” Electrochimica Acta, vol. 49, no. 24, pp. 4189 – 4196,2004.

[12] U.S. General Services Administration, “GSA Advantage! Store,” 2013.[Online]. Available: https://www.gsaadvantage.gov/advantage/s/search.do?searchType=0&db=0&q=0:0reconrobotics&p=3

[13] P&R Infrared, “Recon Scout Throwbot - P&R Infrared.” [Online].Available: http://www.pr-infrared.com/shop/recon-scout-throwbot/