Mechatronics and Remote Driving Control of the Drive-By-Wire for a Go Kart

sensors

Article Mechatronics and Remote Driving Control of the † Drive-by-Wire for a Go Kart

Chien-Hsun Wu * , Wei-Chen Lin and Kun-Sheng Wang

Department of Vehicle Engineering, National Formosa University, Yunlin 63201, Taiwan; [email protected] (W.-C.L.); [email protected] (K.-S.W.) * Correspondence: [email protected] This paper is an extended version of the paper published in: Wu, C.H.; Lin, W.C.; Lin, Y.Y.; Huang, Y.M. † System Integration of Drive-by-wire for a Go Kart. In Proceedings of the 2019 IEEE Eurasia Conference on IOT, Communication and Engineering, Yunlin, Taiwan, 3–6 October 2019.

Received: 31 December 2019; Accepted: 20 February 2020; Published: 23 February 2020

Abstract: This research mainly aims at the construction of the novel acceleration pedal, the brake pedal and the steering system by mechanical designs and mechatronics technologies, an approach of which is rarely seen in Taiwan. Three highlights can be addressed: 1. The original steering parts were removed with the fault tolerance design being implemented so that the basic steering function can still remain in case of the function failure of the control system. 2. A larger steering angle of the front wheels in response to a speciﬁc rotated angle of the steering wheel is devised when cornering or parking at low speed in interest of drivability, while a smaller one is designed at high speed in favor of driving stability. 3. The operating patterns of the throttle, brake, and steering wheel can be customized in accordance with various driving environments and drivers’ requirements using the self-developed software. The implementation of a steer-by-wire system in the remote driving control for a go kart is described in this study. The mechatronic system is designed in order to support the conversion from human driving to autonomous driving for the go kart in the future. The go kart, using machine vision, is wirelessly controlled in the WiFi frequency bands. The steer-by-wire system was initially modeled as a standalone system for one wheel and subsequently developed into its complete form, including front wheel steering components, acceleration components, brake components, a microcontroller, drive circuit and digital to analog converter. The control output section delivers the commands to the subsystem controllers, relays and converters. The remote driving control of the go kart is activated when proper commands are sent by the vehicle control unit (VCU). All simulation and experiment results demonstrated that the control strategies of duel motors and the VCU control were successfully optimized. The feasibility study and performance evaluation of Taiwan’s go karts will be conducted as an extension of this study in the near future.

Keywords: vehicle control unit; go kart; machine vision; WiFi; drive-by-wire; remote control

1. Introduction A technology known as drive-by-wire, also called “x-by-wire” or “by-wire,” may change the way people drive or the service model. A vehicle with this type of system focuses mainly on electronics to control a wide range of vehicle operations, including: acceleration, braking and steering [1]. By replacing conventional throttle systems, drive-by-wire systems can signiﬁcantly reduce the number of mechanical parts in a vehicle. This reduces weight and increases operational accuracy, and prolongs the period between each routine service for mechanical maintenance and other adjustments. Some drive-by-wire systems even require nearly no service. Less weight and better accuracy can lead to higher fuel eﬃciency and lower emissions [2].

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With the growth of electronics technologies and electrical parts in vehicles, the number of vehicles equipped with drive-by-wire systems are increasing. They are highly computer-based and connected wirelessly to services such as OnStar or Toyota Safety Connect. These features enhance vehicle safety and reliability. Furthermore, a decision-making control algorithm is utilized to manage the autonomous maneuvering of the vehicle in emergency situations [3]. Kalinowski et al. developed an autonomous driving algorithm for a Formula SAE (Society of Automobile Engineers) vehicle. The low-level controller and actuators were setup and studied. The acceleration, braking and steering by wire system equipped in the vehicle were documented and integrated with the low-level controller and safety module [4]. Mokhiamar et al. proposed a control system for skid steering vehicles to enhance the motion dynamics, which especially has a significant benefit on stabilizing the lateral motion and improving the handling characteristics [5]. Gruyer et. al. surveyed recent studies on autonomous driving technologies and controls for the purpose of emulating and replacing the driver’s behaviors with robotic functions. Regarding the autonomous level, the successful beginning steps include some well-known assistance systems such as adaptive cruise control (ACC), automatic emergency braking (AEB), electronic stability control (ESC), lane departure warning (LDW), etc. [6]. In [7], the authors proposed an interacting multiple model approach based on an observer for highly non-linear vehicle dynamics. Through experimental vehicle signals, the algorithm has shown a rapid and robust identification of the faults from the sensor and actuator. For autonomous vehicles, the drive-by-wire technology is regarded as the foundation to increase vehicle control. From various x-by-wire functions, the steer-by-wire system might be the most crucial one in a vehicle. To meet the drivers’ maneuvers and commands, the most significant issue is to handle the wheels. In the research, a proposed sliding mode predictive tracking control (SMPC) has been proposed to deal with the conditions of model uncertainty and disturbance for tracking the wheel steering angle [8]. An integrated system of an electric assisted steering motor and sensors can replace the mechanical steering system in the vehicle. However, two crucial issues should be concerned before commercialization of steer-by-wire systems: (1) maintaining reliability and (2) improving fault-tolerance, where fault detection and isolation (FDI) is required [9]. In [10], Wang et al. studied an autonomous vehicle driving system to achieve such applications. Several key issues including object recognition, classification methods, data registration, data fusion and 3D city modeling were concerned. In complex and changing urban areas, new mobile laser scanning (MLS) systems will be considered for applications. Furthermore, developing rapid, automated and intelligent techniques is required by using machine learning-based methods and a special processing framework [10]. Gao et. al. studied the development of intelligent transportation system (ITS) and vehicle to X technologies capable of detecting a large number of traffic information in the test vehicle [11]. Siegel et al. proposed modern vehicles with an interface for cellular, mesh networking, WiFi, etc. These technologies cover a large variety of range, latency, bandwidth and other specifications as well as market penetration. Moreover, the study revealed that the radio system possessed different robustness to motion, line-of-sight obstruction and antenna design, and thus not all technologies can be properly employed for the specific application [12]. Therefore, this study will focus on the development and application of the go kart industry. From the original steering column, a power steering mechanism capable of manual/remote driving switch control was added. When an abnormal situation occurs, the vehicle control unit (VCU) switches the remote driving mode to manual driving so that the driver can independently control the go kart steering wheel to change the direction of the vehicle. This study includes the design of a steer-by-wire system and signal output of an accelerator with a braking pedal and a VCU that can achieve simple remote driving. The go kart that preserved the original steering wheel, accelerator and braking pedals was further provided with manual driving capable of dual-function mode switching. Sensors 2020, 20, 1216 3 of 13

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2.1. Hardware Configuration of the Acceleration/Brake-by-Wire System TheSensors accelerator 2019, 19, x and braking pedal were developed using Hall-effect sensors. Based3 of on13 the principleThe acceleratorof voltage, anddivider braking circuits pedal for werethe sensors developed of the using accelerator Hall-effect and sensors. braking Based pedal on were the regulatedprinciple of Theto voltage, acceleratoroutput divider 0– 5and V circuits brakingvoltage, for pedal theas sensorsshownwere developed ofin theFigure accelerator using 1. WhenHall-effect and brakingthe sensors. sensor pedal Basedposition were on regulated theof the accelerator/brakingto outputprinciple 0–5 Vof voltage,voltage, pedal asdivider was shown changed, circuits in Figure for the the1 voltage. Whensensors was the of sensortheconverted accelerator position into and ofthe thebraking position accelerator pedal signal were/braking of the regulated to output 0–5 V voltage, as shown in Figure 1. When the sensor position of the accelerator/brakingpedal was changed, pedal the voltage through was the converted change of into the the induced position voltage. signal Finally, of the accelerator the accelerator/braking/braking pedal accelerator/braking pedal was changed, the voltage was converted into the position signal of the pedal output an output signal to the VCU. The schematic configuration is shown in Figure 2. throughaccelerator/braking the change of thepedal induced through voltage. the change Finally, of the induced the accelerator voltage. /Finally,braking the pedal accelerator/braking output an output signalpedal to the output VCU. an The output schematic signal to configuration the VCU. The isschematic shown inconfiguration Figure2. is shown in Figure 2.

FigureFigure 1. TheThe 1. The working working working principle principle principle of ofof the thethe acce accelerationleration/brake-by-wireleration/brake-by-wire/brake-by-wire system. system.

Figure 2. The schematic configuration of the acceleration/brake-by-wire system.

The digital-to-analogFigure 2. TheThe schematic schematic converter configuration conﬁguration (DAC) outputs of of the the analog acceleration/brake-by-wire acceleration voltages/brake-by-wire from a microcontroller, system. and the DAC module is an I2C (Inter-Integrated Circuit) bus-controlled DAC. A DAC allows the user to send Thean analog digital-to-analog signal, such converter as a sine (DAC) (DAC)wave, fromoutputs outputs a digital analog analog source, voltages voltages such from from as the a a microcontroller, microcontroller,I2C interface on and the the 2 DAC microcontroller. module isis anan II2 CTheC (Inter-Integrated(Inter-Integrated 12-bit DAC conv Circuit)erter Circuit) can bus-controlledaccept bus-controlled up to 4096 DAC. possibleDAC. A A DAC inputs DAC allows toallows provide the the user an user analog to sendto send an 2 ananalog analogoutput, signal, signal, where such ansuch as output a sine as wave,avalue sine of from wave, zero a is digital fromzero and source,a digitalan output such source, asvalue the of Isuch C4095 interface as is fullthe scale. onI2C the interfaceThe microcontroller. full scale on the microcontroller.The 12-bitis determined DAC converterThe by 12-bitthe reference can DAC accept convvoltage uperter tothat 4096can supplies accept possible the up VCC inputs to 4096 pin. to possibleIn provide addition, inputs an the analog supply to provide output, voltage an where can analog an be any value within 0–5 V. The microcontroller programming generates PWM (pulse width output,output valuewhere of an zero output is zero value and of an zero output is zero value and of 4095an output is full scale.value Theof 4095 full is scale full isscale. determined The full by scale the modulation) values within 0–255; the DAC module transfers the input value in a range of 0–4096 to isreference determined voltage by the that reference supplies voltage the VCC that pin. supplies In addition, the VCC the supplypin. In addition, voltage can the be supply any value voltage within can the output value mapped to 0–5 V form, as shown in Figure 3. The schematic configuration is shown 0–5 V. The microcontroller programming generates PWM (pulse width modulation) values within be anyin Figurevalue 4. within 0–5 V. The microcontroller programming generates PWM (pulse width modulation)0–255; the DAC values module within transfers 0–255; thethe inputDAC valuemodule in atransfers range of the 0–4096 input to value the output in a range value of mapped 0–4096 to the0–5 output V form, value as shown mapped in Figure to 0–53 .V The form, schematic as shown conﬁguration in Figure 3. The is shown schematic in Figure configuration4. is shown in Figure 4.

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FigureFigure 3. The 3. The schematic schematic configuration conﬁguration configuration of the acceleration/brake-by-wire accelerationacceleration/brake-by-wire/brake-by-wire system. system.system.

Figure 3. The schematic configuration of the acceleration/brake-by-wire system.

Figure 4. The schematic configuration of the acceleration/brake-by-wire system. Figure 4. The schematic configuration conﬁguration of the accelerationacceleration/brake-by-wire/brake-by-wire system.system. 2.2. Mechatronics of the Steer-by-Wire System Figure 4. The schematic configuration of the acceleration/brake-by-wire system. 2.2. Mechatronics of the Steer-by-Wire System 2.2. MechatronicsThe schematic of the configuration Steer-by-Wire of anSystem ideal steer-by-wire steering system is shown in Figure 5. TheAccording2.2. Mechatronics schematic to the conﬁgurationexpected of the Steer-by-Wire steering of requirements an System ideal steer-by-wire from the driver, steering the output system torque is shown of the steering in Figure 5. Themotor schematic is regulated. configuration The 12 V (direct of ancurrent ideal voltage) steer-by-wire is used to steering supply power system to convertis shown the inmotion Figure 5. AccordingThe to theschematic expected configuration steering requirementsof an ideal steer-by-wire from the driver,steering the system output is shown torque in of Figure the steering 5. Accordingof the steeringto the expected wheel into steering linear motion.requirements The mini frmumom the steering driver, torque the output is 10.34 torque Nm, as of shown the steering in motorAccording is regulated. to the The expected 12 V (directsteering current requirements voltage) from is usedthe driver, to supply the output power torque to convert of the steering the motion motorFigure is regulated. 5a; when Thethe steering 12 V (direct is in the current extreme voltage) position, is the used minimum to supply steering power torque to convert is 11.07 Nm,the motionas of themotor steering is regulated. wheel into The linear12 V (direct motion. current The voltage) minimum is used steering to supply torque power is to 10.34 convert Nm, the as motion shown in of theshown steering in Figure wheel 5b. into Thereby, linear a smoothmotion. steering The mini functionmum and steering desirable torque feeling is of 10.34 balance Nm, and as motion shown in of the steering wheel into linear motion. The minimum steering torque is 10.34 Nm, as shown in Figurestability5a; when of exact the steering linearity iscan in be the obtained extreme under position, various the driving minimum situations. steering The torque driving is force 11.07 and Nm, as FigureFigure 5a; when 5a; when the thesteering steering is inis inthe the extreme extreme posi position,tion, thethe minimumminimum steering steering torque torque is 11.07 is 11.07 Nm, Nm, as as showntorque in Figure changes5b. of Thereby, the steering a smooth shaft are steering shown functionin Table 1. and desirable feeling of balance and motion shownshown in Figure in Figure 5b. Thereby,5b. Thereby, a smooth a smooth steering steering fu functionnction andand desirable desirable feeling feeling of balanceof balance and andmotion motion stability of exact linearity can be obtained under various driving situations. The driving force and stabilitystability of exact of exact linearity linearity can can be be obtained obtained under under variousvarious drivingdriving situations. situations. The The driving driving force force and and torque changes of the steering shaft are shown in Table1. torquetorque changes changes of the of thesteering steering shaft shaft are are shown shown in in TableTable 1.1.

(a)

Figure(a 5.) Cont.

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(b)

FigureFigure 5. Schematic 5. Schematic conﬁguration configuration ofof the steer-by-wire steer-by-wire(b) system system by ideal by ideal design: design: (a) neutral (a) neutralposition; position; (b) (b) extremeextreme position. position. Figure 5. Schematic configuration of the steer-by-wire system by ideal design: (a) neutral position; (b) extreme position. TableTable 1. 1.Speciﬁcation Specification of the steering steering shaft shaft torque. torque.

SteeringSteering Wheel Wheel CargoCargo Weight Weight Tie-Rod Force Tie-Rod Force Steering Shaft Torque Table 1. Specification of the steering shaft torque.Steering Shaft Torque (Nm) PositionPosition (kg) (kg) (kg) (kg) (Nm) Steering Wheel Cargo Weight Tie-Rod Force Neutral 70 16.74 (Dual Wheel) Steering Shaft 10.34 Torque (Nm) NeutralPosition (kg) 70(kg) 16.74 (Dual Wheel) 10.34 ExtremeExtreme 70 70 17.91 (Dual Wheel) 17.91 (Dual Wheel) 11.07 11.07 Neutral 70 16.74 (Dual Wheel) 10.34

Extreme 70 17.91 (Dual Wheel) 11.07 The stabilizationThe stabilization function function of of linear linear displacement displacement makes it it easier easier for for the the driver driver to control to control the vehicle the vehicle whenwhen driving driving under under the the bumpy bumpy road. road. The The CreoCreo ParametricParametric®® (2.0,(2.0, PTC PTC Needham, Needham, MA, MA, USA) USA) was first was first The stabilization function of linear displacement makes it easier for the driver to control the vehicle usedused to design to design the motorthe motor mount, mount, and and the the ANSYS ANSYS®®(R13, (R13, ANSYS, ANSYS, Canonsburg,Canonsburg, PA, PA, USA) USA) was was utilized utilized for when driving under the bumpy road. The Creo Parametric® (2.0, PTC Needham, MA, USA) was first stressfor analysis stress analysis on the on selected the selected 6065 6065 aluminum aluminum alloy. allo They. The stress stress analysis analysis results show show that that the the mount mount is used to design the motor mount, and the ANSYS® (R13, ANSYS, Canonsburg, PA, USA) was utilized capableis capable of carrying of carrying 18 Nm 18 Nm of rotational of rotational torque, torque, as as shown shown in Figure 6a.6a. In In addition, addition, the the mechanism mechanism is is fixedfor stress on the analysis steering on bracketthe selected of the 6065 go kart.aluminum The direct alloy.ion The of thestress force analysis is along results the contacted show that surfaces the mount on fixed on the steering bracket of the go kart. The direction of the force is along the contacted surfaces bothis capable sides, of and carrying the fixed 18 Nm tensile of rotational force of torque, 5 kg is as simulated, shown in Figureas shown 6a. In in addition, Figure 6b. the However, mechanism the is on bothmaximumfixed sides, on the andtorque steering the and fixedbracket steering tensile of the torque forcego kart. of of Thethe 5 kg directDC is simulated,(Direction of the Current) force as shownis motoralong in theis Figure 3.5contacted Nm6b. and surfaces However, 21 Nm on the maximumrespectively,both sides, torque and which and the steering meets fixed the tensile torque requirement force of the of DC of5 realkg (Direct isvehi simulated,cle Current) steering. as motor Atshown present, is 3.5in Figurethe Nm steering and 6b.21 However, system Nm respectively, is notthe whichequippedmaximum meets the with torque requirement a steering and steering angle of realsensor torque vehicle and of a steering.steeringthe DC po(Direct Attentiometer. present, Current) theIt onlymotor steering outputs is 3.5 system the Nm steering and is not 21torqueequipped Nm withbased arespectively, steering on the angle whichnumber sensor meets of stepsandthe requirement aof steering the stepping potentiometer.of real mo vehitorcle and steering. Itcontrols only At outputs present,the steering the the steering steeringdisplacement system torque of isbased thenot on the numbersteeringequipped ofwheel. with steps aThe ofsteering thesteering stepping angle angle sensor motor cannot and and abe steering a controls feedback potentiometer. the signal steering because It displacement only the outputs steering the ofis steering thenot steeringexact. torque The wheel. based on the number of steps of the stepping motor and controls the steering displacement of the The steeringresearch anglewill correct cannot this be problem a feedback in future, signal and because the actual the archit steeringecture is notis shown exact. in The Figure research 7. will correct steering wheel. The steering angle cannot be a feedback signal because the steering is not exact. The this problemresearch will in future, correct and this theproblem actual in architecturefuture, and the is actual shown archit in Figureecture7 is. shown in Figure 7.

(a)

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Figure 6. (a(a) )Motor Motor mount mount vs. vs. stress stress for forthe thesteer-by-wire steer-by-wire system; system; (b) bracket (b) bracket vs. stress vs. stressfor the for steer- the steer-by-wireby-wire system. system.

Figure 7. Mechanical design of the steer-by-wire system.

3. Mechatronics of the Vehicle ControlControl UnitUnit 3.1. Hardware Configuration of the Remote Controller 3.1. Hardware Configuration of the Remote Controller The remote control function is realized using wireless transmission. The channel selection of The remote control function is realized using wireless transmission. The channel selection of output power and protocol setting are controlled through the serial peripheral interface (SPI), and output power and protocol setting are controlled through the serial peripheral interface (SPI), and connected to various microcontroller chips for completing the transmission work of wireless data, as connected to various microcontroller chips for completing the transmission work of wireless data, as shown in Figure8. The schematic configuration reveals that the digital signal of the microcontroller is shown in Figure 8. The schematic configuration reveals that the digital signal of the microcontroller converted to an analog output of 0.5 to 4.5 V using a DAC module, and a linear change of left-to-right is converted to an analog output of 0.5 to 4.5 V using a DAC module, and a linear change of left-to- rotation and setting 2.5 V under the center of the steering wheel are defined. The remote control is right rotation and setting 2.5 V under the center of the steering wheel are defined. The remote control provided for the VCU to control the positive/negative rotation of the steering motor and steering is provided for the VCU to control the positive/negative rotation of the steering motor and steering signals, as shown in Figure9. signals, as shown in Figure 9.

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FigureFigure 8. 8.The The control control conﬁgurationconfiguration of of the the remote remote controller. controller.

FigureFigure 9. 9.The The schematic schematic conﬁgurationconfiguration of of the the remote remote controller. controller.

3.2. Hardware3.2. Hardware Conﬁguration Configuration of the of Vehicle the Vehicle Control Control Unit Unit ThisThis study study integrated integrated the independentthe independent controls controls of theof the steering steering wheel, wheel, accelerator accelerator and and brake brake pedal, pedal, as shown in Figure 10. If the status of the manual driving signal is determined, the VCU control as shownpedal, in as Figure shown 10 in. Figure If the status10. If the of status the manual of the manual driving driving signal signal is determined, is determined, the VCU the VCU control control strategy strategy cancels the remote control mode of the go kart, and switches back to the manual driving cancels the remote control mode of the go kart, and switches back to the manual driving mode. Therefore, mode. Therefore, the mode selection between the remote driving and the manual driving can be the mode selection between the remote driving and the manual driving can be realized, and provides a realized, and provides a reaction time for the driver. The schematic configuration of the VCU consists reactionof two time DACs, for the providing driver. independent The schematic control configuration of the accelerator of the VCUand brake consists pedal, of controlling two DACs, the providing DC independentmotor through control the of themotor accelerator driver to and complete brake pedal,independent controlling control the of DC the motor steering through wheel the and motor driverintegrating to complete a wireless independent transmission control receiver, of the steeringas shown wheel in Figure and integrating10. The indexes a wireless of optimization transmission receiver,include as shown lower cost, in Figure higher 10 performance. The indexes and of better optimization feasibility. include The optimization lower cost, process higher includes performance three and bettersteps: feasibility. 1. Building The optimizationthe specificatio processn table of includes the lowest three control steps: precis 1. Buildingion and fast the system specification response table time of the lowestof controlthe acceleration precision system, and fast brake system system response and the st timeeering of system. the acceleration 2. Selecting system, the optimal brake combination system and the of the acceleration system, brake system and the steering system from the table in step 1. 3. steeringof the system. acceleration 2. Selecting system, the brake optimal system combination and the ofsteering the acceleration system from system, the table brake in systemstep 1. and3. the Calculating the appropriate steering motor size and the gear ratio and designs of the micro-controller steering system from the table in step 1. 3. Calculating the appropriate steering motor size and the gear with the 8-bit control precision. ratio and designs of the micro-controller with the 8-bit control precision. Sensors 2019, 19, x 8 of 13

FigureFigure 10. 10.The The schematic schematic conﬁguration configuration of of the the vehicle vehicle control control unit. unit.

3.3. Control Strategy of the Vehicle Control Unit In order to achieve the remote control mode, the control flow is shown in Figure 11. First, a remote control switch is provided on the go kart. When the conditions of the remote control mode are met, the VCU will activate the remote control mode and the vehicle will be controlled by the remote control. Next, if the conditions of the acceleration pedal >0%, the steering wheel position is neutral and the vehicle speed >0% are met, the control of the throttle, brake and steering can be executed by the controller. If the human driving mode is on or the above conditions are not satisfied, the VCU decelerates the vehicle to stop status while the driver takes over the control of the vehicle. As vehicle speed is less than 15 kph with the larger wheel turning angle, the wheel turning angle is decreased while steering or parking; as the speed is higher than 15 kph with the smaller wheel turning angle, the stability of the straight driving can be increased. The control strategies accommodate various driving environments and instantaneous drivers’ requirements.

Figure 11. The control flow of the vehicle control unit.

4. Experiment Results In this study, the drive-by-wire system with a steer-by-wire system for the go kart was built, as shown in Figure 12a. The control-by-wire of the steering wheel integrated with the accelerator and

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Sensors 2020, 20, 1216 8 of 13 Figure 10. The schematic configuration of the vehicle control unit. 3.3. Control Strategy of the Vehicle Control Unit 3.3. Control Strategy of the Vehicle Control Unit In order to achieve the remote control mode, the control ﬂow is shown in Figure 11. First, a remoteIn controlorder to switch achieve is provided the remote on thecontrol go kart. mode, When the the control conditions flow ofis shown the remote in Figure control 11. mode First, are a met,remote the control VCU will switch activate is provided the remote on controlthe go kart mode. When and the the vehicle conditions will beof controlledthe remoteby control the remote mode control.are met, Next, the VCU if the will conditions activate of the the remote acceleration control pedal mode> 0%,and thethe steering vehicle wheelwill be position controlled is neutral by the andremote the vehiclecontrol. speedNext, >if0% the are conditions met, the controlof the acce of theleration throttle, pedal brake >0%, and the steering steering can wheel be executed position by is theneutral controller. and the If thevehicle human speed driving >0% are mode met, is onthe or control the above of the conditions throttle, arebrake not and satisﬁed, steering the can VCU be deceleratesexecuted by the the vehicle controller. to stop If the status human while driving the driver mode takes is on over or the the above control conditions of the vehicle. are not As satisfied, vehicle speedthe VCU is less decelerates than 15 kphthe vehicle with the to larger stop status wheel while turning the angle, driver the takes wheel over turning the control angle of is the decreased vehicle. whileAs vehicle steering speed or parking; is less than as the 15 speedkph with is higher the larg thaner 15wheel kph turning with the angle, smaller the wheel wheel turning turning angle, angle the is stabilitydecreased of while the straight steering driving or parking; can be as increased. the speed The is higher control than strategies 15 kph with accommodate the smaller various wheel drivingturning environmentsangle, the stability and instantaneous of the straight drivers’ driving requirements. can be increased. The control strategies accommodate various driving environments and instantaneous drivers’ requirements.

FigureFigure 11.11. TheThe controlcontrol ﬂowflow ofof thethe vehiclevehicle controlcontrol unit.unit.

4.4. ExperimentExperiment ResultsResults InIn thisthis study,study, thethe drive-by-wire system system with with a a st steer-by-wireeer-by-wire system system for for the the go go kart kart was was built, built, as asshown shown in inFigure Figure 12a. 12 Thea. The control-by-wire control-by-wire of the of thesteering steering wheel wheel integrated integrated with with the theaccelerator accelerator and and brake pedal steering were developed for the electric go kart. In the future, this will provide the foundation for the development of autonomous driving technology, as shown in Figure 12b. The accelerator and brake pedal control methods are the same for drive-by-wire. As an example, for the accelerator, the output command resolution of actual control is 8-bit, and the demanded as well as actual delay time is 1 ms, as shown in Figure 13a. In addition, the brake pedal mainly controls the drive motor to reverse for achieving the braking eﬀect. The output command resolution of actual control is 8-bit too, and the demanded as well as actual delay time is 1 ms, as shown in Figure 13b. Sensors 2019, 19, x 9 of 13

brake pedal steering were developed for the electric go kart. In the future, this will provide the Sensorsfoundation 2019, 19, x for the development of autonomous driving technology, as shown in Figure 12b. 9 of 13 brakeSensors pedal2020 steering, 20, 1216 were developed for the electric go kart. In the future, this will provide9 of 13 the foundation for the development of autonomous driving technology, as shown in Figure 12b.

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Figure 12. (a) The hardware configuration of steer-by-wire in a real go kart; (b) hardware configuration of drive-by-wire using the steering wheel, accelerator and brake pedal.

The accelerator and brake pedal control methods are the same for drive-by-wire. As an example, for the accelerator, the output command resolution of actual control is 8-bit, and the demanded as well as actual delay time is 1 ms, as shown in Figure(b) 13a. In addition, the brake pedal mainly controls Figurethe driveFigure 12. motor 12.(a)( a )Theto The reverse hardwarehardware for conﬁgurationachieving configuration the of braking steer-by-wire of st eer-by-wireeffect. in aThe real output goin kart; a commandreal (b) hardware go kart; resolution conﬁguration (b) hardware of actual configurationcontrolof drive-by-wire is 8-bit of too, drive-by-wire and using the the demanded steering using wheel,the as st welleering accelerator as wheel,actual and delayaccelerator brake time pedal. isand 1 ms, brake as shownpedal. in Figure 13b.

Figure 13. (a) Accelerator voltage vs. time for the drive-by-wire; (b) brake pedal voltage vs. time for

the drive-by-wire.

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SensorsFigure2020, 20 13., 1216 (a) Accelerator voltage vs. time for the drive-by-wire; (b) brake pedal voltage vs. time for10 of 13 Figure 13. (a) Accelerator voltage vs. time for the drive-by-wire; (b) brake pedal voltage vs. time for the drive-by-wire. the drive-by-wire.

The steeringsteering wheelwheel angle angle is is treated treated as as the the objective objective of theof steeringthe steering control control for drive-by-wire. for drive-by-wire. Here, The steering wheel angle is treated as the objective of the steering control for drive-by-wire. Here,the output the output command command resolution resolution of actual of actual control control is 8-bit, is and8-bit, the and demanded the demanded as well as as well actual as actual delay Here, the output command resolution of actual control is 8-bit, and the demanded as well as actual delaytime is time 25 ms, is 25 which ms, which is mainly is mainly limited limited by the by physical the physical stepper stepper motor. motor. Attempting Attempting to achieve to achieve exact delay time is 25 ms, which is mainly limited by the physical stepper motor. Attempting to achieve positionexact position control control will slow will downslow down the system the system response, response, as shown as shown in Figure in Figure 14. 14. exact position control will slow down the system response, as shown in Figure 14.

Figure 14. Steering wheel angle vs. time for the drive-by-wire. Figure 14. Steering wheel angle vs. time for the drive-by-wire.

This study was completed using the remote cont controlrol mode for the drive-by-wire system, and the This study was completed using the remote control mode for the drive-by-wire system, and the corresponding specification speciﬁcation is shown in Table2 2.. First,First, thethe testtest waswas carriedcarried outout forfor thethe remoteremote controlcontrol corresponding specification is shown in Table 2. First, the test was carried out for the remote control mode to drive straight in unmanned mode, as shown in Figure 1515a.a. In the same mode, the test was mode to drive straight in unmanned mode, as shown in Figure 15a. In the same mode, the test was performed to turn left in unmanned mode, as shown in Figure 1515b.b. Finally, Finally, the remote control in performed to turn left in unmanned mode, as shown in Figure 15b. Finally, the remote control in passenger modemode waswas testedtested to to verify verify the the feasibility feasibility of of the the wire wire control control system system of theof the electric electric go kartgo kart for passenger mode was tested to verify the feasibility of the wire control system of the electric go kart formeeting meeting the the technical technical development development goals, goals, as shown as shown in Figure in Figure 15c. 15c. for meeting the technical development goals, as shown in Figure 15c.

(a) (a)

Figure 15. Cont.

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(b)

(c)

Figure 15.15. TheThe system system veriﬁcation verification of drive-by-wire:of drive-by-wire: (a) remote(a) remote control control to go to straight; go straight; (b) remote (b) controlremote tocontrol turn left;to turn (c) remoteleft; (c) controlremote tocontrol turn rightto turn under right the under passenger the passenger mode. mode.

Table 2. The main specifications of the go kart. Table 2. The main speciﬁcations of the go kart. Item Parameters Item Parameters Curb (kg) ≤40 Go Kart Weight Curb (kg) 40 Go Kart Weight Gross (kg) 110≤ Type Gross (kg)Direct 110Current Propulsion Motor TypePeak power (kW) Direct2 Current Propulsion Motor PeakPeak powertorque (kW)(Nm) 702 PeakResolution torque of (Nm) actual control (bit) 870 Acceleration-by-wire ResolutionDelay time of(ms) actual control (bit) 18 Acceleration-by-wire DelayResolution time (ms)of actual control (bit) 81 Drive-by-wireDrive-by-wire Brake-by-wire ResolutionDelay time of(ms) actual control (bit) 18 Brake-by-wire DelayResolution time (ms)of actual control (bit) 81 Steer-by-wire ResolutionDelay time of(ms) actual control (bit) 258 Steer-by-wire Delay time (ms) 25 5. Conclusions This paper presents a hardware platform for an electric go kart equipped with a drive-by-wire system possessing a remote control mode to complete the functions of acceleration-by-wire, brake-

Sensors 2020, 20, 1216 12 of 13

5. Conclusions This paper presents a hardware platform for an electric go kart equipped with a drive-by-wire system possessing a remote control mode to complete the functions of acceleration-by-wire, brake-by-wire and steer-by-wire. The feasibility of applying this to the real vehicle was evaluated for the remote control mode integrated with the drive-by-wire system. The results of the acceleration-by-wire and brake-by-wire experiments showed that the output command resolution of actual control was 8-bit, and the demanded as well as actual delay time was 1 ms; the steer-by-wire experiment results showed that the output command resolution of actual control was 8-bit, and the demanded as well as actual delay time was 25 ms. This research aimed at the experimental assessment of the x-by-wire system of a light-duty vehicle with extra low cost as well as optimized performance (drivability, safety, operability, robustness). Therefore, the industrial contributions are solid. The benefits and novelty can be summarized as follows: (1) Competitive cost for aftermarket commercialization: a micro-controller with the 8-bit control precision and a WiFi module are integrated for providing the full function focusing on light-duty vehicles. With the modified steering system, the total cost is USD 200, which is extremely competitive for the aftermarket x-by-wire kits. All light-duty vehicles with peak output power below 2 kW can be equipped. (2) Self-developed customized VCU: the micro-chip, WiFi module and the DAC interface are properly integrated for the VCU hardware based on the customized requirements of the I/O ports and the wireless data transmission rate. The research can be slightly modified and implemented to other types of vehicles (golf carts, all-terrain vehicles, etc.) efficiently to significantly reduce the R&D period and resources for developing another x-by-wire VCU. For the standard operation procedure (SOP) of the intelligent human/machine interface switch, in order to achieve the remote control mode, the control flow is shown in Figure 11. First, a remote control switch is provided on the go kart. When the conditions of the remote control mode are met, the VCU will activate the remote control mode and the vehicle will be controlled by the remote control. If the conditions of the acceleration pedal >0%, the steering wheel position is neutral and the vehicle speed >0% are met, the control of the throttle, brake and steering can be executed by the controller. If the human driving mode is on or the above conditions are not satisfied, the VCU decelerates the vehicle to stop status while the driver takes over the control of the vehicle. (3) Standard operation process for the customized x-by-wire system: the drive-by-wire system should concern lower cost, higher performance and better feasibility. The optimization process is as follows: (1) Building the specification table of the lowest control precision and fast system response time of the acceleration system, brake system and the steering system. (2) Selecting the optimal combination of the acceleration system, brake system and the steering system from the table in step 1. (3) Calculating the appropriate steering motor size and the gear ratio and designs of the micro-controller with the 8-bit control precision. (4) Outstanding performance: for the x-by-wire system, we have improved the low-speed drivability as well as high-speed stability. A larger steering angle of the front wheels in response to a specific rotated angle of the steering wheel has been devised when cornering or parking at low speed, while a smaller one has been designed for high speed. Meanwhile, the system accommodates various driving environments and drivers’ requirements.

Author Contributions: Conceptualization, C.-H.W. and W.-C.L.; methodology, C.-H.W.; software, W.-C.L. and K.-S.W.; validation, W.-C.L. and K.-S.W.; formal analysis, C.-H.W. and W.-C.L.; investigation, C.-H.W.; data curation, W.-C.L. and K.-S.W.; writing—original draft, C.-H.W.; writing—review and editing, C.-H.W.; visualization, C.-H.W.; resources, C.-H.W.; supervision, C.-H.W.; project administration, C.-H.W.; funding acquisition, C.-H.W. All authors have read and agreed to the published version of the manuscript. Funding: The authors would like to thank the Ministry of Science and Technology of the Republic of China, Taiwan, for ﬁnancial support for this research under Contract No. MOST 107-2221-E-150-036 and 108-2221-E-150-012; and thanks to the Industrial Technology Research Institute (ITRI) project for advanced vehicle control. Sensors 2020, 20, 1216 13 of 13

Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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