Abstract:
A two-wheel, self-balancing vehicle is disclosed. In one aspect, the two-wheel, self-balancing vehicle comprises a first wheel and a second wheel, the first wheel and the second wheel being spaced apart and substantially parallel to one another. The two-wheel, self-balancing vehicle further comprises a foot placement section connecting the first wheel and the second wheel. The two-wheel, self-balancing vehicle further comprises a set of position sensors in the foot placement section, the set of position sensors configured to generate inclination angle signals and velocity signals of the two-wheel, self-balancing vehicle. The two-wheel, self-balancing vehicle further comprises a first gravity sensor and a second gravity sensor in the foot placement section, the first gravity sensor and the second gravity sensor configured to generate weight signals and gravity angle signals. In addition, the two-wheel, self-balancing vehicle comprises a control logic configured to output control signals that control the movement of the two-wheel, self-balancing vehicle in response to the inclination angle signals, the velocity signals, the weight signals, and the gravity angle signals.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to self-balancing vehicles and methods for controlling the self-balancing vehicles. 
       BACKGROUND 
       [0002]    In some aspects, self-balancing vehicles are controlled through a yaw or steering control structure. For example, turning of the self-balancing vehicles may be achieved through a handle bar structure that ascends from the platform upward toward the chest of a user.  FIG. 1  illustrates one example of a conventional two-wheel self-balancing vehicle with a yaw or steering control structure. The conventional two-wheel self-balancing vehicle with a yaw or steering control structure utilizes a control principle of a single inverted pendulum system. 
         [0003]    As shown in  FIG. 1 , a two-wheel self-balancing vehicle  100  with a yaw or steering control structure comprises a first wheel with direct current (DC) motor  10 , a second wheel with DC motor  12 , a foot placement section  14  and a yaw or steering control structure  16 . With two parallel wheels controlled independently by two DC motors, two-wheel self-balancing vehicle  100  can move forward, backward, and make relatively stable turns. The maximum moving speed of two-wheel self-balancing vehicle  100  could be up to 10 miles per hour. To operate two-wheel self-balancing vehicle  100 , a user may stand on foot placement section  14 , and the user&#39;s feet are separated to left and right. Foot placement section  14  may be one section or area affixed to first wheel with DC motor  10  and second wheel with DC motor  12 . Foot placement section  14  may comprise a first portion  11  and a second portion  13  located on the same plane. Yaw or steering control structure  16  may comprise a handle bar structure, including for example, a grip, a handle, and/or a pole. 
         [0004]    By sloping forward or leaning backward the user&#39;s body, the user can control two-wheel self-balancing vehicle  100  to accelerate or decelerate. A left turn or a right turn may be accomplished by sending the turn signals through yaw or steering control structure  16 . One of the disadvantages of this design is that with yaw or steering control structure  16 , two-wheel self-balancing vehicle  100  is larger and heavier than a vehicle without a central control structure (e.g., a handle bar structure). The user also has to exert hand control using yaw or steering control  16 . 
         [0005]      FIG. 2  illustrates one example of a control diagram  200  of two-wheel self-balancing vehicle  100 . As shown in  FIG. 2 , micro-electro-mechanical systems (MEMS) sensors, such as an accelerometer and a gyroscope may be used to detect the inclination angle of foot placement section  14 . The inclination angle of foot placement section  14  may be used in combination with yaw or steering control input from yaw or steering control structure  16  as input signals to a proportional-integral-derivative (PID) control and driving control of two-wheel self-balancing vehicle  100 . 
         [0006]      FIG. 3  illustrates an embodiment showing the inclination angle of foot placement section  14  of two-wheel self-balancing vehicle  100 . As shown in  FIG. 3 , when foot placement section  14  is tilted down or up by the user, the accelerometer and gyroscope sensor sense the motion and calculate the inclination angle. The inclination angle information, after being compared with a desired balance angle, may be sent to the PID and center control unit. Together with the yaw and steering control input, DC motor control signals may be generated and sent to a driver to control the movement of first wheel with DC motor  10  and second wheel with DC motor  12  to maintain the balance of two-wheel self-balancing vehicle  100 . For signal processing purpose, the PID and center control unit may also receive the current speed information from first wheel with DC motor  10  and second wheel with DC motor  12 , and the current information from drivers. 
         [0007]    In this implementation, two-wheel self-balancing vehicle  100  may suffer from their large size and dimensions of the yaw or steering structure, which may be required to handle the vehicle&#39;s turn movement. This may result in the vehicle&#39;s incapability to turn surrounding its own center of gravity. 
         [0008]    In some aspects, self-balancing vehicles have two platform sections or areas that areas that are independently movable with respect to one another and that thereby provide independent control and/or drive of the wheel associated with the given platform section/area. The angle control of self-balancing vehicles have two platform sections or areas can be achieved by measuring the angle difference between the left and right sides&#39; angle difference, thus eliminating the need for a structure for controlling. 
         [0009]      FIG. 4  illustrates an example of a two-wheel self-balancing vehicle  400  having independently movable foot placement sections. In this embodiment, a first foot placement section  42  and a second foot placement section  44  can move independently from each other, which may eliminate the need of a yaw and steeling control structure, and make space for the center space between the left side of second foot placement section  44  and the right side of first foot placement section  42 . A first sensor and control module, which includes an accelerometer and a first gyroscope, may be required on first foot placement section  42  sense the tilted angle of first foot placement section  42 . A second sensor and control module, which includes an accelerometer and a first gyroscope, may be required on second foot placement section  44  to sense the tilted angle of second foot placement section  44 . 
         [0010]      FIG. 5  illustrates an embodiment of a control diagram of a two-wheel self-balancing vehicle having independently movable foot placement sections. As illustrated in  FIG. 5 , the yaw angle information may be extracted from the tilted angle information obtained from the first sensor and control module and second sensor and control module, as described with reference to  FIG. 4 .  FIG. 6  illustrates an embodiment showing an example of turning movement examples of a two-wheel self-balancing vehicle having independently movable foot placement sections.  FIG. 6  illustrates one or more turn movement examples by operating first foot placement section  42  and second foot placement section  44  separately. 
         [0011]    However, since each of first foot placement section  42  and second foot placement section  44  moves independently around a center axis of the two-wheel self-balancing vehicle having independently movable foot placement sections, constrains may be introduced to the mechanical design as well as the exterior design of the vehicle. In addition, users operating two-wheel self-balancing vehicle  400  having independently movable foot placement sections would find it difficult to circle around a center point of gravity that is the user himself or herself. Additionally, because first foot placement section  42  and second foot placement section  44  are separated, the center portion between first foot placement section  42  and second foot placement section  44  cannot hold any additional functionalities or accessories. Furthermore, the design of the two-wheel self-balancing vehicle having independently movable foot placement sections also introduces additional costs due to, for example, first foot placement section  42  and second foot placement section  44  being separated. 
       SUMMARY 
       [0012]    A two-wheel, self-balancing vehicle is disclosed. In one aspect, the two-wheel, self-balancing vehicle comprises a first wheel and a second wheel, the first wheel and the second wheel being spaced apart and substantially parallel to one another. The two-wheel, self-balancing vehicle further comprises a foot placement section connecting the first wheel and the second wheel. The two-wheel, self-balancing vehicle further comprises a set of position sensors in the foot placement section, the set of position sensors configured to generate inclination angle signals and velocity signals of the two-wheel, self-balancing vehicle. The two-wheel, self-balancing vehicle further comprises a first gravity sensor and a second gravity sensor in the foot placement section, the first gravity sensor and the second gravity sensor configured to generate weight signals and gravity angle signals. In addition, the two-wheel, self-balancing vehicle comprises a control logic configured to output control signals that control the movement of the two-wheel, self-balancing vehicle in response to the inclination angle signals, the velocity signals, the weight signals, and the gravity angle signals. 
         [0013]    In some embodiments, the set of position sensors comprises an accelerometer sensor and a gyroscope sensor. In some embodiments, the first gravity sensor is located in the left part of the foot placement section and the second gravity sensor is located in the right part of the foot placement section. In some embodiments, the control logic is configured to compare a desired balance angle of the two-wheel, self-balancing vehicle with the inclination angle signals. In some embodiments, the desired balance angle is a function of a speed of the first wheel or the second wheel. 
         [0014]    In some embodiments, the center portion of the foot placement section is attached to at least one sensor or at least one accessory. In some embodiments, the at least one sensor includes at least one of a temperature sensor, a light sensor, a moisture sensor, or a location sensor. In some embodiments, the at least one accessory includes at least one of a camera, a camera mount, or a storage component. In some embodiments, a pole is attached to the center portion of the foot placement section. In some embodiments, the foot placement section comprises one generally flat plane with room for accommodating two human feet. In some embodiments, each of the first gravity sensor and the second gravity sensor senses a pressure of a human foot placed on the foot placement section. 
         [0015]    In some embodiments, the two-wheel, self-balancing vehicle further comprises a third gravity sensor and a fourth gravity sensor, wherein the first gravity sensor is located at the left front part of the foot placement section, the second gravity sensor is located at the left rear part of the foot placement section, the third gravity sensor is located at the right front of the foot placement section, and the fourth gravity sensor is located at the right rear of the foot placement section. In some embodiments, the first, second, third and fourth gravity sensors are configured to generate three-dimensional gravity angle signals. In some embodiments, the two-wheel, self-balancing vehicle further comprises a gravity sensor array located in the left part of the foot placement section or the right part of the foot placement section. 
         [0016]    It is understood that other configurations of the subject technology will become readily apparent to those skilled in the art from the following detailed description, wherein various configurations of the subject technology are shown and described by way of illustration. As will be realized, the subject technology is capable of other and different configurations and its several details are capable of modification in various other respects, all without departing from the scope of the subject technology. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Features of the subject technology are set forth in the appended claims. However, for purpose of explanation, several embodiments of the subject technology are set forth in the following figures. 
           [0018]      FIG. 1  illustrates one example of a conventional two-wheel self-balancing vehicle with a yaw or steering control structure. 
           [0019]      FIG. 2  illustrates one example of a control diagram of the two-wheel self-balancing vehicle shown in  FIG. 1 . 
           [0020]      FIG. 3  illustrates an embodiment showing the inclination angle of foot placement section of two-wheel self-balancing vehicle shown in  FIG. 1 . 
           [0021]      FIG. 4  illustrates an example of a two-wheel self-balancing vehicle having independently movable foot placement sections. 
           [0022]      FIG. 5  illustrates an embodiment of a control diagram of a two-wheel self-balancing vehicle having independently movable foot placement sections. 
           [0023]      FIG. 6  illustrates one or more turn movement examples by operating first foot placement section and second foot placement section separately. 
           [0024]      FIG. 7  illustrates an example of a two-wheel self-balancing vehicle with one or more gravity sensors according to one embodiment of the present disclosure. 
           [0025]      FIG. 8  illustrates an example of a two-wheel self-balancing vehicle with one or more gravity sensors according to one embodiment of the present disclosure. 
           [0026]      FIG. 9  illustrates a control diagram of a two-wheel self-balancing vehicle with one or more gravity sensors according to one embodiment of the present disclosure. 
           [0027]      FIGS. 10A-10D  illustrate turning control examples of a two-wheel self-balancing vehicle with one or more gravity sensors. 
           [0028]      FIG. 11  illustrates diagrammatically of movement control of the wheels of the embodiment of  FIGS. 10A-10D . 
           [0029]      FIG. 12  illustrates a control diagram of a two-wheel self-balancing vehicle with one or more gravity sensors according to one embodiment of the present disclosure. 
           [0030]      FIG. 13  illustrates an example of a desired balance angle of two-wheel self-balancing vehicle with one or more gravity sensors. 
           [0031]      FIG. 14  illustrates an example of a two-wheel self-balancing vehicle with one or more gravity sensors according to another embodiment of the present disclosure. 
           [0032]      FIG. 15  illustrates an example three-dimensional gravity sensing scheme of a two-wheel self-balancing vehicle with one or more gravity sensors according to another embodiment of the present disclosure. 
           [0033]      FIGS. 16A-16F  illustrate turning control examples of a two-wheel self-balancing vehicle with one or more gravity sensors shown in  FIG. 14 . 
           [0034]      FIG. 17  illustrates a control diagram of a two-wheel self-balancing vehicle with one or more gravity sensors according to another embodiment of the present disclosure. 
           [0035]      FIG. 18  illustrates a control diagram of a two-wheel self-balancing vehicle with one or more gravity sensors according to another embodiment of the present disclosure. 
           [0036]      FIG. 19  illustrates an example of a two-wheel self-balancing vehicle with one or more gravity sensors according to another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology may be practiced. The appended drawings are incorporated herein and constitute a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, the subject technology is not limited to the specific details set forth herein and may be practiced without these specific details. In some instances, structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology. 
         [0038]    As described above, two-wheel self-balancing vehicle  100  may suffer from their large size and dimensions of the yaw or steering structure, which may be required to handle the vehicle&#39;s turn movement. This may result in the vehicle&#39;s incapability to turn surrounding its own center of gravity. In addition, two-wheel self-balancing vehicle  400  having independently movable foot placement sections may be constrains with the mechanical design as well as the exterior design of the vehicle. In addition, a user who operates two-wheel self-balancing vehicle  400  having independently movable foot placement sections would find it difficult to circle around a center point of gravity that is the user himself or herself. Additionally, because first foot placement section  42  and second foot placement section  44  are separated, the center portion between first foot placement section  42  and second foot placement section  44  cannot hold any additional functionalities or accessories. Furthermore, the design of the two-wheel self-balancing vehicle having independently movable foot placement sections also introduces additional costs due to, for example, first foot placement section  42  and second foot placement section  44  being separated. Thus, there is a need for a two-wheel self-balancing vehicle with one foot placement section, but at the same time eliminate a yaw and steeling control structure. 
         [0039]      FIG. 7  illustrates an example of a two-wheel self-balancing vehicle  700  with one or more gravity sensors according to one embodiment of the present disclosure. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0040]    Two-wheel self-balancing vehicle  700  with one or more gravity sensors comprises a first wheel with DC motor  70 , a second wheel with DC motor  72 , a foot placement section  74 , a first gravity sensor  76 , a second gravity sensor  78 , and a central control module  79 . 
         [0041]    In some embodiments, foot placement section  74  may be one section or area comprising a first portion  71  and a second portion  73  located on the same plane to offer more design flexibility in terms of mechanical architecture and exterior design. In some aspects, first portion  71  may be a portion between the center axes of two-wheel self-balancing vehicle  700  with one or more gravity sensors and first wheel with DC motor  70 . Second portion  73  may be a portion between the center axes of two-wheel self-balancing vehicle  700  with one or more gravity sensors and second wheel with DC motor  72 . For example, a user may place his/her left foot on first portion  71  and his/her right foot on second portion  73 . 
         [0042]    In some embodiments, first portion  71  may include first gravity sensor  76  and second portion  73  may include second gravity sensor  78 . First gravity sensor  76  and second gravity sensor  78  may sense the weight and gravity angles of a user when he or she stands on foot placement section  74 . Each of first gravity sensor  76  and second gravity sensor  78  may be implemented as a microelectromechanical system (MEMS) sensor. Each of first gravity sensor  76  and second gravity sensor  78  may be placed at the center or any portion of foot placement section  74 . In some aspects, each of first gravity sensor  76  and second gravity sensor  78  may be or may include a pressure sensor. 
         [0043]    Central control module  79  may include an accelerometer, a gyroscope sensor, a power management unit (PMU), Brushless DC (BLDC) Motor Driver Motor drivers, a microcontroller or a central processing unit, and miscellaneous sub-modules, such as wireless communication modules (e.g., Bluetooth or WIFI communication modules). In some embodiments, each of the accelerometer and the gyroscope sensor is capable of generating 3-axis outputs in the x, y, and z directions as illustrated in  FIG. 7  and therefore the set of position sensors generates a combined 6-axis positional outputs. For example, an accelerometer sensor generates outputs of linear accelerations in the x, y, and z directions, and a gyroscope sensor generates outputs of rotational velocity with respect to the x, y, and z directions. 
         [0044]    The accelerometer and the gyroscope sensor can be implemented as a microelectromechanical system (MEMS) sensor, such as an integrated MEMS sensor module. 
         [0045]      FIG. 8  illustrates an example of a two-wheel self-balancing vehicle  800  with one or more gravity sensors according to one embodiment of the present disclosure. Two-wheel self-balancing vehicle  800  with one or more gravity sensors of the second embodiment includes two-wheel self-balancing vehicle  700  with one or more gravity sensors shown in  FIG. 7 . Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0046]    As shown  FIG. 8 , a handle or other accessories  82  may be installed on the center or any portion of foot placement section  84 . Handle or other accessories  82  may or may not be used for control purposes. Handle or other accessories  82  may add more utilities or aesthetic features to two-wheel self-balancing vehicle  800  with one or more gravity sensors, thus greatly enhancing the user experience. For example, the other accessories may include pockets for storing personal belongings, spaces for cameras or camera mounts, additional temperature, humidity, or environmental sensors, and so forth. In some embodiments, the cameras may also provide additional positional and control sensing signals to central control module  79  for safety and operability purposes. For example, the cameras may capture images or video during operation of two-wheel self-balancing vehicle  800  with one or more gravity sensors, and the videos or images may provide collision avoidance opportunities to the user. Further, in some embodiments, the videos or images may be automatically uploaded for surveillance or security purposes. 
         [0047]      FIG. 9  illustrates a control diagram  900  of two-wheel self-balancing vehicle  700  with one or more gravity sensors according to one embodiment of the present disclosure. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0048]    As shown in  FIG. 9 , PID and driving control block  920  may receive gravity angle signal  908  computed from outputs of first gravity sensor  76  and second gravity sensor  78 , and a processed inclination angle signal. The processed inclination angle signal may be generated by comparing an inclination angle signal  916  with a desired balance angle input  922 . Desired balance angle input  922  may include a predetermined desired balance angle of two-wheel self-balancing vehicle  700  with one or more gravity sensors, and the predetermined desired balance angle may be a constant. Alternatively or in addition, desired balance angle input  922  may include a desired balance angle of two-wheel self-balancing vehicle  700  with one or more gravity sensors, and the desired balance angle may be a function of the speeds of first wheel with DC motor  70  and/or second wheel with DC motor  72 . 
         [0049]    Inclination angle signal  916  may be generated by an accelerometer  914  and a gyroscope  912 . In some aspects, accelerometer  914  and gyroscope  912  may be included in central control module  79  shown in  FIG. 7 . 
         [0050]    PID and driving control block  920  may generate one or more movement control signals to drive first wheel with DC motor  70  and second wheel with DC motor  72  separately to balance two-wheel self-balancing vehicle  700  with one or more gravity sensors. In some embodiments, the one or more movement control signals may include one or more adjusted angles for foot placement section  74  and/or one or more adjusted speeds based on the environment. The one or more adjusted angles may prevent the user from falling off of two-wheel self-balancing vehicle  700  with one or more gravity sensors during operation, especially during acceleration and deceleration. The one or more adjusted speeds may be calculated by central control module  79  based on contextual information including for example, environmental sensor data, camera input, and adjusted speed may be implemented automatically. The one or more adjusted speeds may provide additional safety measures to users during operation of the two-wheel self-balancing vehicle  700  with one or more gravity sensors. 
         [0051]    Weight information  906  generated by gravity sensors  902  and  904  may be sent to PID and driving control block  920  to adjust the control parameter as a function of the weight information  906  to optimize the performance of two-wheel self-balancing vehicle  700  with one or more gravity sensors. In some aspects, two-wheel self-balancing vehicle  700  with one or more gravity sensors may be able to support a wider range of the weight thereon with a better driving experience. 
         [0052]      FIGS. 10A-10D  illustrate turning control examples of two-wheel self-balancing vehicle  700  with one or more gravity sensors. Two-wheel self-balancing vehicle  700  with one or more gravity sensors may be controlled by control diagram  900  shown in  FIG. 9 . As shown in  FIGS. 10A-10D , x, y, and z directions are illustrated the same as illustrated in  FIG. 7 . 
         [0053]    A gravity angle may be calculated as the difference of a sensed gravity from first gravity sensor  76  and a sensed gravity from second gravity sensor  78 . For example, a gravity angle may be negative, calculated based on the sensed gravity of first gravity sensor  76  is less than a sensed gravity from second gravity sensor  78 . A gravity angle may be positive, calculated based on the sensed gravity of first gravity sensor  76  is larger than a sensed gravity from second gravity sensor  78 . A gravity angle may be zero based on the sensed gravity of first gravity sensor  76  is substantially equal to a sensed gravity from second gravity sensor  78 . 
         [0054]    As described with reference to  FIG. 7 , each of the accelerometer and the gyroscope sensor is capable of generating 3-axis outputs in the x, y, and z directions as illustrated. An inclination angle (e.g., inclination angle  916 ) may be computed from accelerometer  914  and gyroscope  912 . An inclination angle may be an angle between the plane of foot placement section  74  and a horizontal plane which is perpendicular to the gravitational field pointing downwards along the z-axis. The inclination angle may be calculated as an angle between a gravitational vector of foot placement section  74  and the gravitational field pointing downwards along the z-axis. The inclination angle may be calculated from inclination angle signal  916 . For example, an inclination angle may be negative, calculated based on the angle between the plane of foot placement section  74  and the gravitational field pointing downwards along the z-axis is smaller than 90 degrees. An inclination angle may be positive, calculated based on the angle between the plane of foot placement section  74  and the gravitational field pointing downwards along the z-axis is larger than 90 degrees. An inclination angle may be zero, calculated based on the angle between the plane of foot placement section  74  and the gravitational field pointing downwards along the z-axis is 90 degrees. 
         [0055]    The gravity angle may be combined with inclination angle to drive first wheel with DC motor  70  and second wheel with DC motor  72  to turn two-wheel self-balancing vehicle  700  to different moving directions according to a movement control diagram shown in  FIG. 11 . 
         [0056]    As shown in  FIG. 10A , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  700  left-forward based on a negative gravity angle and a negative inclination angle. As shown in  FIG. 10B , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  700  right-forward based on a positive gravity angle and a negative inclination angle. As shown in  FIG. 10C , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  700  left-backward based on a negative gravity angle and a positive inclination angle. As shown in  FIG. 10D , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  700  right-backward based on a positive gravity angle and a positive inclination angle. 
         [0057]      FIG. 11  illustrates diagrammatically of movement control of the wheels of the embodiment of  FIGS. 10A-10D . 
         [0058]      FIG. 12  illustrates a control diagram  1200  of two-wheel self-balancing vehicle  700  with one or more gravity sensors according to one embodiment of the present disclosure. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0059]    Control diagram  1200  may include control diagram  900  shown in  FIG. 9 . As shown in  FIG. 12 , desired balance angle input  922  may be based on a function of speed feedback signal  924 . Speed feedback signal  924  may include the speed of first wheel with DC motor  70  and/or the speed of second wheel with DC motor  72 . 
         [0060]      FIG. 13  illustrates an example of a desired balance angle of two-wheel self-balancing vehicle  700  with one or more gravity sensors. As shown in  FIG. 13 , a desired balance angle may be an angle between the plane of foot placement section  74  and a horizontal plane which is perpendicular to the gravitational field pointing downwards along the z-axis. The inclination angle may be calculated as an angle between a gravitational vector of foot placement section  74  and the gravitational field pointing downwards along the z-axis. As shown in  FIG. 13 , x, y, and z directions are illustrated the same as illustrated in  FIG. 7 . 
         [0061]    As described with reference to  FIG. 12 , a desired balance angle of foot placement section  74  can be dynamically adjusted as a function of a motor and wheel speed by receiving the speed feedback signals  924  from first wheel with DC motor  70  and/or the speed of second wheel with DC motor  72 . In some embodiments, the desired balance angle may be dynamically adjusted based on a plurality of other factors, such as the motor and wheel speed, the terrain ahead of the user or surrounding the user as determined based on camera data, environmental information regarding weather, temperature, humidity from environmental sensors, and/or location information based on Global Positioning System (GPS) data. 
         [0062]    To further improve the turning mobility, each of first gravity sensor  76  and second gravity sensor  78  may include an array of gravity sensors. 
         [0063]      FIG. 14  illustrates an example of a two-wheel self-balancing vehicle  1400  with one or more gravity sensors according to another embodiment of the present disclosure. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0064]    Two-wheel self-balancing vehicle  1400  with one or more gravity sensors comprises a first wheel with DC motor  70 , a second wheel with DC motor  72 , a foot placement section  74 , a gravity sensor  1402 , a gravity sensor  1404 , a gravity sensor  1406 , a gravity sensor  1408 , and a central control module  79 . First wheel with DC motor  70 , a second wheel with DC motor  72 , a foot placement section  74 , and a central control module  79  are described in details with reference to  FIG. 7 . As shown in  FIG. 14 , x, y, and z directions are illustrated the same as illustrated in  FIG. 7 . 
         [0065]    As described above with reference to  FIG. 7 , foot placement section  74  may be one section or area comprising a first portion  71  and a second portion  73  located on the same plane to offer more design flexibility in terms of mechanical architecture and exterior design. In some aspects, first portion  71  may be a portion between the center axes of two-wheel self-balancing vehicle  700  with one or more gravity sensors and first wheel with DC motor  70 . Second portion  73  may be a portion between the center axes of two-wheel self-balancing vehicle  700  with one or more gravity sensors and second wheel with DC motor  72 . For example, a user may place his/her left foot on first portion  71  and his/her right foot on second portion  73 . 
         [0066]    In some embodiments, first portion  71  may include gravity sensor  1402  and gravity sensor  1404 . Second portion  73  may include gravity sensor  1406  and gravity sensor  1408 . 
         [0067]    Each of gravity sensors  1402 ,  1404 ,  1406  and  1408  may sense the weight and gravity angles of a user when he or she stands on foot placement section  74 . Each of gravity sensors  1402 ,  1404 ,  1406  and  1408  may be implemented as a microelectromechanical system (MEMS) sensor. Each of gravity sensors  1402 ,  1404 ,  1406  and  1408  may be placed at the center or any portion of foot placement section  74 . In some aspects, each of gravity sensors  1402 ,  1404 ,  1406  and  1408  may be or may include a pressure sensor. 
         [0068]    As shown in  FIG. 14 , gravity sensor  1402  may be located at a left-front location of foot placement section  74 . Gravity sensor  1404  may be located at a left-rear location of foot placement section  74 . Gravity sensor  1406  may be located at a right-front location of foot placement section  74 . Gravity sensor  1408  may be located at a right-rear location of foot placement section  74 . In this implementation, much more flexible turning movement can be achieved by using three-dimensional gravity angle signals from gravity sensors  1402 ,  1404 ,  1406  and  1408  at different locations. 
         [0069]      FIG. 15  illustrates an example three-dimensional gravity sensing scheme of two-wheel self-balancing vehicle  1400  with one or more gravity sensors according to another embodiment of the present disclosure. 
         [0070]    As shown in  FIG. 15 , Left Front-Rear (LFR) gravity angle, Right Front-Rear (RFR) gravity angle, and Left-Right (LR) gravity angle may be obtained from gravity sensors  1402 ,  1404 ,  1406  and  1408  shown in  FIG. 14 . 
         [0071]    LFR gravity angle can be obtained as the difference of a sensed gravity from a left-front gravity sensor (e.g., gravity sensor  1402 ) and a sensed gravity from a left-rear gravity sensor (e.g., gravity sensor  1404 ). For example, LFR gravity angle may be negative, calculated based on the sensed gravity of gravity sensor  1402  is less than a sensed gravity from gravity sensor  1404 . LFR gravity angle may be positive, calculated based on the sensed gravity of gravity sensor  1402  is larger than a sensed gravity from gravity sensor  1404 . LFR gravity angle may be zero based on the sensed gravity of gravity sensor  1402  is substantially equal to a sensed gravity from gravity sensor  1406 . 
         [0072]    RFR gravity angle may be calculated as the difference of a sensed gravity from a right-front gravity sensor (e.g., gravity sensor  1406 ) and a sensed gravity from a right-rear gravity sensor (e.g., gravity sensor  1408 ). For example, RFR gravity angle may be negative, calculated based on the sensed gravity of gravity sensor  1406  is less than a sensed gravity from gravity sensor  1408 . RFR gravity angle may be positive, calculated based on the sensed gravity of gravity sensor  1406  is larger than a sensed gravity from gravity sensor  1408 . RFR gravity angle may be zero based on the sensed gravity of gravity sensor  1406  is substantially equal to a sensed gravity from gravity sensor  1408 . 
         [0073]    LR gravity angle may be calculated as the difference of the output sum of the left gravity sensors (e.g., output sum of gravity sensor  1402  and gravity sensor  1404 ) and output sum of the right gravity sensors (e.g., output sum of gravity sensor  1406  and gravity sensor  1408 ). For example, LR gravity angle may be negative, calculated based on the output sum of left gravity sensors is less than the output sum of from the right gravity sensors. LR gravity angle may be positive, calculated based on calculated based on the output sum of left gravity sensors is larger than the output sum of from the right gravity sensors. LR gravity angle may be zero, calculated based on the output sum of left gravity sensors is substantially equal to the output sum of from the right gravity sensors. 
         [0074]      FIGS. 16A-16F  illustrate turning control examples of two-wheel self-balancing vehicle  1400  with one or more gravity sensors. As shown in  FIGS. 16A-16F , x, y, and z directions are illustrated the same as illustrated in  FIG. 14 . 
         [0075]    As shown in  FIG. 16A , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  1400  left-forward based on a negative LR gravity angle, a negative RFR gravity angle, and a zero LFR gravity angle. As shown in  FIG. 16B , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  1400  right-forward based on a positive LR gravity angle, a negative LFR gravity angle, and a zero RFR gravity angle. As shown in  FIG. 16C , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  1400  left-backward based on a negative LR gravity angle, a positive RFR gravity angle, and a zero LFR gravity angle. As shown in  FIG. 16D , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  1400  right-backward based on a positive LR gravity angle, a positive LFR gravity angle and a zero RFR gravity angle. As shown in  FIG. 16E , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  1400  anti-clockwise based on a positive LFR gravity angle, a negative RFR gravity angle, and a zero LR gravity angle. As shown in  FIG. 16F , first wheel with DC motor  70  and second wheel with DC motor  72  may be configured to turn two-wheel self-balancing vehicle  1400  clockwise based on a negative LFR gravity angle, a positive RFR gravity angle, and a zero LR gravity angle. 
         [0076]    In some embodiments, the higher dimensionality of gravity sensors  1402 ,  1404 ,  1406  and  1408  may offer a more complete set of control possibilities, and enable the user to have an accurate control of the movement of two-wheel self-balancing vehicle  1400  based on his or her own body movement. Two-wheel self-balancing vehicle  1400  may respond faster and more precisely to the gesture of the user. 
         [0077]      FIG. 17  illustrates a control diagram  1700  of two-wheel self-balancing vehicle  1400  with one or more gravity sensors according to another embodiment of the present disclosure. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0078]    As shown in  FIG. 17 , PID and driving control block  1720  may receive three-dimensional gravity angle signal  1708  computed from outputs of gravity sensors  1402 ,  1404 ,  1406  and  1408 , and a processed inclination angle signal. The processed inclination angle signal may be generated by comparing an inclination angle signal  1716  with a desired balance angle input  1722 . Desired balance angle input  1722  may include a predetermined desired balance angle of two-wheel self-balancing vehicle  1400  with one or more gravity sensors, and the predetermined desired balance angle may be a constant. Alternatively or in addition, desired balance angle input  1722  may include a desired balance angle of two-wheel self-balancing vehicle  1400  with one or more gravity sensors, and the desired balance angle may be a function of the speeds of first wheel with DC motor  70  and/or second wheel with DC motor  72 . 
         [0079]    Inclination angle signal  1716  may be generated by an accelerometer  1714  and a gyroscope  1712 . In some aspects, accelerometer  1714  and gyroscope  1712  may be included in central control module  79  shown in  FIG. 1400 . 
         [0080]    PID and driving control block  1720  may generate one or more movement control signals to drive first wheel with DC motor  70  and second wheel with DC motor  72  separately to balance two-wheel self-balancing vehicle  1400  with one or more gravity sensors. In some embodiments, the one or more movement control signals may include one or more adjusted angles for foot placement section  74  and/or one or more adjusted speeds based on the environment. The one or more adjusted angles may prevent the user from falling off of two-wheel self-balancing vehicle  1400  with one or more gravity sensors during operation, especially during acceleration and deceleration. The one or more adjusted speeds may be calculated by central control module  79  based on contextual information including for example, environmental sensor data, camera input, and adjusted speed may be implemented automatically. The one or more adjusted speeds may provide additional safety measures to users during operation of the two-wheel self-balancing vehicle  1400  with one or more gravity sensors. 
         [0081]    Weight information  1706  generated by gravity sensors  1402 ,  1404 ,  1406  and  1408  may be sent to PID and driving control block  1720  to adjust the control parameter as a function of the weight information  1706  to optimize the performance of two-wheel self-balancing vehicle  1400  with one or more gravity sensors. In some aspects, two-wheel self-balancing vehicle  1400  with one or more gravity sensors may be able to support a wider range of the weight thereon with a better driving experience. 
         [0082]      FIG. 18  illustrates a control diagram  1800  of two-wheel self-balancing vehicle  1400  with one or more gravity sensors according to another embodiment of the present disclosure. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0083]    Control diagram  1800  may include control diagram  1700  shown in  FIG. 7 . As shown in  FIG. 18 , desired balance angle input  1722  may be based on a function of speed feedback signal  1724 . Speed feedback signal  1724  may include the speed of first wheel with DC motor  70  and/or the speed of second wheel with DC motor  72 . 
         [0084]      FIG. 19  illustrates an example of a two-wheel self-balancing vehicle  1900  with one or more gravity sensors according to another embodiment of the present disclosure. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided. 
         [0085]    Two-wheel self-balancing vehicle  1900  with one or more gravity sensors comprises a first wheel with DC motor  70 , a second wheel with DC motor  72 , a foot placement section  74 , a gravity sensor array  1902 , a gravity sensor array  1904 , and a central control module  79 . First wheel with DC motor  70 , a second wheel with DC motor  72 , a foot placement section  74 , and a central control module  79  are described in details with reference to  FIG. 7 . As shown in  FIG. 14 , x, y, and z directions are illustrated the same as illustrated in  FIG. 7 . 
         [0086]    As described above with reference to  FIG. 7 , foot placement section  74  may be one section or area comprising a first portion  71  and a second portion  73  located on the same plane to offer more design flexibility in terms of mechanical architecture and exterior design. In some aspects, first portion  71  may be a portion between the center axes of two-wheel self-balancing vehicle  700  with one or more gravity sensors and first wheel with DC motor  70 . Second portion  73  may be a portion between the center axes of two-wheel self-balancing vehicle  700  with one or more gravity sensors and second wheel with DC motor  72 . For example, a user may place his/her left foot on first portion  71  and his/her right foot on second portion  73 . 
         [0087]    In some embodiments, first portion  71  may include gravity sensor array  1902 . Second portion  73  may include gravity sensor array  1904 . Each of gravity sensor array  1902  and gravity sensor array  1904  may an array of gravity sensors. Each sensor of gravity sensor array  1902  and gravity sensor array  1904  may sense the weight and gravity angles of a user when he or she stands on foot placement section  74 . Each sensor of gravity sensor array  1902  and gravity sensor array  1904  may be implemented as a microelectromechanical system (MEMS) sensor. In some aspects, each sensor of gravity sensor array  1902  and gravity sensor array  1904  may be or may include a pressure sensor. 
         [0088]    In some embodiments, additional types of sensors may be placed in first portion  71  and second portion  73  to provide additional sensing or control information. For example, sensors that detect outside temperature, body temperature, humidity, and/or other information may be installed. In addition, cameras or camera mounts may be installed in order to detect the surrounding environments or for sensing impending changes. In some embodiments, additional torque sensors may be installed to calculate the torque and send the signal to the on-board processors. In some embodiments, other equipment, such as GPS signal receivers, music players, pockets or slots for storage, and so forth, may be added. 
         [0089]    The exemplary embodiments set forth above are provided to give those of ordinary skill in the art a complete disclosure and description of how to make and use the embodiments of the devices, systems and methods of the disclosure, and are not intended to limit the scope of what the inventors regard as their disclosure. Modifications of the above-described modes for carrying out the disclosure that are obvious to persons of skill in the art are intended to be within the scope of the following claims. All patents and publications mentioned in the disclosure are indicative of the levels of skill of those skilled in the art to which the disclosure pertains. All references cited in this disclosure are incorporated by reference to the same extent as if each reference had been incorporated by reference in its entirety individually. 
         [0090]    The entire disclosure of each document cited (including patents, patent applications, journal articles, abstracts, laboratory manuals, books, or other disclosures) is hereby incorporated herein by reference. 
         [0091]    It is to be understood that the disclosures are not limited to particular compositions or systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. The term “plurality” includes two or more referents unless the content clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains. 
         [0092]    A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.