Patent Description:
In a vehicle, it is suggested that slip is determined from the relationship between the rotation number of front wheels and the rotation number of rear wheels, and a torque split between the front wheels and the rear wheels is feedback-controlled, when the front wheels or the rear wheels slip, such that the difference between the rotation number of the front wheels and the rotation number of the rear wheels becomes the same as a target difference between the rotation number of the front wheels and the rotation number of the real wheels (see, e.g., <CIT>).

The wheels of model cars may slip similarly to the case of vehicles. Therefore, model cars in which traction control is performed to prevent slippage of the wheels have been developed.

However, in such model cars, an operator (user) needs to perform various settings for traction control, which may be a complicated operation for the operator.

In view of the above, the present disclosure has an object of easily reducing the slippage of a model car.

The invention provides a radio control system according to claim <NUM>.

According to the present disclosure, it is possible to easily reduce the slippage of a model car.

Hereinafter, embodiments of the present disclosure will be described in the following order.

<FIG> explains a configuration of a radio control system <NUM> according to a first embodiment.

The radio control system <NUM> includes an operation device <NUM> that functions as a controller, and a model car <NUM> that is wirelessly controlled by the operation device <NUM>.

The operation device <NUM> includes a controller <NUM>, a communication part <NUM>, an operation part <NUM>, and a display part <NUM>. The controller <NUM> is a microcomputer including, for example, a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and the like. The CPU of the controller <NUM> loads a program stored in the ROM into the RAM to executes the program, thereby controlling the entire operation device <NUM> and controlling the operation of the model car <NUM>.

The communication part <NUM> modulates signals to be transmitted (rotation control signal and steering control signal) in a predetermined communication method and transmits the modulated signals from an antenna 12a to the model car <NUM>. When a management data signal (to be described later) is transmitted from the model car <NUM>, the communication part <NUM> receives and demodulates the management data signal, and outputs the demodulated signal to the controller <NUM>.

The operation part <NUM> is a stick, a wheel, a button, or the like that receives an operation of an operator. The operation part <NUM> includes, for example, an acceleration/deceleration operation element 13a for instructing acceleration and deceleration (braking) of the model car <NUM>, a steering operation element 13b for instructing steering of the model car <NUM>, and a switching operation element 13c for switching ON/OFF of traction control to be described later.

When the acceleration/deceleration operation element 13a is operated, the operation part <NUM> outputs a signal indicating the operation amount of the acceleration/deceleration operation element 13a to the controller <NUM>. At this time, the controller <NUM> transmits a rotation control signal to the model car <NUM> so that a travel motor <NUM> (the rear wheels <NUM>) rotates at a rotation number corresponding to the inputted signal indicating the operation amount of the acceleration/deceleration operation element 13a.

When the steering operation element 13b is operated, the operation part <NUM> outputs a signal indicating the operation amount of the steering operation element 13b to the controller <NUM>. At this time, the controller <NUM> transmits the steering control signal to the model car <NUM> so that the model car <NUM> is steered at an angle corresponding to the inputted signal indicating the operation amount of the steering operation element 13b.

Further, the operation part <NUM> outputs a switching signal to the controller <NUM> whenever the switching operation element 13c is operated. The controller <NUM> switches ON/OFF of the traction control whenever the switching signal is received.

The display part <NUM> includes a predetermined display device such as a liquid crystal display or an organic EL display, and appropriately displays information required for driving the model car <NUM> depending on the display control of the controller <NUM>.

The model car <NUM> includes front wheels <NUM>, rear wheels <NUM>, an electric speed controller (ESC) <NUM>, a communication part <NUM>, a battery <NUM>, the travel motor <NUM>, a steering servo <NUM>, and rotation sensors <NUM> and <NUM>. The model car <NUM> is a four-wheel vehicle that travels with two front wheels <NUM> and two rear wheels <NUM>. The front wheels <NUM> and the rear wheels <NUM> have the same diameter.

The steering servo <NUM> is connected to the front wheels <NUM>. The steering servo <NUM> is driven by the steering control signal transmitted from the operation device <NUM>, so that the front wheels <NUM> are steered in response to the steering control signal and the traveling direction of the model car <NUM> is changed. Therefore, the front wheels <NUM> function as steering wheels (non-driving wheels).

The travel motor <NUM> is connected to the rear wheels <NUM>. The model car <NUM> travels as the rear wheels <NUM> are rotated by the travel motor <NUM>. Therefore, the rear wheels <NUM> function as driving wheels.

The ESC <NUM> uses the power of the battery <NUM> to control the rotation number of the travel motor <NUM> (the rear wheels <NUM>) depending on the rotation number control signal transmitted from the operation device <NUM>.

The battery <NUM> is used not only for driving the travel motor <NUM> via the ESC <NUM>, but also as a power supply for individual components in the model car <NUM>, such as the communication part <NUM>, the steering servo <NUM>, the rotation sensors <NUM> and <NUM>, and the like.

The communication part <NUM> receives radio waves of the signals (the rotation control signal and the steering control signal) transmitted from the operation device <NUM> through the antenna 24a and demodulates them. The communication part <NUM> outputs the demodulated signals (the rotation control signal and the steering control signal) to the ESC <NUM> and the steering servo <NUM>.

The radio control system <NUM> has a so-called telemetry (remote measurement) function. The communication part <NUM> modulates management data related to the traveling of the model car <NUM>, such as a temperature and a voltage of the battery <NUM>, a current value of the travel motor <NUM>, and the like, in a predetermined communication method, and transmits the modulated data, as a management data signal, from the antenna 24a to the operation device <NUM>.

The operation device <NUM> that has received the management data signal displays the management data such as the temperature and voltage of the battery <NUM>, the current value of the travel motor <NUM>, and the like on the display part <NUM> under the control of the controller <NUM>. Accordingly, an operator can control the model car <NUM> while monitoring the management data displayed on the display part <NUM> of the operation device <NUM>.

The rotation sensor <NUM> detects the rotation number of the front wheels <NUM> at predetermined measurement intervals, and outputs a front wheel rotation number signal indicating the detected rotation number to the communication part <NUM>.

The rotation sensor <NUM> detects the rotation number of the rear wheels <NUM> at predetermined measurement intervals, and outputs a rear wheel rotation number signal indicating the detected rotation number to the communication part <NUM>.

The front wheel rotation number signal and the rear wheel rotation number signal are collectively referred to as wheel rotation number signals.

The communication part <NUM> uses the telemetry function to transmit the wheel rotation number signals inputted from the rotation sensors <NUM> and <NUM>, as a part of the management data signal, to the operation device <NUM>. Hence, the controller <NUM> of the operation device <NUM> can constantly recognize the rotation number of the front wheels <NUM> and the rear wheels <NUM> of the model car <NUM>.

<FIG> explains the configuration of the rotation sensor <NUM>. In <FIG>, a steering mechanism that is connected to the steering servo <NUM> to steer the front wheels <NUM> is omitted for convenience of description.

As shown in <FIG>, the front wheel <NUM> is rotatably connected to a wheel hub <NUM> vertically supported between an upper arm <NUM> and a lower arm <NUM> extending from a chassis (not shown) toward the outside of the vehicle body.

The rotation sensor <NUM> is a magnetic sensor for detecting the rotation number based on changes in the magnetic field. The rotation sensor <NUM> is fixed to the wheel hub <NUM> so that a magnetic field detection portion faces the front wheel <NUM>. At this time, the magnetic field detection portion of the rotation sensor <NUM> is fixed while being spaced by a predetermined distance in a radial direction about the rotation axis of the front wheel <NUM>.

A magnet 28a is fixed to an inner peripheral surface 21a of the front wheel <NUM> on the wheel hub <NUM> side. The magnet 28a is fixed while being spaced by the same distance as that of the magnetic field detection portion of the rotation sensor <NUM> in the radial direction about the rotation axis of the front wheel <NUM>.

Therefore, the magnet 28a and the magnetic field detection portion of the rotation sensor <NUM> are disposed to face each other while being spaced by the same distance about the rotation axis of the front wheel <NUM>.

When the front wheel <NUM> rotates, the magnet 28a also rotates by the rotation of the front wheel <NUM>. The rotation sensor <NUM> detects the rotation number of the front wheel <NUM> by detecting the magnetic field changed by the magnet 28a using the magnetic field detection portion.

The rotation sensor <NUM> has the same configuration as that of the rotation sensor <NUM>.

Next, the traction control will be described. In the first embodiment, the controller <NUM> and the rotation sensors <NUM> and <NUM> function as a control device for performing the traction control.

When the model car <NUM> travels on a road surface (low µ road surface) with a small coefficient of friction, for example, the rear wheels <NUM> that are the driving wheels may slip (idle). When the rear wheels <NUM> slip, the driving force from the travel motor <NUM> is not transmitted to the road surface and, thus, the model car <NUM> cannot travel stably.

On the other hand, when the model car <NUM> travels around a corner, an operator may intentionally slip the rear wheels <NUM> that are the driving wheels to perform so-called drift driving in which the model car <NUM> slides sideways.

Therefore, when the traction control is turned on by the operation of the switching operation element 13c, the traction control is performed in the radio control system <NUM>. Accordingly, the slippage of the rear wheels <NUM> is eliminated at an early stage, and the model car <NUM> travels stably.

When the traction control is turned off by the operation of the switching operation element 13c, the traction control is not performed in the radio control system <NUM>. Accordingly, an operator can intentionally perform the drift driving.

<FIG> explains the flow of signals in the traction control. The controller <NUM> of the operation device <NUM> receives the wheel rotation number signals from the rotation sensors <NUM> and <NUM> of the model car <NUM> at predetermined communication intervals. Here, the communication interval is, for example, an interval at which the communication between the operation device <NUM> and the model car <NUM> is performed.

When the wheel rotation number signals are received, the controller <NUM> calculates the rotation number difference between the front wheels <NUM> and the rear wheels <NUM>. Here, the controller <NUM> calculates the rotation number difference by subtracting the rotation number (that is, the rotation number of the front wheels <NUM>) indicated by the front wheel rotation number signal from the rotation sensor <NUM> from the rotation number (that is, the rotation number of the rear wheels <NUM>) indicated by the rear wheel rotation number signal from the rotation sensor <NUM>.

The controller <NUM> determines that slippage has occurred when there is a rotation number difference between the front wheels <NUM> and the rear wheels <NUM>. Here, the rotation sensors <NUM> and <NUM> may have measurement errors. Therefore, the controller <NUM> determines that slippage has occurred when the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is greater than or equal to a predetermined threshold.

The threshold is set in consideration of the measurement errors of the rotation sensors <NUM> and <NUM>, and the like.

When the tire diameters of the front wheels <NUM> and the rear wheels <NUM> are different, the rotation number difference may be calculated after the rotation number of the front wheels <NUM> or the rear wheels <NUM> is corrected in consideration of the tire diameter ratio of the front wheels <NUM> and the rear wheels <NUM>.

When it is determined that slippage has occurred, the controller <NUM> performs the traction control such that the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is reduced (to be within a certain range). In the traction control, the controller <NUM> performs the feedback control to control the rotation number such that the rotation number of the rear wheels <NUM> is reduced as the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> increases.

For example, the controller <NUM> transmits the rotation number control signal to the model car <NUM> (the ESC <NUM>) so that the rotation number of the rear wheels <NUM> becomes the same as the rotation number of the front wheels <NUM> regardless of the operation amount of the acceleration/deceleration operation element 13a. Accordingly, the ESC <NUM> drives the travel motor <NUM> such that the rotation number of the rear wheels <NUM> become the same as the rotation number of the front wheels <NUM>, which makes it possible to eliminate the slippage.

Further, the controller <NUM> may perform an intermittent operation for alternately switching a high rotation number state and a low rotation number state of the rear wheels <NUM> (the travel motor <NUM>).

<FIG> explains the intermittent operation. As shown in <FIG>, the controller <NUM> determines the rotation number of the rear wheels <NUM> in the high rotation number state (high state) and that in the low rotation number state (low state) of the rear wheels <NUM>.

For example, the controller <NUM> determines, as the high rotation number, the rotation number corresponding to the operation amount of the acceleration/deceleration operation element 13a. Further, the controller <NUM> determines, as the low rotation number, the rotation number obtained by subtracting a return amount from the high rotation number. The return amount is pre-associated with the rotation number difference in such a manner that the return amount increases as the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> increases.

Further, the controller <NUM> determines the duty ratio that is reduced as the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> increases.

Here, the duty ratio is the ratio of a high period corresponding to the high state to the sum of the high period and a low period corresponding to the low state, and is pre-associated with the rotation number difference between the front wheels <NUM> and the rear wheels <NUM>.

The controller <NUM> determines the rotation number (the rotation number in the high state and the rotation number in the low state) of the rear wheels <NUM> based on the rotation number, the duty ratio, and the return amount corresponding to the operation amount of the acceleration/deceleration operation element 13a, and outputs the rotation number control signal for causing the rear wheels <NUM> to rotate at the calculated rotation number to the model car <NUM>. Accordingly, the ESC <NUM> drives the travel motor <NUM> to reduce the rotation number of the rear wheels <NUM>, which makes it possible to eliminate the slippage.

The rotation number of the rear wheels <NUM> in the intermittent operation is not necessarily determined by the above method, and may be determined by other methods.

<FIG> is a flowchart showing the flow of the traction control. It is assumed that the controller <NUM> receives the wheel rotation number signals from the rotation sensors <NUM> and <NUM> at predetermined communication intervals during the traction control shown in <FIG>.

As shown in <FIG>, in step S1, the controller <NUM> calculates the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> based on the wheel rotation number signals transmitted from the rotation sensors <NUM> and <NUM>. In step S2, the controller <NUM> determines whether the rotation number difference calculated in step S1 is greater than or equal to a predetermined threshold. In other words, the controller <NUM> determines whether or not there is a rotation number difference between the front wheels <NUM> and the rear wheels <NUM>.

When there is no rotation number difference between the front wheel <NUM> and the rear wheel <NUM>, that is, when the rotation number difference is smaller than the threshold value (No in step S2), the processing is ended. On the other hand, when there is a rotation number difference between the front wheels <NUM> and the rear wheels <NUM>, that is, when the rotation number difference is greater than or equal to the threshold value (Yes in step S2), the controller <NUM> obtains a signal indicating the operation amount from the acceleration/deceleration operation element 13a in step S3.

In step S4, the controller <NUM> calculates the rotation number of the rear wheels <NUM> that reduces the rotation number difference between the front wheels <NUM> and the rear wheels <NUM>. Then, in step S5, the controller <NUM> transmits the rotation number control signal for causing the rear wheels <NUM> to rotate at the calculated rotation number to the model car <NUM>. Accordingly, in the model car <NUM>, the ESC <NUM> reduces the rotation number of the travel motor <NUM>, that is, the rotation number of the rear wheels <NUM>, thereby suppressing slippage.

Thereafter, in step S6, the controller <NUM> calculates the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> based on the wheel rotation number signals transmitted from the rotation sensors <NUM> and <NUM>. In step S7, the controller <NUM> determines whether or not the rotation number difference calculated in step S6 is smaller than or equal to a predetermined constant range. In other words, the controller <NUM> determines whether or not the slippage has been eliminated.

When the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is not within the certain range, that is, when the slippage has not been eliminated (No in step S7), the processing returns to step S3. On the other hand, when the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is within the certain range, that is, when the slippage has been eliminated (Yes in step S7), the processing is ended.

<FIG> explains a configuration of a radio control system 1A according to a second embodiment.

In the radio control system <NUM> according to the first embodiment, the wheel rotation number signals outputted from the rotation sensors <NUM> and <NUM> are inputted to the controller <NUM> of the operation device <NUM> through the communication parts <NUM> and <NUM>, and the controller <NUM> performs the traction control.

On the other hand, in the radio control system 1A according to the second embodiment, the wheel rotation number signals outputted from the rotation sensors <NUM> and <NUM> are inputted to the ESC <NUM>, and the ESC <NUM> performs the traction control.

The radio control system 1A is different from the radio control system <NUM> according to the first embodiment only in the above configuration, and the other configurations are the same.

Next, the traction control will be described. <FIG> explains flow of signals in the traction control. In the second embodiment, the ESC <NUM> and the rotation sensors <NUM> and <NUM> function as a control device for performing the traction control.

The ESC <NUM> receives the wheel rotation number signals from the rotation sensors <NUM> and <NUM> at predetermined measurement intervals. Here, the measurement interval is an interval for detecting the rotation number using the rotation sensors <NUM> and <NUM>. The measurement interval is shorter than the communication interval between the operation device <NUM> and the model car <NUM>.

When the wheel rotation number signal is received, the ESC <NUM> calculates the rotation number difference between the front wheels <NUM> and the rear wheels <NUM>. The ESC <NUM> determines that slippage has occurred when there is a rotation number difference between the front wheels <NUM> and the rear wheels <NUM> (when the calculated rotation number difference is greater than or equal to a predetermined threshold).

When it is determined that slippage has occurred, the ESC <NUM> performs the traction control such that the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is reduced (to be within a certain range). In the traction control, the ESC <NUM> performs the feedback control to control the rotation number such that the rotation number of the rear wheels <NUM> is reduced as the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> increases.

For example, the ESC <NUM> drives the travel motor <NUM> such that the rotation number of the rear wheels <NUM> becomes the same as the rotation number of the front wheels <NUM> regardless of the rotation number control signal transmitted from the controller <NUM>. Accordingly, the rotation number of the rear wheels <NUM> becomes the same as the rotation number of the front wheels <NUM>, which makes it possible to eliminate the slippage.

Similarly to the first embodiment, the ESC <NUM> may perform an intermittent operation for alternately switching the high rotation number state and the low rotation number state of the rear wheels <NUM> (the travel motor <NUM>). Accordingly, the ESC <NUM> drives the travel motor <NUM> to reduce the rotation number of the rear wheels <NUM>, which makes it possible to eliminate the slippage.

<FIG> is a flowchart showing flow of the traction control. It is assumed that the ESC <NUM> receives the wheel rotation number signals from the rotation sensors <NUM> and <NUM> at predetermined measurement intervals during the traction control shown in <FIG>.

As shown in <FIG>, in step S11, the ESC <NUM> calculates the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> based on the wheel rotation number signals transmitted from the rotation sensors <NUM> and <NUM>. In step S12, the ESC <NUM> determines whether the rotation number difference calculated in step S11 is greater than or equal to a predetermined threshold. In other words, the ESC <NUM> determines whether there is a rotation number difference between the front wheels <NUM> and the rear wheels <NUM>.

When there is no rotation number difference between the front wheel <NUM> and the rear wheel <NUM>, that is, when the rotation number difference is smaller than the threshold value (No in step S12), the processing is ended. On the other hand, when there is a rotation number difference between the front wheel <NUM> and the rear wheel <NUM>, that is, when the rotation number difference is greater than or equal to the threshold value (Yes in step S12), the ESC <NUM> obtains the rotation number control signal transmitted from the controller <NUM> in step S13.

In step S14, the ESC <NUM> calculates the rotation number of the rear wheels <NUM> that reduces the rotation number difference between the front wheels <NUM> and the rear wheels <NUM>. In step S15, the ESC <NUM> drives the travel motor <NUM> such that the rear wheels <NUM> rotates at the calculated rotation number. Accordingly, in the model car <NUM>, the rotation number of the travel motor <NUM>, that is, the rotation number of the rear wheels <NUM> is reduced, thereby suppressing slippage.

Next, in step S16, the ESC <NUM> calculates the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> based on the wheel rotation number signals transmitted from the rotation sensors <NUM> and <NUM>. In step S17, the ESC <NUM> determines whether the rotation number difference calculated in step S16 is smaller than or equal to a predetermined threshold. In other words, the ESC <NUM> determines whether or not slippage has been eliminated.

When the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is not within a certain range, that is, when the slippage has not been eliminated (No in step S17), the processing returns to step S13. On the other hand, when the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is within a certain range, that is, when the slippage has been eliminated (Yes in step S17), the processing is ended.

The present disclosure is not limited to the above-described specific examples, and may adopt various modifications.

For example, in the above embodiments, the rear wheels <NUM> are provided as first wheels (driving wheels), and the front wheels <NUM> are provided as second wheels (non-driving wheels). Further, the traction control is performed based on the rotation number difference between the front wheels <NUM> and the rear wheels <NUM>.

However, the first wheels and the second wheels are not limited thereto. For example, the first wheels may be the front wheels <NUM> and the second wheels may be the rear wheels <NUM>. For example, in the case of a four-wheel-drive model car, each of the first wheel and the second wheel may be any one of the four wheels.

In the above embodiments, the case where the model car <NUM> is a four-wheel car has been described. However, any model car having two or more wheels may be used.

In the above embodiments, the travel motor <NUM> is provided as a driving source. However, an engine may be provided as the driving source.

As described above, the control device for the model car <NUM> according to the embodiment includes the rotation sensors <NUM> and <NUM> for detecting the rotation number of the first wheels (the rear wheels <NUM>) and the rotation number of the second wheels (the front wheels <NUM>) of the model car <NUM>, and the controller (the controller <NUM> and the ESC <NUM>) for controlling driving of the driving source (the travel motor <NUM>) of the model car <NUM> such that the rotation number difference between the first wheel and the second wheel is reduced when the rotation number difference is greater than or equal to a threshold value.

Accordingly, when the wheels (the rear wheels <NUM>) of the model car <NUM> slip, the control device controls the driving of the driving source (the travel motor <NUM>) such that the rotation number difference between the front wheels <NUM> and the rear wheels <NUM> is reduced.

Therefore, the slippage of the model car <NUM> can be easily reduced without requiring an operator to perform various settings related to the traction control.

The first wheels (the rear wheels <NUM>) are the driving wheels that are rotated by the driving source (the travel motor <NUM>), and the second wheels (the front wheels <NUM>) are the non-driving wheels that are not rotated by the driving source. The controller (the controller <NUM> and the ESC <NUM>) controls the driving of the driving source such that the rotation number of the first wheels is reduced.

Accordingly, the rotation number of the rear wheels <NUM> as the driving wheels that may cause slippage can be reduced, thereby eliminating the slippage at an early stage.

The rotation sensors <NUM> and <NUM> are installed at the model car <NUM>, and the controller <NUM> is installed at the operation device <NUM> for wirelessly controlling the operation of the model car <NUM>.

Accordingly, the operation device <NUM> can perform the calculation for controlling the rotation number of the rear wheels <NUM> and, thus, the calculation amount in the model car <NUM> can be reduced. In other words, the power consumption and the processing load in the model car <NUM> can be suppressed, and the traveling distance of the model car <NUM> can be increased.

The rotation sensors <NUM> and <NUM> and the controller (the ESC <NUM>) are installed at the model car <NUM>.

Accordingly, the rotation number of the rear wheels <NUM> can be reduced by receiving the wheel rotation signals from the rotation sensors <NUM> and <NUM> without performing wireless communication with the operation device <NUM>. The ESC <NUM> can receive the wheel rotation signals from the rotation sensors <NUM> and <NUM> at the measurement intervals shorter than the communication intervals.

Therefore, it is possible to improve the responsiveness of the traction control.

The controller (the controller <NUM> and the ESC <NUM>) intermittently operates the driving source (the travel motor <NUM>).

Accordingly, the slippage can be eliminated at an early stage.

The controller (the controller <NUM> and the ESC <NUM>) can switch execution and non-execution of the driving control depending on an operator's operation of the operation element (the switching operation element 13c).

Claim 1:
A radio control system (<NUM>), comprising:
a model car (<NUM>) having a first wheel (<NUM>) and a second wheel (<NUM>); and
a control device having a rotation sensor (<NUM>, <NUM>) configured to detect a rotation number of the first wheel (<NUM>) and a rotation number of the second wheel (<NUM>) of the model car (<NUM>),
characterized in that the control device further comprises:
a controller (<NUM>, <NUM>) configured to perform driving control of a driving source (<NUM>) of the model car (<NUM>) such that a rotation number difference between the first wheel (<NUM>) and the second wheel (<NUM>) is reduced when the rotation number difference is greater than or equal to a threshold,
wherein the first wheel (<NUM>) is a driving wheel that is rotated by the driving source (<NUM>),
the second wheel (<NUM>) is a non-driving wheel that is not rotated by the driving source (<NUM>),
and
the controller (<NUM>, <NUM>) performs the driving control of the driving source (<NUM>) such that the rotation number of the first wheel (<NUM>) is reduced.