Electric skateboard with strain-based controls and methods

An electric weight sensing skateboard using one or more strain gauge systems to detect rider-induced strain on one or both trucks, an inertial sensor to detect accelerations and balance position, and wheel speed sensors. Throttle is controlled by rider position, for example, lean forward to increase speed, lean back to slow down. Several drive methods include a rider position detection velocity setpoint control, torque setpoint control, and direct velocity/torque control. A throttle remote is not required. Rider weight activates the motors.

INTRODUCTION

The popularity of electric skateboards has grown considerably over the past several years. Many companies have entered this market, with slightly differing designs. Generally speaking, these vehicles require a handheld remote, lack the ability to sense the rider's body position to control the throttle and detect the rider, and have suffered from various issues, such as safety and reliability problems related to requiring the rider to manually control the throttle with a handheld remote, and a lack of rider-on detection, and a lack of ability to reduce drivetrain drag when the rider is manually pushing. A need exists for a more intuitive, reliable, safer control system for these electric vehicles.

DESCRIPTION

The following sections describe selected aspects of exemplary electric skateboards, as well as related systems and/or methods. The examples in these sections are intended for illustration and should not be interpreted as limiting the entire scope of the present disclosure. Each section may include one or more distinct embodiments or examples, and/or contextual or related information, function, and/or structure.

Definitions

“Substantially” means to be essentially conforming to the particular dimension, range, shape, concept, or other aspect modified by the term, such that a feature or component need not conform exactly. For example, a “substantially cylindrical” object means that the object resembles a cylinder, but may have one or more deviations from a true cylinder.

Electric Weight Sensing Skateboard:

Electric skateboards according to the present teachings overcome the issues described above by using one or more strain gauge systems to detect rider-induced strain on one or both trucks (wheel/axle assemblies), an inertial sensor to detect accelerations and balance position, and wheel speed sensors.

The present disclosure provides systems, apparatuses, and methods relating to electric skateboards. In some embodiments, electric skateboards may include:

A skateboard (FIG. 1-4) including a deck101to receive the feet of a rider; one (or multiple) motors102(bldc hub motors or external belt driven motors) and motor controller103and battery105and wheels104disposed on front skateboard truck106and rear skateboard truck108configured to propel the electric skateboard100; a first strain gauge110attached to a skateboard truck and configured to sense rider weight and center of gravity strain on the skateboard100induced by imbalanced forces exerted upon the front truck106and rear truck108; an optional second strain gauge112attached to the other truck and configured to sense rider weight and center of gravity strain on rear truck108and the deck101induced by forces exerted upon the front and rear trucks106,108; at least one drive motor102configured to drive at least one wheel104, wherein the drive motor(s)102are configured to drive the wheels104in response to weight imbalance of the deck101and rider center of gravity sensed by the strain gauge(s)110,112, to cause the vehicle100to move linearly in response to forces on the front and rear trucks106,108and are only (or variably) activated (FIG. 9) by strain gauge110,112sensing of the rider's weight as to not activate when there is no rider on the skateboard deck101and only when the inertial sensors114determine a substantially level vehicle100.

An inertial balance sensor114attached to the deck101and configured to sense inclination of the board100, wherein the drive motor(s)102are configured to drive the wheels104only when the skateboard100is properly oriented in a reasonable riding position, such as substantially level to the ground.

If only a single strain gauge110is utilized, a method will be used to allow the rider to zero the strain gauge110signal while standing centered on the board deck101, this tared zero setpoint will be used to determine the difference in the strain gauge110measurement from zero and therefore the center of gravity position of the rider.

Many different motor drive methods (FIG. 10-17) may be selected by the rider through means such as a smartphone with a wireless connection.

One such method (FIG. 10,13) is to control the velocity setpoint of the skateboard and rider determined by using the strain gauge(s) to sense the center of gravity (CG) of the rider; wherein, when the CG is sensed toward the forward truck the desired speed will be incremented faster in the speed controller loop; and when the CG is sensed toward the rear truck the desired speed will be decremented slower in the speed controller loop; the rate of increment/decrement may be determined by the amplitude of the CG from center. This method has the advantage of allowing the rider to comfortably stand centered on the board while powering forward at the desired speed. The rider would lean forward to accelerate (increase velocity), lean back to slow down (decrease velocity) until zero speed is reached.

Another control method (FIG. 11, 14) is to use the above described method to sense CG but to increment or decrement a torque set point in a torque controller loop instead of a speed controller loop. The rider would lean forward to increment the commanded torque set point and lean back to decrement the commanded torque set point; the rate of increment/decrement may be determined by the amplitude of the CG from center.

A selectable option would allow advanced riders to, when leaning back, also continue in reverse after zero speed is reached.

Another control method (FIG. 12, 15) is to use the sensed CG to directly control the commanded motor drive torque setpoint. The rider would need to continually lean forward to maintain forward torque and maintain a lean back to apply negative torque.

Another control method (FIG. 16, 17) is to use the sensed CG to directly control the commanded motor drive velocity setpoint. The rider would need to continually lean forward to maintain forward velocity and lean back to reduce velocity.

A manual coasting mode may be selected wherein an inertial sensor attached to the board and configured to sense accelerations from rider pumps (pushes) and inclination of the board, the drive motor(s) being configured to command a motor torque to cause the vehicle to have very little or no drag feeling in the drive train when a rider push is sensed by the inertial sensor or strain gauge(s). The controller in manual mode will be self-powered by regenerated power from the drive motors, the minimal amount of regeneration power is captured to run the controller and allow the low-drag torque control as this mode is useful when the battery has been nearly depleted.

A traction sensing controller is configured to sense the wheel speeds and adjust drive motor torque to keep the wheel rotational velocities relatively similar, especially in situations when one drive wheel has more traction compared to the other which may be sensed by a controller configured to read the strain gauge sensors on the trucks and determine which wheel has more rider weight and therefore more traction.

Springed suspensions200(FIG. 7,8) on the trucks106,108between the wheels and deck are utilized to improve ride comfort, traction, stuck wheels, and reduce rider fatigue. Strain gauges110,112may be mounted directly to the spring suspensions200to measure the induced stress caused by the rider's weight.

A folding deck configured to hinge near the middle with one truck nesting in front or behind the other truck improves portability.

The rider weight measurement may also be used to set the aggressiveness of the proportional-integral-derivative (PID) speed/torque controller (also referred to as a PID loop) of the motor controller. For example, a softer control may automatically be implemented for lightweight riders, and a stronger, more aggressive control for heavier riders, thereby greatly adding to the safety of the vehicle.

FIG. 6is a plan view of an illustrative full bridge strain gauge sensor suitable for use in vehicle100and others.FIG. 5is a schematic circuit diagram of an illustrative strain gauge sensor and amplification circuit suitable for use in vehicle100and others.

The drive arrangement may use any combination of brushless direct current (i.e., BLDC) hub motors102with integrated tires104. In other examples, a separate wheel and drive motor (brushed or brushless) may be utilized, with power transferred via a chain or belt or transmission. In some examples, a hubless wheel may be driven by a friction drive motor.

An inertial balance position sensor114is coupled (e.g., mounted) to deck101, and configured to sense a tilt position of the vehicle. Balance position sensor114may include a combined microelectromechanical systems (MEMS) inertial sensor, such as a six-axis rate gyro and accelerometer. In some examples, sensor114is configured to provide a measurement of the position (inclination and inertial movement) of the entire vehicle100. Sensor114is preferably mounted on a circuit board103which is attached to deck101. Sensor114may be disposed in any suitable location on the frame. However, a location closer to the center of the vehicle may provide reduced centrifugal force errors caused by vehicle movement.

A rechargeable battery105and battery protection circuit is mounted to deck101to provide power for the vehicle. Battery105may include any suitable power storage device, such as a lithium ion battery.

A first full-bridge strain gauge110,112is bonded onto a truck106,108of skateboard100. An example of a full-bridge strain gauge is shown inFIG. 6. Strain gauge110,112may include a flexible, insulating substrate138supporting one or more conductive foil zig-zag patterns140. Deformation of pattern140changes the electrical resistance of the pattern, which can be measured at leads141. The change in resistance can then be used to infer the magnitude of induced stress, according to known methods.

Strain gauge110,112may be located at or near center region of truck106,108, or anywhere a majority of strain is induced onto the truck caused by the rider's weight. In some examples, a single or half-bridge strain gauge may instead be used. In this example, strain gauge110,112is bonded to truck106,108longitudinal with the axle on a bottom surface, such that the strain gauge will detect strains from the rider's weight.

As shown inFIG. 5, the analog output of strain gauge136may be amplified with an amplifier circuit142. Circuit142may include any suitable amplification components, and is illustrative in nature. The rider's weight on a truck can be derived from the analog voltage, when an operational amplifier is used to detect the voltage shift caused by the strain gauge pairs stretching and/or compressing in response to the induced stresses on the truck. Circuit142provides a method for measuring these small voltage changes and supplying an output voltage (corresponding to the rider's weight) to a microcontroller (seeFIG. 18). As the rider steps anywhere onto the skateboard deck, a strain is induced and detected by the strain gauge sensor110,112, thereby indicating when a rider is present and enabling the motor drive system. A magnitude of the induced stress may be proportional to rider weight. This control system may be referred to as the rider-detect system or rider detection. When the rider steps off the vehicle the control system will stop driving the wheels (e.g., by shutting off the motors), such that the vehicle comes to a stop, and/or may disable the motor(s).

The rider's weight may be precisely calculated based on a magnitude of the detected strain, and this weight may be used to adjust the aggressiveness of the throttle control and motor current PID loop. This facilitates a less aggressive control with a lightweight rider and a tighter more aggressive control for a heavier rider, with granular variation in between. This feature increases safety and helps to prevent falls from an overly aggressive system with light rider, or from an underpowered system with heavy rider. In other words, the vehicle's throttle loop will be matched appropriately to the rider's weight, as sensed by the strain gauge(s).

In examples where rider modes are selectable, for example, a new rider may select a more sluggish, less responsive “learning” mode that provides a safer and more comfortable system. Meanwhile, an expert rider may select a very fast and responsive system. In some examples, this rider mode can be communicated to motor controller circuit103through a wireless connection device150disposed on vehicle100, such as a Bluetooth Smart (also known as BLE) module, e.g., using a smartphone app.

In some examples, vehicle100may save in memory the desired settings of each individual rider, e.g., according to his or her measured weight, and/or may recall a previously established profile (e.g., through a wireless connection to a smartphone). Such a profile may include information regarding throttle aggressiveness, maximum speed, and/or the like.

Strain gauges are initially calibrated to center when zero strain is applied to the frame. However, strain gauges have a known tendency for their accuracy to drift over time. In some examples, the control logic of vehicle100may calibrate, upon startup, the zero points of any or all strain gauges. The calibration may be averaged and saved in memory over several startup events to prevent inadvertent strain adversely affecting the calibration. Accordingly, as the vehicle is used it will be gradually calibrated with each power-on cycle.

The user may be directed to power the vehicle without any weight or strain applied to the frame, such that at startup the strain gauges can be automatically zeroed/centered to cancel out drift. Drift will be gradual over time, so this power-up calibration may be configured to affect the drift value by a small amount, as to avoid erroneous calibration by an accidental strain applied during startup.

An erroneous calibration may be detected for example if, upon power-up, a very large calibration need is measured. This error will be ignored and the rider may be warned accordingly. A full user-initiated calibration method may be provided as well (e.g., a “tare” button or command).

In some examples, strain gauges may be centered by detecting when a sensor is being quickly saturated while vehicle100is ridden. In these examples, the gauge will be slowly centered over time to ensure full movement in both directions. In some examples, center calibration of the zero point of a strain gauge may be achieved using a digital to analog converter (DAC) output of the microcontroller connected to the strain gauge through a high value resistor (e.g., 470K Ohms). This DAC output will essentially replace a potentiometer152of circuit142,146(seeFIG. 5) and allow the microcontroller to adjust the center points of the strain gauge full bridge system.

In some examples, a remote control feature may be implemented to control vehicle100using a portable electronic device (e.g., a smartphone) and installed app or handheld remote, via wireless module150. This feature may be enabled or disabled by the rider detection circuit, the rider detection weight threshold may be adjusted using the rider's smartphone app and wireless module150, such that only riders above a certain weight are permitted to use the vehicle (e.g., preventing children from unauthorized use).

Vehicle100may further include instructions414stored in a memory416of a data processing system418(e.g., a personal computer) having its own processor420. Instructions414may be supplied to computer418as a download from a computer network (e.g., the Internet) or on a physical medium (e.g., on a portable memory storage device such as a thumb drive, CD, or DVD). Control system400may be configured to connect to computer418, which may upload instructions414to vehicle100. Instructions414and computer418may provide for modification of instructions or parameters stored in memory408of the balance control system. Control system400may connect to computer418through wired or wireless methods, e.g., by a data cable or by a wireless connection using radio frequency signals and protocols, or by other suitable wireless means.

CONCLUSION