Note: Descriptions are shown in the official language in which they were submitted.
WEIGHT SENSING SUSPENSION TRUCK FOR ELECTRIC SKATEBOARD
FIELD
This disclosure relates generally to electric skateboards, and more
particularly to a weight sensing
suspension truck that can be used with an electric skateboard.
BACKGROUND
An early example of an electric skateboard design is disclosed in US patent
no. 4,069,881. Since
then, the capability and popularity of electric skateboards have grown rapidly
with the advent of
compact brushless motors and energy dense lithium batteries, with new products
entering the
market every year. Some of these electric skateboards include a handheld
remote for the rider to
control the power and braking force on the motors, wherein the remote is
tethered to the
skateboard in some known designs, and wirelessly communicates with the
skateboard in in other
known designs.
While skateboards with handheld remotes are relatively popular, they have a
number of
drawbacks. One obvious drawback is that a rider's hand is occupied holding the
remote thus
making it difficult for the rider to hold anything else with that hand.
Further, the remote if wireless
can be easily lost or misplaced. Also, the remote even if tethered to the
skateboard presents a
separate component that complicates storage and handling.
Other known electric skateboard designs have been proposed which use a rider's
body position
and/or foot placement to control the skateboard. For example, US patent no.
6,050,357 mentions
several methods of sensing rider weight and foot pressure, so that the
skateboard can be
accelerated by applying more weight with the front foot and slowed down by
applying more weight
with the rear foot. US patent no. 7,293,622 discloses another design wherein
the entire deck is
mounted on a tilting surface, and leaning forwards or backwards will cause a
measured change
in deck angle to regulate motor power. In US patent no. 9,004,213, a
skateboard deck is disclosed
which includes a pressure sensitive pad that a user engages with his or her
foot, similar in concept
to a gas pedal on a car. Japanese patent no. 2003237670A discloses a
skateboard with multiple
sensors that detect a rider's center of gravity over the deck, regardless of
where the rider's feet
are located, while Japanese patent no. 20130081891A1 discloses pressure
sensitive pads on a
skateboard deck as a means of control input.
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What is common in all of these foot based control devices is that the weight
or pressure sensing
is on or attached to the deck of the skateboard. This design approach presents
certain limitations,
including precluding the use of third party decks that are desirable but are
not compatible with
motorized or electric skateboards.
SUMMARY
According to one aspect of the invention, there is provided an electric
skateboard truck
comprising: a base plate mountable to an underside of an electric skateboard
deck and
comprising a weight sensor positioned to directly or indirectly measure a
force exerted on the
base plate by the skateboard deck; and a hanger pivotably coupled to the base
plate, and
comprising an axle for coupling to a pair of wheels.
The base plate can comprise a suspension spring, and the weight sensor can be
a strain gauge
mounted on a flexing portion of the suspension spring that flexes when the
truck is subjected to
a rider weight. In particular, the suspension spring can be a leaf spring in
which case the strain
gauge is positioned on a flexible surface of the leaf spring. Alternatively,
the weight sensor can
be a displacement sensor mounted on a displacing portion of the suspension
spring that displaces
when the truck is subjected to a rider weight. The displacement sensor can be
selected from a
group consisting: an optical sensor, a magnet and Hall effects detector, a
capacitive sensor, and
an inductive sensor.
Alternatively, the base plate can comprise a planar section and a hanger mount
section extending
downwardly from the planar section and configured to couple to the hanger. In
this case, the
weight sensor is a pressure sensitive resistor (FSR) sensor assembly mounted
on top of the
planar section and comprises a pair of plates sandwiching an FSR sensor.
Optionally, the hanger
mount section comprises a cut-out that causes a stress concentration in a
location in the base
plate when the truck is subjected to a rider weight; in this case, the weight
sensor is a strain gauge
located at the stress concentration location of the base plate.
The electric skateboard truck can further comprise a pair of wheels coupled to
the axle and at
least one motor rotationally coupled to the pair of wheels. The at least one
motor can be a motor
mounted in a hub of each wheel of the pair of wheels.
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According to another aspect of the invention, there is provided a truck kit
for an electric skateboard
comprising a front truck and a rear truck. The front truck comprises: a front
base plate mountable
to a front underside of an electric skateboard deck and comprising a front
weight sensor
positioned to directly or indirectly measure a force exerted on the front base
plate by the
skateboard deck; and a front hanger pivotably coupled to the front base plate,
and comprising a
front axle for coupling to a front pair of wheels. The rear truck comprises: a
rear base plate
mountable to a rear underside of the electric skateboard deck and comprising a
rear weight sensor
positioned to directly or indirectly measure a force exerted on the rear base
plate by the
skateboard deck; and a rear hanger pivotably coupled to the rear base plate,
and comprising a
rear axle for coupling to a rear pair of wheels. At least one of the front and
rear pair of wheels is
rotatably drivable by at least one motor, and the at least one motor is
controlled by at least one
controller that is communicable with the front and rear weight sensors.
The truck kit can further comprise at least one controller electrically
communicative with the front
and rear weight sensors, and for electrically coupling to a motor. The at
least one controller can
comprise at least one skate controller circuit electrically communicative with
the front and rear
weight sensors, and at least one motor controller electrically communicative
with the least one
skate controller circuit and for electrically coupling to the motor.
According to another aspect of the invention, there is provided an electric
skateboard comprising:
a deck; at least one motor; a battery electrically coupled to the at least one
motor; a front truck
assembly, a rear truck assembly, front and rear pairs of wheels, and at least
one controller
communicative with the front and rear weight sensors and the at least one
motor. The front truck
assembly comprises a front base plate mounted to a front underside of the deck
and which
comprises a front weight sensor positioned to directly or indirectly measure a
force exerted on the
front base plate by the skateboard deck, and a front hanger pivotably coupled
to the front base
plate and which comprises a front axle. The rear truck assembly comprises a
rear base plate
mounted to a rear underside of the deck and which comprises a rear weight
sensor positioned to
directly or indirectly measure a force exerted on the rear base plate by the
skateboard deck, and
a rear hanger pivotably coupled to the rear base plate and which comprises a
rear axle. Each
pair of wheels are mounted to the front and rear axles respectively, and at
least one of the front
and rear pairs of wheels is coupled to and rotatably driven by the at least
one motor. The at least
one controller can be communicative with the front and rear weight sensors and
the at least one
motor, and comprises a processor and a memory having encoded thereon program
code
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executable by the processor to operate the at least one motor in response to
measurements
received from the front and rear weight sensors.
According to another aspect of the invention, there is provided a method for
controlling an electric
skateboard comprising front and rear weight sensors mounted respectively to
front and rear
baseplates of the electric skateboard, and a motor rotatably coupled to drive
wheels of the electric
skateboard. The method comprises: repeatedly reading measurements taken by the
front and
rear weight sensors and determining a total weight and weight distribution of
a rider on the electric
skateboard; when the determined total weight is within a defined margin of a
baseline weight,
operating the motor to accelerate the skateboard when the weight distribution
is higher on the
front baseplate than on the rear baseplate, and operating the motor to
decelerate the skateboard
when the weight distribution is higher on the rear baseplate than on the front
baseplate; and
identifying a kick event when the determined total weight momentarily
decreases beyond a
defined kick threshold, and operating the motor to limit acceleration of the
skateboard during the
kick event, and operating the motor to sustain skateboard speed or to
decelerate the skateboard
for a selected time period after the kick event ends. The selected time period
after the kick event
ends can be between 0.5 and 3 seconds. Operating the motor to limit
acceleration of the
skateboard during the kick event can comprise operating the motor in a
regenerative braking
mode. Identifying the kick event can further comprise: detecting an
acceleration of the skateboard
when the total weight momentarily decreases below the defined kick threshold
but is above a
weight threshold indicating that a rider has one foot on the skateboard.
The method can further comprise detecting a bounce event, which comprises
identifying a period
of increased total weight followed by a period of reduced total weight with no
associated
acceleration of the skateboard during the period of reduced total weight, and
filtering out detected
bounce events from the step of identifying a kick event.
According to another aspect of the invention, there is provided a computer
readable medium
having encoded thereon program code executable by a processor to: repeatedly
read
measurements taken by the front and rear weight sensors and determine a total
weight and weight
distribution of a rider on the electric skateboard; when the determined total
weight is within a
defined margin of a baseline weight, operate the motor to accelerate the
skateboard when the
weight distribution is higher on the front baseplate than on the rear
baseplate, and operate the
motor to decelerate the skateboard when the weight distribution is higher on
the rear baseplate
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than on the front baseplate; and identify a kick event when the determined
total weight
momentarily decreases beyond a defined kick threshold, operate the motor to
limit acceleration
of the skateboard during the kick event, and operate the motor to sustain
skateboard speed or to
decelerate the skateboard for a selected time period after the kick event
ends.
According to another aspect of the invention, there is provided an electric
skateboard comprising:
a deck, at least one motor; a battery electrically coupled to the at least one
motor; a front truck
assembly comprising a front base plate mounted to a front underside of the
deck and comprising
a front weight sensor positioned to directly or indirectly measure a force
exerted on the front base
plate by the skateboard deck, and a front hanger pivotably coupled to the
front base plate and
comprising a front axle; a rear truck assembly comprising a rear base plate
mounted to a rear
underside of the deck and comprising a rear weight sensor positioned to
directly or indirectly
measure a force exerted on the rear base plate by the skateboard deck, and a
rear hanger
pivotably coupled to the rear base plate and comprising a rear axle; front and
rear pairs of wheels
that are mounted to the front and rear axles respectively, wherein at least
one of the front and
rear pairs of wheels is coupled to and rotatably driven by the at least one
motor; and at least one
controller communicative with the front and rear weight sensors and the at
least one motor. The
controller comprises a processor and a memory having encoded thereon program
code
executable by the processor to: repeatedly read measurements taken by the
front and rear weight
sensors and determine a total weight and weight distribution of a rider on the
electric skateboard;
when the determined total weight is within a defined margin of a baseline
weight, operate the at
least one motor to accelerate the skateboard when the weight distribution is
higher on the front
baseplate than on the rear baseplate, and operate the at least one motor to
decelerate the
skateboard when the weight distribution is higher on the rear baseplate than
on the front
baseplate; and identify a kick event when the determined total weight
momentarily decreases
beyond a defined kick threshold, operate the at least one motor to limit
acceleration of the
skateboard during the kick event, and operate the at least one motor to
sustain skateboard speed
or to decelerate the skateboard for a selected time period after the kick
event ends.
According to another aspect of the invention, there is provided a truck base
plate for an electric
skateboard. The truck base plate is mountable to an underside of an electric
skateboard deck
and pivotably mountable to a truck hanger, and comprises a weight sensor
positioned to directly
or indirectly measure a force exerted on the truck base plate by the
skateboard deck.
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BRIEF DESCRIPTION OF THE FIGURES
Figures 1 is a side elevation view of an electric skateboard having a pair of
weight sensing
suspension trucks according to one embodiment.
Figures 2A ¨ 2C are respective perspective, side elevation and rear views of a
weight sensing
suspension truck having a strain gauge sensor mounted to a leaf type
suspension spring in the
truck's base plate, according to another embodiment.
Figures 3A ¨ 3C are respective perspective, side elevation and rear views of a
weight sensing
suspension truck having an optical displacement sensor mounted to a leaf type
suspension spring
in the truck's base plate, according to another embodiment.
Figures 4A ¨ 4C are respective exploded perspective, side elevation and rear
views of a weight
sensing suspension truck having a pressure sensitive resistor mounted on the
truck's base plate
according to another embodiment.
Figures 5A ¨ 5C are respective perspective, side elevation and rear views of a
weight sensing
suspension truck having a strain gauge sensor mounted at a concentrated stress
section of the
truck's base plate according to another embodiment.
Figure 6 is a flowchart depicted a method performed by a motor controller to
control the operation
of the electric skateboard.
Figure 7 is a graph of weight detected by the front and rear suspension trucks
over a time period.
DETAILED DESCRIPTION
Overview
Directional terms such as "top", "bottom", "upwards", "downwards",
"vertically", and "laterally" are
used in the following description for the purpose of providing relative
reference only, and are not
intended to suggest any limitations on how any article is to be positioned
during use, or to be
mounted in an assembly or relative to an environment.
Additionally, the term "couple" and variants of it such as "coupled",
"couples", and "coupling" as
used in this description is intended to include indirect and direct
connections unless otherwise
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indicated. For example, if a first device is coupled to a second device, that
coupling may be
through a direct connection or through an indirect connection via other
devices and connections.
Similarly, if the first device is communicatively coupled to the second
device, communication may
be through a direct connection or through an indirect connection via other
devices and
connections.
Furthermore, the singular forms "a", "an", and "the" as used in this
description are intended to
include the plural forms as well, unless the context clearly indicates
otherwise.
Embodiments of the invention disclosed herein relate generally to a weight
sensing suspension
truck for use in an electric skateboard. More particularly, a weight sensor is
mounted in a base
plate of each of a front and rear truck assembly of the skateboard, and is
positioned to directly or
indirectly measure a force exerted on each respective base plate by the
skateboard deck, and is
configured to output a measurement signal. One or more controllers are
communicative with
each truck assembly to receive their respective measurement signals. The
controller(s) uses
these measurement signals as inputs to control one or more electric motors
that drives one or
more wheels of the skateboard, such as the two rear wheels. The electric
motor(s) in some
embodiments is located in the hanger of one of the trucks, or in the hub of
one of more wheels;
in other embodiments, the motor(s) is mounted to the skateboard deck or
elsewhere on the truck,
and is rotatably coupled to the drive wheels, for example, by a drive chain.
In some embodiments, one of the controllers comprises a processor and a memory
having
encoded thereon a motor control program that is executable by the processor to
control operation
of the motor using the measurement signals received from the weight sensors.
More particularly,
the received measurement signals are used to determine the weight distribution
of a rider on the
skateboard, and the controller will operate the motor(s) in different modes
based on the
determined weight distribution. One operating mode is known as a kick assist
control mode,
which comprises using the received signals to determine whether a kick event
has occurred,
limiting acceleration of the motor(s) during a determined kick event, and
sustaining speed or
decelerating the motor after the kick event has finished.
In some embodiments, a kit is provided comprising the front and rear weight
sensing suspension
trucks for mounting to a skateboard deck; this kit can optionally include one
or more of the
controller(s), the motor(s), and a battery for powering the motor(s). In some
other embodiments,
an entire electric skateboard is provided comprising a deck, the front and
rear weight sensing
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suspension trucks mounted respectively to front and rear undersides of the
deck, the one or more
controllers which is communicative with the front and rear weight sensing
suspension trucks, the
motor(s) which is communicative with the one or more controllers and is
mechanically coupled to
drive wheels of the skateboard, and a battery that is electrically coupled to
the motor. In some
other embodiments, only the base plate of the weight sensing suspension truck
is provided; this
weight sensing base plate comprises the weight sensor and can be combined with
third party
hangers to form a complete truck assembly. By locating the weight sensor in
the base plate of the
truck assembly, end users can keep their original truck hangars, which
optionally comprise an
integrated motor and drive chain, thereby providing a broad use for
aftermarket upgrades.
Furthermore, the base plate is a stationary component of the truck and is
relatively well protected
and shielded from foreign objects encountered on the road, which should reduce
the exposure
risks compared to prior art electric skateboards which place sensors on other
parts of the
skateboard.
Apparatus
Referring now to Figure 1 and according to a first embodiment, an electric
skateboard 10 generally
comprises a deck 12, a front weight sensing suspension truck 14 mounted to a
front underside of
the deck 12, a rear weight sensing suspension truck 16 mounted to a rear
underside of the deck
12, a pair of motor controllers 18, a skate controller circuit 19, a pair of
motors 20 each integrated
into a hub of each of the rear wheels 22, and a battery 24 that is
electrically coupled to the motor
controllers 18 to supply power thereto. The skate controller circuit 19 is
communicative with weight
sensors 26 (shown in Figures 2 to 5) in the front and rear weight sensing
suspension trucks 14,
16 and with the motor controllers 18via controller communication cables 28;
alternatively, the
skate controller circuit 19 can be communicative with the weight sensors 26
and motor controllers
18 by wireless means known in the art (not shown). The motor controllers 18 in
turn are electrically
coupled to the motors 20 by power cables 29.
Referring now to Figures 2A to 2C, each of the front and rear weight sensing
suspension trucks
14, 16 comprise a base plate 30 fixedly mounted to the underside of the deck
12, and a hanger
32 pivotably mounted to the bottom of the base plate 30. The base plate 30 in
this embodiment
comprises a leaf spring, wherein one end ("top end") of the leaf spring is
mounted to the underside
of the deck 12, and another end ("bottom end") comprises a pivot cup for
receiving a pivot arm 34
of the hanger 32. The leaf spring serves as a suspension means and is
configured to flex by an
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amount proportional to an applied force on the deck 12. The leaf spring can be
selected to have
a design stiffness that causes the leaf spring to deflect into a maximum
flexed position where the
top and bottom ends do not touch when a maximum design weight is applied to
the deck 12.
In this embodiment, the weight sensor is a strain gauge 26 that is mounted on
the inside surface
of the leaf spring at around its midpoint. The strain gauge 26 measures the
strain on the leaf
spring when weight is applied to the base plate 30 from the deck 10 and the
leaf spring flexes.
The measured strain is then transmitted to the skate controller circuit 19
which then converts the
measured strain into a force measurement in a manner well known in the art. In
other words, the
strain gauge indirectly measures the force exerted on the base plate 30.
The truck shown in Figures 2A-2C is the rear truck 16 and comprises the motors
20 each
integrated into the hub of each of the rear wheels 22. Such "hub" motors are
known in the art and
thus are not described in detail here. The rear wheels 22 are attached to the
hanger 32 via an
axle 36. The hanger has an opening and is attached to the baseplate via a
kingpin and pivot
pushing as is standard in the art of truck design. A motor power cable extends
from each motor
20 along the hangar and terminates at one of the motor controllers 18. These
motor controllers
18 convert the fixed DC battery voltage into a variable voltage supply
suitable for spinning the
motors 20. The command signal for determining the motor power comes from the
skate controller
circuit 19, which is connected to both the front and rear weight sensors 26.
This skate controller
circuit has a memory having encoded thereon a motor control program for
setting the desired
motor power level based on what it measures from the front and rear weight
sensors 26, as will
be described in more detail below. The front truck 14 has the same design as
the rear truck 16,
with the exception that the front truck 14 does not comprise a hub motor. In
particular, the front
truck 14 has a base plate 30 featuring a leaf spring, and a strain gauge as
the force sensor 26. A
sensor communication port (not shown) is provided for connecting to the
controller communication
cable 28.
According to second embodiment, the front and rear trucks 14, 16 have the same
design as in
the first embodiment, except that the strain gauges are replaced by
displacement sensors as the
weight sensors 26. Referring now to Figures 3A to 3C, one suitable
displacement sensor is an
optical displacement sensor 26 that is positioned on the inner surface of the
top end of the leaf
spring, facing the inner surface of the bottom end of the leaf spring, such
that the optical
displacement sensor 26 can detect a change in the distance between the ends of
the leaf spring
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("displacement measurement"). The optical displacement sensor 26 outputs a
signal comprising
the displacement measurement to the skate controller circuit 19, which then
converts the
displacement measurement into a force measurement in a manner well known in
the art. In other
words, the optical displacement sensor 26 indirectly measures the force
exerted on the base plate
30. Suitable optical displacement sensors include commercially available
optical displacement
sensors well known in the art, such as triangulation sensors, intensity
sensors, time of flight
sensors and interferometer sensors.
Alternatively, other displacement sensors known in the art can be used as the
weight sensor 26
instead of the optical displacement sensor, such as a magnet and Hall effects
detector, capacitive
sensors, and inductive sensors. The use of such sensor to measure displacement
are well known
in the art and thus not described in detail here.
In other embodiments, the front and rear trucks 14, 16 have a different
suspension design than a
leaf spring, but still comprise a weight sensor 26 in the base plate to
directly or indirectly measure
the force applied to the base plate 30. Referring now to Figures 4A to 4C and
according to a third
embodiment, the weight sensor 26 comprises a pressure sensitive resistor (FSR)
sensor that
allows for direct force measurement with minimal electrical signal
conditioning. The base plate
30 comprises a planar section 50, and a hanger mount section 52 extending
downwardly from
the planar section and comprising a lower cup washer for engaging with a
kingpin and a pivot cup
for engaging with the hanger pivot. A FSR assembly 40 is fixedly mounted to
the top of the base
plate planar section 50, and comprises a FSR baseplate 42, an FSR boardplate
46, and the FSR
sensor 26 sandwiched in between the FSR baseplate 42 and the FSR boardplate
46. The FSR
assembly 40 is held together and mounted to the base plate 30 by a series of
dowels 44 that
extend through openings in the FSR baseplate 42, FSR boardplate 46, and the
planar section of
the base plate 30. A communication cable (not shown) is connected to the FSR
sensor 30 and
extends to a sensor port (not shown) at one end of the FSR assembly 40; the
communication
cable 28 couples to this port to enable the skate controller circuit 19 to
receive measurement
signals from the FSR sensor 26. The FSR boardplate is also provided with a set
of bores 48 for
receiving fasteners (not shown) for mounting the truck 14, 16 to the deck 12.
Referring now to Figures 5A to 50, and according to a fourth embodiment, the
weight sensor 26
is a strain gauge that is mounted on a concentrated stress part of the base
plate 30. Like the third
embodiment, the base plate 30 comprises a planar section 50 and a hanger mount
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extending downwardly from the planar section 50 and comprising a lower cup
washer 53 and a
pivot cup 54. Unlike the solid lower cup washer in the third embodiment, the
lower cup washer
53 in the fourth embodiment comprises a cut-out 56 that results in a stress
concentration to be
located at the part of the lower cup washer 53 that connects to the planar
section 50 of the base
plate 30. The strain gauge 26 is located at this stress concentration
location, and is effective to
measure the strain at the location when a force is applied to the base plate
30.
In a fifth embodiment (not shown), the weight sensor 26 is a capacitive
sensor, and the front and
rear weight sensing truck 14, 16 comprises an elastomeric material in the base
plate, wherein
changing thickness of the elastomer material changes the separation distance
of metal plates
resulting in a measurable capacitance change by the capacitance sensor.
Motor Control Program
Referring back to Figure 1, the motor controller 18 can be a general purpose
motor controller
known in the art, such as known motor controllers which can convert DC power
from the battery
24 to run a three-phase AC current for the hub motor 20 and to allow the
modulation of the motor
power. The skate controller circuit 19 is an interface circuit comprising a
processor and a memory
having encoded thereon the motor control program, and which has input ports
communicative
with the weight sensors 26 of the front and rear trucks 14, 16, and output
ports communicative
with the motor controllers 18. The skate controller circuit 19 operates to
receive measurement
signals from the weight sensors 26, executes the motor control program, and
then sends out
control signals to the motor controllers 18 for how much power or braking
force should be provided
by the motors 20.
Referring now to Figure 6 the motor control program when executed by the
processor of the skate
controller circuit 19 performs the following steps:
On start-up (step 100), the motor control program reads the front and rear
weight sensors 26,
converts each measurement to a force, and computes the sum of the two measured
forces to
establish a baseline weight for the rider currently on the deck 12 (step 102).
This baseline weight
can also be updated during the course of operation by looking at the time
average weight over
the trucks 14, 16.
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During operation, the motor control program continuously or repeatedly reads
the front and rear
weight sensors 26 and determines the total summed weight applied to the deck
12. While the
total summed weight remains within a defined margin of this baseline weight,
the controller
executes a weight sensing control mode (step 104). When the total summed
weight is outside
the defined margin of the baseline weight, the controller 19 may prevent
additional power to the
motors 20 as a safety measure in case the rider has fallen off the board or
one of the sensors 26
was damaged or the sensor signals compromised. . When the weight sensing
control mode is
executed, the controller 19 monitors the weight distribution over the front
and rear trucks 14, 16
and will instruct the motor controller(s) 18 to increase or decrease operation
of the motor(s) 20
based on the weight distribution. For example, when the weight distribution is
higher over the
front truck 14 than the rear truck 16, the controller 19 instructs the motor
controller(s) 18 to drive
the motor(s) 20 in a forward direction, with the amount of motor output being
proportional to the
percentage weight distribution over the front and rear trucks 14, 16. In
contrast, when the weight
distribution is higher over the rear truck 16 than the front truck 14 the
controller 19 instructs the
motor controller(s) 18 to cause the motor(s) 20 to reverse torque thereby
performing regenerative
braking, with the amount of regenerative braking being proportional to the
percentage weight
distribution over the front and rear trucks 14, 16.
During operation, the motor control program continuously monitors for a kick
event (step 106).
Referring to Figure 7, a kick event is detected by a momentary reduction in
the total weight
summed between the front and rear weight sensors 26, often accompanied by a
simultaneous
acceleration in the wheel velocity. A threshold for determining a kick event
can be selected from
a detailed analysis of multiple people riding and kicking skateboards with a
high speed data logger
recording the truck weight signals. For example, the kick threshold can be
selected to be -80%
of the total weight, however, it is possible that the kick threshold can be
between 50% to 90% of
total weight.
Thus, a kick event is logged whenever the controller 19 determines that a
total weight on the deck
is less than the selected kick threshold but still high enough to ensure that
the rider has one foot
on the deck, and a control mode kick assist sequence is executed (step 108).
Optionally and not shown, the motor controller program includes a bounce
sensing module which
determines whether a rider is bouncing instead of kicking, and filters out
rider bounce as potential
false triggers to ensure that only actual kicks are detected as kick events.
The bounce sensing
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module distinguishes the difference between a rider kicking the skateboard and
the rider bouncing
on the deck, by identifying a bounce event as a period of high weight followed
by a period of
reduced weight, with no associated acceleration of the wheels while the weight
is reduced. Such
bounce events are filtered out from the kick event detection step.
When the control mode kick assist sequence is initiated, the motor control
program may try to
limit the motor acceleration by instructing the motor controller (s) 18 to
cause the motor(s) 20 to
switch into regenerative braking mode to put a drag force on the skateboard 10
in order to provide
a resistance against which the rider is kicking so that the deck velocity does
not increase too
much during the kick event (step 110). That way, the rider's kicking energy
can be converted and
stored as battery energy and then released more gradually during the period in
between each
kick, so that the board has a more steady velocity.
Once the motor control program determines that the total weight has returned
to within the defined
margin of the original baseline value, the motor control program assumes that
the rider no longer
has one foot on the ground, the rider most likely still only has one foot on
the deck, and the other
foot is freely swinging forwards and getting prepared for the next kick.
During this time period,
the rider is balancing with just one foot on the deck and any sudden
acceleration or deceleration
would be undesirable. Thus the motor controller program instructs the motor
controller(s) 18 to
operate the motor(s) 20 to sustain speed or slowly decelerate over a specified
period (which can
be user selectable) after the kick event (step 112). A possible default
specified period can be
between 0.5 to 3 seconds. The motor control program then monitors for
additional kick events
(step 114) for a predetermined time period, and executes the control mode kick
assist sequence
108 again if another kick event is detected during this time period. If no new
kick events are
detected during this time period, the motor control program assumes that the
rider has planted
both feet on the deck again, and reverts to the weight sensing control mode
104.
In an alternative embodiment, the skate controller circuit 19 can be provided
with a different motor
control program, including those in the art such as taught in US patent no.
6,050,357.
Operation
With a rider standing in the center of the deck 10, both front and rear weight
sensors 26 will output
a similar weight and the skateboard 10 remains neutral. When the rider shifts
more weight towards
the front truck 14, the skate controller circuit 19 will detect this and cause
the motor controllers 18
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to cause the motors 20 to accelerate forward. When the rider leans backwards
and puts more
weight on the rear truck 16, the skate controller circuit 19 will cause the
motor controllers 18 to
slow down the motors 20 for braking.
In the kick assist mode, the motor controllers 17 operate the motors 20 in a
constant speed
feedback loop in order to simulate the velocity profile that a regular non-
electric skateboard
experiences while being ridden. During the period when the rider is kicking,
the skate controller
circuit 19 instructs the motor controllers 18 to limit acceleration of the
motors 20 in order to keep
the skateboard 10 from running away. When the rider has his or her foot in the
air, the skate
controller circuit 19 instructs the motor controllers 18 to cause the motors
20 to maintain the
existing wheel velocity with a slight deceleration profile. This is intended
to mimic the behavior of
kicking a non-electric skateboard on flat ground.
The motor control program of the electric skateboard 10 allows for a seamless
transition between
electric-only power to human-powered kick assistance, and enables the electric
skateboard to
operate as an electric assist device rather than a fully powered electric
vehicle. This feature is
expected to provide riders with the benefit of exercise, give them a sense of
legitimacy and
satisfaction from kicking a skateboard, and extend the range of the battery.
It is contemplated that any part of any aspect or embodiment discussed in this
specification can
be implemented or combined with any part of any other aspect or embodiment
discussed in this
specification.
While particular embodiments have been described in the foregoing, it is to be
understood that
other embodiments are possible and are intended to be included herein. It will
be clear to any
person skilled in the art that modifications of and adjustments to the
foregoing embodiments, not
shown, are possible.
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