United States Patent [19J
`Ribbe
`
`[54] SPEED CONTROL SYSTEM FOR A
`REMOTE-CONTROL VEHICLE
`
`[75]
`
`Inventor: David J. Ribbe, Cincinnati, Ohio
`
`[73] Assignee: Hasbro, Inc., Pawtucket, R.I.
`
`[21] Appl. No.: 08/794,438
`
`[22]
`
`Filed:
`
`Feb. 5, 1997
`
`[51]
`[52]
`[58]
`
`[56]
`
`Int. Cl.6
`........................................................ H02P 7/29
`U.S. Cl. ............................. 318/16; 318/293; 388/829
`Field of Search ............................. 318/16, 293, 139;
`388/825, 828, 829
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,349,986
`4,749,927
`4,999,556
`5,043,640
`5,065,078
`5,103,146
`5,136,452
`5,150,027
`5,216,337
`5,218,276
`
`9/1982 Tsukuda .................................... 46/254
`6/1988 Rodal et al.
`............................ 318/599
`3/1991 Masters ................................... 318/599
`8/1991 Orton ........................................ 318/16
`11/1991 Nao et al. ................................. 318/16
`4/1992 Hoffman ................................... 318/16
`8/1992 Orton . ... ... ... ... .... ... ... ... ... ... .... ... . 361/33
`9/1992 Suzuki .................................... 318/581
`6/1993 Orton et al.
`.............................. 318/16
`6/1993 Yeom et al.
`.............................. 318/16
`
`I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US005994853A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,994,853
`Nov. 30, 1999
`
`2/1996 Juzswik et al. ......................... 318/293
`5,495,155
`5,571,999 11/1996 Harris ...................................... 200/565
`5,577,154 11/1996 Orton ...................................... 388/811
`
`OTHER PUBLICATIONS
`
`TX5/RX5 Remote Controller with Nine Functions, Product
`Description(Nov. 1994).
`
`Primary Examiner---Bentsu Ro
`Attorney, Agent, or Firm-Marshall, O'Toole, Gerstein,
`Murray & Borun
`
`[57]
`
`ABSTRACT
`
`A remote-control vehicle includes a controller that produces
`a pulse-width modulated (PWM) motor control signal and a
`forward/reverse motor control signal in response to a trans(cid:173)
`mitted digital signal specifying one of a multiplicity of speed
`control states, each of which has a direction and a PWM duty
`cycle associated therewith. A MOSFET switch turns on and
`off in response to the PWM signal to control the flow of
`current between a battery and a motor to thereby control the
`speed of the motor. A relay, coupled between the battery and
`the motor, switches in response to the forward/reverse signal
`to change the direction of current flow through the motor to
`thereby control the direction of the motor.
`
`23 Claims, 3 Drawing Sheets
`
`54
`
`

`

`U.S. Patent
`
`Nov. 30, 1999
`
`Sheet 1 of 3
`
`5,994,853
`
`FIG. 1
`
`10 i
`
`12
`
`18
`
`FIG. 2
`
`54
`
`

`

`U.S. Patent
`
`Nov. 30, 1999
`
`Sheet 2 of 3
`
`5,994,853
`
`34
`\
`
`51
`
`52
`
`OSC.
`
`56
`
`62
`
`64
`
`TIMING
`GENERATOR
`
`58
`
`60
`
`LATCH
`
`MODULATOR
`
`54
`
`22
`
`16
`\
`
`70
`
`DEMODULATOR
`
`LATCH
`
`FIG. 3
`
`72
`
`76
`
`74
`
`PLA
`
`78 F/R
`
`START
`
`80
`
`82
`
`FILTER
`
`84
`
`86
`
`83
`
`88
`
`OSC. t - - - -~
`
`FIG. 4
`
`

`

`U.S. Patent
`
`Nov. 30, 1999
`
`Sheet 3 of 3
`
`5,994,853
`
`16
`
`~
`
`104
`
`12
`
`+
`V-=-
`- _l
`
`T3 I-----' .....______._ 9 4
`
`PWM
`
`90
`
`START
`
`80
`
`F/R
`
`78
`
`98
`
`99
`
`FIG. 5
`
`t ~ f 100
`
`102~
`
`

`

`5,994,853
`
`1
`SPEED CONTROL SYSTEM FOR A
`REMOTE-CONTROL VEHICLE
`
`BACKGROUND OF THE INVENTION
`The present invention relates generally to motor speed
`controllers and, more particularly, to speed controllers for
`remote-control toy vehicles.
`
`10
`
`DESCRIPTION OF RELATED ART
`It is known to use pulse-width modulated (PWM) signals
`to control the flow of current through a motor in, for
`example, a remote-control vehicle, to thereby control the
`speed of the motor. For example, Nao et al., U.S. Pat. No.
`5,065,078; Orton, U.S. Pat. No. 5,577,154; and Suzuki, U.S.
`Pat. No. 5,150,027 each discloses a remote-control device
`using a PWM signal to control the power provided to a
`motor. In these devices, the duty cycle of the PWM signal is
`increased to increase the speed of the motor and is decreased
`to decrease the speed of the motor. Typically, however,
`remote-control vehicles receive an analog control signal that
`must be demodulated and used to produce a PWM control
`signal of varying duty cycle. For example, the device of Nao
`et al. (U.S. Pat. No. 5,065,078) uses a stretched analog PWM
`signal developed from a received analog PWM control
`signal to generate a PWM motor control signal. Likewise, 25
`Suzuki (U.S. Pat. No. 5,150,027) develops an analog PWM
`signal from a received control signal, compares the PWM
`signal with a pulse signal generated by a one-shot circuit,
`and detects the difference between the widths of the two
`signals to determine the pulse width of a PWM motor
`control signal. Such analog decoding circuits require numer(cid:173)
`ous components, which adds to the weight of the remote(cid:173)
`control vehicle and reduces the life of a battery powering the
`vehicle.
`Remote-control vehicles have also used elaborate circuits 35
`to effect forward and reverse motor functions. For example,
`Nao et al. (U.S. Pat. No. 5,065,078) develops a stretched
`analog PWM signal from a received analog PWM control
`signal, compares the stretched PWM signal with a pulse
`signal generated by a one-shot circuit, and detects the
`difference between the trailing edges of the two signals to
`determine the direction of a motor. Other prior art motor
`control circuits, such as those disclosed in Tsukuda, U.S.
`Pat. No. 4,349,986, and Juzswik et al., U.S. Pat. No.
`5,495,155, use an H-bridge circuit, having semiconductor
`devices in the legs thereof, to drive a motor in both the
`forward and reverse directions. Typically, the semiconductor
`devices of such H-bridge circuits are operated to turn one leg
`of the bridge circuit off while turning the other leg on which
`changes the direction of current flow through the motor and,
`thereby, reverses the direction of the motor. However,
`H-bridge circuits typically require a relatively high amount
`of power to operate and develop voltage drops across the
`numerous semi-conductor devices connected in series with
`the motor, which reduces the amount of power supplied to
`the motor. These circuits also tend to increase the depletion
`of the battery which reduces the use time of the battery.
`
`2
`a multiplicity of speed control states, each of which has a
`direction and a PWM duty cycle associated therewith. A
`speed controller located on the vehicle decodes the received
`digital signal to identify the specified speed control state and
`5 produces a PWM signal and a forward/reverse signal in
`response thereto. The PWM signal, which controls the speed
`of a motor, is coupled to a switch, preferably comprising a
`semiconductor switch such as metal oxide semiconductor
`field effect transistor (MOSFET), and controls the flow of
`current between a power source, such as a battery, and the
`motor. The duty cycle of the PWM signal is varied from
`speed control state to speed control state to vary the speed
`of the motor. The forward/reverse signal controls the opera(cid:173)
`tion of a further switch coupled between the motor and the
`battery to change the direction of current flow through the
`15 motor. Preferably the further switch comprises a dual input,
`quadruple output relay, such as a double pole, double throw
`relay. In one embodiment, the relay has two sets of two
`outputs connected together such that each of the connected
`sets of outputs is coupled through one of the relay inputs to
`20 one of a set of motor terminals.
`According to another aspect of the present invention, a
`speed control system for use in a remote-control vehicle
`includes a receiver that receives a digital control signal and
`produces a digital state signal specifying one of a multiplic(cid:173)
`ity of speed control states and a speed controller responsive
`to the digital state signal that develops a forward/reverse
`signal and a PWM speed signal based on the specified one
`of the multiplicity of speed control states. A first switch is
`coupled between a power source and a motor and is respon-
`30 sive to the PWM signal for delivering a power signal from
`the power source to the motor. A second switch is coupled
`between the power source and the motor and is responsive
`to the forward/reverse signal to control the direction of the
`motor. Preferably, the receiver produces a digital state signal
`specifying one of at least six speed control states, three of
`which are forward states and two of which are reverse states.
`The speed control system of the present invention may
`include circuitry for producing a ramped duty cycle PWM
`signal, varying between three or more different duty cycles
`over a first period of time, in response to a change between
`40 two non-consecutive speed control states in a second period
`of time that is less than the first period of time. The speed
`control system may also include a switch that prevents the
`use of one of the speed control states when in a first position
`and that allows the use of the one of the speed control states
`45 when in a second position.
`According to another aspect of the present invention, a
`remote-control vehicle includes a transmitter module having
`a speed position sensing device that detects one of a mul(cid:173)
`tiplicity of speed positions and a digital signal transmitter
`50 coupled to the speed position sensing device that produces
`a digital control signal indicating one of a multiplicity of
`speed control states corresponding to the detected one of the
`multiplicity of speed positions. The remote-control vehicle
`also includes a vehicle having a receiver that receives the
`
`:~g~;~h:n!u1~;f:~:; o~ s~i;:1a~o~~~l ::ft::~
`
`1 0
`
`SUMMARY OF THE INVENTION
`The present invention relates to a remote-control vehicle
`that provides a variable duty cycle PWM signal to a motor
`to vary the speed of the motor while simultaneously con(cid:173)
`trolling the direction of the motor using simple, lightweight,
`and cost effective switching networks that do not have large
`voltage drops associated therewith.
`In particular, a remote-control vehicle according to the
`present invention receives a digital signal specifying one of
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a side view of a toy vehicle having a speed
`control system according to the present invention;
`
`55 ~!!~#yi~~n:~~
`A speed controller on the vehicle develops a forward/reverse
`signal and a PWM speed signal based on the one of the
`multiplicity of speed control states specified by the digital
`state signal. A first switch is responsive to the PWM signal
`60 for delivering a power signal to a motor on the vehicle and
`a second switch is coupled to the motor and is responsive to
`the forward/reverse signal to control the direction of the
`motor.
`
`

`

`5,994,853
`
`3
`FIG. 2 is a partial cut-away view of a transmitter unit used
`with the toy vehicle of the present invention;
`FIG. 3 is a block diagram of an encoder/transmitter
`located in the transmitter unit of FIG. 2;
`FIG. 4 is block diagram of a first portion of the speed
`control system according to the present invention; and
`FIG. 5 is circuit schematic diagram of a second portion of
`the speed control system according to the present invention.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Referring now to FIG. 1, a remote-control toy vehicle 10,
`illustrated as a toy car, includes a battery 12 electrically
`coupled to a motor 14 through a speed control system 16.
`When energized, the motor 14 actuates a drive mechanism,
`preferably comprising a differential drive mechanism, to
`cause rotation of one or more wheels 18 which, in turn,
`causes the vehicle 10 to move. The drive mechanism may be
`coupled between the motor 14 and the wheels 18 to drive the
`wheels 18 in any known or standard manner.
`An antenna 22 receives a digital speed control signal from
`an operator-controlled transmitter unit 26 (FIG. 2) and
`delivers this signal to the speed control system 16. The speed
`control system 16 decodes the received signal to identify
`which one of a multiplicity of possible speed control states,
`each having a direction and a PWM duty cycle associated
`therewith, is being requested by the operator. The speed
`control system 16 then produces a PWM signal and a
`forward/reverse signal in response to the identified speed
`control state and uses these signals to control the connection
`between the battery 12 and the motor 14 to thereby control
`the speed and direction of the motor 14.
`FIG. 2 illustrates the hand-held transmitter unit 26 used to
`control movement of the vehicle 10 of FIG. 1. The trans- 35
`mitter unit 26 includes a trigger 28 pivotally coupled to a
`brush mechanism having a wiper arm 29 disposed in contact
`with a position sensing device 30 which, in turn, is electri(cid:173)
`cally coupled to a signal encoder/transmitter 34 mounted on
`a PC board. A battery 36 supplies power to the encoder/
`transmitter 34.
`To control the speed of the toy vehicle 10 of FIG. 1, an
`operator may either pull or push on the trigger 28 to move
`the trigger 28 away from a center position illustrated in FIG.
`2, which causes movement of the wiper arm 29 relative to
`a common electrode 42 and a series of position sensing
`electrodes 44a, 44b, 46, and 48, all of which are electrically
`connected or coupled to the encoder/transmitter 34. A turbo
`mode or expert/beginner switch 50, the operation of which
`will be described hereinafter, is electrically coupled between
`the position sensing electrodes 44a and 44b.
`During movement of the trigger 28, the wiper arm 29
`remains in constant contact with the common electrode 42,
`which is preferably connected to an electrical ground, and
`also comes into contact with zero, one, or two of the position
`sensing electrodes 44a, 44b, 46, and/or 48. When such
`contact is made, the electrodes 44a, 44b, 46, and/or 48 are
`electrically coupled to the common electrode 42 and are,
`therefore, grounded. Otherwise these contacts remain at an
`open high state. The ground or open high signals developed 60
`at the electrodes 44a, 44b, 46, and 48 are detected by the
`encoder/transmitter 34 via lines 51, 52, and/or 53. The
`signals on the lines 51, 52, and 53, in combination, comprise
`a digital request for one of the multiplicity of speed control
`states.
`For example, when the trigger 28 is in the center position
`illustrated in FIG. 2, the wiper arm 29 does not contact any
`
`10
`
`20
`
`4
`of the position sensing electrodes 44a, 44b, 46, or 48, which
`leaves each of the lines 51, 52, and 53 in an open high state
`indicating that no movement of the vehicle 10 is desired.
`However, when the trigger 28 is pulled slightly back ( and the
`5 switch 50 is in the closed position), the wiper arm 29
`contacts the electrode 44a, sending a ground signal via the
`line 52 to the encoder/transmitter 34 while the lines 51 and
`53 remain in the open high state. This set of signals indicates
`that a minimum forward speed condition is being requested.
`As the trigger 28 is pulled further back, the wiper arm 29
`contacts both of the electrodes 44a and 46, grounding the
`lines 51 and 52 while leaving the line 53 in the open high
`state. This set of signals indicates to the encoder/transmitter
`34 that a medium forward speed condition is being
`15 requested. When the trigger 28 is pulled all the way back, the
`wiper arm 29 contacts only the position sensing electrode
`46, grounding the line 51 and leaving the lines 52 and 53 in
`the open high state. This set of signals indicates that a
`maximum forward speed condition is being requested.
`Likewise, when the trigger 28 is pushed forward from the
`center position illustrated in FIG. 2, the wiper arm 29
`contacts only the position sensing electrode 48, grounding
`the line 53 and leaving the lines 51 and 52 in the open high
`state (indicating that a low reverse speed condition is being
`25 requested), or the wiper arm 29 contacts both the electrodes
`48 and 44b, grounding the lines 52 and 53 while leaving the
`line 51 in the open high state (indicating that a medium
`reverse speed condition is being requested). As indicated
`above, the signal encoder/transmitter 34 detects the signals
`30 delivered from the contacts 44a, 44b, 46, and 48 via the lines
`51, 52, and 53 as a digital signal specifying one of a set of
`six possible speed control states requested by a user (i.e., no
`motion, low forward speed, medium forward speed, full
`forward speed, low reverse speed and medium reverse
`speed).
`In the embodiment illustrated in FIG. 2, when the turbo
`switch ( or the expert/beginner switch) 50 is set to non-turbo
`or beginner mode, the electrode 44a is disconnected from
`the line 52 so that the line 52 stays high even when the wiper
`40 arm 29 comes into contact with the electrode 44a. This
`operation effectively eliminates the full forward throttle
`speed state by preventing the line 52 from being connected
`to ground when the trigger 28 is pulled back. As a result of
`this operation, the encoder/transmitter 34 recognizes the
`45 highest speed position as a lower speed state, such as a
`medium throttle speed state. The switch 50 thereby operates
`to allow an operator to disconnect or eliminate the use of one
`of the potential speed control states, e.g., the state associated
`with the highest speed. Of course the switch 50 and/or other
`50 switches could be connected in other manners to eliminate
`or allow the use of other speed positions if so desired.
`While the trigger 28 and position sensing device 30 have
`been described herein as signaling six separate speed control
`states, it will be understood that the position sensing device
`55 30 could be modified to include more or less electrodes to
`detect and signal more or less speed control states. Likewise,
`the electrodes of the position sensing device 30 could be
`connected in other ways to signal any desired number of
`speed control states. Of course, if more than seven speed
`control states are used, the encoder/transmitter 34 must
`receive a higher number of input signals (four or more) to
`identify a selected one of such a multiplicity of speed control
`states.
`If desired, the transmitter unit 26 may also include a
`65 rotatable dial 56 having position sensors (not shown)
`coupled between the battery 36 and the encoder/transmitter
`34. The dial 56 may be operated in any desired manner to
`
`

`

`5,994,853
`
`10
`
`5
`send steering commands to the encoder/transmitter 34 which
`may encode and transmit these commands to the vehicle 10.
`However, because such a steering control mechanism is not
`necessary for implementation of the speed control system 16
`of the present invention, the operation of such a steering
`control mechanism will not be described further herein.
`The encoder/transmitter 34, illustrated in more detail in
`FIG. 3, encodes the information on the lines 51, 52, and 53
`into, for example, three bits of a digital speed control signal,
`modulates the digital speed control signal onto a carrier and
`transmits the modulated carrier to the toy vehicle 10 of FIG.
`1 via an antenna 54. As a result, the encoder/transmitter 34
`operates as a digital signal transmitter. As illustrated in FIG.
`3, the encoder/transmitter 34 includes a latch circuit 56 that
`latches the signals on the lines 51, 52, and 53, along with 15
`appropriate steering command signals, onto a digital bus 58
`connected to a modulator 60. An oscillator 62 produces, for
`example, a 27.145 MHz, a 49.86 MHz, or any other desired
`stable frequency signal and delivers this signal to a standard
`timing generator 64, which provides appropriate timing
`signals to the modulator 60.
`The modulator 60 uses the signals provided by the timing
`generator 64 to produce a serial digital control signal having
`serial bits corresponding to the digitally encoded speed
`control and steering control signals on the bus 58. This serial
`digital control signal, which may be of any desired length
`but, preferably is a byte in length, may also include clock
`bits and/or other information. The modulator 60 then modu(cid:173)
`lates and amplifies the serial digital control signal using, for
`example, amplitude modulation (AM), to produce a modu(cid:173)
`lated control signal. The modulator 60 then transmits the
`modulated digital control signal to the vehicle 10 via the
`antenna 54. If desired, the modulator 60 may periodically
`develop a sync, reset, or other signal (stored in a memory
`thereof) to be transmitted to the vehicle 10. Operation of the
`oscillator 62 and the timing generator 64 is well known and,
`therefore, will not be described further herein.
`The speed control system 16 of FIG. 1 is illustrated in
`more detail in FIGS. 4 and 5. Referring to FIG. 4, the
`modulated digital control signal produced by the modulator
`60 (FIG. 3) is received by a receiver including the antenna
`22 and a demodulator 70, which may comprise any standard
`AM demodulator such as, for example, any known super(cid:173)
`regenerative demodulator or, alternatively, any superhetero(cid:173)
`dyne demodulator. The demodulator 70 demodulates the
`received control signal and produces a digital state signal
`comprising a serial, digitally encoded control signal having
`a number of the bits thereof specifying a requested one of the
`multiplicity of speed control states. A serial-to-parallel latch
`72 samples the output of the demodulator 70 and delivers the
`digital state signal to a speed controller, illustrated as a
`programmable logic array (PLA) 74, via a digital bus 76.
`The PLA 74, which may include a microprocessor, hard(cid:173)
`wired logic elements, and/or any other desired or known
`circuitry, decodes the bits of the digital state signal corre(cid:173)
`sponding to the requested one of the speed control states and
`produces a forward/reverse (FIR) signal on a line 78, a
`START signal on a line 80, and a voltage signal on a line 82
`in response to the requested speed control state.
`Preferably, the PLA 74 produces a high FIR signal on the
`line 78 when a reverse speed control state is decoded and
`leaves the FIR signal on the line 78 low when a forward or
`stop speed control state is decoded. The PLA 74 produces a
`high START signal on the line 80 when the PLA 74 actively
`detects and decodes a non-zero speed request.
`The voltage signal on the line 82, which may vary
`between any of a number of discrete levels, is delivered to
`
`6
`a PWM signal generator 83 which produces a PWM signal
`having a duty cycle corresponding to one of the requested
`speed control states. The voltage signal on the line 82 may
`be provided through a low pass filter 84 (such as a voltage
`5 choke or an L/C network) to a first input of a comparator 86.
`The output of a triangular wave or ramping oscillator 88 is
`connected to a second input of the comparator 86, which
`produces a constant amplitude PWM signal on a line 90
`having a duty cycle corresponding to the voltage level
`delivered from the filter 84. In particular, whenever the
`voltage signal from the filter 84 is greater than the ramped
`voltage signal from the oscillator 88, the comparator 86
`produces a high pulse on the line 90. As will be understood,
`the duty cycle of the PWM signal on the line 90 increases as
`the voltage signal from the PLA 74 increases.
`Preferably, the levels of the voltage signal produced by
`the PLA 74 are set so that, when a 7.2 voltage source, such
`as a battery, is used with the system, the comparator 86
`produces a PWM signal having a duty cycle of about 100
`percent ( constant on) in response to a full forward throttle
`20 speed control state, a PWM signal having a duty cycle of
`about 80 percent in response to a medium forward or
`maximum reverse throttle speed control state, and a PWM
`signal having a duty cycle of about 40 percent in response
`to a minimum forward throttle or a minimum reverse throttle
`25 speed control state. The 40 percent PWM duty cycle relates
`to approximately 1/3 of the full motor speed, the 80 percent
`PWM duty cycle relates to approximately 2/3 of the full
`motor speed and the 100 percent PWM duty cycle relates to
`maximum or full motor speed. If desired however, these or
`30 other PWM duty cycles could be associated with any
`number of speed control states in any other desired manner.
`Moreover, the PWM signal produced by the comparator 86
`preferably has a peak voltage of approximately five volts
`and a frequency of approximately 200 Hz. However, other
`35 peak voltages and frequencies could be used instead.
`The PLA 72 may also be designed to detect higher voltage
`sources, such as 9.6 volt batteries, and lower the voltage
`levels provided to the PWM signal generator 83 in response
`thereto. In such a case, the duty cycles of the PWM signal
`40 produced by the PWM signal generator 83 will be reduced
`from the values given above. However, because of the
`higher voltage power source, the PWM signal generated by
`the PWM signal generator 83 will operate to drive the motor
`14 in a manner similar to the case in which 7.2 volt batteries
`45 are used. In such a configuration, the PLA 72 and the PWM
`signal generator 83 operate as a voltage regulator to control
`the speed of the motor 14 to be the same when different types
`of batteries are used.
`The filter 84 is designed to prevent the voltage signal on
`50 the line 82 from switching between multiple (three or more)
`consecutive speed control states too quickly. The filter 84 is
`especially useful when, for example, the trigger 28 (FIG. 2)
`is pulled back to the full forward throttle position from a no
`speed condition in a very short period of time. In such a case,
`55 the filter 84 provides a controlled change in the requested
`speed control state over a predetermined period of time
`greater than the time in which the actual change in the speed
`control state was received. The effective time constant of the
`filter 84 may be chosen, for example, to provide a Y4 second
`60 delay between the time in which the voltage level at the
`output thereof changes between a no speed level (i.e., a zero
`percent PWM duty cycle) and the time in which the voltage
`level at the output thereof rises to a full throttle level (i.e.,
`a 100 percent duty cycle). Of course, other delay times may
`65 be used as well.
`As will be understood, the ramping voltage level pro(cid:173)
`duced by the filter 84 causes the comparator 86 to produce
`
`

`

`5,994,853
`
`7
`a PWM signal having a duty cycle that increases in a ramped
`manner, i.e., a ramped PWM duty cycle. Such a ramped
`PWM duty cycle signal reduces wear and tear on the motor
`14 and on the gears of the drive mechanism within the
`vehicle 10, slightly reduces battery and motor heat and, 5
`thereby, slightly increases play time. It also makes the
`vehicle 10 easier to operate by reducing, for example, wheel
`spin in response to an initial high throttle input signal.
`While the control system 16 has been described herein as
`using a PLA 74 and an analog PWM signal generator 83, it 10
`will be understood that other types of analog or digital
`circuits may be substituted therefor, including microproces(cid:173)
`sor circuits, standard digital PWM waveform generator
`circuits, etc. without departing from the invention.
`Referring now to FIG. 5, a preferred circuit for imple- 15
`men ting control of the motor 14 using the PWM, the START
`and the FIR signals developed by the PLA 74 and the PWM
`signal generator 83 is illustrated. Generally speaking, the
`PWM and START signals control the operation of a semi(cid:173)
`conductor switch, preferably comprising a MOSFET switch 20
`94, to provide a PWM current signal from the battery 12 to
`the motor 14. The FIR signal controls the operation of a relay
`96 that controls the direction of current flow through the
`motor 14. As illustrated in FIG. 5, the relay 96, which may
`comprise a double pole, double throw relay, includes two 25
`inputs and four outputs, wherein two of the outputs are
`associated with each of the two inputs. Preferably, pairs of
`the outputs are connected together at relay output lines 98
`and 99 and these lines are coupled through the inputs of the
`relay 96 to different terminals of the motor 14, as illustrated 30
`in FIG. 5.
`Upon receiving a speed control signal specifying a for(cid:173)
`ward state, the PLA 74 produces a low voltage or off FIR
`signal which leaves the relay 96 configured as illustrated in
`FIG. 5. At that time, the comparator 86 produces a PWM
`signal having a specific duty cycle, for example, 40 percent
`or 80 percent, and delivers this PWM signal to the base of
`then-type transistor Tl. The high pulses of the PWM signal
`turn the transistor Tl on which, in turn, saturates the p-type
`transistor T2 thereby switching on the transistor T2. The
`START signal, which is set high whenever the PLA 74
`produces non-zero duty-cycle PWM signals, turns on a
`transistor T3. When the transistors T2 and T3 conduct,
`current flows from the battery 12 to the gate of the M OSFET
`94 which saturates the MOSFET 94 thereby turning on the
`MOSFET 94. At this time, a connection between the relay
`output line 98 and ground is established, thereby allowing
`current flow between the battery 12 and the motor 14. In
`particular, current flows from the battery 12, through the line
`99, through the relay 96 into a first motor terminal 100, 50
`through the motor 14 to a second motor terminal 102, back
`through the relay 96 to the relay output line 98, and then
`through the MOSFET switch 94 to ground. Flow of current
`in this manner energizes and drives the motor 14 in the
`forward direction. When the PWM signal goes low, the 55
`transistors Tl, T2 and the MOSFET switch 94 turn off which
`stops the flow of current through the motor 14. Of course,
`the higher the duty cycle of the PWM signal, the more
`current that flows through the motor 14, which causes the
`motor 14 to rotate at a higher speed.
`When the PLA 74 decodes and identifies a reverse speed
`control state, it sets the FIR signal high which, in turn,
`switches on transistors T4 and TS. At this time, current flows
`from the battery 12 through the coils of the relay 96 to
`ground, causing both contacts of the relay 96 to switch. 65
`Switching of the relay contacts reverses the direction of
`current flow through the relay inputs which, in turn, reverses
`
`8
`the direction of current flow through the motor 14 causing
`the motor 14 to rotate in the reverse direction. If desired,
`when the FIR signal goes high, the START signal can be
`held low for a short period of time so that the first high pulse
`of the PWM signal produced by the comparator 86 of FIG.
`4 may be delayed slightly to prevent the MOSFET switch 94
`from conducting while the relay 96 is switching. This
`operation prevents arcing within the relay 96 which extends
`the life of the relay 96. Also, if desired, a voltage source may
`be connected to a terminal 104 to prevent current from
`flowing through the MOSFETswitch 94 when, for example,
`a temperature sensor device (not shown) detects that the
`temperature of the motor 14 is too high.
`While a MOSFET switch 94 has been illustrated for use
`as a switch responsive to the PWM signal generated by the
`comparator 86, other switches, including other types of
`power semiconductor switches can be used as well. FET
`switches are considered to be preferable, however, because
`FET switches have only a very low voltage drop between the
`source and drain terminals thereof, which allows more
`current to flow through the motor 14. Likewise, although a
`double pole, double throw relay 96 has been illustrated
`herein for use in changing the direction of current flow
`through the motor 14, other types of relays or switches could
`be used instead.
`Although the toy vehicle 10 described herein is illustrated
`as a car, it should be noted that this vehicle could be any
`other type of vehicle, including a truck, an airplane, a boat
`or any other remote-control vehicle having a motor that
`drives a drive mechanism in forward and reverse directions.
`Moreover, if desired, the turbo mode or expert/beginner
`switch 50 illustrated in FIG. 1 may be located on the toy
`vehicle 10 and the PLA 74 may determine if certain ones of
`the multiplicity of speed control states need to be locked out
`of use to, for example, eliminate the possibility of having a
`35 full throttle speed control state. Still further, the turbo mode
`or expert/beginner switch 50 could have multiple positions
`enabling or disabling further combinations of the multiplic(cid:173)
`ity of speed control states.
`While the