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| − | {{TOC right}}
| + | #REDIRECT [[Kart]] |
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| − | [[File:Kart_dc_module.jpg|center|600px|DC motor module]]
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| − | == DC motor ==
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| − | The DC motor is a [http://www.conrad.ch/ce/fr/Search.html?search=%22modelcraft%20rb%20350018%202a723r%22 Modelcraft RB350018-2A723R].
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| − | It is powered in 12 V and draws a maximal current of 0.7 A.
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| − | The [[Media:Kart_dc_stepper_schematic.pdf|control board]] hosts a dual full-bridge
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| − | and a circuitry to create the switching dead-times and the direction of the current.
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| − | == FPGA design ==
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| − | The DC motor controller has to generate a <code>pwm</code> and a <code>forwards</code> signals to control the [[Kart|kart's]] speed.
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| − | The <code>speed</code> is set in the [[Kart/serial_link#SmartPhone_to_Kart|DC motor speed register]], while the frequency is given by the
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| − | prescaler in the [[Kart/serial_link#SmartPhone_to_Kart|DC motor prescaler register]] with the formula f = fclk / (PWMsteps * prescaler) = 10M / (16 * prescaler).
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| − | To begin with, the [[Kart#FPGA_Design|design environment]] has to be downloaded,
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| − | which contains the registers and events manager and an empty <code>dcMotorPwm</code> block which is to be completed.
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| − | === Functionality ===
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| − | The block receives a <code>speed</code> signed number and has to drive the DC motor with a <code>pwm</code> and a <code>forwards</code> signal.
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| − | These signals are internally converted to two driving signals to control an [http://en.wikipedia.org/wiki/H_bridge H-bridge]
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| − | (they take into account the dead-times to avoid short-circuiting the motor while switching).
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| − | The mean amplitude of the DC motor's voltage is controlled by a [http://en.wikipedia.org/wiki/Pulse-width_modulation Pulse Width Modulation] (PWM).
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| − | The <code>forwards</code> signal is derived from the sign of the <code>speed</code> control.
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| − | The <code>pwm</code> signal is derived from the absolute value of <code>speed</code>.
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| − | {{WarningBox|content=
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| − | The [http://en.wikipedia.org/wiki/Pulse-width_modulation PWM] signal is implemented with the help of a free-running counter and a comparator.
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| − | However:
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| − | * the power transistors cannot switch at too high frequencies
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| − | * there is a need for a dead time where all power transistors are open between the PWM transitions
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| − | Because of this, the PWM period is limited to a certain value.
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| − | This is achieved with the help of an '''en''' signal generated by a counter dividing the clock frequency.
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| − | The counter only increments when this signal is '1'.
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| − | }}
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| − | {{TaskBox|content=
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| − | Draw the schematics of the <code>dcMotorPwm</code> block.
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| − | }}
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| − | The minimal value of the PWM signal is studied in another part of the [[Kart|kart project]].
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| − | The period of the <code>en</code> pulse train is set in the [[Kart/serial_link#SmartPhone_to_Kart|DC motor PWM period register]]
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| − | and given by the formula f = fclk / (PWMsteps * prescaler) = 10M / (16 * prescaler).
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| − | === Hardware orientation ===
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| − | The mechanical design can either lead the Kart to drive forwards or backwards when a positive voltage is applied to the DC motor.
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| − | In order to cope with this, a setup signal, <code>normalDirection</code>, is provided to the block.
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| − | <code>normalDirection</code> being '1' means that a positive voltage applied to the DC motor lets the kart drive forwards.
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| − | {{TaskBox|content=
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| − | Update the schematics of the <code>dcMotorPwm</code> block in order to cope for the different mechanical design possibilities.
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| − | }}
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| − | The setup bit is configured in the [[Kart/serial_link#Hardware_control_register|hardware control register]].
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| − | === Bluetooth connection ===
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| − | When the Bluetooth connection is lost, the DC motor should not turn.
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| − | In order to cope with this, a control signal, <code>btConnected</code>, is provided to the block.
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| − | When <code>btConnected</code> is '0', the DC motor must stop.
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| − | {{TaskBox|content=
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| − | Update the schematics of the <code>dcMotorPwm</code> block in order to stop the motor on connection loss.
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| − | }}
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| − | The BT connection bit is configured in the [[Kart/serial_link#Hardware_control_register|hardware control register]].
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| | [[Category:Kart]] | | [[Category:Kart]] |
