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| + | #REDIRECT [[Kart]] |
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| − | The [[Kart|kart's]] stepper motor controller module generates 4 coil driving signals and receives a ''stepper end'' input.
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| − | [[File:Kart_stepper_module.jpg|center|1400px|stepper motor module]]
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| − | == Stepper motor ==
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| − | === Hardware ===
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| − | The '''stepper motor''' is a [[Media:SP3575M0906-A.pdf|Nanotec SP3575M0906-A]].
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| − | It has a step angle of 7.5°, and as such 48 steps per turn.
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| − | It is attached to a 100:1 reductor, which leads to an output axis with 4800 steps per turn.
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| − | The [[Media:Kart_dc_stepper_schematic.pdf|DC/stepper control board]] hosts a dual full H-bridge to control the 4 coils of the stepper motor.
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| − | The '''end switch''' is connected between one of the FPGAs I/O with an internal pull-up enabled and the GND. The logic is internally reverted (i.e. a '1' is read when the switch is closed).
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| − | === Connector ===
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| − | The cables are connected as follows:
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| − | :{| cellpadding="4" cellspacing="0" border="1"
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| − | ! Signal
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| − | ! Color
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| − | |-
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| − | | phase 1
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| − | | white
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| − | |-
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| − | | phase 2
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| − | | blue
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| − | |-
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| − | | phase 3
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| − | | red
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| − | |-
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| − | | phase 4
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| − | | yellow
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| − | |-
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| − | | +5V / 2A
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| − | | brown, black
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| − | |}
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| − | == FPGA design ==
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| − | [[File:Kart_stepper_block.jpg|right|500px|stepper motor module]]
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| − | The [https://en.wikipedia.org/wiki/Stepper_motor stepper motor] controller has to generate the [https://en.wikipedia.org/wiki/Stepper_motor#Phase_current_waveforms 4 phases] to turn the kart's steering wheels to the desired angle.
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| − | The <code>target angle</code> is set in the [[Kart/serial_link#SmartPhone_to_Kart|desired steering angle register]].
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| − | To begin with, the [[Kart#FPGA_Design|design environment]] has to be downloaded.
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| − | It comprises the <code>stepperMotorController</code> block which contains the registers and events manager and an empty <code>angleControl</code> block which is to be completed.
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| − | === Functionality ===
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| − | The block receives a <code>targetAngle</code> unsigned number and has to step the coils at each occurrence of the <code>stepEn</code> signal until the desired angle is reached.
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| − | The coils are controlled through the 4 outputs <code>coil1</code> to <code>coil4</code>. When a '1' is applied, the corresponding coil is magnetized.
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| − | {{WarningBox|content=
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| − | To control the stepper, one coil at a time should be magnetized, known as [https://en.wikipedia.org/wiki/Stepper_motor#Wave_drive_(one_phase_on) '''wave drive'''].
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| − | The switching frequency should also be chosen carefully. A frequency of 285 Hz is near the slip limit of the motor.
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| − | The frequency is given by the formula : f = 100k / prescaler.
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| − | A prescaler ('''clockDivider''') of '''400''' (i.e. a frequency of 250 Hz) is a great first approach.
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| − | }}
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| − | The steering angle, <code>actual</code>, is estimated with the help of a counter which increments or decrements each time the coils change.
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| − | It is joined with a logic signal, <code>reached</code>, telling if the desired angle has been reached.
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| − | This information is sent back to the [[Kart#Android_App|controlling smartphone]].
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| − | === Zero position ===
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| − | A switch contact, providing the signal <code>stepperEnd</code>, has to be mechanically fitted on the kart in order set one end of the wheels' direction movement.
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| − | As soon as <code>stepperEnd</code> is '1', the stepper motor is stopped and the <code>actual</code> angle is reset.
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| − | With this, the steering motor will not try to turn further than what the kart's mechanical structure allows it to do in one of the directions.
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| − | In the other direction, it is the programmer's task not to request a too large <code>target</code> angle.
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| − | This also means that the angles are always considered as positive numbers, the zero position being given by the <code>stepperEnd</code> switch.
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| − | {{WarningBox|content=
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| − | * In order to limit the current consumption, turn off the current in all the coils when the stepper motor is not turning any more.
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| − | * Make sure that both the first and the last pulse of the coil control signals have the same duration as all the others.
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| − | }}
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| − | {{TaskBox|content=
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| − | Draw the schematics of the <code>angleControl</code> block.
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| − | }}
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| − | === Hardware orientation ===
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| − | The mechanical design allows for the following variations:
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| − | * the <code>stepperEnd</code> switch can be placed such as to detect the maximal steering angle either on the left or on the right side
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| − | * switching the coil controls in the sequence <code>1 - 2 - 3 - 4 - 1 - 2 - …</code> can result in the kart to turn either to the left or to the right
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| − | In order to cope with all possibilities, 2 setup signals are provided to the block:
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| − | * <code>sensorLeft</code> being '1' means that the <code>stepperEnd</code> switch has been placed such as to react when the wheels are oriented to the maximal steering angle on the left side
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| − | * <code>clockwise</code> being '1' means that the sequence <code>1 - 2 - 3 - 4 - 1 - 2 - …</code> lets the steering turn to the right
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| − | [[File:Kart stepper hw orientation.svg|center|stepper hardware orientation controls]]
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| − | {{TaskBox|content=
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| − | Update the schematics of the <code>angleControl</code> block in order to cope for the different mechanical design possibilities.
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| − | }}
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| − | The corresponding setup bits are configured in the [[Kart/serial_link#Hardware_control_register|hardware control register]].
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| − | === Initial position ===
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| − | The [[Kart/serial_link#Hardware_control_register|hardware control register]] also contains the bit <code>restart</code> allowing to let the stepper motor turn all the way to the angle where the <code>stepperEnd</code> switch is pressed.
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| − | This has to be sent by the [[Kart#Android_App|remote control smartphone]] after a successful Bluetooth pairing, together with the appropriate <code>sensorLeft</code> and <code>clockwise</code> setup bits, in order for the FPGA hardware to discover the zero angle position.
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| − | Obviously, this should only be done after the [[Kart/serial_link#SmartPhone_to_Kart|Stepper motor period register]] has been set to a proper value.
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| − | Restarting to the zero position can also be a help if too much current has been drawn from the batteries and the FPGAs' power has sunk in a way that they have performed a reset.
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| − | {{TaskBox|content=
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| − | Update the schematics of the <code>angleControl</code> block in order to turn all the way to the <code>stepperEnd</code> position once the input <code>restart</code> has been set.
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| − | The stepper motor should wait for the <code>restart</code> signal to be released before acting normally.
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| − | It should not turn while a first <code>restart</code> has not been performed, at choice either directly on startup or once requested from the smartphone.
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| − | }}
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| | [[Category:Kart]] | | [[Category:Kart]] |
