Kart/stepper motor controller
The kart's stepper motor controller FPGA generates 4 coil driving signals and receives a stepper end input.
It has a step angle of 7.5°, and as such 48 steps per turn. It is attached to a 100:1 reductor, which leads to an output axis with 4800 steps per turn.
The control board hosts a current source which is directed to one (or more) of the stepper motor's coils.
The cables are connected as follows:
Signal Color phase 1 white phase 2 blue phase 3 red phase 4 yellow power brown, black
To begin with, the design environment has to be downloaded.
It comprises the
stepperMotorController block which contains the provided I2C bus interface
and an empty
angleControl block which is to be designed.
The block receives a
target unsigned number and has to step the coils at each occurrence of the
enStep signal until the desired angle is reached.
The current in the coils is given by the 4 outputs
The steering angle,
actual, is estimated with the help of a counter which increments or decrements each time when when the coil control signals change.
The block provides the estimated angle,
actual, together with a logic signal,
reached, telling if the desired angle has been reached.
This information is sent back to the controlling smartphone.
A switch contact, providing the signal
stepperEnd, has to be mechanically fitted on the kart in order set one end of the wheels' direction movement.
As soon as
stepperEnd is activated, the stepper motor is stopped and the
actual angle is reset.
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.
In the other direction, it is the programmer's task not to request a too large
This also means that the angles are always considered as positive numbers, the zero position being given by the
- In order to limit the current consumption, turn off the current in all the coils when the stepper motor is not turning any more.
- Make sure that both the first and the last pulse of the coil control signals have the same duration as all the others.
The mechanical design allows the following variations:
stepperEndswitch can be placed such as to detect the maximal steering angle either on the left or on the right side
- switching the coil controls in the sequence
1 - 2 - 3 - 4 - 1 - 2 - …can result in the kart to turn either to the left or to the right
In order to cope with all possibilities, 2 setup signals are provided to the block:
sensorLeftbeing '1' means that the
stepperEndswitch has been placed such as to react when the wheels are oriented to the maximal steering angle on the left side
clockWisebeing '1' means that the sequence
1 - 2 - 3 - 4 - 1 - 2 - …lets the steering turn to the right
The corresponding setup bits are configured in the hardware control register.
The hardware control register also contains the bit
restart allowing to let the stepper motor turn all the way to the angle where the
stepperEnd switch is pressed.
This has to be sent by the remote control smartphone after a successful Bluetooth pairing, together with the appropriate
clockWise setup bits, in order for the FPGA hardware to discover the zero angle position.
Obviously, this should only be done after the Stepper motor period register has been set to a proper value.
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.
The stepper motor design leaves 14 free pins. Pins 1 to 12 are foreseen for test purposes.