Low Level

LowLevel v3.1 PCB

Functionality:

• The LowLevel Board (LLB) is a daughter board (shield) for an Arduino Mega microcontroller. It implements drive-by-wire, turning a trike into a CAN-bus based vehicle compatible with commercial self-driving equipment. The LLB communicates over the CAN bus with the higher-level autonomous system or manual control from the receiver system. It directly manages the actuators: the throttle to the motor, the turning servo, and the brakes.

• Motion directives are received on a CAN bus interface, processed, and articulated.
• System status (turn angle, wheel linear velocity) is reported back to CAN bus.

• LLB v3.x has the following interfaces:
  • One CANbus channel on two connectors; a DB9-M and a three-pin screw terminal. The board includes a 120 ohm terminating resistor.
  • X3 Motor (DB-15M): Interface to E-bike controller
    • Analog voltage (approximately 0v to 4v) output to hub motor throttle
    • Digital outputs for activating reverse and regenerative braking.
    • PWM output for PWM-operated braking (no longer used)
    • Analog inputs for hall sensor feedback from motor controllers supporting this feature. These inputs are NOT 36V SAFE. They absolutely require external supporting circuitry.
    • A few spare connections for future expandability, such as a second DAC output and one digital GPIO.
  • Steering Header (RJ45):
    • Two sets of pins to support analog potentiometers (5v, signal input, ground) giving angle of front wheels
    • One PWM output (with its own ground) to drive the steering actuator.
    • This cable is broken out into its component signals using an RJ45 patch jack, mounted near the steering actuator.
  • X4 (ODO): Cyclometer (reed switch) input jack. This is pulled high by default, and brought low when the magnet passes the sensor.
  • High current pluggable terminal for solenoid brakes:
    • Connections for ground, 12v, and 24v.
    • Two relay outputs to solenoids: on/off and 12/24V.

• The LowLevel runs on 5V power, and provides outputs for sensors. Note that the Arduino Mega 2560's regulator has a fairly low current limit, and should not be used for any significant current supply. The Arduino's DC input jack accepts 12V, and its USB port may be connected to a typical USB power supply. The 12V is provided by a DC-DC converter from the main battery (36 to 50V).

LowLevel v2.1 PCB

Functionality:

• The LowLevel Board (LLB) a daughter board (shield) for an Arduino Mega microcontroller. It interprets messages from higher-level autonomous systems or manual controls (RC, joystick). It directly manages the state of the actuators; the hub motor, the turning servo, and the brakes.

• The first version of the LLB was called MegaShieldDB. It had similar functionality, but different connectors.

• Depending on the current firmware or operating mode, motion directives are received on one of three interfaces;
  • ElcanoSerial from the combined C3/ C4/ C6 High Level board
  • RC receiver
  • Manual Joystick

• LLB v2.x has the following low-level interfaces:
  • X2 Cruise (DB-25F) - ElcanoSerial messages from High Level.
  • X3 Motor ( DB-15M): Analog voltage (0,4v) output hub motor.
  • X1/X5 Turn Sensors (RJ45): SPI wheel angle sensor digital inputs. (These are not used. They are provided if the turn sensor is digitized to reduce noise. Present turn sensors are analog.)
  • X4 (ODO): Cyclometer (reed switch) input jack. Board layout was incorrect. This signal should connect to Arduino pin D2, but it does not.
  • JP9 (8 pin): Joystick analog input signals. (not currently used)
  • JP12 (3 pin): Pulse output signal to steer. (Need signal and ground. 5V is not used since both the steer servo and low-level board produce 5V)
  • JP11 (3 pin): Pulse output signal to apply main brakes. (No longer used)
  • JP5 (4 pin): Left wheel angle sensor analog input. (Little used since it covers 360 degrees and is less accurate)
  • JP6 (4 pin): Right wheel angle sensor analog input. (Trike prefer this, since it is +/- 30 degrees, and more accurate)

• LLB v3.x makes significant wiring changes:
  • Removes the ElcanoSerial connection and the DB-25F.
  • Removes JP9, joystick analog inputs.
  • Removes headers currently used to interface the RC receiver.
  • Adds one CANbus interface on a DE-9F socket. For legacy compatibility ElcanoSerial may be available on this interface as well.

• The LowLevel runs on 5V power, which it provides to sensors and servos on JP9, JP12, JP11, JP5 and JP6. A 9.6V battery supplies Vin to the Arduino, which regulates it to 5V and 3.3V. The RJ45 connectors send Vin, which must be regulated on the other end to 5V. Our trike uses a 36V battery to drive the hub motor and a 12V battery to drive the steering and brake servos. Each of these three actuators has a separate electronic subsystem, which generates 5V, but are not used by LowLevel. The 5V supply from the motor is used as an indication of whether 36V power is switched on.