Test robot

Table of contents

Mainboard
Wiring

Mainboard

Functionality

Closed loop speed control of 3 brushless DC motors.
- Designed for Pololu 37D Metal Gearmotors with quadrature encoders.
- Motor driver current limited to 3.0 A.
- Motor driver supply voltage up to around 16.8V (maximum voltage of 4S LiPo batteries). Limited by ceramic capacitors that are rated to 25 V.
Reverse voltage protection MOSFET on the motor driver supply side.
Two 5 V small hobby servo outputs with 50 Hz PWM signals.
One BLDC ESC (Electronic Speed Controller) signal output using DShot300 protocol.
Reverse voltage protected motor power output for thrower ESC.
Isolation between microcontroller and motor drivers.
STM32G441KBT6 microcontroller.
- Powered through USB connector.
Micro-USB socket for communicating with a computer over virtual COM port.
Two ball detector inputs.
10-pin SWD (Serial Wire Debug) connector.
One UART interface with solderable pads.
Two M2 mounting holes.

Connectors

Top

Bottom

Cable directions

Dimensions

Firmware

Binary firmware file

picr23-mainboard-firmware_v1_0_0.bin

Connect STLINK programmer to the mainboard and to a computer with USB. Drag or copy the *.bin file to the STLINK drive.

Sending commands to mainboard

Struct in firmware

typedef struct __attribute__((packed)) Command {
  int16_t speed1;
  int16_t speed2;
  int16_t speed3;
  uint16_t throwerSpeed;
  uint16_t servo1;
  uint16_t servo2;
  uint8_t disableFailsafe;  // 1 to disable failsafe, anything else to enable
  uint16_t delimiter;
} Command;

Using with python’s struct library

disable_failsafe = 0

struct.pack('<hhhHHHBH', speed1, speed2, speed3, thrower_speed, servo1, servo2, disable_failsafe, 0xAAAA)

Using HTerm

Download HTerm.
- https://www.der-hammer.info/pages/terminal.html
Connect a micro USB cable to the mainboard.
Open HTerm.
Select the correct port.
- On Windows the ports are listed in the Device Manager.
- On Linux running dmesg can list recently connected devices.
Leave other settings to defaults.
Press Connect.
In HTerm under Input control change Type to HEX.
Send 0A 00 0A 00 0A 00 00 00 00 00 00 00 00 AA AA to set all the motors to rotate at the speed of 10.
- Byte order is little endian, which means that least significant byte is first.
Send F6 FF F6 FF F6 FF 00 00 00 00 00 00 00 AA AA to set all the motors to rotate at the speed of -10.
- Negative values are two’s complement of the positive value.
10 is relatively low speed, so if any of the motors is rotating fast, the motor power wires might need to be reversed (because the encoder values need to count in a positive direction if the speed is set to a positive value) or the encoder signal connections might be faulty.

Receiving data from mainboard

Struct in firmware

typedef struct __attribute__((packed)) Feedback {
  int16_t speed1;
  int16_t speed2;
  int16_t speed3;
  int16_t position1;
  int16_t position2;
  int16_t position3;
  uint8_t sensors;
  uint16_t delimiter;
} Feedback;

Using with python’s struct library

actual_speed1, actual_speed2, actual_speed3, motor1_position, motor2_position, motor3_position, sensors,  feedback_delimiter = struct.unpack('<hhhhhhBH', received_data)

Thrower speeds

Thrower speeds are sent to thrower motor controller using DShot protocol. Speed values are between 48 - 2047 for 0 to 100% speed.

Servo values

Servo signal (PWM) frequency is 50 Hz (period 20 ms or 20000 µs). Values correspond to pulse width in µs. Value of 1000 changes pulse width to 1 ms (1000 µs). Value of 2000 changes pulse width to 2 ms (2000 µs).

Wiring