常见问题 + 练习FAQ + Practice

常见问题Frequently Asked Questions

练习Practice

练习 1：理解坐标系（纸上练习）Exercise 1: Understanding Coordinates (Paper Exercise)

机器人在 (0, 0)，车头朝 y 轴正方向（0°）。The robot is at (0, 0), facing the positive y-axis (0°).

1. 直走 50cm，现在坐标是？Drive straight 50cm. What are the coordinates now?
2. 右转 90°，再直走 30cm，现在坐标是？Turn right 90°, then drive straight 30cm. Coordinates?
3. 左转 45°（现在朝向 45°），再直走 20cm，现在坐标大约是？Turn left 45° (now facing 45°), then drive straight 20cm. Approximate coordinates?

练习 2：补全代码Exercise 2: Complete the Code

下面的 updatePosition() 函数缺了关键部分，补全它：The updatePosition() function below is missing key parts. Fill them in:

void updatePosition() {
    double cur_v = VerticalEncoder.position(deg);
    double cur_h = HorizontalEncoder.position(deg);

    double arc_v = (cur_v - last_vertical)
                   * DEG_TO_RAD * (WHEEL_DIAMETER_V / 2.0);
    double arc_h = /* (A) */;

    double angle = IMU.rotation(deg) * DEG_TO_RAD;
    double delta_angle = /* (B) */;

    double chord_v, chord_h;

    if (/* (C) */) {
        chord_v = /* (D) */;
        chord_h = /* (E) */;
    } else {
        double radius_v = /* (F) */;
        double radius_h = /* (G) */;
        chord_v = 2 * radius_v * sin(delta_angle / 2.0);
        chord_h = 2 * radius_h * sin(delta_angle / 2.0);
    }

    double avg_angle = /* (H) */;

    pos_x += /* (I) */;
    pos_y += /* (J) */;

    last_vertical = cur_v;
    last_horizontal = cur_h;
    last_angle = angle;
}

提示：答案全在代码实现那一节的完整版代码里，但试着先自己想再对照。Hint: All answers are in the complete code from the Code Implementation section, but try to figure them out yourself first.

练习 3：找 Bug（调试练习）Exercise 3: Find the Bug (Debugging Practice)

下面 4 段代码各有一个 Bug，找出来并说明会导致什么问题：Each of the 4 code snippets below has one bug. Find it and explain what problem it causes:

Bug 1：

// 编码器角度转距离
double arc_v = (cur_v - last_v) * (WHEEL_DIAMETER_V / 2.0);

Bug 2：

// 判断是否转弯
if (delta_angle == 0) {
    chord_v = arc_v;
} else {
    double radius_v = arc_v / delta_angle + OFFSET_V;
    chord_v = 2 * radius_v * sin(delta_angle / 2.0);
}

Bug 3：

void updatePosition() {
    double arc_v = (VerticalEncoder.position(deg) - last_vertical) * DEG_TO_RAD * (WHEEL_DIAMETER_V / 2.0);
    double angle = IMU.rotation(deg) * DEG_TO_RAD;
    double delta_angle = angle - last_angle;
    // ... 计算 chord_v, chord_h, 更新 pos_x, pos_y ...
    last_vertical = VerticalEncoder.position(deg);  // 注意这一行
    last_angle = angle;
}

Bug 4：

// 偏移补正
double radius_v = arc_v / delta_angle + OFFSET_V;
// OFFSET_V = -4.0（竖轮在旋转中心左边 4cm）
// 但实际安装时竖轮在旋转中心右边

练习 4：调参挑战（实机练习）Exercise 4: Tuning Challenge (On-Robot Practice)

1. 装好定位轮，运行定位程序Install tracking wheels and run the tracking program
2. 让机器人手动控制走一个正方形（每边 60cm），回到起点Manually drive the robot in a square (60cm per side), back to the start
3. 看程序报告的坐标离 (0, 0) 差多少Check how far the reported coordinates are from (0, 0)
4. 目标：走完正方形后，x 和 y 误差都在 5cm 以内Goal: after completing the square, both x and y error should be within 5cm

练习 5：写你自己的 MoveTo（分三步）Exercise 5: Write Your Own MoveTo (Three Steps)

不要一口气写完整的 moveTo。按下面三步来，每步写完测试通过再进下一步：Don't try to write the complete moveTo all at once. Follow these three steps, testing each before moving on:

第一步：写 turnTo(targetAngle)Step 1: Write turnTo(targetAngle)

• 让机器人原地转到目标角度Make the robot turn in place to the target angle
• 用 P 控制：power = (targetAngle - currentAngle) * kPUse P control: power = (targetAngle - currentAngle) * kP
• 记得用 normalizeAngle 防止转大圈Remember to use normalizeAngle to prevent going the long way
• 角度误差 < 3° 时停Stop when angle error < 3°

第二步：写 driveForward(distance)Step 2: Write driveForward(distance)

• 假设已经面对目标方向，只做直走Assume you're already facing the target direction — just drive straight
• 用定位系统读当前位置，算走了多远Use the tracking system to read current position and calculate distance traveled
• 用 P 控制：power = remainingDistance * kPUse P control: power = remainingDistance * kP
• 距离 < 3cm 时停Stop when distance < 3cm

第三步：合并成 moveTo(x, y)Step 3: Combine into moveTo(x, y)

• 算出目标方向 atan2(dx, dy)Calculate target direction with atan2(dx, dy)
• 同时控制直行和转弯（参考 MoveTo 函数那一节的思路）Control driving and turning simultaneously (refer to the MoveTo section)
• 加超时退出和到达退出（距离 < 5cm）Add timeout exit and arrival exit (distance < 5cm)
• 挑战：加 slew rate 限制（每次循环功率变化不超过 10）Challenge: add slew rate limiting (max power change of 10 per loop)

提示：每步都先在纸上画图 → 写伪代码 → 再写 C++。Tip: For each step, draw a diagram → write pseudocode → then write C++.

参考资料References