Want to save channels AND keep Reverse?

If your goal is to save channels because you want to use CH3 and CH4 for other things (like servos, lights, or standard ESCs), you can compress your setup down to 2 channels total while keeping full forward/backward control.

To do this, you just need a tiny hardware addition: an external logic inverter (NOT gate chip) or a driver board that natively supports a PHASE / ENABLE (or DIR / PWM) control scheme rather than raw IN1 / IN2.

code

motor start one by one

Stagger your motor starts in code: Instead of turning both PWM pins on at the exact same millisecond, start Motor A first, wait 100–200 milliseconds for it to smooth out, and then spin up Motor B. This splits the massive initial current surge in half.

// 正确做法： analogWrite(motorA_PWM, 200); // 启动第一个电机 delay(150); // 关键：等待 150 毫秒，避开启动电流瞬间 analogWrite(motorB_PWM, 200); // 再启动第二个电机

frequency

  • PWM-dat

    analogWriteFrequency(M1_IN1, 10000); analogWriteFrequency(M1_IN2, 10000); analogWriteFrequency(M2_IN1, 10000); analogWriteFrequency(M2_IN2, 10000);

issues analysis

full-throttle stuttering

方案一：在代码中限幅（最快、最安全的软解决方法） 既然电池持续输出只有 6A，那我们就不要让油门真的跑到 100%。在微型机器人或设备开发中，为了保护电池，经常会在软件里做限幅。

如果你使用的是 Arduino（0~255 的 PWM 范围），把最大输出限制在 180 到 200（大约 70%~80% 的动力）。

效果： 限制了电机的最高功耗，将其压在电池的 6A 持续电流以内，电机不仅不会持续停顿，而且运转会非常稳定。

方案二：加大电容容量（如果必须跑满 100% 动力）如果你的应用场景必须压榨出电机的全部动力，1000µF 的电容可能在全油门下有些力不从心。操作： 可以尝试并联更多的电容，或者直接换成 2200µF 或 3300µF（耐压 16V 或 25V）的大电容器，并确保电容两端的引脚直接焊接在驱动板的 $VM$ 和 $GND$ 上。线路越短，电容吸载的效果越好。

The Startup Power Crush

A single standard 380 motor can easily demand a sudden surge of 3A to 4A just to start turning from a dead stop (inrush current).

One Motor: When you start just one motor, it pulls ~4A. Your battery easily handles this because it's well under its 13A peak limit. It runs smoothly.

Two Motors: When you try to start both motors simultaneously, their combined initial surge jumps to 8A to 10A+.

🛠️ How to Fix This with Your Current Battery

You don't necessarily need to buy a new battery yet. Try these three adjustments first to see if you can bypass the stuttering:

Stagger your motor starts in code: Instead of turning both PWM pins on at the exact same millisecond, start Motor A first, wait 100–200 milliseconds for it to smooth out, and then spin up Motor B. This splits the massive initial current surge in half.

Beef up your capacitors: Solder a large electrolytic capacitor (e.g., $1000\mu\text{F}$, 16V or 25V) directly across the power input ($VM$ and $GND$) of each DRV8871 board. These capacitors act like tiny, lightning-fast turbo reservoirs that feed the motor's initial startup spike so the battery voltage doesn't sag.

Check the ILIM Resistors: Look at the tiny SMD resistor connected to the ILIM pin on your DRV8871 breakout boards. If it says "303" (30kΩ), it's restricting you to 2.1A. Swapping it out for an 18kΩ to 22kΩ resistor will raise the chip's ceiling to ~3A, giving the 380 motors the breathing room they need to spin up smoothly.

Tech Specs & Compatibility: DRV8871 H-Bridge vs. 380 DC Motor

The DRV8871 can drive a 380 DC motor, but its success depends entirely on the specific variant of the 380 motor and the mechanical load it faces. Because 380 motors range from low-power office equipment variants to high-drain RC hobby motors, you must match their current profiles.

1. Specification Comparison

Specification DRV8871 Driver Limits Standard 380 Motor High-RPM RC 380 Motor
Operating Voltage 6.5V to 45V 6.0V to 12.0V (Compatible) 7.2V to 11.1V (Compatible)
Continuous Current ~2.0A (Thermal dependent) 0.4A to 1.2A (Compatible) 2.5A to 5.0A (Overload Risk)
Peak / Stall Current 3.6A (Hard Limit) 1.5A to 3.5A (Safe) 8.0A to 15.0A+ (Triggers Protection)

2. Operational Scenarios

Scenario A: Successful Deployment (Low-Power / Geared 380)
  • Application: Small robotics, desktop automation, highly-geared actuators, low-load DIY projects.
  • Why it works: The motor's stall current stays under 3.5A. The DRV8871 handles the running current easily.
  • Safety Feature: The DRV8871 features an ILIM pin. If the motor suddenly stalls, the driver clamps the current safely instead of burning out.
Scenario B: Driver Overload / Failure (High-Speed RC 380)
  • Application: RC cars, boats, high-velocity fans, direct-drive heavy loads.
  • Why it fails: Upon startup or under load, high-spec 380 motors pull over 4A instantly.
  • Behavior: The DRV8871 will enter Overcurrent Protection (OCP) or hard-clamp the current via its internal current-limiting resistor. The motor will stutter, drop voltage, or produce almost no startup torque.

3. Configuration & Hardware Advice

Tuning the ILIM Resistor

The current limit ($I_{LIM}$) of the DRV8871 is set by an external resistor ($R_{ILIM}$) connected from the ILIM pin to GND. The formula for setting the limit is:

$$I_{LIM} = \frac{64,000}{R_{ILIM}}$$

  • Default Breakout Boards: Most pre-made modules (like Adafruit) ship with a 30kΩ resistor, capping the current at ~2.1A.
  • Maximizing Output: To push the driver to its safe peak of 3A, swap the resistor to ~21kΩ. Do not go below 18kΩ ($3.5A$) to avoid unintended OCP tripping.
Thermal Management

If you run the DRV8871 close to 2A continuously:

  • Ensure the bottom thermal pad of the IC is soldered to a generous copper pour on your PCB.
  • Stick a miniature copper or aluminum heatsink onto the chip if it operates in a closed enclosure.

4. Alternative Drivers (If your 380 motor demands more power)

If your 380 motor is a high-drain hobby variant, bypass the DRV8871 and use one of these beefier alternatives:

  • Discrete MOSFET ESC (Electronic Speed Controller): 10A–30A rated, standard for RC applications.
  • BTS7960 / IBT-2: High-current H-bridge capable of up to 43A peak (massive overkill, but very cool running).
  • VNH5019: Robust automotive-grade driver handling up to 12A continuous and 30A peak.

stuttering

This "stuttering" or intermittent rotation (spinning, stopping, then spinning again) at maximum throttle is a classic symptom in RC models. Here are the three most common causes, ranked from most likely to least likely:

1. Low Voltage Cutoff (LVC) — The Most Common Cause

This is the most probable culprit.

  • The Mechanism: When you push the throttle to maximum, the motors require a massive amount of instantaneous current. If the battery is low or aging (high internal resistance), its voltage will instantly drop below a safe threshold.
  • The Protection: The receiver or ESC (Electronic Speed Controller) detects this voltage drop and cuts off power to protect the battery from over-discharging (especially critical for LiPo batteries).
  • The Loop: Once the motors stop, the heavy load on the battery disappears, causing the battery voltage to bounce back up. The system thinks it's safe again and restores power. Since your throttle is still at max, the voltage instantly drops again, triggering another cutoff. This creates the continuous stuttering loop.

2. Electromagnetic Interference (Brush Noise)

If your toy boat uses brushed motors (common in standard toys, characterized by two power wires connected directly to the motor):

  • At full throttle, the carbon brushes inside the motor generate heavy sparking and electromagnetic interference (EMI).
  • If the motor lacks filtering capacitors (usually small ceramic discs soldered to the motor casing), this interference can travel up the wires and cause the RC receiver to glitch or reboot continuously. The motor cuts out during the reboot and kicks back in once it reconnects, causing a jerky motion.

3. Over-Current or Over-Heat Protection

  • Over-Current Protection: Running two motors at maximum throttle might exceed the maximum current rating of the main board. The board temporarily cuts power intermittently to prevent itself from burning out.
  • Mechanical Binding: Check if the propeller shafts are tangled with seaweed, hair, or lack lubrication. Excessive resistance forces the motors to draw significantly more current, easily triggering the protection loops mentioned above.

🛠️ Troubleshooting Steps:

  1. Test with a Fully Charged/New Battery: Try again with a fresh, high-quality battery pack. If it works fine when fully charged but starts stuttering as the battery drains, it is purely a battery performance/capacity limitation.
  2. Perform a Dry Run (Out of Water): Lift the boat out of the water and push the throttle to maximum.
    • If it spins normally in the air but stutters in the water, the battery is definitely too weak or old to handle the high load (water creates much higher resistance and current draw than air).
  3. Check the Drivetrain: Spin the propellers manually with your fingers. They should turn smoothly. If they feel stiff, clean the shaft and apply a drop of RC marine grease or lightweight oil.

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