How To Messure Rc Car Motors

Want to squeeze every last drop of performance out of your RC car? Understanding and measuring your RC car motor is the key! It's more than just slapping a motor in and hoping for the best. Knowing how to measure the characteristics of your RC motor allows you to optimize your setup for speed, torque, and efficiency. In this guide, we'll dive deep into how to measure RC car motors like a pro, from the basics to advanced techniques.

Understanding RC Car Motors

Before we start measuring anything, let's establish a solid understanding of what we're working with. RC car motors come in two primary flavors: brushed and brushless. Each type has its own set of characteristics, pros, and cons, which affect how we measure and interpret their performance.

Brushed Motors

Brushed motors are the older technology, but still commonly found, especially in entry-level RC cars. They're relatively simple in design, consisting of a rotating armature (the part with the windings) and stationary magnets. Carbon brushes physically contact the commutator on the armature, providing the electrical connection that makes the motor spin.

Here are some key features of brushed motors:

1. Simplicity: Easy to understand and relatively inexpensive.
1. Maintenance: Require periodic maintenance, as the brushes wear down over time and need replacing. The commutator also requires periodic cleaning and resurfacing.
1. Efficiency: Generally less efficient than brushless motors due to friction and electrical losses from the brushes.
1. Durability: Can be durable, but the brushes are a wear item, impacting overall lifespan.

Brushless Motors

Brushless motors are the modern standard for high-performance RC cars. They eliminate the physical contact of brushes and commutators, resulting in significant improvements in efficiency, power, and lifespan. Instead of brushes, brushless motors use electronic speed controllers (ESCs) to energize the windings in a specific sequence, creating a rotating magnetic field that drives the rotor.

Here's a look at brushless motor characteristics:

1. Efficiency: Much more efficient than brushed motors, converting more electrical energy into mechanical power.
1. Power: Capable of delivering significantly more power than brushed motors of similar size.
1. Maintenance: Require virtually no maintenance due to the absence of brushes.
1. Durability: More durable than brushed motors due to fewer wearing parts.

Key Measurements for RC Car Motors

Now that we have a basic understanding of RC car motor types, let's delve into the key measurements that determine their performance. Whether you are trying to measure brushed RC car motors or measure brushless RC car motors, the measurements will help you determine what makes each motor tick. Here are some crucial parameters to consider when measuring the performance of RC car motors:

Voltage (V)

Voltage is the electrical potential difference that drives the motor. It's like the pressure in a water pipe. Higher voltage generally results in higher motor speed. Always make sure that the voltage you are using is within the motor's specified range to prevent damage. Using a voltmeter, you can measure the voltage supplied to the motor by the battery or ESC. Make sure to set the voltmeter to DC voltage (VDC) to get an accurate reading.

Fact: Most RC cars use batteries ranging from 7.2V Ni MH packs to

11.1V Li Po packs and even higher for larger scale models.

Current (Amps - A)

Current is the flow of electrical charge through the motor. It's like the amount of water flowing through a pipe. Higher current generally results in higher torque (the motor's ability to turn a load). Measuring current is crucial for understanding the motor's power consumption and ensuring that your battery and ESC are adequately rated. You can measure current using an ammeter or multimeter with current measuring capabilities. Clamp-on ammeters are also useful, as they allow you to measure current without directly connecting to the circuit.

Caution: Always ensure that the ammeter is properly connected in series with the motor circuit. Exceeding the ammeter's current rating can damage the meter.

RPM (Revolutions Per Minute)

RPM measures how fast the motor is spinning. It's a direct indication of the motor's speed. Higher RPMs generally mean faster acceleration and top speed for your RC car. RPM is often specified by the motor manufacturer as its no-load RPM (the RPM the motor achieves when there's no load attached). You can measure RPM using a tachometer. There are two main types: contact and non-contact.

1. Contact Tachometers: These require physical contact with the motor's shaft.
1. Non-Contact Tachometers: These use a laser or light beam to measure the speed without physical contact. These are generally safer and easier to use.

Torque (Nm or oz-in)

Torque is the twisting force that the motor can produce. It determines the motor's ability to overcome resistance and accelerate a load. Higher torque is particularly important for off-road RC cars and vehicles that need to climb hills or navigate rough terrain. Torque is a more difficult characteristic to directly measure without specialized equipment such as a dynamometer. However, you can indirectly assess torque by observing the motor's performance under load. For example, a motor that can quickly accelerate a heavy RC car has high torque. The stall torque, the torque at which the motor completely stops rotating, is the maximum amount of torque the motor is capable of producing.

Motor Temperature

Monitoring motor temperature is crucial to prevent overheating and potential damage. Excessive heat can demagnetize magnets in both brushed and brushless motors, reducing their performance and lifespan. You can measure motor temperature using an infrared thermometer or temperature probe. Aim the thermometer at the motor casing and record the temperature after a few minutes of operation. As a general rule, it's best to keep motor temperatures below 160°F (71°C) for brushed motors and 180°F (82°C) for brushless motors. Consider adding a heatsink or fan to your motor if temperatures consistently exceed these limits.

KV Rating (Brushless Motors Only)

The KV rating is a specific characteristic of brushless motors. It represents the motor's RPM per volt. For example, a 3000KV motor will spin at 3000 RPM for every volt applied to it (under no load). The KV rating is an important factor in determining the motor's speed and torque characteristics. Lower KV motors generally produce higher torque and lower top speed, while higher KV motors produce lower torque and higher top speed. While you can't directly measure the KV rating with common tools, you can calculate it by measuring the motor's RPM at a known voltage and dividing the RPM by the voltage.

Example: If a brushless motor spins at 7400 RPM when supplied with 7.4 volts, the KV rating would be approximately 1000 KV.

Tools for Measuring RC Car Motors

To accurately measure RC car motors, you'll need a few essential tools. Investing in quality instruments will ensure reliable results and prevent inaccurate data that could lead to poor tuning decisions.

1. Multimeter: A versatile tool for measuring voltage, current, and resistance. Look for a multimeter with DC voltage and current measurement capabilities.
1. Tachometer: Measures the motor's RPM. Choose either a contact or non-contact tachometer based on your preference and ease of use.
1. Infrared Thermometer: Measures the motor's temperature without physical contact.
1. Watt Meter: A watt meter measures the voltage, current, and power (watts) consumed by the motor.
1. Dynamometer: For advanced measurement, you can use a motor dynamometer to accurately measure torque and power output under different load conditions.

Step-by-Step Guide to Measuring RC Car Motors

Now, let's walk through a step-by-step guide to measuring the key parameters of your RC car motor.

Measuring Voltage and Current

1. Safety First: Disconnect the motor from the ESC and ensure that the battery is fully charged.
1. Connect the Multimeter: Connect the multimeter in series with the motor circuit. To measure current, connect the positive lead of the battery to the positive lead of the multimeter, then connect the negative lead of the multimeter to the positive terminal of the motor. Connect the negative terminal of the motor to the negative lead of the battery.
1. Apply Power: Briefly apply power to the motor by connecting the battery.
1. Record Readings: Record the voltage and current readings displayed on the multimeter. The current reading will indicate the motor's current draw under no-load conditions.

Measuring RPM

1. Safety First: Secure the RC car so it doesn't move. Remove the pinion gear or disconnect the motor from the drivetrain to allow it to spin freely.
1. Prepare the Tachometer: For a contact tachometer, attach the appropriate tip to the tachometer shaft. For a non-contact tachometer, ensure that the laser beam is properly aligned.
1. Measure RPM: For a contact tachometer, gently press the tip against the motor shaft while it's spinning. For a non-contact tachometer, aim the laser beam at the motor shaft.
1. Record Readings: Record the RPM reading displayed on the tachometer.

Measuring Motor Temperature

1. Run the Motor: Run the motor under typical operating conditions for a few minutes.
1. Prepare the Thermometer: Turn on the infrared thermometer and set it to the appropriate measurement scale.
1. Measure Temperature: Aim the thermometer at the motor casing and record the temperature reading.

Interpreting Your Measurements

Once you've collected your measurements, it's time to interpret them and use them to optimize your RC car's performance.

Voltage: Compare the voltage reading to the battery's rated voltage. A significant drop in voltage under load may indicate a weak battery or a poor connection. This is especially true when measuring the voltage supplied to an RC car motor.

Current: High current draw can indicate that the motor is working too hard. This can be caused by excessive gearing, a binding drivetrain, or a motor that's not well-suited for the application. Remember to factor in the current draw when measuring RC car motors for ESC selection.

RPM: Compare the RPM reading to the motor's specified no-load RPM. A significant drop in RPM under load may indicate a weak motor or excessive resistance in the drivetrain.

Temperature: If the motor temperature is consistently high, consider using a lower gear ratio, adding a heatsink or fan, or switching to a motor with lower KV rating.

KV Rating: Use the KV rating to select a motor that's appropriate for your desired speed and torque characteristics. Higher KV motors are generally better for high-speed applications, while lower KV motors are better for torque-oriented applications. When measuring RC car motor performance, take into account the KV rating alongside RPM.

Advanced Measurement Techniques

For more advanced analysis, you can use a dynamometer to measure the motor's torque and power output under different load conditions. A dynamometer applies a controlled load to the motor and measures the resulting torque and RPM. This data can be used to generate a torque curve, which shows the motor's torque output at different RPMs. This information is incredibly valuable for optimizing gearing, selecting the right motor for your application, and fine-tuning your RC car's performance. The dyno is useful when measuring RC car motors for optimum performance.

Conclusion

Measuring your RC car motor is a crucial step in optimizing its performance, ensuring longevity, and making informed decisions when upgrading components. By understanding the key parameters, using the right tools, and following these step-by-step instructions, you can unlock the full potential of your RC car and gain a competitive edge on the track. Remember to stay safe, take accurate measurements, and have fun experimenting with different motor setups. Now go forth and measure those motors!