The Advantages of Brushless Sensorless Motors

Introduction

Brushless sensorless electric motors are becoming the go-to choice for RC vehicles and other hobbyist projects demanding high power in a small package. Advances in motor control algorithms and falling costs have made sensorless brushless motors more accessible than ever.

But what exactly are sensorless brushless motors and why are they superior to traditional brushed DC motors? In this article, we’ll provide an in-depth look at brushless sensorless technology and discuss the many advantages it provides for RC use. Whether you’re new to the hobby or a seasoned RC veteran, there are good reasons to consider switching to sensorless brushless power.

We’ll cover the operating principle of sensorless motors, their advantages compared to brushed motors, considerations when selecting and controlling sensorless motors, and recommendations for integration into your next RC project. By understanding this innovative motor technology, you can harness it to build high-performance, reliable, and efficient RC creations. Let’s explore the sensorsless brushless revolution!

Key Takeaways

Brushless sensorless motors eliminate brushes and commutators for higher efficiency and less maintenance.
Sophisticated control algorithms precisely drive the motor without physical sensors.
Advantages include more power, higher rpm, better torque, less noise, and improved reliability compared to brushed motors.
Careful selection of Kv rating, poles, and size is needed to match the application.
Electronic speed controllers designed for sensorless brushless are required for operation.
Drop-in replacements offer an easy upgrade path for existing brushed RC vehicles.

Brushed vs Brushless Motor Operation

To understand the benefits of brushless sensorless operation, let’s first look at how standard brushed DC motors work. Brushed motors have stationary magnets in the case called the stator. The central rotor contains wound wire coils that spin inside the stator field. Electricity is delivered to the spinning rotor through brushes contacting a mechanical commutator.

As the rotor turns, the brushes switch polarity in the coils to reverse the electromagnetic fields. This pushing and pulling between the stator and rotor creates rotational force. A major downside is that the brushes wear down over time, creating sparking, noise, and reduced efficiency.

In a brushless motor, the electromagnets are moved to the stator with permanent magnets on the rotor. Electricity is switched electronically by an external control circuit instead of a mechanical commutator. This eliminates the need for brushes and enables new control algorithms.

With modern brushless designs, the external electronic speed controllerprecisely times the switching of stator fields to keep the rotor spinning. This is where the term “sensorless” comes from – the controller tracks the rotor position without physical sensors. Let’s look closer at the benefits this provides.

Higher Efficiency and Less Maintenance

Eliminating brushes and the commutator is perhaps the biggest advantage of brushless operation. The sliding friction and sparking of brushes causes significant energy losses, heat, and wear in brushed motors. It also requires periodic brush replacement and reconditioning of the commutator.

In contrast, brushless motors have no sliding contacts or sparking losses. This improves efficiency, reduces heat, and eliminates routine maintenance. Bearings are the only mechanical wear point in a brushless motor. You can focus on driving your RC rather than motor upkeep!

Efficiency gains of 5-15% are common when switching from brushed to brushless operation. Your batteries will last longer and run cooler, giving longer run times. Brushless motors also better hold their performance over the motor lifetime. Save energy and reduce heat with efficient brushless operation.

More Power in a Smaller Package

By removing the brushes and commutator, more windings can fit into the same size motor. The improved copper fill factor allows brushless motors to generate higher torque and power density compared to similarly sized brushed motors. More power from a more compact motor helps reduce overall vehicle weight.

It’s not uncommon to see two to three times the power from a brushless motor over an equivalent brushed motor. Handling upgrades are less necessary because brushless systems can use a smaller motor to deliver the same power.

The power density improvements are especially important for applications like RC planes. A lighter, more powerful motor improves thrust while minimizing battery usage. For RC cars, smaller motors reduce unsprung weight for better suspension response. Take advantage of high torque in a small package with brushless power!

Higher RPM Operation

In addition to higher torque, brushless motors can reach much higher maximum rpm than brushed designs. While brushed motors typically top out around 10,000-15,000 rpm, brushless motors can often reach over 30,000 rpm.

Freed from the mechanical limits of brushes and commutation, properly designed brushless motors experience lower parasitic losses at high rpm. Less rotating mass also helps reach higher speeds.

Higher rpm capability improves top speed in RC cars and allows using smaller, faster spinning propellers on multirotor drones. Combine high torque and high max rpm to get the best of both worlds from your brushless motors!

Improved Torque Delivery

Careful electronic timing of the stator fields in a brushless motor also improves torque delivery. The controller can precisely direct torque production as needed for the load condition. Smoother and more consistent torque reduces cogging effects sometimes felt in brushed motors.

Startups, slow speed operation, and low speed torque are all enhanced with brushless control algorithms. Even at stall, brushless motors can deliver their full rated torque. Acceleration feelssmoother with properly controlled brushless power.

Electronic control also enables advanced telemetry and limiting functions. Built-inCurrent limiting protects electronics from overload conditions. Smart features like temperature and voltage monitoring help prevent damage and diagnose issues. Take advantage of smarter torque delivery with brushless setups.

Lower Noise

Lacking brushes and the commutator, brushless systems run much quieter than equivalent brushed motors. Less mechanical contact meansfewer sources of audible noise. While brushed motors produce a high-pitched squeal at high rpms, brushless operation stays smooth and quiet.

Quieter running is a major benefit for RC use, letting you better enjoy the peacefulness of nature or your neighborhood. Noise reductions also help keep your RC creations in good standing with the community and neighbors.

For applications like drones, lowered noise also provides stealth benefits. Brushless systems can maintain short audible distances, keeping your UAV quiet and unnoticed. Reduce annoying noise with the smooth operation of brushless motors.

Enhanced Durability and Reliability

The brushless design offers several inherent reliability advantages over brushed systems. As discussed earlier, the lack of brushes and a commutator eliminates the components most prone to wear and failure. With routine brush maintenance eliminated, brushless motors keep running trouble-free over more operating hours.

Brushes also create internally arcing conditions which slowly degrade insulation. Brushless operation produces virtually no problematic arcing to compromise windings over time. Bearings become the only limiting factor for average brushless motor lifetime.

The controller algorithms in sensorless systems also add protection against faults and overload conditions. By monitoring torque, rpm, voltage, and temperature, the ESC can take action to prevent damage when issues arise. The reliability improvements of brushless translate into more driving uptime to maximize your enjoyment!

Considerations When Selecting Brushless Motors

Now that we’ve discussed the many benefits of sensorless brushless motors, let’s go over some tips for selecting the right motor for your RC project. With so many options available, here are some key factors to consider:

Kv Rating: Kv specifies rpm/volt and must be sized appropriately for your voltage and gearing setup.
Max Power: Ensure your motor can deliver the needed power for acceptable performance.
Poles: Lower pole counts allow higher rpm operation.
Size: Diameter and length should fit within the space constraints of your chassis or airframe.
Weight: Lighter motors reduce rotating mass for better acceleration and handling.
Connectors: Opt for bullet connectors or soldertabs for secure electrical connections.
Cooling: Larger motors may require active cooling for heat dissipation under heavy loads.

Matching these criteria to your specific platform and performance goals will ensure you select an optimal sensorless brushless motor for your application. Check manufacturer specifications carefully during the selection process.

Sizing the Electronic Speed Controller Properly

An electronic speed controller (ESC) designed for sensorless brushless motors is required to operate them. The ESC generates the multi-phase power switching signals needed. When selecting an ESC, the continuous and burst current ratings must align with the motor ratings.

An underrated ESC will lack the capacity to deliver full power, while an oversized ESC provides unnecessary cost and bulk. For peak efficiency and control, the ESC and motor capacities should be properly matched.

Consider a programmable ESC to allow customizing control parameters like throttle curves, braking, and voltage limits. Programmable ESCs help tune performance to match your driving style and preferences.

Recommendations for Integrating Brushless Motors

Here are some tips for smoothly integrating high-performance brushless sensorless systems into your RC project:

For RC cars, select a drop-in compatible combo for easy upgrade. Match motor Kv to vehicle weight and desired top speed.
On multirotors, calculate total thrust needs, and ensure motor and prop combo can deliver the required lift.
Carefully measure clearances to confirm the motor housing will fit within the chassis or airframe.
Use appropriate gauge wire and connectors rated for expected motor current. Follow best wiring practices to reduce noise.
Add an external capacitor to smooth current flow if the ESC lacks one. Minimize voltage spikes.
Monitor temps and consider forced cooling if running motors at high power for extended periods.
Follow manufacturer guidance for properly programming and calibrating the ESCs.
Run bench tests for tuning before full installation. Check for vibration, current spikes, and overheating issues.

With some planning and smart integration techniques, sensorless brushless motors can deliver tremendous performance benefits over brushed systems with minimal headaches.

Brushless Sensorless Use Cases

Now let’s look at some of the top applications taking advantage of high-performance brushless sensorless motors:

RC Cars

Brushless sensorless power offers an easy drop-in upgrade over old-school brushed systems. Look for combo deals bundling a compatible ESC and motor. Bolt-in sensorless combos require minimal diffs from upgrading a brushed RC car. Expect dramatically increased torque, speed, and acceleration.

RC Boats

Marine environments are especially rough on brushed motor internals due to moisture. Sealed brushless motors are impervious to water damage. Their increased efficiency also extends run times on a single battery charge. Freed from brushed limitations, brushless boats reach incredible speeds.

RC Aircraft

For both fixed wing RC planes and multirotor drones, brushless motors generate much higher power to weight ratios essential for flight. Their smooth operation and high rpm capability also help provide stable, controlled flight. Choose motors optimized for minimum weight and your desired thrust.

Electric Skateboards

The high torque and efficiency of brushless motors make them popular for e-skate builds. Their small form factor easily integrates into a deck. Look for sensorless motors designed for high-load, low RPM operation matched to wheel size.

Robotics Projects

Custom robot builders take advantage of compact, powerful brushless motors for drive systems and actuators. The electronic control enables precise position and speed control. Choose gearing to optimize torque output.

Most Common Motor Sizes

Brushless sensorless motors are produced in many sizes optimized for different applications. Here are some of the most common sizes:

10-20mm micro motors – tiny “coreless” motors for micro drones and robotics.
22-28mm motors – multirotor drones, small RC cars/boats, lightweight aircraft.
35-50mm motors – larger drones, 1/10 scale RC cars, park flyers.
60-90mm motors – large RC cars and planes, high power multirotors.
100mm+ motors – very large drones and planes, high speed RC boats.

Larger motors naturally produce more power at the expense of increased weight. Select the minimum size necessary to deliver acceptable performance for your platform.

Brushless Motor Manufacturers

Many companies now produce quality sensorless brushless motors optimized for RC use. Here are some of the most popular brushless motor brands:

T-Motor – High-efficiency motors made for multirotors and aircraft.
Hobbywing – Respected brand making drop-in brushless systems for RC cars.
DYS – Wide range of inexpensive brushless motors. Good for budget builds.
O.S. – Leading model engine maker now producing brushless motors.
Emax – Known for durable, high-value brushless drone motors.

Check forums and reviews to help select reputable, recommended brushless motors for your application. Avoid cheap no-name brands that skimp on quality.

Sensored vs Sensorless Brushless Motors

Some RC brushless motors use integrated Hall Effect sensors for positional feedback. These “sensored” motors send this feedback to the ESC for even better low-speed control. Sensorless motors rely solely on the ESC algorithms to orient the rotor fields properly.

For most RC use, sensorless operation provides adequate performance at a lower cost. Sensored motors focus on applications demanding precise speed or position control like CNC machines and advanced robotics.

Sensorless brushless delivers excellent performance for the average hobbyist and keeps costs down. But sensored operation offers benefits for low-speed control if you need absolute precision.

Brushless Inrunner vs Outrunner Design

Two common winding configurations exist for RC brushless motors – inrunner and outrunner styles. Inrunners place the permanent magnets on the spinning rotor, surrounded by the wound stator. Outrunners flip this arrangement with the magnets fixed to the outer case and an internal wound rotor spinning around them.

Inrunners tend to generate higher torque but lower maximum rpm. Their compact form factors make inrunners well-suited for size-constrained applications like multirotors. Outrunners trade some torque for higher speed capability and lower inertia. This makes them great for RC planes and some high-speed cars.

Consider the speed and torque requirements of your project when selecting between inrunner and outrunner brushless designs. Both offer high performance – just tuned for different operating ranges.

Adjusting Kv Rating

The Kv rating defines the rpm per volt characteristic of a brushless motor. This determines how input voltage translates into motor speed and torque. Kv must be properly matched to your power system voltage and gearing to achieve desired performance.

Higher Kv yields more rpm but lower torque. Lower Kv provides more torque at reduced rpm. Changing pinion/spur gear ratios allows further tuning the speed-torque operating point after selecting the motor Kv.

Consult motor sizing calculators to appropriately match Kv rating, gearing, and power system voltage for your RC build goals. Adjust Kv higher or lower as needed to dial in speed and acceleration.

Controlling Brushless Motors Without an ESC

While dedicated ESCs provide plug-and-play control of brushless motors, it is also possible to directly drive them from microcontrollers and other electronics. generating the properly sequenced field switching signals commands the motor.

This requires knowledge of motor electronics and coding skills but enables complete customization. Direct control also minimizes latency compared to off-the-shelf ESC units. Consider direct drive for ultra-performance applications demanding the fastest response times.

Brushless Sensorless vs Coreless Motors

Some ultra-small brushed motors used in RC toys and micro drones adopt a “coreless” design. This refers to lacking a laminated core in the rotor. Instead, the rotor comprises wound copper coils only. Coreless motors are cheap but inefficient compared to true brushless.

For serious performance, opt for true brushless sensorless systems. Their laminated cores greatly improve magnetic flux density and motor efficiency. Don’t settle for lower performance just to save money upfront. You’ll reap the benefits of optimized brushless motors for years to come.

Permanent Magnet Brushless Motor Materials

The permanent magnets adhered to the rotor strongly influence the performance of brushless motors. Different rare earth magnet materials offer varying magnetic flux density and temperature resistance. Common options include:

Ferrite – Inexpensive but low performance. Used only in very small hobby motors.
Samarium Cobalt – Maintains good flux at high temps. Common in RC motors.
Neodymium – Offers the highest flux density but degrades quickly above ~150C.

Look for neodymium or samarium cobalt magnets when selecting RC brushless motors. Avoid cheaper ferrite magnets to maximize power density.

Brushless Motors for On-Road vs Off-Road

Brushless systems provide performance benefits to all types of RC vehicles. But motors can be tailored to better match either on-road or off-road use. Here’s how brushless motors differ between surface types:

On-Road Brushless

Lower Kv rating for controllable torque on grippy tarmac.
Low pole counts enable higher rpm for top speed.
Moderate ride height allows longer motors.
Focus on efficiency and runtime over extreme torque.

Off-Road Brushless

Higher Kv compensates for wheel slip in low traction conditions.
More poles for increased low-end torque and crawling ability.
Shorter motors to fit into tougher suspension designs with higher ride height.
Extreme torque delivery to power through challenging terrain.

While you can certainly run either motor type on any surface, matching your brushless specs to the intended driving environment will maximize performance and enjoyment.

Brushless RC Airplane Motor Features

Here are some of the ideal features to look for when selecting a brushless motor for an RC airplane build:

High power-to-weight ratio minimizes dead weight.
Low Kv optimized for larger propellers driven at moderate rpms.
Outrunner design places coils on inner rotor for lower inertial mass.
High pole count for maximum torque during takeoff and climbing.
Shorter motor widths help