Most important tool every RC Electric Hobbyist must have

Temperature Meter (temp gun)

Temperature Meter (temp gun)

The most important tool that every RC Electric Hobbyist must own is a temp (temperature) gun of some sort! You ask why? Well it will save you lots of money, that is why.

It doesn’t matter if you build your RC models or don’t. Having a temp gun in your toolbox will certainly help out. Heat is the worst enemy for any part of our electric power system. Managing the heat that is generated by our RC components is what will help save them. Too much heat that builds up in any electrical part of the power system can certainly destroy that component.

There are many temp guns out there that you can pick up. I have been using the Duratrax Flashpoint infrared temp gun for so many years. It is very easy to use and very cost effective.

 

How to use a Temp Gun Effectively

Periodic spot checks must become a standard for you as you run your RC vehicle. What you will want to do is every 5 runs of your RC vehicle, check the temperature of the brushless motor and electronic speed controller. To get an accurate reading, the measurement must be completed within 30 – 60 seconds of the RC vehicle coming to rest. Waiting too long may allow your heat sinks to remove heat providing you with a false reading. Next, you will want to use the temp gun as instructed in its manual. For best results, take measurements of many different locations on the motor and ESC. Allow the temp gun to read and retain the maximum temperature as you are taking readings from multiple different locations.

As your LiPo batteries begin to age, you will want to make certain that you are measuring the temperatures once every few runs. LiPo batteries will produce more heat when their internal resistance begins to rise as they age.

Factors that influence Temperature Readings

Keep in mind that there are many influences on the temperature of these components. These factors will skew your readings. What you want to watch out for is any sign that the power system is under higher then normal load. Here is a list of factors that can influence your running temperature.

  • Higher Ambient Temperatures (outdoor temperature for example)
  • Increased load on motor with aggressive throttle use
  • Binding of Driveline Components
  • Aging LiPo batteries
  • Length of Run Time

Using a Temp Gun for the First Run of a New Build

When running your setup for the first time, you want to be certain that you have selected conservative gearing or prop sizes. In RC Airplanes it is much easier to bench test your system. You are able to run up your motor and take measurements every 45 seconds.  For an RC car or boat build, you will have to run bring the vehicles in after 45 seconds. At this point take measurements of the motor, ESC and LiPo batteries.

If all  components are well under 140F/60C, run the vehicle for another 45 seconds and return to take measurements. Keep increasing the run time by 45 seconds if all components are under 140F/60C up to the maximum run time for your system.

If the temperature exceeds the safe limit, either the maximum allowable run time or maximum continuous load has been exceeded. Reduce the load and or run time and check the system again.

Determining Maximum Run Time

In the process described above, determine your total run time that will drain 80% capacity of your LiPo’s. Each time you run the vehicle for the 45 second period and reach about 3 total minutes, it would be a good idea to record how many mAh is placed back in to the LiPo Battery. Determine the amount of mAh that is placed back in the battery by charging the single battery and recording the value on the charger.

For example – If you were to get a 4 minute 15 seconds run time and replace 4000mAh from a 5000mAh battery, this should be considered your maximum run time. 80% of the batteries capacity has been drained. This is to ensure Long LiPo life while getting the better part of a batteries discharge curve.

To the run time calculator to help calculate run time based off of elapsed time and capacity placed in to the pack.

Application of using High or Low Motor / ESC Timing

Most hobbyists who operate electric RC vehicles understand that motor timing can be controlled. The questions is how many actually change the timing of their setup? If you haven’t already read the article on timing, click the link to view the article.

Applications of High and Low Motor Timing

Applications of High and Low Motor Timing

Do you have to change timing?

The short answer to this question is you generally don’t need to. Many ESC’s whether sensorless or not have a default setting that works well with most brushless motors. Performance of these ESC’s are already operating in a range that is suitable for many applications. Years ago I was messing around with timing a lot more than I am today. In fact it is very rare that I will change the default settings of an ESC in terms of timing.

When should you change Timing?

There are a few reasons why you would want to open up the software for your ESC and make a change to the settings. Here are those few key reasons listed below:

  1. Your brushless sensorless motor is not operating correctly
  2. To squeeze more RPM out of your brushless motor setup.
  3. Setup is operating with high temperatures.

Application of Using High Timing

If your RC car, boat or plane is not operating at the speed you are hoping for, changing the timing may get you there. Changing motor timing is not going to add a significant amount of speed. It is something you are able to adjust if going up a prop size or pinion gear size is too much. Or it is something you can adjust since it’s quite easy to do and does not cost anything other than time.

Before changing the timing, you will want to be certain that your power system is not operating at its maximum thermal potential. If so, you do not have the room necessary to increase timing. Increasing the timing will certainly add heat to your system. Upon an increase to timing you will also want to re-check the temperatures of your power system components. This will ensure that you are still operating within spec.

Application of Using High Timing – Synchronization Issues

If you have a motor that you spin up and it starts making a loud screeching type noise and slowing down, you should try changing the motor timing. The screeching noise is a telltale sign that the brushless motor you are running is losing its synchronization with the ESC. Increasing motor timing may help solve this issue.

Application of Using Low Timing

Low motor timing is commonly used on motors that have a low magnetic pole count and a hot wind. This may be something similar to a one turn, 4 pole brushless motor with a Delta wind termination.  These high strung motors do not like high motor timing. Other applications for low motor timing is to maximize run time, power efficiency and torque. If you need the most amount of torque in your setup, use low motor timing.

Changing Timing, Where to Start

Plan to experiment with motor timing and do not know where to start? The perfect place to start when adjust timing is on the low end. Low timing offers the least amount of performance. As you are increasing timing you will want to monitor temperatures to ensure that you do not exceed maximums. It is also best to monitor performance to understand how much of an increase you are seeing or not seeing.

Keep in mind, if you hear screeching from the motor while operating on low timing, try increasing the timing and try again.

In general motors with more magnetic poles tend to prefer higher timing settings.

Timing Explained for Brushless Motor and ESC’s

Brushless Motor Timing

Brushless Motor Timing

Timing is critical to a brushless motors operation. Without the correct amount of timing, a brushless motor may not operate efficiently or even at all. We will be exploring timing for brushless motors in this article. A few key focuses will be on what does brushless motor timing refer to, advantages of low and high timing, and lastly fixed timing vs variable timing.

What is timing within a Brushless Motor?

Timing is defined as the relationship of the position of the rotor relative to the exact moment when a stator winding is energized. Altering the position of the rotor at the moment the winding is powered up is controlling the timing.  There are 2 ways that you are able to alter the timing of a brushless motor. The more common and well known method of timing adjustment is done within the ESC. The second and much less common method of timing adjustment is adjusting the physical endbell of the motor. This method is more common with brushless motor for RC cars.

Advancement or increasing the timing is firing the stator winding phase earlier in the rotational cycle of the motor.

Advantages of High Motor Timing

Most would think that increasing your motor timing is specifically for high performance only. For the most part this is true, however, it is not always the case. When increasing the timing, the most general advantage that you may see is an increase in performance. Increasing the timing typically increases the amount of RPM that you will see out of your setup. Further advancing motor timing also makes it easier for a brushless motor and ESC to sync when operating in sensorless mode. Increasing the motor timing does have its share of disadvantages. These disadvantages are described below in the advantages of low motor timing section and vise versa.

Advantages of Low Motor Timing

A low motor timing offers the potential for a very efficient power system. Low motor timing tends to draw less current. When less power is drawn from the battery, you can expect lower overall temperatures and longer run times. In addition, low motor timing increase the amount of torque potential of your power system. If you are looking for more low end acceleration, adjusting timing to a lower amount will help get you there.

Fixed vs Variable (electronic) Timing

Adjustment of the end bell on a brushless motor is an example of a fixed mechanical adjustment. Once it is set, you can not change the timing when the motor is running, Motors that contain sensors also operate in a fixed mode of operation. Follow this link to read more on sensored motors vs sensorless. A fixed timing mode is limited as timing is best altered depending on several factors. Factors that affect timing include motor load, motor output RPM, number of poles, strength of the inductance within a motor and several more.

Sensorless motors and ESC’s do not use a known position of the rotor for timing purposes. Sensorless ESC’s rely on the back EMF that is produced in order to get the ESC and motor in sync. For this reason, the timing of the motor can actually be varied as the motor is in use. It is known that sensorless ESC’s are very efficient in the RPM range of a typical brushless motor.

ESC’s that are capable of handling timing automatically have significant advantages. Firstly, the decisions for any adjustments are handled by a complex algorithm. It is unlikely that the formula makes a mistake under normal running condition. Secondly, the user does not need to have any prior knowledge of the power system. Lastly, adjustments in timing are handled in order to optimize performance, efficiency and smooth operation. Fixed timing would not be able to accomplish this.

Setting the timing on an ESC that is capable of automatically determining the best range, allows the user to move up or down within this range.

Brushless Motor timing selection

Brushless Motor timing selection

ESC’s that run in Hybrid Sensored/Sensorless mode

Some ESC’s have specific modes that allow both fixed timing and variable timing. A perfect hybrid example is with a sensored motor and sensored/sensorless ESC. What happens is that the motor operates in sensored mode to get the car moving.  Sensored operation with fixed timing allows instant synchronization with the motor and ESC. Acceleration from 0 RPM is very predictable with no hesitation. Once a higher RPM is reached, the ESC automatically switches in to sensorless operation. Sensorless operation is most efficient at the high RPM end of the overall range.

ESC Boost  ( common for RC Cars only )

Boost timing is typically activated when selected on your ESC programming screen. On a Castle Creations ESC, it can only be selected while the power system is operating in sensored mode. Timing advance will start at a predetermined minimum RPM threshold. Timing will be added linearly until the motor achieves the high RPM threshold. From there timing will remain constant at its full setting.

Castle Creations CHEAT MODE

Castle Creations CHEAT MODE

ESC Turbo  ( common for RC Cars )

This is a type of timing when enabled will set a predetermined amount of timing advance at a specific trigger point. This trigger point can be either based on a specific throttle input such as 100%, an RPM value or both. These parameters are programmed in to the ESC. In some cases an ESC will also allow delay to be programmed in to allow a user to exit a corner before the “turbo” function kicks in.

Selecting advancement that is best for your Application

The easiest way to select the correct amount of timing for your application is by trial and error. To accomplish this, you will need to have measurement tools that are able to measure the power consumption and heat within the power system. We will get deeper in to this in the next article talking about the applications of brushless motor timing.

 

Comparing Combustion Engine and Brushless Motor Performance Fundamentals

Combustion engines and brushless motors serve the same purpose in the radio controlled scene. The purpose of these two technologies is to provide the main source of mechanical power to drive our boats, planes and cars forward. In this comparison we will be looking at  4 different parameters. These parameters will include output RPM, physical engine / motor size, timing and lastly load. We will look at how many fundamentals from combustion engines that we can apply to brushless motors.

Output RPM Performance Comparison

Combustion Engine Comparison

In this first example I would like to do a comparison between my wifes daily driver and mine. We both drive Toyota’s that have 1.8L engines. However, my wifes Toyota Matrix makes 130hp (@6000 RPM) and my Toyota Corolla makes 170hp. (@7600 RPM) Both engines have the same displacement, (physical size) however there’s a significant power difference. Where does the power difference ultimately come from?

As you probably were able to guess from the heading of this paragraph, the difference is in the output RPM. The Toyota 2ZZ-GE engine makes 170hp as it is able to scream all the way to 8200 RPM. The Toyota 1ZZ-FE engine on the right hand side of the image below, is only able to reach a 6400 RPM redline.

Power is produced when a motor or engine is able to output torque at a specific RPM.  Power = Torque x Rotational Speed.  This tells us that as long as both engines in this comparison are able to produce the same amount of torque, the higher RPM output of the 170hp engine is what ultimately allows it to get there.  A 7600 RPM peak power output is about 27% higher then a 6000RPM peak power output.  I would expect there to be a difference of 27% in power delivery. This is nearly true as the power output is 31% higher.

Where does the gas engine get the extra power from?

The gas engine will be able to produce more power as it is able to burn more fuel per second. If we take a look at the total amount of air entering the engine, we know that the engine will consume 1.8L of air for every 2 rotations of the output shaft. This would equate to 5400 Litres of air per minute on the 130hp engine and  the 170hp engine will consume 6840 Litres of air. More air means more fuel is burned.

Comparing 2 Toyota Engines that have the same displacement but different power outputs.

Comparing 2 Toyota Engines that have the same displacement but different power outputs. 2ZZ-GE left, 1ZZ-FE right

Brushless Motor Comparison

Would you expect this same fundamental to be true in a brushless motor? The short answer is absolutely. Higher Output RPM in both Brushless motors and Combustion Engines help us to achieve more output power.

If we take the same brushless motor, apply the same input voltage  but change the Kv of the motor, we can expect different results. The higher Kv motor will be able to output more power utilizing the same formula as above. This power electrically comes from the higher Kv motor requiring more current to spin higher RPM’s. Electrical power is determine from the formula – Power = Voltage x Current.

Performance for Different Engine / Motor Sizes

Combustion Engines:

This is such a great comparison to look at. For the example in this comparison, we will use a Ford Mustang and a Ferrari 458 Italia. The Ford Mustang in 2015 produces 435 horsepower at 6500 RPM from it’s 5.0L engine. A 2012 Ferrari 458 Italia is able to produce 570 horsepower at 9000 RPM from a 4.5L engine.  The smaller engine from Ferrari is able to out produce the Mustang quite easily. This can be very common with combustion engines, where size of the engine really doesn’t tell you the entire picture in terms of power output. Running the same calculation as above, the mustang consumes 16 250 litres of air per minute, while the 458 Italia consumes 20 250 litres of air per minute. Yet again, you can see that the engine with the higher amount of horsepower is consuming a lot more air per minute.

The 5 litre engine has a 11% advantage in size vs the 4.5L engine. However, the 4.5L engine has a 38% advantage in output RPM equating to a theoretically simplified 25% overall gain in power. The actual power difference between the engines is about 30%.

Popular Turbo vs Size Comparison

To take it a step further the 3.5L V6 that can be found in the Ford Raptor is able to produce 450hp at 5000 RPM. The big difference here is that this V6 has a turbo that pushes 16 pounds of boost down the throat of the engines intake manifold. That is where the power comes from.  A 3.5L is able to produce more power than the 5.0L found in the Mustang even when it is spinning 1500 RPM slower!

Boost pressure is what allows more air to enter the engine. For every 14.7psi of boost pressure, you are getting another atmosphere of air into the engine. At 16 pounds of boost, this is equivalent to 1.089 atmospheres more.

Performing a similar theoretical calculation as above, the 3.5L engine consumes about 18 000 litres of air per minute. This is of course higher than the consumption rate of the Mustang.

Car Engine Size HP RPM Boost Absolute Air per min (litres) Displacement Advantage RPM Advantage Boost Advantage Theoretical HP
Mustang 5.0 435 6500 14.7 16250 1.00 1.00 1.000 435
458 Italia 4.5 570 9000 14.7 20250 0.90 1.38 1.00 542
Raptor 3.5 450 5000 30.7 18274 0.70 0.77 2.09 489

Brushless Motor vs Physical Size and Power Output

In a brushless motor the same performance fundamental can not be expected. A smaller brushless motor spinning at higher RPM will not necessarily be able to keep up in power output as a larger motor. Even if the larger motor is spinning at a slower rate.

The big difference here is that an electric motor requires the physical size difference to be able to fill more motor space with copper. Copper being the windings that are found on the stator. Optimizing the space for more windings allows a motor manufacture to increase the gauge of wire being used, allowing more current to pass through the motor. More current equates to more power. I suppose the saying there’s no replacement for displacement is not so true anymore for ICE and rather more applies to brushless motors. I would gladly take a larger brushless motor when ever I can if I’m looking for more power.

Changing Timing vs Power Output

Combustion Engines

Combustion engines have spark plugs that control the explosion timing of the gases in the combustion chamber. In addition, they also have valves that control the timing of air and fuel entering the engine or exhaust exiting the engine. Changing  ignition timing or even valve timing is able to increase power delivery. Not only can power be increased, overall power delivery can be optimized and smoothed.

Brushless Motors

In fact this same principle is true for Brushless motors. The electronic speed control is typically what is used to control timing. Brushless speed controls are able to control the timing electrically. Feedback received by the ESC allows timing changes continuously depending on load, speed and other factors.

How Load Effects Performance

Combustion Engines

Combustion engines are able to have horsepower specifications given at specific RPM intervals. Knowing what the values are are important in order to understand the potential without testing. What is interesting or uninteresting about combustion engines, is that as you increase the load on these engines, the power delivery will not increase. Combustion engines struggle to produce more power when overloaded. This is why it’s important to load an internal combustion engine correctly so that power is optimized.  It is uncommon for a combustion engine to have any power output specification in terms of peak vs continuous output.

Brushless Motors

Brushless motor manufactures typically do not place power outputs in data sheets. However, if they do, they must or certainly should specify whether the value is a continuous rating or a peak rating. Brushless motors operate entirely different then combustion engines. The biggest difference is if you place additional load on a brushless motor, that motor will do its best to push that load. The problem comes when you realize it was not fit for the extra load, resulting in a burned up motor. This is not an example of mechanically stressing the motor parts as you can easily do this in both brushless motors and combustion engines. it is an example of stressing the electrical windings within the brushless motor.

It’s important to understand this as it is very easy to overload the brushless motor and think all is well.

 

Compare Equal Size Brushless Motors with Very Different Kv’s

Brushless motors come in many different winding choices. These winding choices are critical to the specific application that you are looking to place a motor in to. However, did you ever wonder how a brushless motor is able to perform equally in terms of power when Kv is changing?

Continuous Power Output Limitation

The first topic to dig in to is, what truly is limiting the power output of a brushless motor? The true electrical limitation to a brushless motor is heat. Too much heat as we’ve discovered in another article, will destroy the brushless motor.

Brushless motors do not operate with 100% efficiency. If they did, we would not have to worry about heat in any way. However, a typical brushless motor will operate between 80 to 90% efficiency.

Compare Equal Size Brushless Motors with Very Different Kv's

Compare Equal Size Brushless Motors with Very Different Kv’s

We are going to follow an example throughout this article. Let’s take a look at a 1750w motor where this power can be delivered continuously.  If we assume an efficiency of 90%, our 1750w motor will be delivering 10% of 1750w in heat. This roughly equates to 175w. If you have ever touched a 100w old school incandescent light bulb while it was on, you would know what about 90w of heat feels like. Our motor has to be able to dissipate 175 watts of power in order to not over heat. Anything more and the motor should not be rated for 1750 watts.

A larger motor simply is able to dissipate more waste heat. If we look at an inrunner motor, the motor is capable of removing heat by the surface area of the case. Increase the surface area by increasing the size of the motor and you are able to remove more heat allowing a higher amount of power to be produced.

The Heat Producing Parameter of Brushless Motors

We have also learned from a previous article that heat is produced by current. Voltage does not directly impact the amount of heat that a motor will expel. The more we load our brushless motors, the more current we should expect to draw from the battery pack.

If current produces heat in our brushless motors, how is it possible that the high Kv motor (draws more current) is able to have the same output as the low Kv motor? Surely, we would expect that drawing such a high amount of current would contribute to significant waste heat.

The answer is in the data chart below. Motor one is on the top, and motor two is on the bottom.

Continuous Wattage (Watts) Kv Value (RPM/v) Voltage Current Rm (ohms) Io (Amps)
1750w 2600 11.1v 158A 0.0047 5.83
1750w 580 44.4v 40A 0.0831 0.92

Waste Heat produced by each Brushless Motor

We know the limitation to power output is waste heat. In order to understand how both of these motors will end up producing similar waste heats, we can use the above data set. Two forms of waste heat produced is known as copper losses and iron losses. Copper losses are found in the windings of the motor while iron losses represent the power consumption to keep the motor rotating.

To calculate the Copper Losses, we take the square of the current and multiply this by the Rm. To calculate the iron losses, we take the voltage and multiply it by the Io.

Motor Copper Losses Iron Losses Total Losses
Motor 1 / 2600 Kv 117 watts 65 watts 182 watts
Motor 2 /   580 Kv 133 watts 41 watts 174 watts

As we can see, both motors end up producing similar waste heats. These values closely match the waste heat calculated by taking 10% of the total wattage of the motor. Now the point here is not how closely we can get back to the original number we were expecting. You may try this on a motor and your results may be significantly different.

Conclusion

The point here is that motors running at higher voltage will have a higher internal winding resistance. The higher resistance results in significant waste heat. Most would expect the higher current running through the first motor would result in a lot of waste heat. However, it’s not as bad as the motor with a much higher kv has the  While on the other hand, the high no load current of motor one running at a lower voltage still produces wasted power leading to heat.

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