Converting a Gas/Glow RC Plane to Electric

There was a time when internal combustion was the norm and there was literally nothing else on a  flightline. Electric power systems are now the norm and are much more common than glow or gas and as urban development encroaches on flying fields all over the globe we must become quieter should we wish to hang onto our much cherished flying sites.  Nothing irritates people faster than the sound of a 2 stroke edger flying through the sky. Electric systems are not only quieter but cleaner and easier to use.

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Is it difficult to convert from Glow/Gas to Electric?


It's not difficult at all. There are various companies that make drop in equivalent motors. Such as the Turnigy Easy Match motors. This makes the process easy but it’s not the only way. Turnigy also make two other exceptional motor lines, Propdrive and SK3. These motors are well known to hobbyists the world over and I’m sure you know someone that uses one of those brands.  I’ve owned several Easy Match, Propdrive , SK3 motors and they have all served me well. They are exceptionally well priced for what you get and I can honestly say I highly recommend them.   

Easy Match comes in an assortment of sizes ready to drop straight into your aircraft. You will need to replace the engine mount that is currently installed in your plane and switch over to an electric version. The process is not difficult and should only take 10 minutes.

https://hobbyking.com/en_us/hxt-alloy-composite-firewall-mount-85-36mm.html

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Glow Engine Electric Size Conversion


.10 Glow
https://hobbyking.com/en_us/turnigy-g10-brushless-outrunner-1100kv.html
https://hobbyking.com/en_us/turnigy-g10-brushless-outrunner-810kv-10-glow.html
 
.15 Glow
https://hobbyking.com/en_us/turnigy-g15-brushless-outrunner-810kv.html
https://hobbyking.com/en_us/turnigy-g15-brushless-outrunner-950kv.html
 
.25 Glow
https://hobbyking.com/en_us/turnigy-g25-brushless-outrunner-710kv.html
https://hobbyking.com/en_us/turnigy-g25-brushless-outrunner-870kv.html
 
.32 Glow
https://hobbyking.com/en_us/turnigy-g32-brushless-outrunner-600kv.html
 
.46 Glow
https://hobbyking.com/en_us/turnigy-g46-brushless-outrunner-420kv-46-glow.html
https://hobbyking.com/en_us/turnigy-g46-brushless-outrunner-550kv-46-glow.html
https://hobbyking.com/en_us/turnigy-g46-brushless-outrunner-670kv-46-glow.html
 
.60 Glow
https://hobbyking.com/en_us/turnigy-g60-brushless-outrunner-400kv-60-glow.html
https://hobbyking.com/en_us/turnigy-g60-brushless-outrunner-500kv-60-glow.html
https://hobbyking.com/en_us/turnigy-g60-brushless-outrunner-300kv-60-glow.html
 
1.10 Size
https://hobbyking.com/en_us/turnigy-g110-brushless-outrunner-295kv-1-10-glow.html
 
1.60 Size
https://hobbyking.com/en_us/turnigy-g160-brushless-outrunner-245kv-160-glow.html
https://hobbyking.com/en_us/turnigy-g160-brushless-outrunner-290kv-160-glow.html
 

The Benefits of Converting to an Electric Brushless System 

The modern electric motor has many benefits and not just the obvious ones like regular tuning, fuel availability and the never ending oily mess that needs to be cleaned off your model. A glow engines lacks the flexibility that an electric system offers because generally a glow engine is designed to accept a very narrow selection of propellers. This is because an electric engine  hand has a much wider selection RPM range depending on the battery used. This means we can vary the prop selection unlike a glow or gas engine allowing us to get the best peformance from the motor.
 
Many models cannot swing a larger prop so an electric setup is far superior to gas or glow. The ability to use different motors setups allows you to get the very best setup for your aircraft without any sacrifices. As an example we could run the G45 motor on a 4S 2200mah Lipo battery swinging a 12x6 prop and fly a trainer around quite comfortable. With that same motor you could use a 5S or even a 6S with a smaller prop and use this in a sports plane. Provided we do not push the motor, ESC or batter beyond its limits the electric system is incredibly reliable and it will perform the same for years without any special maintenance, tuning or cleaning.

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Are there other motors I can use?

We spoke earlier about Propdrive and SK3 motors. I have a lot of experience with these motors. Yes they are also a pretty good option but what to choose? Well, there is a fairly simple rule of thumb that I use. It all boils down to watts. Power is the rate at which energy is generated or consumed and hence is measured in units (watts) that represent energy per unit time. For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100watt hours (W. · h), 0.1 kilowatt hour, or 360 kJ. Many modelers will be familiar with the Watts per pound rule of thumb. This is a simple guide that will allow you to determine the power output required for your model aircraft. 
 
Ideally you should aim for 100w/per pound (100w/per 500grams). Although a plane may fly with 50w/per pound it would be considered quite underpowered and would be a handful to fly. If you are after a hardcore 3D or high performance setup you would consider 150-200w/per pound (150-200w/per 500grams). 200w/per pound would be a weapon!

Power Guide

  • <50-80w/lb – Gliders, park flyers and trainers
  • >80-100w/lb - Sport flying / Aerobatics aircraft
  • 100 to 150w/lb – 3D Aerobatics and EDF jets.
  • 150 to 200w/lb – Only for the insane and reckless.
If aim for 100w/lb in your conversion you should be satisfied with the results. Don’t be concerned about a plane being too powerful. (Have you ever heard someone even say that) A little throttle control / management is all that is genuinely required. There are no hard and fast rules when it comes to electric conversions so a little bit of experimentation is generally required. A google search can often yield the results you’re after because you may also find that someone has done the hard work for you.

Once you've chosen a suitable motor that is capable of delivering the required thrust and watts, then play around with propeller selection; increasing/decreasing prop diameter and pitch will have a big effect on how your airplane flies, but be careful to stay within the recommended range as stated by the motor manufacturer. To ensure that you do stay within the rating of the battery, motor and ESC you will require a wattmeter. They are reasonably inexpensive but if they only save you one component it will immediately pay for itself.
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What does a watt meter do and why do I need one?

Simply put, a watt meter measures the current draw on your electrical system  and displays the results live (watts, amps and volts). The watt meter is placed in series, between your battery and ESC and takes only seconds to use.
Think of a watt meter as an insurance policy that pays off very quickly. At less than $20 if a watt meter only saves you one ESC, Battery or motor you’l be very thankful. If it happens to save you an entire aircraft and a bag full of regret then it should be look upon as more of an investment. 


What is a Watt 
Watt is the unit of power (symbol: W). The watt unit is named after James Watt, the inventor of the steam engine. One watt is defined as the energy consumption rate of one joule per second. 1W = 1J / 1s. One watt is also defined as the current flow of one ampere with voltage of one volt.

How do you calculate watts
To determine the wattage, use a simple multiplication formula. The ampere (or amps) is the amount of electricity used. Voltage measures the force or pressure of the electricity. The number of watts is equal to amps multiplied by volts.
e.g. (V)x(A)=W   or  (voltage)x(amp draw)=(watts)  or (11.1)x(30)=333watts


How to do you calculate Ampres (amps)
The formula for Watts is Volts times Amps. To calculate amps divide volts by watts.
e.g. (W)/(V)=A   or  (Watts)/(Voltage)=(Amps)  or (333)/(11.1)=30Amnps
.
 
Why is it important to know how many watts or amps my system is drawing?
Your electrical system has a limit that should not be exceeded. As you exceed the limit of your electrical system heat is generated and resistance increases, as resistance increases so does heat, until you let all the magic smoke out. At this point you regret not using a watt meter and you fork out for a new motor or ESC.
Different loads, for example a new prop, can have a massive impact on current draw. Going from a 3s battery to a 4s is a good example where a wattmeter is critically important.  Get into a habit of using it.

What do I do if the Watts indicate that I’m exceeding the limits? 
We need to remember that amps are pulled not pushed. If you want to reduce Watts reduce your load. This may mean smaller tires, smaller props, different gearing etc. If the motor is rated for a much higher current draw you could use a higher rated ESC.
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How do you choose the right propeller?

The larger the prop the more efficient so we ideally want to use the largest prop that will reasonably fit the aircraft. You should ensure that the prop can easily clear the ground, even in a heavy landing.  Electric props are generally thinner and more efficient however there is no reason that you could not use the thicker gas/glow versions on an electric motor. To better understand how much thrust each prop will produce at a given RPM you can use a thrust calculator.  A thrust calculator is going to be close but it is still a guide. http://www.godolloairport.hu/calc/strc_eng/index.htm 

How do I know what battery to use?

The cell count or voltage will be determined by the prop and motor you intend to use. All brushless motors will have a range of batteries types that can be used. For example the motor may suggest 2S-3S battery. This means a 2cell or 3cell battery. (The S stands for series).  

Where do I install the battery.

There are two considerations for battery installation.  You can access the battery and the battery can be easily removed for charging and inspection. This is important as you should never recharge the battery in the plane. This is a very bad idea and not recommended by any manufacturer or for that matter hobbyist. Lipo batteries must be connected to a balance port and charge port on the charger. The battery is often positioned to balance the aircraft so that CG is correct  without the need to for additional weight. You may find that the previous location of the fule tank makes for a perfect position for the battery. A simple balsa battery tray may make it easier for you to complete the conversion.

Understanding the Battery C Rating?

There are plenty of pretenders on the market. I have tried many packs and found Turnigy to be very good. There are some packs that are cheaper but definitely not as reliable. Given the expense of batteries choose a pack that has a decent warranty and a well-known brandThe C rating of a battery (or cell) is used to indicate the continuous current draw (amps) the cell will support. By multiplying the C rating times the cell capacity in milliamp/hours (mAh), the continuous current in milliamperes (mA) of a cell is easily calculated. Example - For a 2000 mAh battery with a 15C rating, the continuous current that may be drawn out of the battery is 2000 mAh x 15 = 30000 mA, or 30 Amps (A) (divide by 1000).
 
There is also another rating that is applicable to a battery known as peak or "burst" current discharge rating. Peak current is higher than continuous C rating. It indicates that a battery will deliver higher current than the C rating for brief instances. For ease of calculations, LiPo Calc does not take peak current into account. This figure varies widely with battery type and in most applications is not required for calculating a suitable battery pack configuration. 

What ESC Should I Use? 

An electronic speed controller or (ESC) is a device used to control an electric motors speed and direction.  ESCs can be commonly found radio controlled models with the most common type being used for brushless three phase motors. An ESC generally plugs into the receiver's throttle control channel where it is controlled by pulse width modulated signals.

How does an ESC work?

Much like a servo, an ESC is controlled via a PWM signal. Depending on the throttle position, a microprocessor rapidly drives a set of FETs (field-effect transistor) to create 3 phase AC current to drive your Brushless motor.   The rapid switching of the transistors is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds. It also allows much smoother and more precise variation of motor speed in a far more efficient manner than the mechanical type with a resistive coil and moving arm once in common use.

Do I need a receiver battery?

A Battery Eliminator Circuit is typically part of the electronic speed controller (ESC) and its sole function is to provide 5~6v to the electrical system. A BEC negates the need to carry an additional battery pack but rather uses the main motive power battery pack. A BEC regulates a higher voltage to 5-6v and sustain between 1-5amps depending on the ESC specifications. R/C BECs in their simplest form use a linear fixed voltage regulator, however, it is more common to find a switching regulated type of BEC. It is not uncommon to need more power than the integrated BEC can supply. In this case you will need to use either a separate receiver pack or a separate stand alone BEC.

Many companies make standalone BECs that can handle higher voltages and higher servo loads. Keep in mind if you do decide to power the receiver with another source besides the BEC that is built into an ESC, that BEC must be disabled. Disabling the integrated BEC is as simple as cutting only the positive line of the receiver wire. Although permanently disabling the BEC is not very favorable since it may work well in another application later. So there are other options to disabling the positive wire and one is to use a servo extension between the BEC plug and receiver, then cutting the positive wire on the extension. 

What happens if I run out of battery power?

Most ESC incorporates a low-voltage-cutoff (LVC) circuit that monitors the voltage of the battery pack and when the voltage has reached a predetermined level, power is either reduced or cut completely to the drive motor(s) in order to get you home, hopefully in one piece. If this happens whilst you’re flying an aircraft, the power to the propeller would be cut but the operation of the control surfaces would be the only system maintained in order to perform a dead-stick landing. Without this feature, all control would be lost when the battery expired, probably resulting in the destruction of the model.

LVC should be avoided because you have likely reduced the serviceable life of your battery and tempted fate with a deadstick landing. There are ways to avoid this,  such as timing your flight or using a telemetry system. FrSky, as well as Turnigy, have some great systems that allow you to easily and simply monitor your flight battery. Some are even capable of talking to you in flight.
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