ElectroFlightRC - Basics of Electric Flight

Useful tools and gadgets related to electric flight

Table of Contents

Useful Tools and Gadgets

When it comes to RC planes, there are many tools and gadgets that are quite useful. I’m not going to go through all of them but just the ones that are useful for electric planes. By no means is this an exhaustive list. New products come out all the time but here are a few things I tend to keep in my flight box:

Watt Meter

This is a particularly useful tool. A watt meter will allow you to measure (at the very least) watts, amps and volts of your plane's power setup. You plug it inline between the battery and ESC and as you apply throttle it displays current Amp draw, registered volt levels and total watts. This will help you determine if you are over Amp’ing your ESC or motor and to determine total input watts. You will see more about how to use a Watt meter in the section about “Measuring the performance of your Power Setup”.

Here is an example of a watt meter:

This is a “Watts Up” meter and it measures 8 DC values:

1. Amp-Hours

2. Watt-hours

3. Amps

4. Watts

5. Peak Amps

6. Peak Watts

7. Minimum voltage (“sags”)

8. Voltage

As you can see in the picture, this particular model does not come with any connectors at the end of the wires. You can attach whatever connectors you use. Just remember that one side is to connect to the battery and the other side is to connect to your load (ESC) so make sure to put the correct male or female connectors (if applicable).

There are other meters that are multi-purpose and that also serve as data loggers. For example the Powerlog 6s multifunction monitor and data logger shown below:

This device serves as a watt meter like the Watts Up, but also has additional features like individual LiPo cell monitor up to 6s, LiPo temperature sensor, infra red tachometer, motor KV monitor, user alarm and data logger. All this in one litte device.

As you can see, this device comes with Deans connectors, but you can make adaptors to mate them to whatever type of connectors you use (if you don’t use Deans connectors that is). For example:

Cell Voltage Meter

A cell voltage meter is a device that displays the individual cell voltage of your LiPo battery by connecting it to the balance plug. As with the Watt meter devices, there are many different models including multifunction models like the Powerlog 6s multifunction monitor and data logger (see the Watt meter example above).

Here is a picture of a relatively simple model:

This model flashes from one value to the next. It cycles through total voltage and the voltage of each cell up to 6 cells. This is a great tool at the field to tell if your battery is charged before a flight. It doesn’t do much other than that.

Here is another example of a more feature-rich model:

This model displays the total battery voltage and the voltage of each individual cell at the same time. It also has an alarm which can be triggered if a cell’s voltage drops below a user configurable setting. This device could be used in flight to warn you of a low battery voltage situation. Just connect this device to your battery’s balance plug and strap it down safely inside your plane. If you hear the buzzer go off, you know your battery is getting low. Make sure to give yourself enough warning so that you still have enough power in the battery to safely execute a landing. The only drawback of this method is that you may not hear the buzzer if the plane is too far from you or if there is a lot of noise around you from other planes. See the Telemetry section below for better alternatives.

Anyway, again there are lots of different models with a wide range of features. Make sure you pick a device that will meet your needs and do your research before making a purchase.

Telemetry Devices

How do you tell if your batteries are getting low while you are in flight? Well, you can use a timer. Start with a conservative time and see how many mAh you put back in after charging. If you only used 50% lets say, then you know you can increase your timer a bit. Keep doing this until you maximize your flight time without compromising your safety margin in case you have to abort a landing or two, or if there is lots of wind (drains more power). That works pretty well, but if you don’t have a built-in timer on your transmitter - or if it doesn’t trigger automatically when you push the throttle stick up, you may forget yourself and end up in a dead-stick situation. Wouldn’t it be nice to have a fuel gauge that would tell you how much fuel you have left in your batteries? Well, there are tools out there that do exactly that - Live Telemetry Devices.

Some newer transmitters have this capability built-in, such as the Spektrum DX8 and some Futaba transmitters (don’t know exactly which one(s) as I am a Spektrum/JR guy). Take a look at the features of the DX8 here. The telemetry features are only available with certain receivers which support telemetry. The DX8 is able to monitor battery voltage, temperature, signal quality and RPM. The newly anounced Futaba 18MZ is capable of monitoring something like 20 different sensors. These transmitters display the telemetry on the screen for easy reference, but can also warn you through an audio or vibration alarm if a monitored value passes a user configurable threshold (low battery voltage for example).

There are also other less expensive products out there if you aren’t looking to replace your transmitter and all your receivers. I personally use a product from Quanum which I purchased at HobbyKing. Here is a picture of the product:

Out of the box, this device can display the total battery voltage, the voltage of each cell and the temperature from one provided temperature sensor. With the addtional Amp meter, you can also display the Amp draw and the total mAh used (this is your fuel gauge). Here is a picture of the Amp meter module and wiring diagram:

This device takes a little soldering, but it’s fairly simple to do. It’s worth the little bit of work especially when you see the benefits you get from it.

With this device installed in your plane, you have no more guess work. You can see the total mAh drawn from the battery. So, following the 80% rule, if you are flying your plane and you glance at the mAh on the screen and you see that you’ve only used 2200 mA (from a 5000 mA battery) when your timer goes off, you know that you still have plenty of time left to fly before you reach 80% or 4000 mAh. However, if the reading says that you’ve used 3600 mAh or more, you better start thinking about landing - that way you still have a margin of error.

It’s also useful to see the voltage of each individual cell, but it’s just too much to look at when you’re flying. It’s much easier to just look at the mAh number - it’s much more useful anyway.

The way I safely look at the reading is by putting my plane into a straight and level flight at a good altitude and then I raise my transmitter up (the Quanum device is mounted to the antenna of my transmitter) and I follow the plane with my transmitter. I can then peek at the display and still have the plane in view.

The Quanum device also has a buzzer that goes off when the voltage of any individual cell drops too low, but that threshold is not user configurable (as of this writing) and is set too low that it would be too late for my taste to just rely on the alarm. I still use a timer to keep track of time. I actually have two timers on my transmitter that automatically turn on when I give some throttle and turn off when the throttle is off. I have one set for two minutes after the first one. That way, if I the telemetry reading tells me that I still have some mAh’s left and decide to keep flying after the first timer goes off, I still have a two minute reminder to look at the Quanum device.

As with the other devices, there is a good selection of devices out there with a wide range of features. As always, make sure to do your research before making your purchase and pick something that will fit your needs. There is no point in buying the most expensive most feature-rich device if you aren’t going to use most of the features anyway - especially if there is a less expensive device that will give you everything you need. The cost of all these electronics drops every year so if you can’t afford it now, you will eventually find the more expensive devices for a fraction of the price in the near future - probably the next season :o)

Hand-held infra-red thermometer

This is a great tool for measuring the temperature of your battery, motor and ESC after a flight. There are a lot of different models, but any one should do the trick. Even if they aren’t accurate to 1/1000’th of a degree, you will still have a close reading of the temperature of whatever you are trying to measure. Here are pictures of a couple different models:

It’s a good idea to check the temperature of your motor, ESC and battery after a flight to make sure they aren’t running too hot - especially when you first try a new power setup or change any components in your power setup (i.e. battery, motor, ESC, propeller). Once you know a particular power setup works well without over-heating any components, you shouldn’t have to check it again unless you suspect there is something wrong or if it’s hotter outside then when you tested the power setup before. However, it is always a prudent practice to check the temperature once in a while.

If the temperature of your motor goes too high, the magnets could get demagnetized. For Neodymium/rare-earth magnets (common in electric RC motors), they will lose a fraction of their magnetism if heated to or beyond 176°F (80°C) and they will completely demagnetize if heated above their Curie temperature - around 590°F (310°C). See here for details. The exact temperatures that affect the magnets in any motor depends on the grade and quality of the magnets, so take the above numbers with a grain of salt. Ask the manufacturer of your motor if you really want to know what temperatures will affect your specific motor.

If the temperature of your ESC goes too high, you risk damaging it and it could even start to smoke and/or catch on fire. In the worst case, the damage could manifest during flight and you could experience a complete failure of your ESC. This could also be even worse if you are using a BEC built-in to your ESC and it suffers damage as well. In that case, you would not only lose power to the motor, but you would also lose power to your receiver and servos. I always use a separate external BEC for added safety.

If the temperature of your battery gets too high, you risk damaging it and if additionally pushed too hard, the battery could puff and potentially explode. Well not necessarily explode, but the cell pouches could rupture in which case the battery would release lots of smoke and hot gas/flames and potentially start a fire. The best case scenario of an over-heated battery would be a reduced lifespan (number of cycles) and/or reduced performance. The worst case would be an in-flight failure and fire causing loss of power to the ESC/motor and to the receiver/servos. See the section on batteries for more information on battery safety and usage.