ElectroFlightRC - Basics of Electric Flight

Electric planes are not like glow or gas planes. When the battery is connected, they are armed and dangerous without that friendly reminder of an idling motor. If you’re not careful, you could hurt yourself, you could hurt others or just create a big mess.

Imagine you’re working on your new plane. You’re excited as you get close to completion. You’re at the point where you want to setup and trim your servos. So what do you do? Simple! Turn your transmitter on. Bind it to the receiver if you have not done so already. Plug in your main battery. Then the BEC and ESC power up. The receiver connects to the transmitter and the servos are on. So you start playing with your servos and the linkages but then you inadvertently touch the throttle when you try to move one of the control surfaces! What happens now? You guessed it... that’s when you realize that motor was just waiting to pounce... whap! big mess... or even injury! It’s happened to me before as I’m sure it’s happened to many others as well. In my case, I accidentally pushed the throttle forward, the prop started spinning fast and before I even had the chance to pull the throttle back, a plastic bag got sucked in with some parts in it. It all went flying with a big whap / clang noise. The bag was shredded and the parts all over the place and the prop was broken. I was lucky it wasn’t worse. At best, this kind of event is embarrassing. At worst, you need stitches or in the case of really big planes, you could lose a finger.

So what can we do to avoid this kind of finger chopping peril? Well, there are several things you can do:

Elastic:

This is probably the lowest tech, the cheapest and simplest practice. Take an elastic (one of the ones you use for fixing the wing to the fuselage) and attach it to the metal bar at the back of your transmitter by looping the elastic. Then pull the elastic down and wrap it around the bottom of the transmitter until it reaches the throttle stick. Then just hook the elastic to the stick. Voila! The stick is held down and you can still move it side to side if you want to play with the rudder. Very simple. However, you have to be careful not to activate the throttle while you are in the process of stretching the elastic and hooking it to the throttle stick. The easiest way to do that is to hook the throttle stick before turning anything on.

Remove the propeller:

Another simple and inexpensive practice would be to remove the prop to work on your plane to, lets say, work on your servo trimming. This way, you can’t get hurt even if you hit the throttle stick.

Again, very simple, but this could be a bit of a pain to take the prop off and put it back on again.

Throttle Hold:

One of the heli guys at my club got me onto this one. If your radio supports Throttle Hold for plane models, this is an easy way to deactivate the throttle with the flick of a switch. You do, however, have to remember to flick the switch ;-)

Arming Switch:

This is something I add to all my planes. It just adds a good layer of safety to prevent accidental throttle activation. I mount my arming switch near the receiver switch for easy access. Essentially, the arming switch is a switch between the battery and the ESC. This only works if you use an external BEC (or other setup to power your receiver/servos) because if you use a built-in BEC, it won’t get power unless the ESC has power - which is what we are trying to prevent. We want to power the receiver and servos without powering the ESC.

What kind of switches can we use for an arming switch? Well, since we will be dealing with lots of current (Amps), toggle switches will not work. They are just not made to handle high Amps. The best thing to do is to build a switch using the same gauge wire you are using between the battery and ESC and a pair of connectors (with the outside connector “shorted” to close the circuit). Here is a picture of a product you can purchase, but you can also make them if you prefer:

These are fairly inexpensive and work very well. The “Key” is actually just a 45 Amp Anderson Power Pole connector. If you use this type of arming switch, just make sure you don’t lose the “key” or you won’t be able to fly ;-)
You can find this product here.

The other kind of arming switch I’ve found is pretty cool but quite a bit more expensive. It’s an electronically controlled switch activated by a magnetic switch shaped like a fuel dot. Here’s a picture:

When you pull the little magnet off the fuel dot, it turns the main switch on. When you put it back, the main switch turns off. When the power is on, a bright LED turns on inside the fuel dot. Pretty cool.

You can find this product here. They are made by Emcotec and there are different models which can handle a variety of voltages and Amps.

LiPo Tips

Another common safety issue related to electric RC is fire. You’ve undoubtedly heard about some RC enthusiast burning his garage down or setting fire to his car because of a LiPo fire. The truth is that LiPo batteries do store lots of energy and if they are mistreated and abused, they can come back and bite you. However, if handled with respect and maintained properly, the use of LiPo batteries can be very safe. Here are a few suggestions that can help:

Storing LiPo’s

When storing LiPo batteries, you want to protect them from 2 things: physical damage and high temperatures. You want to store your batteries in a cool place, in a container that will protect them from physical damage and, just in case anything were to happen to the batteries, you want to pick a location away from any flamable or combustible materials.

I use a metal toolbox to store my batteries and that seems to do a good job. Other good storage containers would be any metal box that would fit your batteries well. Other good examples would be ammo boxes or cash boxes. Any relatively well sealed metal box should be suitable.

See this link for some more detailed discussion on Making LiPo’s safe and dealing with problems.

Transporting LiPo’s

Transporting LiPo’s basically follows the same rules as storing LiPo’s. You want to make sure that your batteries are safe from physical damage and that they are not stored in a hot car. The same kind of container as what you use for storage should work fine for transport but just make sure not to leave your batteries in your car - especially if it’s a hot sunny day. Regardless, make sure that whatever container you use will contain your batteries if anything happens.

If left in a hot car, at the very least the heat could damage the batteries and reduce their life span. In extreme cases, it is possible that a battery could puff - and who knows, maybe even burst. It’s not a good idea to leave your batteries unattended in a car.

See this link for some more detailed discussion on Making LiPo’s safe and dealing with problems.

Working with LiPo’s

When you are working with LiPo batteries, you need to pay attention not to short them. You could damage the batteries or even cause a fire. Two activities in particular come to mind.

The first is when you are putting new connectors on a battery. Make sure to do one pole at a time and keep the other pole well insulated and away from the one you are working on. I’ve had a couple scares while putting new connectors on before. It definitely wakes you up!

The other is when you connect your battery to any circuit for the first time. Make sure to look all of your wiring over as carefully as possible before connecting a battery to it for the first time. Make sure all connections are well insulated and that you don’t have any shorts in your wiring. This is a fairly easy thing to do and should not take very long but it could save you from a damaged ESC or battery. For example, I once was asked by a member of my club to hand launch a plane for them. It was a maiden flight. During his pre-flight test, he checked all the control surfaces and all was fine. He asked me to get ready to launch the plane but I asked him to give her a little throttle to make sure the prop was spinning in the right direction. When he pushed the throttle up, I heard a clunking noise come from the motor and then I saw smoke. I quickly opened the hatch and disconnected the battery. In the end, the problem was that the connectors on the three wires between the motor and ESC were not insulated from each other and they shorted. It was something he intended to do later during his build and he forgot. The end result was a fried ESC but at least we didn’t launch the plane. It could have been worse.

Smoke Detector and Fire Extinguisher

Another couple good items to have around your workshop are a smoke detector and a fire extinguisher. I keep a smoke detector in my battery storage toolbox and one in the box that is part of my charging station. Hopefully, you will never need these devices, but they are certainly a good thing to have around.

Disposing of LiPo’s

LiPo batteries are safe to dispose of in the regular garbage if they are completely discharged. The simplest way to discharge them completely is to submerge them in a non-metallic bucket of salt water and leave them there for about a week. Once completely discharged (zero volts), LiPo batteries are completely inert and cannot start a fire. It is then safe to just throw them in the garbage.

There are many ways to dispose of LiPo batteries and there are varying opinions on which way works best or is the safest. Overall, I like the salt water approach but it takes a long time. I don’t really mind that. You can double check that the battery is completely discharged by driving a nail through it. Some say that the salt water is corrosive and the battery may not discharge fully if the battery gets too corroded. Driving a nail through the battery is a good way to check for full discharge. Be careful when you do this just in case the battery still has a charge. You can simply drop the battery back in the bucket at the first sign of any activity.

Anyway, here is a link for more information on Safe LiPo Preparation for Disposal.

Other General Tips

Spark eliminator

It can be a little scary when you get that big spark when connecting your battery to your ESC. Ok, first thing you need to know is that this is completely normal and not dangerous. Well, I suppose it could be dangerous if you were in a highly flammable environment like if there were gas fumes in the air. Can you say Kaboom! Ya... Don’t do that ;-)

The spark usually occurs with higher voltage applications - typically 6s or more, but could still occur with less voltage. The higher the voltage, the bigger the spark. I find that Deans connectors are terrible for this. They let go a bigger spark than most of the other connectors I’ve used. Maybe it’s just because the spark is more visible. Anyway, when you connect your battery, the capacitors in the ESC charge very quickly and that’s what causes the spark. Essentially, the electricity jumps (or arcs) across the poles before they touch.

So what is all the fuss about? Well, arguably, the only thing that is of any real concern is the potential for damage to the connectors. Your connectors can experience some charring or “corrosion” where the spark occurs. Over time, your connectors could deteriorate and need to be replaced. Depending on the type of connector and the voltage, there may not be an issue or the damage could occur on the first connection. Just make sure to inspect your connectors on a regular basis. Replace them if necessary.

As well as the damage to the connectors, there is some debate over the possibility of damage to the ESC. This is a topic that is discussed quite a bit in the hobby and you should do your research before you get into any large electric projects. There are those who say they have never had a problem and those who say they have experienced lots of damaged ESC’s. My take on it is that there should be no issues unless you start to get really big - like 12s or more. Even at 12s, I’ve heard of setups that have no issues.

What can be done? Some use a spark eliminator circuit. They are very simple and they work well. Essentially, they are just a resistor. There are many discussions on what type and how much resistance to use for various applications. Please do your research before taking any action.

There are some larger ESC’s that come with a spark arrestor / eliminator like the Hacker JETI 170.

As I said before, there is lots of debate on the need for a resistor to eliminate the spark. Here are a couple of links that should provide a good illustration of the difference in opinion:

A discussion on RCGroups.com

FAQ on Castle Creations Website. See the third question.

Personally, I’ve had 8s and 10s setups without a spark eliminator and I did not experience any problems. However, it may be a good idea to contact the manufacturer of your ESC and ask them what they think of your particular application. That way you are covered if anything happens. Again, this is really only a concern with higher voltage setups such as 6s and beyond - although I would say its more like 12s and beyond.

I suppose that if a spark eliminator does not cause any damage to your ESC, there is no harm in using one. At the very least, it would prevent premature wear on your connectors.

Wiring Diagram

If you've read through the various sections on this site, you start to realize there are lots of different components involved in the wiring of an electric powered plane. The following is an example wiring diagram that includes all of the safety tips and components mentioned. It includes the "live" telemetry module from Quanum, the Anderson Power Pole arming switch, and a separate external BEC.

So what does all this wiring look like when you’re done? Take a look

That’s what it looks like with the Anderson Power Pole arming switch, but it would be similar with the Emcotec arming switch.

Also note that the position of the wires in the above diagram are not necessarily attached at the correct location on the components. For example, the balance plug on the battery typically comes out of the battery on the same side as the main leads.

Cooling

There are no motors, ESC’s or batteries that are 100% efficient meaning that 100% of the input Watts are converted to mechanical power. So what happens to the Watts that are lost? That's easy. It's converted to heat. So if the efficiency of your power system is 70%, that means that 30% of the watts are transformed into heat. That’s why it is important to provide good cooling to the components in your power system.

All you have to remember is that the air has to flow over the motor, ESC and batteries and the outlet should be larger than the inlet. If insufficient airflow is making it to the motor, you can always make a scoop to push the air towards the motor. There are lots of good examples on the forums of cooling ventilation. A heat sync may also be a good option for inrunner motors.

Reversing a brushless motor

If your motor is turning the wrong way, it’s very simple to reverse it. Just switch any two of the three wires. It doesn’t matter which of the three you pick. That’s it. Also, some ESC's have a programmable option for motor direction. That can be useful for larger setups where you want to solder the three wires directly instead of soldering connectors. Soldering the wires directly is more efficient for performance.

Idling RPM

When your throttle is off, an electric motor stops completely. Actually, if your plane is moving forward in the air and you don't have the brake set on the ESC, it will still spin but only because of the force of the wind. Some pilots like the braking effect this has, but I find it more realistic to have an idle so that the motor still spins when my throttle is off. I do this by pushing the throttle trim up to the half mark before I take off. I find that my plane acts more like a gas or nitro plane when there is an idle. This is debatable but I think it is probably better for your motor too. If it doesn't have to rev up from zero every time you push the throttle from the bottom.