Dez's Precision Aerobatics Page

Introduction:

Just recently several interested F3A pilots who were inquiring about the new electric set-ups that are emerging in F3A pattern today have contacted me. What differences can you as an R/C pilot expect when jumping into the world of electrics? Imagine changing from a glow engine to an electric motor overnight! In this section of my site I'd like to summarize my thoughts into points and expand on the points over time. Here are my thoughts.

Immediate bonuses:

Right from the start, these are the things you will love about your new set up. In point form here are my favorites in ranking.

1. Clean airframe. No need to clean fuel exhaust. Airplane stays new looking.
2. Can start the motor and take off alone. No need for assistance. No need to test or tune engine.
3. Engine is vibration free. No servo wear, no screws rattling off, or vibration damage or wear.
4. Next to none motor maintenance; no valves to set, no low end to tune, no high-end needle adjustments. No breaking in. No motor mount that rattles loose or wears out.
5. No smoke trail in the air to give away mistakes.
6. No fuel to buy or to run out of. No fuel problems, no dirt in the fuel, no filling the tank. No CG changes during flight.

Some disadvantages:

1. High set-up cost to convert.
2. Charging takes time. You must limit your training flights to about 8 minutes
3. Wait times between flights if you are waiting to recharge.
4. Less power in the cool weather.

Some Dangers:

1. Improper charging of Lipo batteries can be very dangerous
2. shorting out the wires of the batteries.
3. Care in how you connect the batteries before flights.

About electric motor setup:

The main difference you will find in installing an electric motor is obviously the lack of need for soft mounting. No soft mount is needed at all and I don't use a soft mount in either of my planes. The Hacker set-up noise tests right on the limit. 92-93 dB. The Plettenberg will sound test even less, I am told in the 88 to 89 dB range, and this is without soft mounting.

Also, since there is no vibration at all, one is able to build lighter airframes with less re-enforcement needed. Fire walls don't have to be fuel proof or as thick. In fact, the more air-cooling holes the better. Heat is a big issue and the more you can cool your motor, speed controller and batteries, the better. Below is a basic drawing of how the Motor, controller and batteries should be put together when you are using the 2 5S3P packs in series. You will see an Item labeled Medusa. That is just an optional Watt meter wired in at the times that you want to test your setup. The motor of course will hook into your ESC (electronic speed controller)

 

 

 

 

Wire length limitation:

To answer a question about wiring and how long a wire can be, I simply looked at my speed controller manual and this is what it says.

"The battery wiring has to be as short as possible; they do not have to be longer than 15 cm. For these reasons a current measurement has to be done only with a pliers amme- ter. Any measurement with an inserted ammeter (resistance) can cause destruction of the Speed Controller . The lengths of the engine power wires are not critical that much, but they also should be as short as possible. Long wires should be twisted because of an otherwise possible receiving disturbance."

I did not add any wire between the Motor and Speed controller. However I used about 6 inches worth of wire from the other end of the speed controller to the battery. Also I used what wire there was on the batteries and simply put connectors on them. I used the Astro Zero Loss connectors (PN 527) for my planes. A bit expensive but beautiful and light.

Also, use 13 gage wire which also comes pre wired in the Motor and controller

Watch the battery placement:

The batteries are now your fuel. Their placement in the model controls your CG and even a slight variation in where they are placed each time will effect your flight characteristics and trim. Try to mount them somewhere convenient because you should remove them to charge. It is safer and besides you want to put in a fresh pair to go flying again.

Some radio set-up differences to keep in mind:

On the radio settings, you must only reverse the servo direction for throttle channel and set the ATV from 0% (low end) to 100% (top end). Putting the ATV over 100% will not boost power. It may actually mess things up for you. I found this out in the beginning of last season.

The Speed controller must be set up according to the electric motor you are using. Instructions that come with the controller you use are usually good. You basically have the choice to configure 3 different parameters. 1.) Motor Break on/off 2.) Frequency. 3). Timing.

Motor Brake on/off

Turn the "brake off" is what we use for pattern F3A. By having the brake set on, it is my experience that you might run into trouble while idling the plane. I have had the motor cut out unexpectedly on the ground while on low idle with brake set on and the noise that the motor makes is not pleasant (with the Hacker motor). Not as bad with the Plettenberg. I have been corrected and recently been told that the brake works this way which is different than I once thought. The motor doesn't use battery power to brake. Braking actually just shorts out the motor windings and this creats the effect. A brake will only be as strong as a particular motor design will allow . If you have access to a motor try touching the wires together and turn the motor with your hand. You will sense resistance.

Frequency and Timing

These settings will depend on the motor being used. Check your instructions for the setting best for your motor.

After you figure out the settings required for your motor there is a "beep" menu that the speed controller cycles through where you choose the appropriate settings you need simply by waiting for the special beep tones you expect to hear and then select the setting by moving the throttle stick. This is a one-time process and is not difficult after you figure it out for the first time.

Note: Be very careful to use the 8 kHz Switching frequency and not more that 18 degrees Timing mode. I am using the Jetti Hacker controllers and the settings are not the same as what is available on the Shcultze controllers.

Setting the throttle curve:

Here is a step by step method I used to set up the throttle curve of the Plettenberg electric motor using the Hacker Jetti Master 90 controller, and Futaba 9WC2 radio.

1. Reverse your servo throw direction for the throttle using the Futaba radio.
2. Program the controller for No break, Timing mode 4, and Switching frequency Mode 2. The beep settings you should expect to hear are:

• 2 beeps (for No break)
• 5 times 4 beep tones (For timing mode 4)
• 5 times tone, beep... (Frequency mode 2)

1. On futaba radio, if you want to use the the throttle curve function, do the following steps:

• Activate the Throttle curve function by choosing from MODEL menu, "THR", Activate.
• Go to the Throttle curve adjustment screen by choosing from Condition Menu, "TCV"
• Use the 13 points to dial in your preferred throttle setting points.
• I use a knob to adjust my low end idle by assigning a knob in the "TCV" screen.
• While in "TCV", choose the "VOL" button which brings you to another screen. Choose your preferred knob and choose"PRE"

Note: Make sure that your ATV is set to 100% 100% and that your throttle trim is set to neutral!!

A brief description of how to turn on a motor and then go fly (using electric set-up)

1. Turn on transmitter. Put throttle to idle, dial back low idle knob to lowest setting.
2. Turn on airplane receiver and wait for the series of beeps.
3. My Hacker controller beeps 5 times before the motor is able to start. This is a safety feature of the speed controller.
4. After the 5 beeps use the low end dial and slowly turn knob until motor activates
5. Choose the desired low idle RPM. I usually know by the sound, but you could set it by the radio tachometer.
6. Put on your timer if you desire to keep track of flight time.
7. Throttle up and take off.

As a note: You will feel that the battery is near the end of charge and still in the safety zone if the plane doesn't have as much vertical pull. This is the signal to throttle back and land as soon as possible. The speed controller will automatically stop the motor anyway in safe time so that you don't damage your batteries.

In order not to be too hard on my batteries I don't fly more than 8-minute practice flights. This I find a disadvantage. I like longer training flights when working on a specific man oeuvre. I'm sure you would all agree that the extra couple of minutes would be nice.

That's all there is to it. Simple isn't it?

Is it safe to run the electric motor at full power for extended periods?

It is actually more efficient for an electric motor to run at full power. I use full power a lot of the time in my flights just because of my configuration last year. Don't worry about that. What you have to worry about however is heat and to ensure that you have sufficient cooling in your airplane. Maximum temperatures are included in the documentation of the motor and speed controller. Use of a heat detector gun is recommended and this way you can monitor you engine heat just after landing.

More importantly, a Wattmeter is a must. This detects excessive current draw that you are having in the motor, prop configuration. Also it can be an early warning system for something about to go wrong.

A wattmeter hooks inline between the batteries and controller and you just run as normal, it will output all the data in real time. If you have the Medusa Pro then you can plug it into a laptop and record your data and graph it for your records.

The Dangers of Heat to electric motors and usefulness of the Wattmeter: as described to me by Chad Northeast.

Field strength of magnets (what makes the motor work) is a function of temperature, the higher the temperature the lower the field strength, the lower the field strength the lower the efficiency, the lower the efficiency the higher the current draw....So, what the heck is that important for?

Well Neodymium magnets (Plettenberg motor magnets) basically de-magnetize at around 125 C, so say you plunk a huge prop on your motor (like a 22x12 on the Plett) the watt draw from the motor will be massive because the current is so high to turn that prop. Some of that draw is going into heat....get that motor up to 125C and boom the motor demagnetizes, draws a lots more current yet, fry's the controller and probably seriously injures your batteries. If you're lucky it won't catch on fire.

A Wattmeter is the only way to tell what your system is actually doing. You can determine how your batteries are holding up, even determine your maximum flight time from the data presented.

An IR temp gun and wattmeter are two invaluable tools to have in you're your electric setup. In a glow system if you damage an engine most likely it is something replaceable like a ring or piston...no biggie..... Compare it to if you damage an electric motor or controller, it goes in the garbage.

Thanks Chad, we get the point :)

I hope that this answers some questions as to what is involved in flying electric F3A. Please feel free to ask questions. If I don't know the answers right away then it might be something I should be looking into finding out about anyway.