So you wanna try ELECTRIC !!!
OK, let's pass on some of the information that I, as a complete newcomer to this phase of RC modeling, have managed to accrue. 1st of all, I have been in RC since approximately 1979 (AMA 31280). I just returned to the fold after a 14 year absence only to discover that 75% of what I knew was now OBSOLETE. After one SHORT season of trying 3D (magic Extra), and a LONG winter, I decided to give electric a shot, hoping that I could recoup some of my flying skills before the field dried up enough to fly the REAL models.
WHAT MODEL ?
POWER PLANTS
BATTERIES
SPEED CONTROLS
RECEIVERS
SERVOS
MATERIALS
ADHESIVES
CARBON FIBER
PROPELLERS
POWER CALCULATIONS
CLOSING
Here, therefore, is what I have learned, as well as some examples of what and what NOT to do. I am NOT an expert, just an amateur who tries to do things as cheaply as possible.
As a EP (electric power) newbie, do NOT go out and spend big bucks on a model that I can guarantee that you will repeatedly crash while learning this new phase of RC. Instead, join the ranks of the 'Foamy Flyers', those who have discovered that these things are EASY & FUN to build, as well as being CHEAP. Those wonderful folks at Dow Chemical invented something called 'BlueCor', an EPP (Expanded PolyPropylene) material designed to use as underlayment under the new composite wood floors. Available at Lowes for Approx. $30, you will get 30 2X4 sheets of this stuff, enough to build AT LEAST 30 of these small scale 'Foamys'. Obviously light blue in color (great against a blue sky), it has a 'skin' on both sides, one of which is COVERED with black printing. Use a good alcohol from 'Home Depot' (S-L-X) with a BUNCH of paper towels to clean it off. Unfortunately, some of the 'imprints' will still be left in the BlueCor, but not TERRIBLY noticeable (put it on the bottom side). By the way, it transfers THROUGH the towels unto your hands.
One of the BEST sites to get free plans for EXCELLENT flying models is:
The two favorites are the 30" span 'Ultimate Bipe' (GREAT flyer), as well as the 32" '3DX Mini' (fast 'pattern' type). As more of these sites are found, I'll add them in the 'attachments' to this series. There is also a 40" version of the Bipe that Joey Acosta and I are both flying as well. The 3DX is NOT the ideal choice for 1st model, try either of the Bipes.
Whole new world here from what us 'Glo Flyers' are used to! There are MANY sizes and combinations of motors and gearboxes out there, and I will tell you what my PERSONAL choices are, and I GUARANTEE that everyone else will probably disagree.
First of all, however, a reminder! Large diameter/low pitch props are for slow flying, 3D type aircraft, whereas the smaller diameter/hi pitch props are more for SPEED.
Normal (brushed) motor - - -
These are the electric motors that everyone is used to, a permanent magnet outer 'field', with a rotating rotor' (duh) that is either attached to the propeller (direct), or to a 'gearbox' with many ratios available. The gearbox allows the relatively high speed/low torque motor to drive larger props at lower speeds. While there are some 'exotic' versions of these motors around that utilize 'hall effect sensors' to 'commutate' the rotor, the most common motors utilize 'brushes' that transfer the current to the rotor. Now, you KNOW that these thing create 'sparks', and 'sparks' create INTERFERENCE to radios. While the use of capacitors can help to reduce this effect, be aware that the problem DOES exist, and care must be taken. GOOD motors (read EXPENSIVE) utilize a 'carbon' brush against a copper commutator, while the 'cheapies' use a simple 'spring loaded' piece of wire. This combination of 'sparking' (heat), as well as mechanical wear, cause these motors to have a finite life span. They operate at lower voltages, 4.8 to typically 7.2 (based on NiCad/NiMh chemistry). BUT THEY ARE INEXPENSIVE). When you buy a GWS 350C gearbox/motor with 'D' gearing, it WILL work for a 'park flyer', but DON'T expect this combo to drive a 3D model. When it doesn't, you may say to yourself: "Self, what if I put a BIGGER battery on it, say 11-14 volts". The answer is EASY, you will have LOTS of power, and a VERY short motor lifespan. Alternatively, you can change to a TOTALLY DIFFERENT style of motor, and then get the performance you wanted in the FIRST place.
Newer technology 'Brushless' motor - - -
As stated, the LATEST technology utilizes a completely different method of transforming ELECTRIC power to MECHANICAL power. A 'brushless' motor usually LOOKS the same, but internally it's a whole new world. Instead of a mechanical arrangement to transfer the current to the rotating portion of the motor, the ;rotor' is a collection of permanent magnets, and the outer 'field' winding is actually three (3) separate winding, controlled by a 'multiphase' motor controller. Each of the 3 winding is activated sequentially, creating a 'rotating field' that the magnetic 'rotor' tries to keep up with. The faster the 'fields' rotate, so goes the 'rotor, and therefore the propeller. MAJOR advantages to this technology are:
The higher efficiency means longer flight times, as well as less heat in the whole system. There are basically 2 type of brushless motors, the 'inrunner' (picture #1, rotor INSIDE a 'can', like a conventional motor), as well as an 'outrunner', the magnets are in a 'bell' housing, and rotate on the OUTSIDE of the motor, Picture #2. The 'inrunner' type is great for updating the 'gearbox' arrangement (the power you wanted). The 'outrunner' style is ideal for 'direct drive' applications. BOTH styles offer FANTASTIC improvements over the 'brushed' type. The 'outrunner' style is sometimes referred to as CD-ROM motors, as these were the first application of this technology, and indeed have been removed from computer CD-ROM drives and used in EP flyers. You will find MANY articles on 'rewinding' these motors. Probably the BIGGEST disadvantage is that no two look alike, as every manufacturer has their own version. Additionally, they have NOWHERE NEAR the power capability of units designed for RC.
We're ALL used to the 'old standby' Nickel Cadmium (NiCad) batteries, and they are totally useful in EP applications. In general, however, they are being supplanted by the Nickel Metal Hydride (NiMh) batteries, which offer higher power densities (more available power per given weight). For all intents and purposes, voltages are the same, a 4 cell pack is 4.8 volts.
Note: A 'cell' is the minimum item capable of storing electrical power, a collection of 'cells' is called a 'battery'. A 4 cell battery is therefore a collection of 4 'cells', approx. 1.2 volts each.
The 'latest and greatest' technology is 'Lithium Polymer' (LiPo), and is what has REALLY made EP flight what it is today. A single 'cell' is rated at 3.7 volts, and may be combined with other cells to make packs of 7.4 volts, 11.1 volts, etc.. In addition, much higher capacity 'packs' can be made by combining them in series (additive voltage) as well as 'parallel' (additive current). However, the absolute BEST part is the WEIGHT factor, approximately ONE HALF the weight of NiMh batteries. Refer to the following diagram for the effects of combining these cells in series and parallel combinations. I have also included the 'shorthand' notation for these combinations. Like NiMh/NiCad, many different 'capacities' are available, but DO NOT mix and match them, stay with one size per pack.
NOW FOR THE BAD NEWS! In the 'old' days, overcharging or over discharging would ultimately lead to an early demise for the batteries (and usually for the plane they were used in). LiPo cells MUST be charged ONLY with a charger that automatically 'cuts off' when the pack is charged, and they must NEVER be discharged below 2.5-3 volts per cell. When a LiPo heats, it can easily 'burst' and, since the chemicals used burst into FLAMES when exposed to oxygen, GUESS WHAT. This can also happen when the 'crash' causes the cells to rupture. As if 'rekitting' wasn't enough!
DO NOT SHORT OUT THE OUTPUT LEADS !!!!!
Occasionally (but not often), manufacturers agree on something, and most have agreed that a way of measuring each individual cell for voltage is a good idea. Almost all commercial LiPo packs have a secondary connector with leads that allow testing/charging of EACH CELL INDIVIDUALLY. Most chargers available today charge in the normal way, that is all cells at once, using the 'Power' connector. Eventually, as prices continue to come down, you MAY see chargers that utilize these advance test/charge features. This figure shows the most common technique:
There are a NUMBER of reputable manufacturers out there, so the battery pack you need shouldn't be a problem. You can also purchase individual cells, and make up your own combinations. One oddity you should be aware of is that a special solder/flux combination is needed, as the tabs on the individual cells are made from aluminum.
CAUTIONS:
NEVER charge these LiPo packs unattended, 'cause fire is a nasty thing. Some people use discarded pressure cookers to contain them, others a metal pan on cement. Yeah, the charger is supposed to control everything, but 'S..T Happens'.
Since there is no throttle on an electric motor, we need some sort of speed control. They are referred to as 'Electronic Speed Controls' (ESC's). Since the motors come in two flavors, so do the ESC's, both 'brushed' and 'brushless'. THEY ARE NOT INTERCHANGEABLE. The brushed version has two output wires, plus a conventional servo connector and battery leads. The brushless has a third motor lead. MOST, but not ALL, have a built-in 'Battery Eliminator Circuit' (BEC) that will supply power to your receiver and servos, ONLY enough for the 'micro' style, 3-4 servos. So you DON"T need a second battery pack.
Both styles (usually) also have 'low battery' capability, such that when a 'cutoff' voltage is reached, power to the motor is shut off, but the receiver and servos continue to work. If this feature is NOT available, an 'add-on' circuit board with adjustable cutoff can be added. This may also be required if you are using LiPo packs with a controller designed for a small NiCd/NiMh pack (different voltages, LiPo CRITICAL).
When I first got started, I was 'thinkin cheap', so I seriously considered a GWS single-conversion receiver. DON'T DO IT, unless you can guarantee that you will NEVER fly with ANYBODY ELSE, or in any situation where you MIGHT get interference from someplace. These single-conversion receivers DO NOT have the signal rejection capability of the NORMAL RC unit. Hitec offers a model 555 that is EXCELLENT, and is low weight. Removing the case save additional weight. There are others as well, just look at the 'wish-books'.
Damn, ANOTHER expense! I can't emphasize ENOUGH the importance of extra weight in these aircraft. A normal or even older 'mini' won't cut it, you HAVE to go for the low-weight micros. All manufacturers offer individual micro servos, as well as complete 'flight packs'. Do NOT get the battery, as it's NOT needed (see BEC, above). Also, look around on the internet, as some good buys are available out there.
As mentioned WAY earlier, start cheaply using the 'BlueCor' material. Later, you can adapt whatever designs you like best to a material called 'Depron'. Still an expanded polypropylene propylene material, its available in multiple colors and thicknesses. It's definitely much 'prettier' than BlueCor. There is a similar item to BlueCor available at Home Depot, pink in color, also by Dow, but doesn't have the 'skin', and is not as good.
You can experiment also with Expanded Polystyrene Styrene (EPS), you know it by its use in picnic coolers and foam wings.
Mini control horns are available, but Nylon 'Ty-Raps' also work well, just a little more work. Mini 'snap-links' as well.
Visit 'Staples' for sticky back Velcro, hang ALL your electronics (except servos) with these.
No HERE's an area subject to personal choice.
EPOXY - the old standby, works great, 5 minute is fine.
'FOAM SAFE' CA - Note the 'Safe' part, as conventional CA eats the foam IMMEDIATELY. Good for 'quickie' repairs, and items you don't want to hold in place for 5 minutes.
Disadvantages:
VERY slow to cure, almost ALWAYS paired with accelerator.
VERY brittle, likely to break loose under shock conditions.
GORILLA GLUE (polyethylene) - Excellent glue, if you're willing to wait 12-24 hours. Also available from 'Elmers'. Shelf life (like CA) is limited once opened, so buy the small bottles. IT FOAMS/EXPANDS AS IT CURES, so plan ahead.
LO-TEMP HOT GLUE - My personal favorite! PLEASE notice the 'lo-temp' portion of the label. A conventional glue gun is TOO HOT. You can buy the lo-temp gun and glue at almost any hobby store, I got mine at A.C Moore. Slow enough to allow applying a two foot strip, and then placing it. GREAT for quick repairs and 'filling-in' as well. It's all I use except for control horns, where I prefer the CA.
The EPP/EPS savior! Both EPS and EPP are NOT the most rigid materials in the world, so some support is usually needed in both the wings and fuselage areas. Available in a variety of shapes, diameters, and lengths. NOT CHEAP, but amazingly strong.. Some caution IS advised, however. These rods/tubes are made from 'strands' of the carbon fiber material, held together with typically a resin or epoxy binder. If tiny strands break off, and become embedded in your skin, they are a B...H to find and remove. PAINFUL as well.
Not as simple as before, you're faced with a whole new array of diameters and pitches. 2 major manufacturers, your choice, but I advise checking with your dealer as well as those experienced with EP. Even MORE difficult is matching the propeller to your power plant and battery combination, as WELL as the type of flying you want to do.
OK, now it starts to get TOUGH!
I'm going to continue this discussion using LiPo batteries and brushless motors as examples. NiCad/NiMh share some attributes, but NOT ALL.
Electric power has certain rules that you MUST understand in order to avoid blowing (expensive) stuff up.
BATTERIES
LiPo packs are rated in Milliampere Hours (mah). A pack rated at 1500 mah is THEORETICALLY good enough to deliver a constant current of 1500 ma (1.5 amperes) for a period of 1 hour. A new pack, properly charged, probably WILL do this. In actuality, while flying, this same pack may be asked to deliver anywhere from 200 ma (motor off, no servo movement), to 15+ amperes (full speed, servos moving against an air load). LiPo cells are TYPICALLY rated at 10C discharge rate (10 times the rated mah figure). NOT true for all packs, check the manufacturers rating. As the technology develops, these numbers will increase, I've already seen advertisements for 15C rated packs. Unlike the NiCad/NiMh cells, LiPo's can be charged in 1 HOUR at their rated mah specification. Expect about 10-20% extra (6-12 minutes), and you should be 'good to go'. As mentioned earlier, series/parallel connections can give you a multitude of mah/voltage combinations.
ESC's
ALL of them have a maximum voltage rating, as well as a maximum current rating. A thing called 'Ohms Law' comes into play when using these devices. EVERY item in the path between the battery and the motor windings has a finite 'resistance' to passing current. Current passing through this 'resistance' causes heat. Heat melts things and burns out components. SO, pay attention to these maximum ratings. All ESC's have a 'typical' and 'max' rating. Typical rating can be translated to be 'continuous' conditions, and max is usually given associated with a time duration. Exceeding these rating is NOT a good idea. Normal flying, especially 3D, encounters both conditions. A saving feature on all quality ESC's is 'thermal shutdown' (self-explanatory), as well as 'current limiting'. Extending this concept of 'resistance', heat wastes power, diverting it from it's primary purpose of turning the propeller. You can minimize some of this by the following:
- Keep all power leads as short as possible
- Use quality connectors (as large as possible) for battery/motor connections
- Use high quality wire (large number of strand, low gauge number) for battery/motor connections
MOTORS
My first motor was a brushless outrunner from an outfit called
It's two guys in Arizona who buy quality components from ANOTHER outfit called
and custom-wind any motor you want. I bought a standard single stator unit with 17 turns on each stator leg, and a 'firewall' mount for $35. I'm more than pleased, and have just ordered a double-stator unit, same windings, for $45 (much more thrust). The first one gave me MORE than enough power for the 'Ultimate Bipe' (small version), as well as the 3DX Mini. The bigger one is for the large bipe.
'gobrushless.com' will sell individual components for all types of outrunners, and also have excellent tutorials on how to wind them yourself. If you are 'all thumbs', or suffer from some arthritis (me), let someone else do the work. I am extremely impressed with the quality of all their parts, as I haven't bent a shaft YET, and I've had some good nose-first landings.
MANY manufacturers offer outrunners in ALL sizes. Wanna convert your .60 size pattern ship to EP, go ahead, the motors are available. The problem is that there is, as yet, no simple way to compare these guys, due to the many variations in batteries/controllers/props and flying style. 'Glo' was easy, certain props worked well on certain sizes engines. They are beginning to specify things a LITTLE better, such as charts that tell you to expect 'X thrust with 3S LiPo and a 8X3.9 prop'. However, it may be specified by manufacturer 'Y' as 'X thrust with 6 NiMh cells and an 8040 propeller'. AGAIN, talk to someone knowledgeable who has possibly tried the combination you're looking at. Lets be honest, folks, where would we be without the RC Hobby shop owners. Alternatively, the 'web' is an excellent source of data, why not start at
http://www.rcuniverse.com
http://www.ezonemag.com/and spend several hours looking at their multiple threads on EP.
Some of the best distributor sites are
http://www.towerhobbies.com
http://www.hobby-lobby.com/
http://www.hobbypeople.net/For the time being, I'll leave you with this gem of info from a friend, "for 3D flying, go with 100 watts per pound of aircraft". Now what the hell does THAT mean?
'Watts' are units of power used in electrical measurements. Simply put, 'watts' are the result of multiplying the applied voltage to a circuit by the amount of current flowing in that circuit.
If you are flying full-throttle (3D hover), with a battery delivering 11.1 volts, and you are drawing 10 amps of current, the 'watts' are equal to 110 (11.1 X 10). If your airplane weight is 1 pound, you don't have much power left for any pull-out maneuver (10%). If you can increase the current (more throttle or more cells) to 20 amps, you will deliver 220 watts to the motor, and have approximately a 2:1 power/weight ratio.
A caveat, can the motor/battery/ESC HANDLE 220 watts? Check the specs, and buy/fly accordingly.
I hope this has been of some help to my fellow 'newbies', and I would appreciate ANY feedback you may care to offer. I hope to have input from other authors, and to add to this data as I discover sources. I'll probably open a separate section of the web site for this purpose, so 'stay tuned' for new stuff.
Bill Capes, fellow flyer and WebMaster
