How and why should we break-in our new helicopter engines? That is the most common question asked by everyone who buys a new engine. The responses to both of those questions are somewhat controversial, and everybody has their own method and reasoning for how and why. Just a few weeks ago, I had a hot and intense debate with a fellow RC heli pilot who happens to build full-size car engines for a living about this very topic. The conclusion that both of us came to was that a new engine needs the piston and ring to seal properly, and therefore you need to break in an engine. If you do not break in a new engine properly, you reduce its power and life.
What do I mean by sealing the piston and ring? Well, when you look at an engine sleeve with the naked eye, you see a smooth shiny surface. You see the same thing in the ring and piston, but if you ever look at these three components under a microscope you will see something completely different. You will see valleys, peaks, grooves and imperfections on the ring, piston, and sleeve. During the break-in process, oil will get in these grooves and valleys to allow the ring to glide over these areas as the piston and ring go up and down in the sleeve. While this is happening, the peaks and imperfections are being smoothed out in all three components. This is the goal of breaking in an engine: to create the largest possible surface area of contact between the ring and sleeve. So why do you say this is necessary? Well, the answer is simple. A properly sealed engine will produce maximum power with the least amount of fuel consumption. When the piston and ring have properly seated, they do not allow combustion gases to escape from the combustion chamber into the crankcase where that energy ends up going to waste. In addition to the previous statement, an improperly seated ring will allow too much fuel to get into the cylinder and the excess oil and fuel will be pushed out of the exhaust port, causing the engine to run improperly due to the fuel not burning completely. This, in my opinion, is one of the reasons why people have tuning issues with their engines.
The Basics
To break in an engine I usually fire up the heli and let it idle for one tank's worth of fuel. I keep it as rich as possible to allow for extra lubrication. The reason for this is while the ring grinds away any imperfections, I want the metal debris to be ejected into the exhaust port easily so that I do not have any unnecessary scarring of the sleeve which could reduce compression. The extra oil will also help the engine cool while it's sitting on the ground idling. Once the first tank is almost empty, I shut off the engine and let it cool. During the cooling phase I make sure the piston is at the bottom of the sleeve. This way when the ring cools, it can go back to its normal shape as there is less compression at the bottom of the sleeve compared to the top section. Tanks two through four are just hovered with the engine still running rich. After every tank I make sure the piston is at the bottom of the sleeve during cool off. During break-in, I also check the temp of the engine to make sure it isn't running abnormally hot. For tanks five and six, I lean out the engine just a bit and do some casual forward flying. Once this has been completed, I tune the engine to my liking and consider the engine to be properly broken in.
Step-By-Step Engine Break-In
Step 1: Install a new glow plug in the engine.
Step 2: Fuel the heli with your pump, but make sure to close the end of the fuel tubing leading to the engine with some fuel line clippers. You do this to keep the engine from flooding during the fueling process.
Step 3: As a general rule, you can start with these settings. Close all needle valves and open them back up by turning the high end needle counter clockwise by two full turns, and open the low end by 1 3/4 turns. If your engine features a mid-range needle, it should also be two turns out. This should be a good starting point, but make sure to consult the manual that comes with your engine for specifics. You will adjust this as needed later.
Step 4: Turn on the radio and heli, and make sure that the carb is in the fully closed position while the throttle stick is in the down position.
Step 5: Prime the engine by unclipping the fuel line clipper and turning the engine over briefly without the glow igniter plugged in.
Step 6: Hold the heli by the rotor
blades and put a foot on the skids. Connect the glow plug igniter and start the heli using your starter.
Step 7: Once it has been started, make sure the engine will idle on its own when the igniter is removed. Let it idle like this and use your temp gauge to monitor the temp of the engine. With the settings above, the engine should be relatively cold.
Strep 8: When the first tank is 90% empty, shut off the engine by pinching the fuel line leading to the carb and let the engine cool down. Make sure the piston is sitting towards the bottom of the sleeve during cool down.
Step 9: For the next 3 tanks I start the heli using the above procedures and I begin to hover the heli. If the heli dies when idling, I lean out the low end needle by turning it 1/8 of a turn clockwise.
Step 10: On the 5th tank I am ready to lean out the engine. I turn my low end needle in 1/8 of a turn at a time until I can pinch the fuel line for at least 7 seconds before the engine dies. On the high end, I lean it out enough so that I still see a nice smoke trail during hover.
Step 11: After the 6th tank, lean out the high end a bit more but keep the smoke trail visible. And then have fun!
Note: Some engine run hotter than others, some run best below 200�F while still others may get up to 260�F or more before they make power. Consult you manual for specifics.
CONCLUSION
I do this to all my engines. I have an O.S. 50 that I've had for almost 3 years; it was originally bought for my Hirobo Evo but now resides in my Raptor. It gets about 6 flights per weekend and the engine still runs great. I opened it up this past weekend just to look it over and all seems good. So if you take the time to break in your engine properly over the course of the first few tanks, it should give you long lasting flying enjoyment for years to come.
Engine Break-In
Tuning For Training
There's no doubt that the RC helicopter industry is one of the fastest growing segments of the radio-controlled hobby world. Not only has the overall quality of kits increased over the years, but prices for "entry level" helis have come down and ARF's (Almost Ready to Fly helicopters) have become a dominant fixture on the heli scene. All in all, it's a great time to get into the hobby.
One obstacle that helicopter newcomers must overcome is knowing whether they have a good setup. A helicopter can be tuned to be extremely sensitive and quick-responding to control inputs (ideal if you're an avid, aggressive 3D pilot), or it can be tuned to feel much more "dead" and deliberate on the controls (which is much better for the beginning pilot). Oftentimes, newcomers to the hobby don't have a clear understanding of how to tune a helicopter's control response, and don't have immediate access to an experienced pilot who can help them sort things out. Thankfully for you--the reader--you have RC Heli magazine!
This installment of Buddy Box will take a look at some of the basic adjustments a pilot can make to his or her helicopter in order to make it a more ideal tool for learning. Three separate categories will be covered: mechanical adjustments (meaning adjustments to the machine itself), software adjustments in the transmitter, and "accessories," meaning additional items that can be purchased for training.
MECHANICAL ADJUSTMENTS
Flybar and Paddles • Proper selection of paddles and flybar tuning will have one of the greatest effects on overall handling. In Issue 9 of RC Heli, we featured an article on the effects of paddle tuning. (This is a great excuse for you to purchase your subscription to RC Heli if you haven't done so already, or you can check our website and download the article.) For a beginning pilot, the name of the game is "stability," so the thicker and heavier the paddle, the better.
For machines like the Hirobo Evo 30/50, the stock paddles allow the pilot to adjust the weight via removable brass and lead inserts in the leading edges of the paddle. If your helicopter has adjustable weight paddles like this, it's best to leave all the weights in while learning to fly. For other helicopters that don't have adjustable weight paddles, the stock paddles are usually on the heavier end of the scale, and are suitable for training. Be aware, though, that some kits are offered with lighter, more aggressive paddles that may not be the best choice for someone just starting out. If this is the case, then a simple visit to a local hobby shop or favorite online retailer can help yield a more appropriate paddle selection. If in doubt about the paddles that were included with any given helicopter, information can be found from local flying buddies or a visit to any of the fine Internet forums available, like the one at www.rchelimag.com
For mini electric helicopters, a slightly different approach may be required. Since paddle selection for mini electrics can be a little more sparse than for larger machines, the use of flybar weights can be a valuable tool. As discussed in our Issue 9 article, moving the flybar weights out to the ends of the flybar makes the helicopter behave the same as if it had heavier paddles.
One advantage of using flybar weights is that it allows a change in the effective weight of the paddle/flybar system without buying any additional parts. Beginning pilots can start with the flybar weights all the way out, and as their skills progress, the weights can be moved in--which gives quicker control response. For this reason, lighter paddles in conjunction with flybar weights may be a viable option to heavier paddles.
Bell-Hiller Mix Ratio Adjustment • Not all helicopters have this capability, but on those that do, this is a very useful adjustment. Bell-Hiller mixing refers to the ratio of direct pitch input from the swashplate (Bell mixing) versus the amount of pitch control from the flybar (Hiller mixing). A pure Bell-type control system is one where the swashplate is directly connected to the main blade grips, thereby controlling the blade pitch entirely. This yields a highly maneuverable helicopter, but doesn't have as much of a stable feel. A pure Hiller control system is one where the swashplate controls the flybar, and the flybar controls the pitch of the main blades. This yields a more stable helicopter, but at the expense of a solid, direct control feel. By changing the ratio of Bell input vs. Hiller input, a helicopter can be fine-tuned to the pilot's desired control feel.
For a beginning pilot, a high Hiller ratio is often desired. Each helicopter model that offers this adjustability goes about it in a different way, so it's important to consult the owner's manual to see if this adjustment is available, and how to do it. Oftentimes, higher Hiller ratio settings will be referred to as the "stability" setting or the "training" setting. As stated earlier, not all helicopters have this particular kind of adjustability, so consult the owner's manual to see if your particular helicopter does.
Washout Arm Adjustment • This is another adjustment that not all helicopters have, but it's useful on those that do. One end of the washout arm connects to the flybar control lever. If this end of the washout arm has more than one place to mount the control ball, then moving the ball to the inside position (the one nearest the mainshaft) gives less leverage to the flybar control arms. As a result, the total amount of paddle deflection is reduced, which helps to slow down the helicopter's cyclic response.
Rotor Head Damping • Softer damping gives a helicopter a softer feel during hovering, which is ideal for a beginning pilot. Many ARF helicopters come standard with soft durometer dampers, and most manufacturers offer a variety of dampers in different durometer ratings. "Durometer" is a numerical reference to the relative hardness or softness of a damper; higher durometer dampers are harder, and lower durometer dampers are softer.
Some helicopters utilize shims between the blade grips and the head dampers to adjust the stiffness of the damping. When this is the case, removing shims will effectively soften the head damping. Check the owner's manual to see how your helicopter's damping is adjusted.
SOFTWARE ADJUSTMENTS
Exponential • This is an adjustment that changes how much the servo moves around the center portion of its travel, in relation to the stick input. By increasing the amount of exponential, the sensitivity of the control response around center stick is reduced, while still retaining full servo travel at the extremes. For a beginner, a modest amount of exponential on cyclic (aileron and elevator) will help the helicopter feel less twitchy during a hover, while still allowing enough travel for loops, rolls, and the like. A good place to start is with 10%-15% expo on cyclic. A word of caution: Using too much exponential (40%-50% or more) can cause the helicopter to feel almost "dead" around center stick, and then suddenly the control inputs will come in with a rush as the transmitter stick reaches maximum.
Each radio manufacturer is different in how they measure exponential. Some transmitters need a positive numerical value to decrease sensitivity around center stick, and some transmitters use a negative number for the same thing. Be sure to check which is needed for your particular brand of transmitter, since using the wrong value will cause the servos to move more around center stick instead of less, and this will cause the helicopter to feel very twitchy.
End Point Adjustment (EPA) or Auto Travel Volume (ATV) • These adjustments are essentially the same; the only distinction is the title a particular manufacturer uses (some manufacturers call it EPA, and others call it ATV). This adjustment limits the maximum
amount of servo rotation for a given stick input. Once a helicopter is fully assembled, EPA/ATV can be used to reduce the total amount of cyclic throw that a helicopter has--for example, from 7 degrees total cyclic pitch down to 5 degrees. Doing this will reduce the total amount of paddle deflection available, much like using the washout arm adjustment listed earlier.
A word of caution: Using too much EPA or ATV on cyclic can create a situation where the helicopter doesn't have enough control authority to adequately handle certain conditions. For example, a pilot could use EPA to reduce the paddle throw to only 2 degrees, which will make for a very docile helicopter, but at that low a setting, the helicopter may not have enough control authority to handle a strong gust of wind or an "emergency" situation.
Do not use EPA /ATV to tame a CCPM heli, instead use the percentage value in the swash menu.
EPA and ATV are used as "global" adjustments, which means that a change in EPA typically affects all flight modes. EPA can be used as a training aid, but it's best thought of as a way to limit total servo rotation to prevent binding up of control surfaces on the helicopter. What follows is an alternative to EPA.
Dual Rates • Think of dual rates as a sort of switchable EPA. Dual rates allow a pilot to set a lower amount of servo travel when the dual rate function is activated, but still retain full servo rotation when the switch is turned off. A common way to use dual rates would be to set a lower percentage (70%-80%) in Normal/Hover mode, and 100% in Idle-Up, which would effectively turn off the dual rates. In doing this, the pilot can have reduced sensitivity during their hovering, and full control authority during aerobatics.
The main thing to remember when using dual rates is that there is such a thing as "too much." If too low a percentage value is used for dual rates, a situation could arise where the helicopter doesn't have sufficient control power to overcome an adverse situation. Much like spices in a food dish, dual rates should be used sparingly.
One advantage of dual rates over exponential is that dual rates allow for a consistent, linear feel to the controls. Don't be afraid to experiment with dual rates and exponential to see which method you prefer.
ACCESSORIES
Training Gear • For a beginning pilot, one of the more "cheek clenching" times can be in the transition between flight and landing (or vice-versa). As the helicopter gets light on the skids, it's easy to have a tip-over accident. To address this, a pilot can use training gear, which in many cases is little more than whiffle balls on the ends of sticks that are attached to the skids. The goal with training gear is to give the helicopter a wider footprint on the ground, so that the chance of tip-over damage is reduced. As the pilot gains confidence in his flying abilities, the gear can be removed and flight can be continued without any additional adjustment to the helicopter.
Wood Blades • While not a "training tool" in the strictest sense, wood main blades do offer a couple of significant advantages for a beginning pilot. First, they're much less expensive than carbon fiber or fiberglass blades, so repair costs are minimized. Second, wood blades typically have a thicker airfoil than fiberglass or carbon fiber blades, resulting in more subdued flight characteristics that are an asset to the new pilot. Third, the lowered replacement costs of wood blades makes the prospect of flying a helicopter (and possibly crashing it) a much less intimidating prospect for a new pilot than having to repair a $2000 carbon fiber and aluminum masterpiece. Additionally, learning how to correctly balance a set of wood blades teaches skills that are useful in other aspects of helicopter ownership.
Plastic Vs. Aluminum Parts • It's tempting to spend the extra money on the aftermarket aluminum pieces for any given helicopter. However, for the new pilot, it's best to stick with the stock plastic pieces while learning to fly. They're less expensive to replace after the inevitable crash, and as with wood blades, the prospect of replacing inexpensive plastic parts is much less intimidating to the beginner.
Computer Flight Simulators • The importance of a good flight simulator cannot be overestimated. A flight sim is a great tool that helps a new pilot learn orientation skills without the worry of crashing a real helicopter. Most flight simulators today offer very realistic flight physics, and most either provide the owner with a dummy controller to use with the simulator, or offer adapter cords for use on the pilot's own transmitter. Either way, all that's required to get a crashed helicopter simulation back in the air is a simple press of the reset button.
There are several good simulators on the market these days. The most common ones in the U.S. are the RealFlight G3.5 simulator, Reflex XTR and FS One. There are also some free simulators available on the Internet for download, but be aware that most of these do not possess very realistic flight physics, so they might not be the best choice as a training tool. Save up the money and buy a well-known, commercially available simulator. You'll be glad you did. A good computer simulator pays for itself after just a couple of simulated crashes. [11]
CONCLUSION
As you can see, it's not necessary to accept a helicopter in the condition in which it arrives from the factory. With a little bit of tweaking, it's possible to set up nearly any helicopter to provide a much less intimidating experience for the new pilot. So don't be afraid to tinker!
Setup Throttle & Pitch Cuves
Throttle curves and pitch curves are some of the new terms you'll run into shortly after beginning the helicopter hobby. Short of a handful of RTF choppers, every model heli out there uses both throttle and pitch curves in its operation, and it's important to understand and be comfortable with the way they work. This topic was touched on in a previous issue, but we decided that it deserved another look. Don't worry, pitch and throttle curves will lose their mystery after a little practical use and experimentation.
What are These Curves?
Computer helicopter radios have many great features that give pilots a large number of options in their setup. Two of these features are the throttle and pitch curves. In most modern radios, these curves are presented as a graph, usually containing five to seven changeable points, with low to high on the X axis and 0 to 100% on the Y axis. The X axis represents the throttle/collective stick position (low being all the way down and high being all the way up). The Y axis represents the output to the servos or ESC. There are usually separate sets of both throttle and pitch curves for all flight modes. This means that for every flight mode you have enabled on your radio, you will need to set the curves for them.
The bottom line is this: The throttle and pitch curve menus allow the user to decide how much or how little throttle and pitch the heli will have at a given stick position. As a side note, after initial setup, establishing throttle and pitch curves is identical in both MPM and CCPM models.
Initial Mechanical and Radio Setup
Before sizing up the mechanical linkages and servo horns, it's important that the radio curves be in a neutral setting. To do this, set all curves as a straight line so that the low stick is at zero, the middle point is set to 50%, and the high stick is set to 100% (you can inhibit the other points and they will set themselves to line up with the others). By default, most radios will already have the curves set this way for a new model.
Next, go through the standard setup, getting the servo throws and links adjusted on the model so that the collective is zero degrees in the middle, and max pitch (most use 10 degrees or so) is the same for both full positive and full negative on the throttle stick. Do all this mechanically, leaving the servo end points at 100% wherever possible. Also, set the throttle servo so it goes from full closed to full open. Do not worry about these settings; even if you don't plan on using the full pitch or throttle range, they can be dialed out later using the curves and end points. Setting a heli up this way allows you to use the radio to change settings as you progress--without needing to change anything mechanically later on.
Your heli should now be at a point where full stick gives max pitch, and full throttle and low stick closes the throttle and gives full negative pitch. Next, we will look at the pitch curves, which are set the same way in both nitro and electric helis.
Pitch Curves
There are a few schools of thought on pitch curves as they pertain to the various flight modes. Most would agree that the Idle Up modes (often referred to as 3D modes) should leave the pitch curve at the linear 0-50-100% settings, going from full negative to full positive pitch, just as we set it up during the initial build above. Where the differences come in is with the normal and the throttle hold (autorotation) modes. For beginners, it may be best to set the normal mode collective so that low stick has very little negative pitch. A pitch range of 10 on top and -2 or -3 on the bottom works very well. This will help with gentle descents and landings, and will lessen the fall rate if the pilot panics and slams down the stick.
There are two standard methods employed to lessen the lower pitch range: using the pitch curves, or using the servo end points. It's best to use the pitch curves for this task. When you make drastic changes to the servo end points, the servo movements become non-linear and their resolution is changed. There is another huge benefit to using curves to make pitch changes instead of using end points or mechanical adjustments: Each flight mode can be changed independently of the other. If you use mechanical or end point changes, every flight mode will be affected by those changes. In other words, try to keep the servo throws as close to 100% on both sides as possible. However, there are times when the use of servo end points may be necessary for modifying pitch range, but the curve menus are there to make these changes, and can do so quite easily.
Setting Normal Mode Pitch Range:
1. Place a pitch gauge on one of the main blades and enter the pitch curve menu for the normal flight mode on the radio.
2. Bring the lowest curve point up from zero to about 35%, and check the low stick pitch with the gauge. If the pitch is too high (above -3 degrees or so), lower the percentage. If it's still below your target point, bring it up some more to get the low stick pitch to the -3 we are looking for.
3. You can leave the other points inhibited and the mid-point at 50% and the high at 100%. This will make it so that when you flip to Idle Up modes, the collective will stay in the same place as long as you are above mid-stick.
It's also simple to use the pitch curves to change the point in the stick travel where the heli will hover. Some pilots prefer to have their normal mode set up so that hovering takes place at mid-stick and with limited total pitch movement. To do this, you can change your middle curve point by raising its value until you get to about 6 degrees on the pitch gauge with the throttle stick in the center of its throw. Using the same method, you can lower the maximum pitch (full stick) to 8 or 9 degrees so that the line is as close to straight as possible. What this does is lessen the angle of the curve line, which lessens the amount of servo movement you get for a given stick movement. This is really nice for beginning pilots because the sticks are not as sensitive when set up this way. With a low of -3 degrees and a high of 8 degrees, hovering will be really docile and precise. Even if you slam the stick up or down in this mode, the heli will not change altitude too fast and you have more time to recover.
The pitch curve for throttle hold is set the same way as normal, except that you will want -4 or -5 degrees on the bottom and full pitch on the top. You need the negative degrees to get the rotor spinning nice and fast during an autorotation, and you will need all the positive pitch you can get to slow the descent and land at the bottom. Many people use the same pitch curves for both normal mode and throttle hold. In fact, some radios use the normal mode pitch curve for throttle hold as well.
Last, the other school of thought on the normal mode pitch curve is to leave it the same as the Idle Up modes; zero (FULL NEGATIVE PITCH) at the bottom, 50 in the middle (0 DEGREES PITCH), and 100 at the top (FULL POSITIVE PITCH), with all other points inhibited. This gives the heli more collective movement with the same stick input, so it is more sensitive to stick changes. But it does help your future flying greatly if you can learn to hover and land nice and stable using the same full collective range you will be using in aerobatic flight. I would recommend setting it up with the lowered pitch range first and trying that out for a while. If you then want a new challenge, try the full range. Again, the beauty of using pitch curves is that you decide how to set things up and it is all done with the radio. No changes need to be made to the heli itself after initial setup, and it only takes a pitch gauge and a few minutes.
Throttle Curves
Once you have mastered setting up pitch curves, throttle curves are a piece of cake. You will use the throttle curve to tell the ESC or throttle servo how much power to give the motor at a given stick level. Throttle hold mode usually does not have a throttle curve associated with it. Instead, you can set a flat line amount indicating where you want the throttle to go when it's in that mode (usually to motor off in electric and to idle in a nitro heli).
The other flight modes are set up differently depending on a number of factors, including whether the machine is electric or nitro, and if you are using a governor/limiter. The key ingredient is this: You generally want to maintain a constant rotor head speed no matter where the stick is positioned. Throttle curves are used to achieve this goal. The four common heli setups for throttle curves are electric non-governed, electric governed, nitro non-governed/governed, and nitro with a throttle limiter. You will need to fly the heli and have a tachometer or other way of measuring available head speed to get the throttle curves set correctly.
Electric: Non-Governed
In normal mode on an electric heli, start with zero as the lowest point - a spot where the ESC is turned off. As your pitch increases, you will need to add more and more throttle to maintain the desired head speed. Most normal mode throttle curves slope up from zero with a curve that flattens out as you get closer to full stick. The throttle curve will be pretty steep from zero stick to about one third stick. The 75% open throttle point will generally fall on the same part of the graph as your 0 degree pitch range does in the pitch curve menu (where this spot lies on your throttle curve depends on rather you are hovering at mid stick or at 1/2 stick). If you are not using full pitch in the normal mode, you will want the throttle curve to taper off below 100% as well to avoid over speeding the head.
For your Idle Up modes, use a simple V curve with 100% at the low and high ends and about 80% in the middle. This will give you full throttle at both ends of the stick for 3D flight and will lower the throttle slightly when at 0 degrees to stop any over speeding. You may find the need to adjust the middle curve point a few degrees to get a consistent RPM - again, use a tachometer to determine where the curves need to be set to. Please see the photos with each section to help clarify the meaning, like they say: "a picture is worth a thousand words."
Electric: Governed
In normal mode leave the lowest point at zero for start-up, but set the other points to an equal level, creating a flat line. Start with a 70 setting all the way across on the curve and see what kind of head speed that gives you. Raise or lower the points, leaving the first point at zero, until the desired normal mode head speed is obtained. For Idle Up modes on a governed electric helicopter the throttle curves are usually a flat line all the way across. No V curve is usually needed with the better-governed ESCs.
Nitro:
Non-Governed/Governed
Nitro helis are more complex with their throttle arrangements. In normal mode, you will start with zero as the lower point. As your pitch increases, you will need to add more and more throttle to maintain head speed. Most normal mode throttle curves slope up from zero with a gentle curve. The 50% throttle point will generally fall on the same part of the graph as your 5/6-degree pitch range in the pitch curve menu. If you are not using full pitch in the normal mode, you will want the throttle curve to taper off below 100% as well, to avoid overspeeding the head.
The Idle Up modes are set using a V curve, just like on electric helis. The exception is that instead of 80% being the middle point, most nitro helis start off with 50% as the middle point. A curve of 100-50-100 is a great starting place on a nitro heli's 3D flight modes.
Nitro: Throttle Limiter
A nitro with a throttle limiter could be set up the same as the example above. The normal mode is, in fact, set in the same way. But many will set the Idle Up modes to be 100% all the way across, letting the throttle limiter keep the heli from overspeeding while getting all the power they can out of the motor. If the throttle limiter fails, they can flip back to normal mode and land safely without overspeeding. If you notice some over speeding with this standard "V" curve, it may help to pull the intermediate points (those between the middle and ends) down in value. This will form more of a "U" shape instead of a "V". The only way to know how much or how little adjustment is needed is to get out there and test it in flight.
Conclusion
The topic of throttle and pitch curves can be a pretty complex subject. But their use becomes second nature with some practice and real-world use of the menus. To keep it simple, remember that the main goal of both of these curves is to keep the head speed constant at any given pitch range, and to deliver the amount of lift desired.
Throttle and pitch curves give the pilot complete control over how much pitch and how much head speed the rotor should deliver. They are powerful tools that allow dramatic changes to flight characteristics without making a single mechanical adjustment to the helicopter. With the information found in this article, you should have a decent starting point from which you can fine-tune these curves to get your heli flying exactly the way you want.
Changing Servo Gears And Cases
There are several reasons you might need to overhaul your servos. One of the major reasons is to repair the gears that stripped after a crash. This is especially true for plastic gears, although metal-geared servos strip out on occasion as well. Some crashes will cause the servo case to crack. Even excessive removal and installation of the servos will cause the mounting portion of the servo to break. The rigors of helicopter flight put a tremendous load on servos, which causes the servo gear trains to wear and get sloppy. That doesn't necessarily mean you have to replace the entire servo; a gear train swap is a much more cost-effective way to get your servos nice and tight again. Here's a simple step-by-step for you to use when it comes to tearing apart those electric workhorses and putting them back together again.
1) Remove the servo from your helicopter, then remove the servo horn.
2) Brush off the servo with a clean brush or rag to remove any dirt and debris that might be hanging around.
3) Remove the four screws on the bottom of the servo. These screws hold the entire servo together.
4) Remove the top case, being careful not to lose any gears that might be loose. The top gear that the servo horn attaches to may come out when you remove the top case. This is normal, since the bearing is usually pressed into the case. To remove the gear from the top case, apply light, downward pressure.
5) Using a digital camera, take a quick picture of the servo train just as it is. Make sure the shot is clear so that you can see all the gears. A side angle works best. You might need this for future reference, should you get stuck during reassembly.
6) Remove the gears one at a time. Starting from the top gear working down, separate each gear and place it on a labeled piece of paper in the same order that you're removing them. (See side note.) Do not remove the metal gear that's pressed on to the servo's motor, as it does not come with a new gear set.
7) Next, prep the new gears by applying white lithium grease. This grease will protect the gears and allow them to operate smoothly. Use sparingly. If rebuilding multiple servos for a CCPM setup, be sure the amount of grease used is similar among all three.
8) Match the new gears to the old ones, and install them in the reverse order in which you removed them. The gear sheet will help you along the way.
9) If the case is cracked, this is the time to replace it. Most servos use a single or double ball bearing on the output shaft, which leads us to the next step.
10) Remove the old bearing(s) in the old case and press them into the new case. (The bearing(s) might be stuck to the top gear; if so, remove them and press them onto the new gear.)
11) Inspect the wire leads, making sure that there's no fraying or loose solder joints. If things look suspect, get out the soldering iron and repair.
12) Install the case bottom. Be sure that the servo leads are not being pinched, and also make certain that they're extruding out of the correct point on the case. Then insert and tighten the four screws.
Conclusion
If you're the type who's intimidated by small moving parts and would rather replace the whole unit, repairing your servos will save you tons of money. This How-To was written to help you overcome that fear and show you how easy it can be. The next time you experience a crash or a servo gear wears out, feel free to dig into that servo and replace those gears.
