What is in the newsletter this month? Muffler Pressure Problem Charging and Cycling Club Member Spotlight Servo Drivers / Testers Servo Centering Recent E-mail Amps or Volts New Radio Impound at Eastaboga Field New Frequency Board at TRCC Field Ball Bearing Noise (Electrical Not Mechanical) Free Postage Stamps

Muffler Pressure By Jerry McCuistion      I was having engine trouble with my chopper so I decided to do some experimenting with muffler pressure. I hooked up a home made manometer and checked the pressure at idle and while hovering. Since my hose wasn't very long I couldn't check full power except for a couple of quick punches. Idle was .5" of water, hover was 2 5/8" of water and with a quick stab at full throttle it didn't change from hover which is around half stick.      Due to the location of the pressure fittings I thought it might have zero pressure or less at some point but that wasn't the case. I got some of the one way valves and am trying one on it at this time. I only got one partial flight on it due to my transmitter battery going bad but it was running ok when I had to quit flying. I will see how it runs when I get my new battery.

Jerry it does sound like you are having pressure problems. The .5 inches of water translates to  .018 psi, which is almost nothing, but this is normal for our engines at an idle speed. Most engines idle with a pressure in the range of .015 to 02 psi. The 2 5/8 inch translates to .091 psi or about .1 psi. I would think that at this speed the pressure on your fuel tank should be more in the range of .6 to .8 psi. Have you removed the baffle from the muffler? If so this could account for the lower pressure readings. I know some modelers will remove the baffle trying to get more rmp from the engine, but at the same time they are lowering the pressure to their fuel tank. Let us know your outcome Jerry. James Goss

The club would like to thank Richard and Loren for fixing the tin on the east end of the shed. The wind had just about pulled all the nails out of it. A new shed is in the making, it will be about 36 feet long and 18 feet wide, all metal.

Jerry wants to remind all club members that the Anniston R/C Club  still has some club hats for sale. So why not get you an extra hat or two.

Charging and Cycling  by Bill Baxter  Hobby Services Manager Some question that come up very often are:  “How do I charge my NiCd battery packs”, and, “Should NiCd batteries be cycled, and how often should they be cycled?” Charging a pack is usually a simple affair.  Attach the charger that came with your R/C system and charge the packs for 12-15 hours.  This will usually guarantee a full charge on the normal 550-600 milliAmp-Hour battery packs that come with most systems.  With larger battery packs, this isn't enough. Charging a battery pack is basically “loading” it with electrical energy, called “Charge”. Charge is measured in Amp-Hours (AH), or milliamp-Hours (mAH).  An Amp-Hour tells you how many amps you can draw from a battery pack for how long.  For example, a 1 AH battery pack will last one hour if you draw one Amp of current from it.  If you draw two Amps, it will last one-half hour.  If you draw one-half Amp, it will last two hours.  And so on. A one AH battery pack is the same as a 1,000 milliAmp-Hour (mAH) battery pack.  We've just adjusted our units to handle battery packs smaller than 1 Amp.  The same formula holds, though.  A 500 mAH battery pack will last one hour if you draw 500 mA from it.  Draw 250 mA, and the pack will last two hours.  You see how it works. Charging is very similar to discharging.  You put current into the battery pack instead of drawing current out of it.  Unfortunately, you have to put more into the pack to fully-charge it than its capacity because there are losses due to inefficiencies that are part of the nature of the cell.  The formula for charging is usually expressed as a fraction of the capacity of the battery pack, so you have C/X=Z.  C is the capacity of the battery pack, X is the basic charge time, and Z is the charge rate, so a 600mAH battery pack charged at 1/10 of its capacity gives us:  600/10=60.  A charge rate of 60 mA. Unfortunately, the charge time in the formula isn't exact.  Because of electrical inefficiencies, you'll need to charge your 600 mAH battery pack at 60 mA for about 15 hours to get a full charge. If you have a more sophisticated charger that uses delta peak detection, you can charge at higher rates.  Usually setting the charge rate as high as C/C to give a one-hour charge is about as high as you want to go.  Higher charge rates can cause serious heat problems, which will damage the battery pack. Deliberately discharging your pack is discouraged by almost all experts on NiCd battery packs because it's too easy to over-discharge them.  A discharge analyzer is designed to stop the discharge before this happens. Good analyzers will discharge the pack to between 0.9V and 1.1V per cell. Any lower, and you risk damaging the pack. Discharge analysis is only really needed no more than once per month or so. Any more times, and you're just adding to the discharge cycles of your pack and reducing the life somewhat. Start out with a fully-charged cell and discharge it on the analyzer.  Take the reading.  It should be within 10%-15% of the pack's rated capacity. Charge the pack and repeat the discharge.  You should get two successive readings that are fairly close.  This will give you a good idea of how good your pack is. Sometimes, the capacity will increase as you repeat the charge-discharge cycles.  As long as the capacity increases, keep cycling.  You should eventually get two successive readings that are reasonably close.  This is the capacity of your pack.  The pack needed some “exercising” to get it going. “Memory” effects are real, but “memory” is not the correct term.  What happens is that an NiCd pack that's been overcharged will wind up with an undervoltage condition.  This undervoltage will cause the equipment to quit working early, as the voltage level drops sooner than expected.  A good discharging with proper charging will cure the problem. At all times, if you don't trust your battery pack, don't use it.  If you're not sure what the discharge results are, don't use it.  You're always better off buying fresh battery packs you can trust than using packs you have questions about.  Remember, a good battery pack is the life of your system.

Club Member Spotlight      Here is Dr. Larry Barksdale with another one of his beautiful airplanes. This is a Bridi “Dirty Birdy” all balsa pattern plane with an os .91 engine. This is not an ARF kit; it is built up balsa and finished all the way by Larry.  Larry has been in the R/C hobby for more years than I can count and has built some of the most beautiful planes you can find at any flying field. Larry is mainly interested in pattern flying and has become very proficient in this area. Larry has been a member of TRCC for many years and is a good supporter of the club. Larry always takes the time to build his planes the way they should be built. His detail work is excellent and his graphics really stand out when his planes are in the air. Larry has the kind of planes that I would be proud to call my own. Keep up the good work Larry.

Servo Drivers / Testers By James Goss      In the past I have built several servo drivers that would operate or drive a servo throughout it range of travel. I used these devices to halfway check for a bad servo. I say halfway because they would only move the servo as I moved the pot knob on the driver. The drivers on the market today are much better designed than mine and have more features that qualify them to be called a servo tester. But up until now I didn't really see a need for an elaborate servo driver I only used mine every now and again. I purchased one at the Perry show this year for around $39 when I saw it in operation in a demo that the designer was putting on. There are several on these servo drivers on the market today and they go by many different names such as servo exciter, servo exerciser, and so on, but they all do about the same thing.      The one I bought is called a servoxciter and is operated with a common 9-volt transistor battery. It has two servo plug connectors, one for Futaba and HiTec and the other is for Airtronics. The unit is a handheld device that will accurately produce the required signal to drive most major brand servos. It drives the servo through its travel range in 256 discrete steps, and this assures that it doesn't miss a bad spot. To operate the servo through its range simply rotate the control knob and the servo will follow. It also has an automatic sweeping mode that will operate the servo through its range at two pre-selected speeds with a slow and high rate. This allows you to view the servo's operation for any length of time you like without turning the control knob. If you hold the servo in your hand while testing it in the auto mode you can feel a bad set of gear teeth as well as see it.     When at the field you can check your servos and make adjustments to their travel range without turning on your radio. But what I really like the most about this device is that it will locate the servo's electrical center for you without having your receiver or radio transmitter turned on. When you start to install the servos in a new installation you know how aggravating it is sometimes to have to rig all this equipment up just to be able to install a push rod. With this device all you do is plug in the servo and adjust the knob until the bar graph shows you the electrical center, quick and simple. Just this feature alone will save me a lot of time in a servo installation. I have already used this device many times since I got it and it proves itself each time I use it. It is well worth the small price and I would recommend it to all modelers that are serious about this great hobby of ours. Check it out at http://www.vexacontrol.com and see for yourself.

Servo Centering By James Goss      Have you ever had a servo such as an aileron or elevator that would not respond as fast as it normally does when compared to the other servos on the plane? I use the aileron as an example because when you are using two aileron servos it is easy to see the difference between the two servos when one is not performing just right. When you release the control stick one aileron centers, but the other one might take its time to return to center. When it does make it to neutral position it keeps on going and stops off center. Each time you operate the stick you may get a different action by the servo, a random response. And then at times the servo may not move at all when the stick is moved. You stop and think for a while because this is really puzzling, what in the world is going on? It's like the servo has a mind of its own and it doesn't want to cooperate with you. How do you troubleshoot something like this?      I have seen this happen many times over the years and I have had several of my own servos to go through this “Adolescent Stage” I call it. There have been many servos thrown away because it appears to indeed be a defective servo. Now don't get me wrong, a servo with internal defects can and will act this way. In most cases it will not be the servo that is at fault, instead it is something much simpler to deal with. Nine times out of ten it is going to be due to added resistance in the wiring between the receiver and the servo. This is more likely to happen with the ailerons because you normally have an extension wire from the receiver to servo. Of course on larger planes you will be using extension cables elsewhere as well so it is even more likely to happen.       If we were able to have a direct wire from the receiver to the servo that was soldered at both ends, this would be ideal. Instead we have to use plug-in extension cables and most of the time they work great. The direct wire would have the least resistance possible, so when plugs are added the overall resistance will be increased. If we have a bad connection at one of the plugs the resistance will become large enough to hamper or impede the signal current if the resistance happens to be in the signal line (white) on Futaba equipment. If in the red line (the positive power supply line) the motor will begin to slow down and also the logic amplifiers may become erratic. Of course the black wire (ground) will alter both the signal and the power supply current because it is common to both.      These bad connections are likely to happen on days when we have drastic temperature changes, but it is not limited to these days only. This is due to the metallic wire expanding and contracting and over a period of time the resistance will build up and become a problem. Also humid days may entice corrosion to occur and with that comes more resistance at the pin connections. This is another good reason to store your planes in a dry storage place. To solve this problem of added resistance in your servo cables may only require you to unplug and reconnect the male and female plugs. Do this several times at both ends of the extension wires and your problem has a good chance of being repaired. At least this is a good temporary field repair that will allow you to get in some flying time. Repeating the plug-in process over and over will allow the pins in the plugs to rub each other and clean themselves. You can also use electronic contact spray cleaner to help remove the corrosion. If you get the cable fixed chances are that in the long run the problem will return.      Of course you don't want to take any chances with your really nice planes. Even if you use the above process and everything seems to be working fine on the ground you may not want to chance it in the air. While in the air the plane goes through a lot of vibrations and turbulence that might reactivate the initial condition. To avoid this you might want to replace the extension with a new cable.

Recent E-mail #1      Hi, if you wouldn't mind I would like to get some more info on the disk plane. From your post I can't come up with the height top to bottom on the fuse, you said it was 3" wide and the measurements for the airfoil were from the bottom. I also would like to know where to buy the coraplast. Is there a site to download drawings or plans? I thought this plane looked like a blast to fly. Thanks for your time.             Jeff LaSalle Hello Jeff,      Glad to see you are interested in the disk plane. If you will go to my web site at: http://nav.to/jgosscacc and click on the “Cow Patty News”, this is a newsletter I write, and look under April 2002 edition, you will find an article on my disk plane. If it doesn't answer all your questions just let me know, I will be more than happy to help you. Jeff, I have found a plane that is even more fun to fly than the disk plane and is a lot faster to build. I call mine the “Postage Stamp” others call it a Pizza Box Plane. I have a write up on this plane in the May or June newsletter I forget which. This is without a doubt the best hovering plane you can build and only cost about $5 to build, this is without hardware of course.  Please build this plane when you have the time and you will see what I am talking about. Good luck! James

#2 Hi! I read one of your articles about Monokote/ultracote and I grew curious in knowing if you'd have an article on COVERING techniques. You see, I'll be covering my first plane soon, and despite the advices of seeking for help, I know I have some "hands skills", hehe...so I'll give it a try, it would make me very happy if I could decently finish my first plane (actually is the fourth, all other three, built 15 yeas ago were painted by then, after that "Japanese paper" with dope...) after it is nicely framed and sanded. I am particularly interested in the "finishing" part of covering; where to cut, where to finish ends, where to "hide" the edges, and so on. So, if you kindly have any information about covering that you could share, I would appreciate! Thanks, Jeff Brazil Hello Jeff, How are things down in Brazil? If you go to my web site at: http://nav.to/jgosscacc you will find an article on covering techniques. If you still have any questions just let me know and I will be happy to help you. James

#3 Hi, I was reading your articles and thought you might be able to answer a question for me. My starter needs more power for my larger engines. Do I need more amps at the same 12 volts or do I need more than 12 volts to get the job done. Bill  Hello Bill,      Volts or Amps?      This subject confuses a lot of people Bill and I will try to clarify it for you. While one may seem more important than the other, actually they are both equally important. In a dc circuit to deliver power to a load such as your starter it requires first a voltage such as your 12-volt starter battery. The voltage source serves as the force (electrical pressure) that forces or pushes (actually pushes and pulls) the electrons through the wires. These electrons in motion are referred to as current flow and are measured in amps. You can't have current flow through a circuit without voltage being present, but you can have voltage without current flow. The amount of power in watts that is delivered to the load is a product of the current times the voltage (P = I x E). What actually makes your starter motor rotate is the current flowing through the armature winding and not the voltage. This current creates an electromagnetic field around the armature to react with the field magnets and produce torque for turning the shaft. The more current that flows through the armature the more torque it develops. In order to get this current flow you must have voltage across the armature.      The amount of current that flows through the armature is determined by the source voltage and the resistance of the armature windings ( I = E/R ). You can see that if you increase the voltage the current will increase as long as R remains the same. Another thing to look at is the ampacity of your 12-volt battery. Ampacity is the amount of current your battery can furnish to the load. Ampacity is stated in ampere-hours and a typical 12-volt battery may be rated at 8 ampere-hours. This means that the battery can supply 8 amps for one hour or 16 amps for ½ hour or 32 amps for 15 minutes and so on. Your starter places quite a large load on the battery and may require between 30 to 60 amps when it locks up to get it turning again. If the battery is not rated for this amount of current its terminal voltage will drop under load from 12-volts all the way down to 2 or 3 volts and you will not get the current you need. This is because of internal voltage drop in the battery. So in this case if you increase the voltage by adding more like cells in series so you now have 24-volts with no load connected, you will have about 4 or 6 volts with a load connected instead of 2 or 3 volts. This larger voltage will allow more current to flow through the armature. If you go to higher current cells the battery's voltage will not drop as much under load and will furnish more current to the armature winding. Higher current cells will have less internal resistance and will allow more current to flow through them without having as much internal voltage drop.      So to answer your question you can do one of two things. You can add more cells in series with your old battery cells so after you do have a large voltage drop in the battery you will still have enough voltage to force the required current through the armature. Or you can use a higher ampacity battery and keep the 12-volts. Here is a check you can make to see if you have an efficient system. Place your dc voltmeter across your starter battery with no load connected and measure the voltage. Now place your starter across the battery and take a voltage reading while the starter is running. How much did the voltage drop? Now take a voltage reading while the starter is turning your largest engine. If your 12-volt battery drops below 8-volts this indicates that you need more battery power to get the most efficient system you can have. If you are getting severe voltage drop be sure to check your leads and connections to see if they are getting hot, if they are you will need to repair them and perform the test again. You can get more information on my web site at: http://nav.to/jgosscacc and look under "Getting to Know Your Electric Starter" Good luck! James Goss

#4 Hi James!  I've read about your Floppy Disk and Ace of Spades planes.  I've also browsed through your web site.  Like me, it seems that you like anything that flys. I've had more fun with this simple piece of flat coroplast than any other RC plane since my Stickit was brand new!  In fact, other than an occasional flight on my Fazer, Stickit, or Spickler Quickee 500, the only planes of my own that I bother to fly are my PBFs.  I love playing with my planes at ground level, but I don't like damaging them.  With the PBF, I can play at ground level without fearing much more than a broken prop.  I love these things!  I really like the bottom spine better than the top version.  It seems to be much more rugged, and the pine wood is lighter to boot.  At the RC Extravaganza a few months ago, one of the better pilots was doing lots of 3D stuff with his 40% Extra, and several other big planes. He saw me doing some wild stuff with my PBF that caught his attention, so I let him fly it.  Within 30 seconds he had spun the PBF into the ground.....and spun it in again a few minutes later.  The PA announcer was really giving this poor guy heck for that!  It was fun!!! I've been trying to keep the motor as close as possible to the leading edge to make the PBF more agile, and also to help keep the motor mount beams from breaking as easily in a crash.  To get it to balance this way, the radio needs to be mounted farther forward than your Spad Park Flyer with the longer motor mount beams.  FYI, I'm thinking the ideal CG is going to end up somewhere between 5.5" and 6.5" back from the leading edge. Keep in touch!  Your Disk Plane post on RCU is what got Foamguy and myself started on this "Squareplane" kick in the first place!  It sounds like you are also one of the "Cool guys who like weird stuff." FYI: Mud Duck has posted some inflight video of my PBF at www.jcrc.com.  Go to the CLUB NEWS link, then look for the picture of the PBF inflight.  Clicking on the PBF will take you to the page of PBF videos.

#5 Hello James, If you can spare a minute, I have a couple technical questions for ya. Our flying field is finally being supplied with electrical power.  That allows me to implement something I've always wanted for all of our members, 12volt power at the models tables.  Now I'm confronted with a lot of options.  A/C power will be available by a plug or junction within 10 to 30 feet from each stand.  For safety reasons we want to avoid having high voltage actually at the table. So, here are my questions keep in mind a minimal budget to get the job done: 1.     What would you say would be the minimum current values you would supply? (I plan in supplying banana, clip-on and an auto style outlet at each).  We want obviously to be able to use the average starter, average fast charger, and such.)  I'll provide a resetable breaker for protection. 2.     Would you supply the 12v from individual plug in style transformers, Larger transformers, or other? Any other advice? Thanks!! Rick Davis TexasHobbies 903-295-6507 [email protected] Hello Rick,      Good to hear from you again. Congratulations on getting power at your field, I would love to have ac power at our field. Some of the guys would probably move in if we did and I would probably be one of them. Being able to use your 12-volt dc starters from the power line requires that you have a rectifier type power supply that can supply a rather large dc current. A typical starter will draw between 30 and 60 amps when it stalls during a startup. There may also be several starters being used at the same time and the current would be additive. DC power supplies of this size will be rather expensive. Small plug-in supplies will not handle the current demand you will require.       I think a better approach would be to install several auto type batteries, maybe one 500-amp battery for four or five stations. Use the 120 volts to drive small 8 amp battery chargers when needed. You may also choose to use a solar cell charger to keep the batteries charged for most of the time and only use the 120 volt charger once a month or when ever needed. I am sure this will be the best way to go considering expense.     The batteries need to be located in a central location among the flight stations. From the battery enclosure I would recommend a minimum wire size of number 10 AWG copper, type uf cable (underground feed) ran underground to the tables. The larger you go in wire size the less voltage drop you will have on the wire. Number 8 AWG will be larger than number 10 AWG and number 6 larger that number 8 and so on. I feel number 10 will do the job because all the high current loads will only be momentary in nature. Number 10 copper can handle 200 amps for short durations of three of four seconds. It is normally rated for 30 amps. So I would run number 10 type uf cable from the battery station to each flight table. Do not parallel the flight stations, run a separate cable from the battery to each flight station unless the flight stations are very close to each other. This system should give the members starting power that is equal to or better than what they now have for their electric starters. Good luck on this project and if I can be of any help in the future just let me know. James Goss

New Radio Impound At The Eastaboga Field Thanks to Pat Thomas and some help from Cecil we have a new radio stand at the Eastaboga flying field. The frame is made of steel and is about the strongest looking radio stand I have seen to this day. It should be there for many years to come. Pat painted it a dark blue and it looks really nice. Thanks again pat!

New Frequency Board at TRCC The TRCC has a new frequency board and it too is about the strongest I have seen at any field. Due to vandalism at the field we were forced to come up with a secure method to house our frequency pins. Again thanks to Pat Thomas we have a NEMA 12 enclosure that will keep all the little pesky trailer park hands away from the pins. The kids made it a game to come by the field and hide the frequency pins in the nearby cornfield and let us try to find them. This game got old in a hurry so we decided to isolate the pins from anyone by concealing then in the industrial enclosure. Time will tell if this is the ideal solution to our problem.

Bearing Noise By James Goss      I am not referring to mechanical noise from a bearing in this article; instead it is in reference to electrical noise generated by the bearing. Here is something for you to think about. The other day one of my friends got in touch with me about his Postage Stamp fun fly plane he has built. It is build exactly like mine, but with an OS .32 ball bearing helicopter engine instead of a bushing engine like I was using. I have the little OS .46 LA engine on my Postage Stamp and it flies smooth and has plenty of power for vertical pull from a hover. The problem he has deals with his plane being very jerky while flying at any speed. Since his plane is identical to mine and also others that fly well, we thought his radio system might be the instigator and he was going to change out his receiver and antenna system. He was using a base mounted antenna like he uses on his helicopters. This was about a week ago and I am waiting the results.      Since then I have build another Postage Stamp and decided to use a little more power up front. This time I am using a Thunder Tiger .36 ball bearing engine. It really flies the plane well and does great maneuvers, but I did notice a difference in the handling of the plane. It was a little jerky in the air and that reminded me of what my friend had said about his stamp. I landed the plane and checked everything out, it all looked fine. I continued and had a couple of good flights with several vertical landings. I can see that more power means more fun with this plane.      On the way home I got to thinking about the random jerking situation and zeroed in on the two types of engines. A bushing engine compared to a ball bearing engine. Now we all know that metal to metal rubbing will generate rf interference for our radios and give us glitches. I started wondering if the steel balls in a ball bearing could roll without any rubbing action between them, the spacers, and the housing of the bearing. At one time or another some sliding instead of rolling of the balls would have to occur and produce a difference of potential between the two objects due to friction. I know ball bearings get hot because of friction while under a load so it only makes sense they will generate small voltages and the electrostatic field that is associated with a voltage. This could explain some of our unexplainable glitches we get from time to time. We blame the wind most of the time while in reality it may be our engine generating the signal.      I decided to look a little deeper into this topic so I setup the following experiment in my shop. I connected a small ball bearing to one end of a ¼ inch dowel 36 inches long and the other end of the dowel to a dremel tool for rotating the bearing at high speed. The outer race of the bearing was anchored to my workbench so only the inner race could rotate. For a sensor I used a small iron core coil with several thousand turns of 36 awg copper magnet wire connected to my oscilloscope. The first run resulted in too much line noise being generated by the drive motor and being picked up by the scope. I used the 36-inch wood dowel to separate the bearing from the motor for just that reason. I then connected the scope through an isolation transformer to cut down on some of the noise pickup and then got a useable signal. There is evidence that electrical noise can be generated by a ball bearing when rotated at high speed. This bearing under test was a new bearing. I imagine all bearings will exhibit this action and the older the bearing the larger the signal amplitude would become. As ball bearings wear with use the balls become out of round so I would think more friction would occur. So this is something to think about and another plus for the bushing engine.      I understand about wavelength multiples and realize the bearing will not act as an antenna as well as a piece of music wire 16 inches long connecting the throttle horn to its servo and being allowed to rub the horn. The wire would radiate much more signal interference than the bearing, but still there has got to be some radiation from the bearing. Of course as I mentioned in my article “Grounding”, if we bond the engine to the negative reference line of the battery it would help eliminate any electrical noise generated by the bearing or any other part of the engine.      I was also wondering why the bearing noise (if that is what it is) has showed up more on the Postage Stamp planes than it has on others. It could be that this plane is very sensitive to any command it receives where other planes flight characteristics are not altered. Having a flat airfoil and a ¼ inch thick wing means when you move a control surface the plane responds instantly. So it may be this relationship that created a jerky in-flight situation. Remember that this type plane wants to fall out of the sky anyway so it doesn't need much encouragement to alter its flight path. Still this is the most fun plane I have ever flown no matter what engine is up front.

Free Postage Stamps Update      Last month I made an offer to build free of charge ten Postage Stamp planes and give them to our club members so we could gather more data and maybe improve it in some way. The list is now in and if you got on the list you can expect your plane soon. I have purchased the coroplast and cut the blanks out today (July 18, 2002). I still need to order some hardware, but other than that the project is now moving along and some should be ready by the first of the month.     For anyone that is interested I have started a separate web page for the Postage Stamp that will give the latest information and new ideas about the stamps. These little planes are now beginning to spread and I am sure we will be learning more about them as time goes by. Simply go to my web site and click on the Postage Stamp square.