Frequently Asked Questions - 2004/05
In the March 2004 issue I provided answers to some frequently asked questions (FAQs) that resulted from the "From the Ground Up" installments I wrote. That article included seven reader questions and their answers (Q-and-As) from the past few months. There are still many questions to be answered; as such, I've been asked to author this new monthly column expressly for addressing any and all beginner/sport-flier inquiries.
Each Q-and-A will have a sequential reference number, so I'll start this column with the eighth question. Because publication space is limited, it has been decided to run five to 10 Q-and-As per column; the number will depend on the overall complexity of the answers.
In addition, I plan on answering questions to be posted on MA's section of the AMA Web site (http://modelaircraft.org/mag/index.htm), where space is not a limiting factor. So make sure you read your monthly MA and then refer to the Web site.
You might notice that I have finally included my E-mail address with my writings. I've resisted doing this for years because I might never be able to leave my basement shop/computer station. As does any modeler, I like to get out and fly because that's what it is all about. Keeping that in mind, I hope you understand that I can't answer everyone personally.
At times I will communicate with you directly, especially if I don't understand your concerns or problems. But even though I can't answer or acknowledge everyone, I do promise to read every single word that arrives in my mailbox.
As do most people these days, unfortunately I receive a considerable amount of spam, or junk mail. To make sure I read every one of your E-mail messages, please follow these simple steps:
- In the "Subject" line type "AMA—FAQ" and then whatever subject you like. This will flag it so that I make sure to read it.
- If you choose to write a letter instead of E-mailing, send it to AMA Headquarters in Muncie, IN and address it: "ATTN: Bob Aberle, FAQ Department." The staff will forward letters to me on a prompt and regular basis.
With all that in mind, let's get started!
Q8: "I noticed that you referred to four- and five-cell receiver battery packs in your series, but I have a single-cell pack rated at 4.8 volts and was wondering what voltage it can reach before needing a recharge."
A8: Your battery pack may look like a single battery cell, but because it is identified as having 4.8 volts, it contains four individual cells. If you multiply the nominal cell voltage of a Ni-Cd or NiMH battery cell—1.2 volts—by 4, you get the 4.8 volts. Most of these four-cell receiver battery packs have simple heat-shrink-wrap cases. If you look closer, you can probably see the outline of the four cylindrical battery cells under the thin wrap.
Receiver battery packs usually comprise four Ni-Cd or NiMH cells. Some pattern and helicopter pilots like faster servo response time and slightly higher output torque, and therefore go to a five-cell pack. As for what voltage to go down to before you stop flying and recharge, I recommend roughly 4.8 volts. A fully charged four-cell pack can reach as high as 5.6 volts. The time it takes to get from 5.6 to the 4.8-volt mark is a function of the battery's rated capacity. The higher the capacity (expressed in mAh), the longer it takes to get to that recommended minimum voltage.
An average 600 mAh-capacity, four-cell battery pack should take approximately two hours to reach that minimum. Much of that has to do with the type of model flown. An RC sailplane will take far fewer commands than an RC aerobatics model. Control commands use up battery power! When the time to reach 4.8 volts starts to get shorter and shorter, the capacity is diminishing and replacement becomes inevitable.
You can easily check receiver-battery voltage at the field with a meter such as the Hobbico Digital Voltmeter Mk III I described in the "Battery Basics" article (on page 59 of the October 2003 MA). This inexpensive instrument not only places a load on the battery, but it tells you when it is time to recharge.
Q9: "When I get home from the flying field I usually leave my transmitter and receiver on for approximately eight hours, until they are almost completely discharged. Then the night before I fly I recharge using the RC manufacturer's charger for 15 hours. Is this a good process?"
A9: I'm not in favor of your process at all. Leaving your transmitter and receiver on for eight hours will probably take the batteries all the way down, and they might even go into reversal. That alone could easily ruin a battery pack.
I assume that when you leave your transmitter on for that long period, you have the antenna retracted or collapsed. If so, the transmitter output circuit is detuned and the output current may be exceeding normal operating parameters. Therefore, you are doing your transmitter no good in this regard.
On the receiver side, as the batteries wear down, the servos will get jittery. Later the control may go hard over, resulting in a stalled servo or, more likely, a damaged servo gear. In both cases, the only safe way to discharge a battery pack—transmitter or receiver—is with a standard discharge or cycling device.
These units are set to cut off or stop discharging when the voltage gets to something near 1.0 volt per cell. By using such a device, you will never take a Ni-Cd or NiMH battery down too far. But even more important, you shouldn't be taking your batteries down after each flight session. The so-called "memory effect" has always been a debatable subject.
The best recommendation is to cycle or discharge-test your battery packs every month or two. Your current practice is unnecessarily shortening battery life.
Q10: "I have a Futaba T6XA transmitter with an eight-cell 600 mAh capacity Ni-Cd battery pack. I tested the pack on a cycler and determined that it had an actual capacity of 585 mAh. When I get to the flying field the meter reads 10.9 volts, and then in 15 minutes of operation it is down to 10.5 volts, and in 15 more minutes it is down to 10.2 volts. Is this normal?"
A10: Since you tested the battery pack and found that it was close to the rated capacity of 600 mAh, yes, it is normal. Most RC transmitters consume roughly 200–250 mA total current when in operation. With the usual 600 mAh battery pack, you should easily be able to obtain approximately two hours of operation.
A typical Ni-Cd battery's voltage tends to drop off rather fast initially, and then it reaches a point of about 9.8–10.0 volts where it will remain relatively constant for quite a while. I'll bet that you would obtain the two hours of operating time before the voltage got down to 8.8 and tripped the alarm built into your transmitter.
If two hours weren't enough, you could purchase AA-size NiMH battery packs of the same physical dimensions with capacity ratings upward of 2000 mAh. That would provide six hours or more of operating time. But if you did that, you would need a new charger capable of much higher current.
Q11: "I first bought the recommended Hitec Neon three-channel RC system and then later bought a basic four-channel system. I realized right away that the throttle control sticks were in different locations. As a beginner, will this cause me any problems?"
A11: Not to be a wise guy, but I'll start out by answering that it shouldn't, but it might. As I explained early in the "From the Ground Up" series, most of my RC transmitters have two dual-axis control-stick assemblies with at least four-channel control capability. But I also own several three-channel systems, including a Neon, that I use on some of my RC sailplanes and parking-lot flyers as a convenience. Three-channel systems aren't just for beginners.
The primary difference in the transmitter configuration is the throttle-control stick's location. Most three-channel transmitters, such as the Neon, have the throttle control on the rear of the case. This is so you can hold the case with your left hand and finger the throttle. Then your right hand is free to operate the single dual-axis (steering and elevator) control stick on the right side of the front of the transmitter case.
On four-channel (and higher) systems there are two separate dual-axis control-stick assemblies. You grip the transmitter case with both hands, and all four primary flight controls are located on the front of it. Your left hand operates the throttle control with a vertical (up-and-down) motion.
So using the three-channel transmitter, the throttle is a side-to-side motion; on a four-channel, dual-stick-assembly transmitter, the throttle is an up-and-down motion. That stick is set for high or more speed at the top and idle at the bottom.
As I pointed out, my student had some experience flying with a four-channel transmitter. Then we went to the flying field with the Neon three-channel system and used a buddy-box trainer cable connecting it to another transmitter.
My student immediately became slightly confused with the new throttle-control location; it actually bothered him for several flights. That reaction prompted my comments in the September issue.
The average sport flier should be proficient at flying with either throttle-control location. Three-channel systems are usually less expensive, so owning several can be a real cost saver. I'll encourage you to own both types of systems. When you are learning to fly RC, if it is at all possible, stick with one system configuration until you are comfortable flying solo with no help from an instructor pilot.
That concludes the published portion this month. With each column I will try to include a few photos to supplement the text where possible.
It is obvious from this start that many modelers have questions and concerns when it comes to battery applications, charging techniques, and general care, but there are many other aspects to this hobby. I encourage you to write or E-mail your questions about anything with which you are having a problem.
I am an electric-power enthusiast, but in more than 50 years of modeling I have flown glow, gas, diesel, rubber, CO2, and hand-launched gliders. Try me with any and all of your questions. If I can't answer a question, I network with a group of experts on a regular basis to act as my consultants. Your questions will get answered!
Also, please let me know if the answers are too broad, too detailed, too long, or not long enough. I need your input! MA
Transcribed from original scans by AI. Minor OCR errors may remain.
