Frequently Asked Questions - 2005/05
By Bob Aberle
E-mail: [email protected]
This is the 14th monthly column in which I will try to give you the best possible answers to questions you have written in or e-mailed to me. Each new question is given a sequential number for identification purposes.
Because publication space is limited, part of this column will appear in print and the columns in their entirety will be posted on the AMA web site at www.modelaircraft.org/mag/faq/index.asp. There, you can access particular questions by subject matter or categories. This was done to help you retrieve data for specific topics. When you call up a question, at the end it reads "Answer ..." Double-click on that word, and the answer and any related photos will be displayed.
Let's start!
Q109: "I worry about my battery pack failing during a flight, causing the crash of my aircraft. I realize that any single point failure could stop my RC system from operating and controlling my model. I heard that there are devices that allow for redundant (more than one) battery packs to power the same RC system. Can you shed some light on this?"
A109: I've seen several so-called redundant battery schemes throughout the years. The idea behind them is that you can use two battery packs, feed them through a control device, and then into your single RC system aboard the model.
I recently received a sample of such a product and it is being passed on to one of the MA columnists for a more detailed review. The device is made by Quest Engineering and Development of Phoenix, Arizona, and it is called the Smart-Fly BatShare. You can find a description at www.smart-fly.com.
Key features of the BatShare:
- Small size: 1.5 inches long, 0.75 inch wide, and 0.25 inch thick.
- Weight: 0.5 ounce — suitable for almost any size model.
- Two input cables for two separate battery packs. Packs should have the same voltage (number of cells) but can have different capacities. In practice, power is drawn equally from both packs and available capacity is the sum of the two.
- Continual monitoring of both packs; the unit switches to the pack with the higher voltage.
- Two output cables that go to your RC receiver (one can be used on an unused channel port).
- Current rating: 12 amps input current per cable (24 amps total).
- Claimed voltage drop: 0.47 V at 6 A and 0.55 V at 12 A.
- Two LEDs provide monitoring for both outputs.
- Price: $54.95.
Quest Engineering offers several other specialty items, so check out their web site.
Q110: "I have a perfectly good Hitec 335 charger that I purchased several years ago to charge Ni‑Cd battery packs. Now I also have several NiMH battery packs and wonder if I can use this same charger. I understand from what I've found on the Web that NiMH cells have a different peak voltage than Ni‑Cd cells, and that as a result, my charger may have difficulty in detecting it."
A110: Your popular Hitec 335 field-type peak-detect charger should have no trouble charging Ni‑Cd and NiMH cells. The actual peak that occurs with NiMH cells is slightly less discernible than with Ni‑Cd cells, but that difference is usually taken into account in the charger circuitry. Some chargers (but not many) allow you to select the peak for either type of cell.
If you want to substitute NiMH cells for Ni‑Cd, you will most likely need to add one more cell, making a total of eight. In other words, an eight-cell NiMH pack will typically replace a seven-cell Ni‑Cd pack.
When you mentioned a "different peak voltage," I think you really meant a different "nominal voltage." We usually refer to a Ni‑Cd cell’s nominal, or average, voltage as 1.2 V. In practice a Ni‑Cd cell can get up to about 1.3 V at full charge and can be discharged to 1.0 or 0.9 V. The nominal voltage of NiMH cells is slightly less than that of Ni‑Cd cells, which is why you often need an extra cell when switching to NiMH.
Many who make this substitution have found their aircraft fly slower when going from Ni‑Cd to NiMH with the same number of cells. Adding one NiMH cell (raising the pack voltage) usually restores comparable performance. If you decide to go to Li‑Poly batteries, however, you encounter a different set of considerations.
Q111: “I noticed in magazine advertisements that the new Hitec Optic 6 RC transmitter can provide RF signals on regular FM (also known as PPM [Pulse Position Modulation]) as well as PCM [Pulse Code Modulation]. Do I need a special receiver to operate PCM? Do any other Hitec RC transmitters operate on PCM?”
A111: Hitec refers to its PCM function as "Q‑PCM" (Quick PCM). As do all PCM RC receivers, Q‑PCM provides fail‑safe operation and includes fail‑safe preset control capability. At this time Hitec offers one receiver for Q‑PCM operation: the HPD‑07RH.
Hitec updated its popular Eclipse transmitter in March 2003, and part of that modification included addition of Q‑PCM capability. Therefore, all Eclipse transmitters sold after that date can operate on Q‑PCM.
Hitec also offers an upgrade for older Eclipse transmitters that includes the new HPD‑07RH seven‑channel Q‑PCM receiver for a $100 charge. As a result, Hitec currently has two transmitters that operate on Q‑PCM (the Eclipse and the Optic 6) and one Q‑PCM receiver (the HPD‑07RH).
Q112: “I just taught a 14‑year‑old how to fly RC. I’ve been using glow‑fueled engines in my airplanes for many years. This young teenager that I am instructing wants to buy an electric‑powered, high‑wing, trainer‑type aircraft. Do you know of any 30‑ or 40‑size trainers that are electric powered and come complete with everything needed, both the power system and the RC system?”
A112: There are several trainers available that come complete and ready to fly with both the power system and radio. For a true beginner I recommend the Multiplex Easy Star RTF trainer. For a good step‑up model consider Hobby Lobby’s Lipol‑One ARF, and for a larger trainer the Hobby Lobby Bonnie 20 ARF is a good choice.
About the Lipol‑One:
- Some assembly work is involved, but the foam parts come prepainted and no covering is necessary.
- Powered by a Model Motors AXI 2204/54 brushless outrunner motor and a two‑cell 700 mAh Li‑Poly battery pack.
- The brushless motor is efficient and durable; the Li‑Poly battery provides long flight times, which is important for a student pilot.
- A detailed review of the Lipol‑One is posted on Sport Aviator (AMA’s online magazine): www.sportaviator.com/ah.asp?CatID=15&ID=59.
About the Bonnie 20:
- A good trainer once the student has progressed beyond basic trainers.
- High‑wing ARF with roughly 420 sq in wing area and an approximate total weight of 60 oz.
- Full four‑channel control: ailerons, elevator, rudder, and throttle.
- Tricycle landing gear (two main wheels and a steerable nose wheel tied to the rudder).
- Good for teaching basic maneuvers that use aileron control, including rolls.
- A review is posted on Sport Aviator: www.sportaviator.com/ah.asp?CatID=1&ID=39.
The three electric‑powered aircraft recommended (Easy Star, Lipol‑One, and Bonnie 20) can provide everything you need to train a young student and introduce them to our wonderful hobby.
Transcribed from original scans by AI. Minor OCR errors may remain.
