RC Flying Today: Wideband RC Systems
ABSTRACT
- Wideband RC systems
- MAT lead/acid gel-cell battery
- What has AMA done for you lately?
- What are you flying over?
WIDEBAND RC SYSTEMS
COMING SOON: I write this in April 1992 to remind you that it is now illegal to import or manufacture wideband RC transmitters. Report & Order FCC 91-103 mandates that wideband RC transmitters may be sold until 1 March 1993 and used until 1 March 1998. After those dates, sale and use, respectively, must end.
If you are harboring any wideband equipment and have ideas about selling it, you should get it narrow-banded now. AMA got you 50 exclusive 72 MHz RC channels and has taught that you must "use them or lose them." Hanging onto "even channels only" to prolong the use of wideband equipment is one way to lose them.
MAT BATTERY
Model Aviation Technology (MAT), 12848 Touchstone Place, Palm Beach Gardens, FL 33418, is importing gelled-electrolyte, sealed lead/phosphoric-acid batteries in plastic cases in the 6 VDC × 1.2 Ah size. Charge retention time and vibration resistance are claimed to be much better than with Ni-Cd batteries. Price: $30.
The folks at MAT have glued the pack to the firewall of a Giant Scale model and flown it often enough to be convinced that the vibration resistance is excellent. The German manufacturer supplied a laboratory test report showing resistance to 10-G vibration and 100-G shock. MAT offers the battery as a replacement for the 1,200-mAh Ni-Cd packs used in helicopters and large stiff-wing airplanes.
You might like it as a backup battery in a 2 × 5 system (such as Ace R/C's "2 × 5" dual-battery-pack installation kit, which was designed for twin five-cell Ni-Cd batteries), because the self-discharge rate is about 3% per month.
You could also use it as an isolated servo power supply, which would keep both the higher voltage and any servo or other noise out of the receiver. Your servos will run faster, generate more torque, and wear out sooner when you use voltage higher than that specified by the manufacturer. Some microservos are critical for voltage.
MAT batteries must be charged at constant voltage (not constant current) to avoid overcharging. MAT recommends that you use an Ace R/C, Inc. six-volt CVC (constant-voltage charger) kit #34K3BC (not supplied).
Fully charged gelled-electrolyte batteries should be maintained on a trickle charger. The manufacturer recommends C/1000, which in this case would be 1.2 mA. Gelled-electrolyte cells should not be fast-charged, and the MAT battery is limited to 600 mA for short periods. Properly maintained MAT batteries are expected to last four to five years through 400 cycles at 5% discharge.
Because the cells contain phosphoric acid and sulphuric acid, fully charged voltage is 6.45 VDC. End-of-service voltage is 5.19 VDC. These numbers are resting voltages measured two hours after the load was disconnected. Battery capacity is rated 1,200 mAh, delivering 120 mA for 10 hours. Cells are capable of delivering about seven times the rating (8.4 amps) for about two minutes. These parameters nicely match expected conditions of use.
Some receiver/servo combinations are designed to use four alkaline batteries (maximum 6.3 VDC); others four Ni-Cds (maximum 5.6 VDC). These values are within the range of the MAT battery. I received a report: a receiver in a Giant Scale model stopped working when asked to drive two servos through a Y cable. The problem appeared when the system was powered by a five-cell Ni-Cd pack (maximum 7.0 VDC), and went away when a four-cell pack was plugged in. The modeler removed the Y connector. The physical size of the receiver was a clue to its voltage sensitivity. Very tiny printed circuit boards will have very narrow printed lines. Increasing the current drawn through a receiver by using high-voltage battery packs or by doubling up servos can heat some traces, lift them off the PCB, and put a voltage drop in the system that acts like a fuse.
So it comes down to: check the system manufacturer before you substitute something like the MAT battery for a five-cell Ni-Cd pack listed in the manufacturer's catalog. Failure may terminate the warranty.
WHAT HAS AMA DONE FOR YOU LATELY?
"RC Flying Tomorrow" might be a good name for this part of my column, because it considers the future of RC flying. You will be affected by the concepts discussed. If you like what I've got to say, please write and say so. If not, please tell me why.
The FAA is actively considering restrictions on Unmanned Aerial Vehicles (which includes our models). One of the things FAA does for man-carrying aircraft is to set minimum altitudes for flying over things on the ground.
Your AMA hosted the first meeting of the FAA UAV Task Force on November 13, 1991, at AMA Headquarters in Reston, Virginia. The sixth meeting was held recently. Input for a Report and Order is to be completed by December 1992. AMA got involved to protect your interests, as reported in Geoff Syles' "PR Roundup" column in the "AMA News" section (page 98) of the March 1992 issue of this magazine. This ought to demonstrate to you that AMA isn't just an insurance company. These remarks were made to lead us into the next section.
WHAT ARE YOU FLYING OVER?
Gordon Cox, President of the Greater Saint Louis Model Association (GSLMA), called to thank me for my report on GSLMA (May 1992 issue, page 59). He also wanted to make the point that the flying site specifications on page four of your AMA Membership Manual ("Recommended RC Flying Site Specifications," Figure 2) need some amplification. In his dealings with the Saint Louis County park officials, he was asked to define the kinds of activities that can be allowed in the overfly area and the safety zone. Gordon notes that AMA provides the insurance but offers few guidelines to answer that question.
AMA's insurance and excellent past safety record impress the park officials. Since the Safety Code is the membership manual and is part of AMA insurance, park officials look to the whole AMA Membership Manual as the set of rules that will keep them (the park officials) out of trouble. They take the "Recommended RC Flying Site Specifications" as gospel. Do you?
We all prefer to overfly a farm or forest. There is no threat to anybody and not much chance of noise complaints. The park officials want as many people as possible to use the park. We might think that a horse-riding path through a forest is okay. They might prefer to put a parking lot in the overflight area. The automobile owners might not like that idea. "What should be under the overflight area?" It is a difficult question.
Obviously, the answer is a matter of risk management. Nobody trusts an RC airplane low overhead, least of all those of us who fly them ("Don't fly over the pits!"). On the other hand, worry diminishes when they are high enough. How high is "high enough," and does that put them in the way of man-carrying aircraft?
If the overflight area is assigned to some purpose (say, a soccer field), then the pilots may have to avoid that field when it is in use. We need a plausible scheme for controlling where pilots send RC airplanes. We've needed it for a long time. We all assume we know what is under our RC airplanes, but how many of us have ever made a controlled test to prove our assumptions?
I suggested to Gordon that he could use the method of the IAC (International Aerobatic Club—for full-scale piloted aircraft). The IAC defines the boundaries of the maneuvering box by stationing people on the corners. The corner monitors have a pipe frame mounted on the ground (for a sighting guide) and a two-way radio. When a plane wanders outside the box, the infraction is radioed back to the judges, and scoring stops. It keeps the full-scale pilots in their place, because they spend their money to enter the competition to get the scores. We might have to treat RC offenders as student pilots, who are not permitted solo flight privileges.
With the IAC scheme, we would need about five people and some equipment in place on the ground before we could let one person fly. Nobody wants to go to a flying site to be a policeman, so you probably don't like that idea.
But there's another possibility. A reader mailed me a clipping that shows a hand-held Global Positioning Satellite (GPS) receiver made by Sony, which retails for $1,350. Another sent an inexpensive sheet for a desktop GPS receiver by CoPilot Electronic Products, Inc., 417 Rawhide, Olathe, KS 66061. This one retails for $795. Prices are obviously on the way down for this very precise navigational tool. Somebody is bound to figure a way to put one in a model airplane.
Last month I talked about ways to keep manned aircraft from running into our models. Our hypothetical GPS receiver can be set up to flash a strobe light whenever a model leaves permitted airspace. Use of GPS lets us measure the model's altitude, too, so adding a strobe light would give us the telemetry to deal with altitude restrictions. Placing GPS in a model airplane would put the whole burden of flight-path control back in the pilot's hands (where we all want it to be), eliminate the need for corner monitors, and solve the overly rare problem (see above).
Adding a GPS-controlled strobe light to your plane would be a bit like putting a bell on your cat. It took us 10 years to get most RCers to accept the need for narrow-band RC equipment. How long would it take to get them to accept a GPS/strobe installation? How long if the FAA mandates the strobe (see the discussion above on UAVs)? Most RC fliers will scream bloody murder about the weight and cost of such a device. We can eliminate some arguments by requiring GPS/strobe only on models above a certain weight (five pounds?) or power level (500 watts?).
What else can we do? Safety is what you think about after you put your hand through the prop. Typically, modelers let things slide until complaints close the field. Then they hang back while someone else does a lot of work to get it reopened, or they join another club. Or they quit the hobby.
If nobody will do the "dog work," RC flying will cease. Just think of this: GSLMA, led by Gordon Cox, negotiates flying privileges for hundreds of fliers in a dozen clubs. That's doing the dog work. I think that members of the GSLMA council should be accorded the status of AMA Leader Members, because they are the people actually leading the hobby. The same applies to club officers everywhere.
I also think that the president of GSLMA (and presidents of all model club associations) should automatically become AMA associate vice presidents (AVPs). What do you think?
Ponder this: The AMA needs workers and your ideas as much as it needs your money. I would prefer to see your ideas discussed in your newsletters (with copies to your VP and AMA Headquarters) but will accept letters.
Set up a standing committee in your club to study the matter and report back. Have answers ready before the complaints come in. The problems will not go away, so you must think about them.
Transcribed from original scans by AI. Minor OCR errors may remain.
