In May of last year, I experienced a battery failure while flying Jim Folline's magnificent PT-19, and the airplane was destroyed. This was the third time in my flying career that something similar had happened and it was the straw that broke the camel's back. All the battery checks, monitors, in-flight warning systems, or fancy analyzers in the world won't save your plane if the battery just flat fails.
Immediately thereafter I spent a goodly amount of time crying loudly on George Steiner's shoulder, and begging him to come up with a Dual Battery System, one that would carry two battery packs, and if one failed, the other pack would continue to carry the load.
From sheer self-preservation, George has now done that, and his Battery Comparitor System is developed to the point that it now has several features that make it even better than just a back-up battery. His system carries two battery packs. but both packs supply power to the receiver, in proportion to their strength. If one pack fails, it is "locked out" of the circuit, and has no effect. Since any electronic circuit takes some power, George's system now utilizes five-cell packs, and these not only overcome the voltage drop in the Comparitor circuit, they actually end up supplying greater power to the servos, and giving a greater voltage drop available to the entire radio system! This will dramatically add to even the time available from just a standard pack.
Let me explain a little bit. The standard voltage available from any normal battery pack is 4.8 volts. The normal receiver requires a minimum of somewhere around 3.9 volts to perform properly. When the battery "goes dead" beyond this point, then everything quits. With Nicads, because they drop voltage very rapidly when they start to reach their discharged state, this quitting of the radio happens darned fast, with little warning. You will usually have less than a minute to get your plane on the ground from the first indication of Battery problems until the control ceases completely. In the PT-19, I started a loop, and instantly realized that there wasn't enough battery left to give me full elevator control. I immediately set up for a landing, and the battery died on final approach. The battery had lasted only seven minutes of the first flight of the day. It had been thoroughly charged and checked.
With the standard battery, the "distance" from a full charge to a dead battery is about .9 volts. With George's system, the receiver "sees" about 5.5 volts normally, so the distance his system has to go before the radio quits is about 1.6 volts drop! Automatically, each battery is going to last longer, and since you have two batteries, you end up with considerably more than just double the battery life you would expect with a standard pack.
A second feature of this system is the increased power available to your servos. They also see the increased voltage, and since many of us are utilizing long extension leads, and chokes in those leads, the average servo with a standard battery pack is a poor, struggling anemic little animal after experiencing the voltage drop from these items, but with George's system, these servos are now being fed approximately twenty percent greater power to begin with, and suddenly your anemic little servo is again a buzzing beast!
The worrier instantly pops up and says, "Will this greater voltage hurt my radio?" No. All radios are designed to operate with up to 6 volts normally, so that they can be used with dry-cell packs if wanted. "So why aren't all radios operating with 5-cell packs?" 5-cell packs aren't as easy to make, they weigh more, they are more expensive, and for most uses, the extra power just isn't needed.
Worrier then asks, "But now I'll have to replace all my 4-cell packs with 5-cell ones?" Nope! George even thought of that one! If you utilize two standard 500 mah packs, (which will give you the ultimate capacity of about one 1,200 mah pack), the extra cells to make those standard packs into 5-cell packs are contained within the circuitry of the Comparitor System. The only thing you do with this system is take out your old switch harness, replace it with the Battery Comparitor System, and plug in the extra pack.
Right now I start to get a severe case of the giggles, just thinking about all the goodies on this system, but I haven't even started yet! The system employs three LED indicators to give you a superb indication of just what is happening with the system. the first LED indicates power going to the radio. Each of the other LEDs are an indicator of its individual battery. However, these LEDs don't just light up. They vary dramatically in their intensity, and the information available from them because of this is wild!
With a good, charged system, when the receiver is turned on, all LED's will glow moderately. Since the transmitter is not yet on, the receiver is not yet oscillating, and it draws only moderate power, so the LEDs are not at full brightness. Switch on the receiver, and instantly there is a noticeable increase in LED brightness, indicating the receiver is now drawing full power, as it should. An excellent indication that the receiver is indeed oscillating.
At this time, with both batteries good, both of their indicators will be glowing moderately bright, which indicates that each is supplying their share of the load. Should one battery drop below the other in voltage, its indicator will glow less and the good batteries will glow more brightly. Should one battery die for any reason (broken battery wires are not uncommon causes of crashes, yes?), that battery will be locked out of the circuit, its indicator will go out, indicating it is dead, and the good battery will assume the entire load, with a brightly glowing LED to indicate that.
When this happens, the modeler instantly gets a case of the shakes! Why? Even with the one totally failed pack, you are still better off than you were with just the one standard pack. Remember the increased voltage, and therefore the increased power and life of a Steiner system? Even with one pack failed, you still have 20% greater life and power than you did with the standard pack!
What about Charging? The unit is charged from the switch circuit the same as a standard system, and you use the same chargers. There's gotta be something wrong with this; nothing's perfect! Yeah, there are a few inconveniences. Two packs weigh more than one, and the system itself is a little bulky, being housed inside a standard Kraft Sport Series receiver case, so you have more things to pack into the plane. The LED indicators are mounted on the face of this case, so the system case has to be installed so that these LEDs are visible sometime. The most obvious installation would be so that the LEDs are visible when you remove the wing (you would then normally check the conditions only when the plane is disassembled), or mount them so that they can be seen through a window (Better). The radio switch is also mounted in the case now, so that a remote pushrod is required to actuate this. It might eventually be offered with a remote switch that could be mounted in the standard manner.
Also, should you wish to use larger than standard battery packs, you will then have to actually build 5-cell packs. It isn't practical to have large cells inside the circuit to make up this difference.
Of course, you also now have something else to check on the plane. Should you never check the indicators, it is entirely possible that you could fly for weeks with a failed pack, since the system will operate perfectly well with one good battery, and that good battery will recharge normally after every session. And, it is entirely possible, sooner or later, that the second battery could fail, and then you'd be up a creek again! You do have to check the system to see if it has done its job.
After six months' work, the system is now fully functional, and is being tested in five prototype units being extensively flight tested. George is not completely ready to go into production with the units,but says he should be so within the month. Price has been pretty well established at around $36.90 for the standard system with the internal 5th-cells, or $30.00 without the extra cells, in which case you will have to have five-cell packs. The units will probably be offered first as kits, but they are well within the capability of virtually anyone to build. Nothing remotely as bad as a servo amp board. They will be available with plugs to fit any radio.
Guys, as I said earlier, I get a severe case of the giggles every time I start thinking about this circuit, especially since it is in existence solely, (Ahem!), because of my insistence. George had about a dozen other projects that he shoved aside to get me off his back. I consider thiis system to be one of the most important advances ever made in the hobby, since almost 80% of the radio fai1ures are one way or another traced to battery failure. This system will eliminate at least 80% of those failures. The system will soon be a feature article in one of the major magazines, but you saw it first here!
For a brochure that will fully describe the system once
we get it ready for release send a self-addressed, 18-cent stamped (GRRrrrr!)
envelope to TAYLORCRAFT, LTD., 216 Willow Ave., Roseville, Calif. 95678