IMAC System Weight and Cost Comparison

I have absolutely no doubt that those that have already invested in the new technologies will not be switching back based on the content of this comparison report, nor is it intended as an assault on their choices... I have great respect for those that in effect put cash on the barrel head and then 'risk it all' to help develop new technologies for the hobby. It's thanks to those brave souls that the technology is as refined as it is, and it's thanks to their support and input that it's improving at a remarkable rate. But for the folks that are still sitting on the fence or are contemplating their first IMAC or Giant Scale project, perhaps this white paper will be of assistance in making a decision.

Where it all Started

The ‘storm of debate’ on batteries has been with us from the start of radio control and the focus of the debate has it's roots in weight. Everybody knows, ‘lighter is better’ when it comes to model performance, and some of the hobby’s greatest improvements in performance are relative to power and weight in the aircraft we all fly. Ever in pursuit of ‘weight savings’, the builder often gets to the end of his project, weighs up the fruits of his efforts and discovers he ‘needs’ to cut the weight buildup by revising his selection of on-board equipment in pursuit of his magic number. I’ve discovered that about the only thing you can do to a model that does not add weight is look at it. Every thing else is weight gain. Everything!Next, having established a train of logic that has ‘weight’ as the core of the debate, the modeler looks for servos, receivers and control components that reduce the deficit of weight gain that appeared in the building process. By the time we’ve finished the control system and are looking at batteries, there seems to be a willingness to compromise both common sense and an inordinate amount of money to assuage the guilt of ‘missing the magic number’.

We Crunch The Numbers...

Let’s have a look at the ‘magic’ in light of a 33% scale IMAC project. We’ll pick a number at random, call it 15lbs (240oz), less batteries and switches. Our project is powered by an ignition engine, and has digital high torque servos so we’ll need to deal with that too. All the technologies compared are fully capable of flying the subject aircraft equally well, with similar system ‘safeties’ and backups.* (see note at bottom of page)

Duralite Plus Li-Ion Redundant System, Basic, Total capacity; 3800mA

Sanyo NiCad Redundant System. Total Capacity, 3000mA

Sanyo NiMH Redundant System, Total Capacity 3900mA

...and the winner is..... Nobody!

Now, a quick look at the numbers would indicate that all three systems shown are in the ‘ballpark’ as far as weight goes the Nicad system and the Li-Ion basic system are less than one ounce different in weight*** , while there's less than 4 ounces difference with the NiMH setup. The Flight time advantage goes to the NiMH system. While Li-Ion comes in a close second and NiCad seems a distant third, whatever flight time advantage a Li-Ion system would enjoy is eaten away by the NiCad's much faster field recharge time.

Folks; if you sit down and figure out what the field support equipment costs for Li-Ion (Chargers, ESV's, Cyclers, Power Boxes, etc) and then have a close look at the cost per ounce of system weight, you really gotta ask yourself just how much of a difference that less than an ounce will have on the way our 16lb (256oz) airplane is going to fly. . For that matter, ask yourself how much of a difference four ounces will have on the way our two hundred and fifty-something ounce plane will fly!

Now, normally, it's not a wise thing to thump folks about the head and shoulders with tire irons or numbers, but just off the cuff here, I'd say "taint no winner, folks; mah scale cain't read less than 1%".

*** When we add in the recommended Low Voltage Cutoff modules, the Nicad system actually weighs an ounce less, with less than 3 ounces difference when compared to the NiMH setup!!

What it all means..

Now, if you’re on or near the top of the heap in aerobatics world, and you intend to compete on the nationals level in pattern and aerobatic events, possibly I can see the weight point, (and you’ll probably get your packs for free at that level) but at this point in comparative technology development and in the vast majority of today’s sport aerobatic ARF IMAC aircraft, the three to less than one ounce of weight difference don’t amount to a hill of beans in aircraft performance. I humbly submit that picking a better prop is a whole lot more useful exercise in better power to weight than throwing a ton of cash into your battery system!

...If not weight; then Why??

On the dependability, reliability and field serviceability points of the great debate, Li-Ion lags behind the others simply because of the safety outcry.. all those safeguards add expense, weight and significant complexity. I pursue critical application radio system setup with one motto: "Every component between the battery and receiver adds risk, reduces reliability." As long as Rx's and servo's fry at 7.2v I can't see how anyone can produce a more reliable system than a parallel NiMH setup with regulated fail-safe switches.

Is the new technology going to 'take over'? Certainly!! Just about the same time we switch over to solar heat, safe nuclear power and cars that run on hydrogen. In the meantime, don't look for the changeover to be complete over the life of your next battery pack. :)

*It should be noted that with the lithium system a Voltage Regulator is absolutely required for each pack. Should you chose to improve the ‘Spaghetti Factory’ wiring situation and further improve current handling and system safety in the Duralite Plus system, they have an outstanding item called the ‘Power Box’ that greatly simplifies system installation.. and it adds $325.00 and 5.24 oz to the system weight.

With the Nicad & NiMH system, unless JR coreless servos are installed in our aircraft, using a voltage regulator is (in my opinion) a superfluous piece of equipment that adds weight, complication and another possible mode of system failure, and they are not used in the comparison. All 3 setups shown have redundant Rx switches, chargeports and packs. Should you care to include the weight of HD regulated Fail-Safe Rx switches to the results, add $30.00 and 1oz (.5oz ea) total to the weights shown for the Nicad and NiMH systems

** The NiMH cell we chose for this comparison is the new Sanyo 4/5 'A' FAUP High Rate NiMH cell... not the more commonly flown 'AA' 2100ma NiMH cell that weighs 3 ounces less per pack than the ones we fly. Why? Because we liked the load performance, durability and fast charge capability of the new heavy duty 4/5 A High Rate cell. And; we preferred to place dependability just a hair higher on the order of priorities than weight when we chose a cell for IMAC Rx applications. Now, had we chosen to list the older and more commonly used standard duty 'AA' NiMH cell in our comparison, an AA sized NiMH system would offer more capacity, longer flight times and weigh less... all while costing less than half of the Lithium Ion system.

Reproduced with the full permision of Steve Anthony of NoBS Batteries.

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