On the batteries John prefers using

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As has become the usual case, one of these askJOHN articles comes about in answer to a question. This one was posed on a forum where I responded *but* was promptly taken to task for offering up one of my typical long winded answers. Basically, I was excoriated for wasting everybody's time. So I copy-and-pasted the information from there, deleted the post, and offer it instead, to those interested, here (where it should have been from the get-go).

So my response was offered to a multi paragraph query from which I've cherry picked bits;

Q1. Is there a down side to overspeccing the power? Plus a related comment . . . (I have) a Power Expander thingummy with a mag switch . . . (and) 2 x AR LiFe batteries . . .

A1. Here's the thing, in answering this, I have to also get into battery chemistry (because it relates voltage to servo output, which affects the servo's specifications). And it's worth touching on the thingummy, and LiFe batteries, all of which explains *why* my response is long-winded. Basically, seemingly simple questions only rarely have correspondingly simple answers because they're often more complex than they appear on first blush. I'll explain (of course).

Context is everything

So once I got going on addressing the effect of battery chemistry on servo performance (as it affects whether you're actually overspeccing the servo), and because I'm often asked which chemistry is my favorite, then *this* white paper also became my opportunity to kill two birds with one stone. Three, actually because we also address the thingummy, about which he didn't actually ask (more a statement of use), but I have a few thought regarding those things, too!

So in addressing servo torque in relation to what a model *needs* means I first need to address how voltage affects servos, which will bring me to battery chemistry! And the comment about 2-batteries and a mag switch leads us down yet another bit of garden path. See how quickly simple questions get complicated?

Anyway, I'm going to try and explain why I think it's wise to;

  1. Overspec the servo for the duty, and
  2. When and why I may underspec, instead, and
  3. Why I prefer certain batteries (but how this also depends on who/what the model's for).

So if I may offer my 2¢ to the immediate questions (this is also know as the TL:DR);

  1. If you can afford it, overspec because then servos are loafing vs. ultimate need.
  2. Because whether you overspec or underspec depends on you and the model
  3. Straight up, I prefer A123 technology because it's easier to live with.

It's my opinion nothing beats a servo that's loafing nearly all the time. There's less stress on it, and if the situation arises it can respond to extraordinary demands as if they were nothing, like an overweight model inadvertently enters a terminal dive at terra firma followed by a panicked pullout where *anything* but an overspec servo may just wave at the problem. But the pilot and the model affect advice on servo selection, too complex for a sound bite answer. And why I prefer LiFePO4 batteries is also too complex, so just trust me if you don't want to read all this.

Follow-on question

Q2. What I was getting at, (while trying not to interrupt a forum thread) was; is there a downside to overspeccing a servo?

Assuming the surface to be moved is the same, does a servo that is rated 4X more than it strictly needs have a downside, like using more current, than a servo that is 2X more (powerful) than it needs to be? Assuming all other parameters are equal.

While I am thinking, I refuse to believe that a surface, say elevator, needs more than the weight of the model to deflect it from its path. Am I wrong?

Let's quickly jump on this in reverse order.

  • Yes, you're mistaken - more later.
  • 4X vs 2X . . . basically, the current draw is going to be the same pretty much regardless of servo. Why? It's because if you need 150oz-in, then either our DS180DLHV or DS1155BLHV is going to consume nearly the exact same amount of current when delivering said 150oz-in of force. Interestingly enough, so will pretty much any other brand of servo, say the Hitec HS-D645MW, instead.

So does this mean, if you can afford it, you should go ahead and throw a DS1155 at a mission that only requires a DS180 because in terms of juice consumed from the pack, if you can afford it, then why not? Simply put, yes!

However, in the real world, *money* usually dictates you *won't* throw a DS1155BLHV at a trainer (where we'd recommend maybe a $30 DS90, instead). Interestingly, and as it turns out, we actually *do* have a customer flying a set of four $160 servos within a SIG Kadet (a superb high wing trainer). Why?

It's because, a) he has more money than God, and b) he stated from the get-go he wanted our best and most powerful standard-size servos, and c) after I told him which servo was most powerful and what they cost, his response was along the lines of; 'Damn the expense, I want the best!', so he's even got one on throttle . . . but I digress.

Long winded answers

Anyway, it's worth noting, overspec actually depends on voltage (as I'll explain in a bit). So, I am going to use as an instructive example our popular DS180DLHV servo, which offers similar performance to the well known Hitec HS-D645MW I mentioned above (and also like old school Hitec HS-5645MG, with which many are also familiar).

Why bring up these particular servos? Two reasons, it's because;

  1. So many modelers are familiar with that level of performance
  2. Both occupy the same market in terms of size vs. price vs performance.

Basically, our DS180DLHV is our most popular standard-class servo with modelers. We suspect it's because 180z-in @ 0.17sec/60° is the sweet spot for a *lot* of modelers. That, and because for $40 you get all-steel gears, 13 o-rings, a finned alloy center case, bronze reinforced at the gear shafts, and for meeting 3 MIL-STDS (meaning it delivers a *lot* of bang for the buck).

So next, since I bring it up, let's eyeball some of the DS180DLHV's specs, and if you please, take note of three things.

  1. Unlike competitors, we give you the specs for 5 different voltages instead of just two. This becomes important in a bit.
  2. The higher the voltage, the better the performance (true for every servo on the planet *regardless* of brand or model number.
  3. And quite naturally, we (and all manufacturers) put lipstick on the pig (meaning we quote performance at the highest voltage). This is important to account for, as you'll see.

Now here's the thing; we're going to need to delve in chemistry, packaging, plus hazards and risks, *before* getting to the why behind why I like to overspec as well as why I select one pack chemistry versus another (in depends on the application).

Anyway, noting there are five voltage ranges specified for this servo (and all ProModeler servos) instead of the usual two, these list across the top of the specs chart and denote the columns disclosing various performance parameters like torque (duh), speed, and current consumption.

Battery Chemistry

Why are there five voltages? Simple, it's because there are two nickle chemistries in common use with two cell-configurations (4-cell and 5-cell), and four lithium chemistries (these 4 are all in a 2-cell configuration). So that's 6 types of chemistry *but* we're divided spec into 5 columns instead of 6. Reason is two are actually almost the exact same thing. Let me explain.

Specifically; the six chemistries are; NiCd and NiMh, plus LiFe, LiFePO4, LiIon, and LiPo.

  • NiCd - 1.2V/cell
  • NiMH - 1.2V/cell

Both of these are effectively the same in terms of end potential (voltage). Moreover, because the nickle chemistries are typically packaged in 4-cell and 5-cell packs configurations (in series) then the math works out to 4.8V (4*1.2V/cell=4.8V) and 6V (5*1.2V/cell=6V). So these are the first two columns, 5V and 6.0V.

And yes, I state 5V instead of 4.8V, but that's because 5V is a *really* common potential in the electronics world. For example, look inside any PC and the power supply in addition to 12V will offer the motherboard 5V, also. That, and it's because we sell a *lot* of servos for robotics, simulators, and other industrial applications where they work in a 5V world. Thus, it behooves us to speak their language. As for modelers, 4.8V or 5V is das macht nichts!

Note; technically, a 6S pack is 7.2V and an 7S pack is 8.4V (almost spot on for the 4th plus 5th columns) but those are really, really heavy packs compared to a 2S lithium based pack (achieving the same potential) and thus, they're at a tremendous disadvantage in aeromodeling where weight is anathema to performance. I mention these configurations only in the interest of completeness. 

Anyway, we'll ignore going forward the two nickle-based chemistries. This, in part because other than differences in charging and handling, they peak at the same potential (1.2V/cell) but also in part because they're well understood and considered obsolete by most in the sport. This, principally because they weigh so much more than an equivalent lithium pack (remember, you need 7-cells to match the voltage of a 2-cell lithium pack, and size-for-size, capacity is greatly reduced in comparison).

Believe me, there's good reason nickle chemistry is on its way out. Nevertheless, because we have customers that still favor these chemistries, we list specs for use with nickle-based packs. So that accounts for the 1st, 2nd, 4th, and 5th columns just with nickle based packs.

The lithium revolution

But the 3rd, 4th, and 5th column also relate to the four lithium types; they're all a bit different in terms of potential (and also, risk) *but* the first two are almost the same and so are the last two lithium chemistries. So we combine the first two into column 3 and the last two lithium chemistries into column 4. But this makes 4 columns instead of 5!

Yes, but then there's reality for the packs in column 4 versus nominal and synthetic juice. Have faith, I'll explain (and it'll make sense) so just hang in there!

Note; potential speaks to voltage, where the higher the voltage of lithium-based cells, the greater the risk of fire. More later. So arrayed from lowest to highest voltage (potential) we have;

  • LiFe - 6.4V
  • LiFePO4 - 6.6V
  • LiIon - 7.2V
  • LiPo - 7.4V

Note; these are all 2S systems so divide by two for the per/cell voltage values. And also, these are nominal voltages, or where 'I' stop using them and recharge (exception being LiPo, which I abuse a bit more than that in the interest of extending flight duration because they're robust and will take it). Learn more here;

Point being, a fully charged LiFePO4 (3.3V/cell nominally) will stand at 6.9V while a fully charged LiPo (3.7V/cell nominally) will also come off charge hotter as well, at 4.15V/cell, which is really close to 8.4V, which they'll hold for a fair little while. And 8.4V is also where the synthetic sources come into play. Hence, the fifth column! I'm not really fond of synthetic sources.

No, the servos don't care but speed controls can and do fail, and when they do, they typically take the BEC circuit with them. So now instead of a deadstick landing, you're a spectator to a crash. That, and they backfeed the receiver through the throttle lead between receiver and ESC and this uses a 3.5A plug, which is inadequate for nearly all models equipped with four or more servos. Go look at the specs again. Anyway, to learn more regarding why I'm not fond of synthetic juice for anything but tiny models where the weight of a separate pack material affects performance, review these articles.

Battery packs

For example, the person who posed the question about overspeccing servos, also mentioned LiFe packs. These are so unreliable in our experience (with three different vendors) we quit selling them, altogether. Simply put, we (ProModeler as a business) don't need a dollar so badly as to put our name to those packs and thus, we leave sales of LiFe packs to those willing to shoulder that risk to their reputation. End of story. You want LiFe? Buy them elsewhere.

LiFePO4 packs, on the other hand, are different. They are muy bueno and are what I use in almost every instance *except* for my 3D-type and sport models where I want the highest voltage possible in order to obtain the highest performance possible from the servo. In these models, I use LiIon packs (and not LiPo). And *that's* the TL;DR of the batteries I prefer. Continue reading, for the rest of the story.

Packaging and hazard

So why not LiPo instead of LiIon since they're slightly higher voltage? Simple, it's because LiPo are by far the least robust due to their packaging, which is a polymer bag (just like LiFe). Basically, by design, LiPo construction is meant to be encased in a protective case, e.g. a laptop, an iPhone, or some EV autos.

Meanwhile, the LiIon and LiFePO4 battery packs are packaged in far more robust metal shells (like NiCd and NiMH cells). Yes, metal shell packs weigh a tiny bit more *but* in exchange for armoring the contents this results in greatly reduced hazard - that's a price I'm willing to pay for added safety.

Why is packaging important? Well, what if a soft-sided flight pack like a LiPo or LiFe shifts slightly during a violent maneuver (e.g. a crankshaft or snap roll maneuver, or maybe a really hard pull out from a dive), thus bumping against the sharp edge of a plywood or carbon fiber part of the structure (former) and as a result, gets dinged or creased? Even if you subsequently smooth it out so the ding is indiscernible, the damage done to the electrolyte is forever and the pack may then be prone to failure. Hard to know. Worse, said failure could involve fire. Fire?

Fire Risk

Yes, fire - and fire is not a risk I am willing to take. At least not for the slight potential difference between LiIon and LiPo, meaning for the sake of a small increase in voltage (really meaning for a tiny little bit more servo-performance) or the slight difference in weight (remember, we're talking about smaller receiver packs, instead of massive propulsion packs.

True, in particular considering I'm not some world class pilot but, instead, I'm a relative nobody (a duffer in point of fact) who couldn't feel the difference in performance between LiPo and LiIon if my very *soul* depended on it! And perhaps most especially true because as a youngster in the Scouts, I would have quite highly prized balsa wood and the cured resin of fiberglass bits (like a cowl) as a substitute for *tinder* when starting a fire! Catch my drift in terms of what a battery bursting into flames within a model airplane really means in it's physical proximity/relationship to my workshop/home? What about yours?

Thus, you'll forgive me if I am rather less than keen on LiPo packs within my models for *anything* other than propulsion (where they absolutely rule except for a few rather specialized applications). This, because they are firmly strapped into place. And then removed from the model.

And take note, LiPo and LiIon packs come out of the model 100% of the times, are charged with my eye on them (whilst puttering in my workshop), placed on a fireproof surface (a 99¢ square of ceramic floor tile works nicely), and are stored (at reduced voltage, so called storage-mode) in specialized bags, which are proof against flame.

Basically, the hazard posed by these LiPo and LiIon cells is well established, and the risk of fire that comes with them - under these conditions - is small, but not zero. Heads up. Reminds me what a college professor once said about the difference between hazard and risk;

  • The hazard are the sharks circling in the water,
  • The risk is what you undertake by jumping in.

The packs John prefers to use

As I mentioned, LiIon are my other preferred pack for 3D-type and sport models but *only* when I can remove them for charging. Otherwise, the *only* pack I'll leave in a model (typically as an aid to balance), and charge in-situ, is a LiFePO4. No exceptions.

The downside to the LiFePO4 include being a little bit more costly, they also deliver significantly lower potential (as a practical matter, and once again, I couldn't tell the difference in servo-performance between LiFe, LiFePO4, LiIon, or LiPo if the Devil himself offered me a deal), and they weigh a little bit more. Ultimately, we all make choices, or put another way, horses for courses!

Note; regarding battery packs, we don't make them. We spec them - so they're built how we want them to be made. That, and we handle two types, and of varying capacities. These being LiIon and LiFePO4. And all have four leads. Four?

- Two DuPont leads, an XT30, plus balance - added big advantage comes of using 2 switches

On leads and benefits

Yes, 4-leads! As for why four leads, two are 20AWG with DuPont connectors. Note; regardless of what you call them, e.g. Futaba, JR, Hitec, or what we use, the Universal connector that works with all of them, they're just a variation of the original Berg connector (the same Berg connector, which E.I. DuPont subsequently purchased and became eponymous as 'their' connector). Anyway, regardless of what you call them, they're *all* rated at 3.5A continuous. Draw more than that you get heat. And heat is *bad* for electronics.

So eyeball the servo specs chart again, scan to the desired voltage, then eyeball the current at the worst case - stalled - and then imagine six or seven servos within your model, maybe not all stalled *but* nevertheless a butt load of servos drawing current and the *why* for using two leads become obvious, or should.

If not, then as an exercise for the student, review these articles and get up to speed.

Anyway, in addition to two DuPont connectors, there is also a JST-XH balance lead/connector, *plus* a fourth connector, this one on a 16AWG lead (thicker, to handle more current) equipped with a yellow 30A connector (called an XT30).

The balance is for reason to do with charging lithium based packs such that the cells stay within a narrow range. And the 30A has to do with getting current in and out at a higher rate. Note; it, plus an available PEXD adapter lets you make use four DuPont connections, if needed.

Four DuPont connectors? What on Earth for? Well, or example, I use one of these PEXD adapters to let me feed two receivers off one battery pack. Thus, each receivers gets 7A (3.5A through each of two DuPont connectors), and with a PEXD adapter attached to the XT30, then I can split the loads for a model equipped with a lot of servos between the two receivers. This is called load balancing in the electrical world.

Anyway, a second major benefit beyond load-balancing, or splitting the current load between two receivers so each only sees half of the total (a big deal with some models), is the attendant redundancy. Redundancy can be a really, really good thing, also!

Major point being, if a receiver takes a crap, then landing the model remains possible with half the control surfaces because two receivers gives me redundant control over my model. Not as good as all the surfaces but half of something beats all of nothing, in my book! After all, even diminished control meets the definition of *control* for a remote control aircraft, right?

Load balancing vs 'thingummy, or 'box' system

So why not use a thingummy or one of the so-called 'box' system? Don't these things (many, all, most?) offer the ability to connect two receivers that switch over automatically and you retain full control in the event of receiver failure. And gyros as well? Well yes, but, all this goodness depends on what is inside working 100%, else now what fails isn't a receiver but what it's plugged into. So every added component adds links to the failure chain, any of which can bring down your model. So the mere act of trying to make things bulletproof exposes you to greater risk, which unless you've studied statistics is counterintuitive to modelers.

Component count matters!

This brings up the major problem for my pea brain as it relates to a thingummy system. They add more complication (in the vernacular, more shit to go wrong). This is because (if you open up a thingummy) you'll realize there are a shit-ton of components inside (shit-ton being technical term for, a lot). Many, many more components than you'd believe! So it follows, now there's much more to go wrong!

Of course the fellows making bank by selling thingummies won't disclose this little fact (meaning they also put lipstick on the pig), but anybody who took a course in statistics in high school or college can work out the implication of a butt load of added components to the risk of failure for a system, any system. The math don't lie, folks!

So believe me, because there are a *lot* of parts associated with thingummy and other 'boxes', then the risk of loss is higher as a consequence of adding safety. Of course, it's your risk, not mine. And yes, we (ProModeler) could become a dealer to sell thingummy boxes (there are many manufacturers looking to sell them), or we could even make our own, but we don't. We choose to focus on servos and solutions instead of gee-whiz gimmicks for the sake of a buck.

Minor point being, our advice in this regard is unbiased because we don't sell the devices (but could) which really means we don't have a dog in the hunt influencing our advice. Major point being, we're all big boys, so in regard to using a thingummy, you pays your money and takes your choice!

So what's my heartache with complication? It's because as an engineer, I had it drummed into me at university that it was almost always better to live by KISS (Keep It Simple Silly). If you're curious to learn more, read this:

This article explores using two receivers in parallel to split the current load of the servos. And I rather like the simplicity of using just two receivers because if one craps out, you retain partial control and thus, you just land the airplane. By this meaning, unlike a thingummy ahead of the receiver, it that thing craps out, now you're a spectator to the crash!

Anyway, ultimately, you do you, and I'll do me so if you'd rather use a thingummy, go ahead. After all, free advice is worth what you paid!

- PEXD adapter allows extraction of 14A of current via four DuPont connectors

Anyway, the battery leads on our packs have silicone insulation (jackets) because it's super flexible and resists abrasion. The wire is the high-strand copper type, the good stuff, best money can buy.  And they're priced fairly.

Note, while we *do* have a dog in the hunt when it comes to batteries, in the interests of full disclosure, multiple leads aren't patented, or anything. If you already have a favored battery supplier, then any of them will build you pack with similar leads, just ask.

Next, let's talk about the two advantages of dual-leads on your pack.

Dual lead battery pack advantages

So one major advantage of dual-leads being it permits the receiver to draw 7A continuous without heat build up. Heat is bad juju for electronics!

Note: any battery pack with a single lead is a 3.5A device.

However, a pack with two leads is capable of delivering 7A because each delivers 3.5A so 3.5A + 3.5A = 7A (they're in parallel and receivers use a bus-structure meaning you can give them juice anywhere, not just at the port marked BAT). And with a PEXD, you can suck out 14A using DuPont connectors. That's a lot but honestly, 7A is enough for almost any model. But do the math for *your* model, OK?

A second major advantage of the dual-lead battery pack is you can use two switches instead of one. Since switches are the #1 failure point in a model airplane, using two in parallel increases safety because odds of both switches failing on the same flight are astronomical!

Anyway, the pack in the above photos, the B2S2500 is our most popular and it's capable of delivering 25A. But we offer them ranging from 650mAh through 6000mAh depending on your needs.

A little more math

I just laid out the fact a B2S2500-10C can deliver 25A so let me explain how you determine this for yourself because the math is easy. All you need are two bits of information; the capacity and the C-rating.

Regarding the 2500mA pack, allow me a brief birdwalk, please related to part numbers;

  • B = Battery
  • 2 = 2-cells
  • S = Series
  • 2500 = Capacity
  • 10C = C-rating

. . . so this pack is actually a 2.5A pack because m=milli and means one thousandths so (2500mA/1000mA/A=2.5A), and current (in A) multiplied by C-rating, or 10C for this particular pack so it works out to 2.5*10=25A.

And since 25A is *far* more current than the four DuPont connectors can deliver (3.5A * 4 = 14A), then the connectors are the the choke point, not the battery itself. So if needs be, the load (servos) can be supplied by as many as four JR-type to deliver 14A, using DuPont leads.

XT30 connectors

But this is *still* less than the XT30 connector can handle (these packs are popular with the turbine crowd where these engines use the XT30 connector for the self-contained electric-start function). The XT30 is rated at 30A (I *like) when a current rating is incorporated into a product part number/name because it requires less thinking).

Eyeball the XT30 for battery connection for self-start on the Xicoy turbine of this photo.

- This baby turbine, a 45N engine, is harnessed by a gearbox for use with a prop!

Background info

Note; LiFePO4 is pronounced Lithium-Iron-Phosphate for its chemistry (Lithium is Li on the Periodic Table, an element), Iron is Fe, another element, and Phosphate is PO4, which is a compound. These are often abbreviated LFP, or also by a brand-reference, as A123 technology (but all are just different names for the very same thing).

However . . .

  • LiFe and LiFePO4 are NOT the same thing!

As further background, A123 Racing, once based in Massachusetts, USA were a battery technology developed at MIT (Massachusetts Institute of Technology) and the inventors, when they found themselves in need of capital to fully commercialize, could find no American company willing to step up to the plate with the required money. American companies being defined as Wall Street-types where quarterly performance is the metric instead of a focus on development, which may take years. Basically, Chinese companies take a longer view and thus have patience American companies don't. As it happens, I admire the discipline to think long term, but that's neither here nor there.

All this by way of explaining how it came to pass that A123 were snapped up by a Chinese entity that commercialized them successfully. This is not a political-statement but a statement of business-fact. That, and to my knowledge, there are zero western producers willing to sell cells in modeling-quantities (true even if we pooled every model company in the USA to combine as one battery pack-buyer). Anyway, while the LiFe is a similar chemistry, in the never-ending quest for cheaper products, they're what results when cost is the focus instead of performance and thus, they are much more cheaply made, one example being the use of a more delicate polymer bag instead of metal shells.

Meanwhile, take for example, Tesla batteries (Panasonic process) are LiIon. Each encased in metal shells. So are the packs used by Chinese automakers (Cherry, Great Wall, et al), although LiFePO4 has promise for battery walls and other stationary storage applications (in general, higher voltage trumps pretty much anything when it moves).

Other American manufacturers like Chevrolet and Ford are using LiPo cells but they both armor and water cool them, too. Moreover, have you noticed in the news how Ford, Hyundai/Kia, and Chevrolet have now issued warnings against parking your LiPo equipped EV inside the garage of your house? Fire risk is the reason, they don't want the liability!

Circling back

So a bit further with regard to overspeccing servos, if you eyeballed the servo chart above, what *should* have leaped out is the DS180DLHV gives you 180oz-in on 8.4V but on 6.6V (the 2S LiFePO4 pack) its torque delivery is down to 130oz-in. So if you're thinking 180oz-in is more than you need because the model calls for 150oz-in but then decide you like using  A123 packs, oops because they offer up a lower voltage level and this = less output (and speed). From the chart, the DS180DLHV on 6.6V only outputs 130oz-in so you'd be underspeccing instead of overspeccing!

And remember, lower voltage means reduced performance is true for every single servo you can buy on this planet and it's entirely due to physics. Major point being . . .

  • Savvy modelers *first* decide on battery technology and *then* select the servos!

Put another way, determine the desired battery chemistry, from this you know voltage, then scope out the servos that will deliver the required torque at that potential *and* bear in mind, if some is good, more is better became a mantra for good reason.

That, and as it relates to speed (another factor voltage affects), never pay for speed you don't need because speed costs money! So if the only place you'll feel it is in your wallet, what's the point?

A perfect example of savvy servo selection

Recently a highly experienced customer asked about servos for an Extreme Flight Muscle Bipe and was delighted that against $800 for 8 servos (the least expensive alternative offered on their site, with the most expensive summing to $1350), because based on how he told me he flew, I guided him to a set of seven DS360DLHV (at $50 each) plus a throttle servo (DS90DLHV at $30).

So he put his model in the sky for a grand total of $380 for the servos, or less than 1/2 the least expensive price. And proving he was savvy, he's so happy he shared this photo!

But did we underspec his servos?


- You can throw money at servos or you can speak with us, first

On underspeccing servos

So to better complete an answer to the question regarding overspeccing servos, let's also discuss underspeccing the servos. Remember, the specs are

In part it's the matter of chemistry (voltage) determining the servo torque spec we should buy, but also bear in mind how back in the day you were limited in what existed, servo wise, due to the motors. By this meaning the available magnets since magnets are fundamentally what limits the power derived from the current of the battery.

Opium Dreams

Back when the Hitec HS-5645MG (180oz-in @ 0.17sec/60°) was one of the most desirable servos on the plant for modelers (remember, I *said* we'd get around to mentioning a Hitec servo), a mini-class outputting 405oz-in @ 0.052sec/60° (like our DS405BLHV) would be considered an opium dream.

By this meaning something you could not buy for any price! Why not? Partly because of batteries back in the way weighing too much for models to deliver 8.4V (7-cells) but also because of available magnet technology. Neodymium magnets are the secret sauce in ultra performance servos like ours and if you don't know diddly about servo motors, this article may help guide you . . .

. . . which like all the articles, is offered because informed decisions are based on knowledge (or put another way, *knowledge* is power).

Wrapping up

So next, let's step away from ARF models and look at kits and plan built models, instead. Take for example someone building a Hellcat from a set of Rich Uravitch's plans. A model dating back to before lithium chemistry and neodymium magnets so much as existed outside of a lab!

Is it any wonder then, how for those plans, he (Rich) specced what was then readily available servo-wise? Maybe something like the aforementioned Hitec HS-5645MG outputting 180oz-in? Of course, but these days?

Honestly, that level of has been surpassed by a country mile! Proof? Take note of how we offer the DS125CLHV, a sub-micro (so called 9g class) outputting 125oz-in (2/3rds the torque, much faster, and only 1/6th the volume). This is one example of formerly opium dream servos.

In addition within the same standard class as the old Hitec design (meaning a 20x40mm footprint), we offer the DS1155BLHV, a servo outputting 1155oz-in (for if there's a need, as was the case with Darrin warping a set of wings for the model below).

- Darrin Covington's museum scale S.E. 2 enables rolls by warping the wings like the full scale

Anyway, since I brought up building other than an ARF, and if you want to go on a mind trip, visit RCSB (my favorite forum), where Darrin began a thread on the above 1/3 scale R.A.F. S.E.2, a de Havilland design from the lead up to WWI . . .

And as usual, for links I offer, clicking opens a new browser tab so you don't lose your place.


The decoder ring
By the way, you don't need a decoder ring to suss out our servo model numbers because . . .
  • DS = Digital Servo
  • xxxx = torque rating in oz-in
  • BL = Brushless motor (and there are DL and CL types)
  • HV = High Voltage (to 8.4V)

Last thing, we have another technical article folks may find of interest;

. . . offered because we don't pretend our servos are unbreakable or infallible.

If I've missed anything, or if you have further questions, just reach out via;

  • info@promodeler.com
  • 407-302-3361

. . . and I'll try to help.

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