As is often the case, an askJOHN
comes about from a question(s) someone asks, which generates a response, which I judge others will find useful. This is the case once again as a fellow has asked around, gotten conflicting information, and decided to go straight to the horse's mouth (that would be me). This, by the way, with regard to one of our servos and whether it'll work with his ESC which comes with a BEC, specifically, the very well regarded Hobbywing Max6 V3.
Note; as usual, links open another tab within your browser (so you don't loose your place), so here goes.
Q. I have an Arrma Kraton 6s EXB 1/8 truck. I'm looking to upgrade my servo and have been eyeing one of your DS635BLHV for some time now. I'm running a Hobbywing Ezrun Max6 V3, and after doing much reading I'm getting conflicting information.
Many people are suggesting that this servo will run fine directly from the Max6 ESC at 7.4v. Some are saying run it at 6v, other are saying buy a UBEC from ProModeler.
I realize you suggest running directly from an independent battery, but this doesn't really appeal to me. My question is will the DS635BLHV run off the Max6, and if so what voltage should I run it at (this is my preferred option)? Will I need a glitch buster? I currently run the Savox SB-2290SG without a glitch buster and have no issues, but I would like a faster, better quality servo. Thanks heaps in advance, can't wait to get one of these beasts.
A. So I responded with, yes, 8.4V, and maybe
. . . while asking him to hold tight because I was working on a
more comprehensive response (this one). He subsequently wrote asking further
questions . . .
Q. I’m now thinking of going with the DS845BLHV.
Looks like an absolute beast of a servo! I think that little extra
torque is worth the money, what do you think? Do you have a
supplier/stockist in Australia? The BEC in the MAX6 only goes to 7.4v @ 25amps (doesn’t have 8.4v). Will 7.4v be fine with the DS845BLHV?
A. To which I responded, yes, no, not really . . . while again asking him to hold on. This is a more comprehensive response.
So now I have several questions and while I initially responded with yes, 8.4V, and maybe to which I added yes, no, not really, now let me expand on this for his benefit . . . and yours.
we're happy to offer our products through stockists in Australia - but -
please realize they run a business and have overhead and profit
So buying through a stockist (what in America we call a hobby shop) will likely require a 30% margin (what they usually earn). This is added on top of what they pay us (the exact same as you'd pay). Plus the postage required to effect delivery to Australia.
So yes, we can sell to stockists/hobby shops - but - you're going to pay 30% more. Or you can buy it from us direct.
Regarding 7.4V and 25A
The servo will work fine on 7.4V because the maximum it's capable of working with is 8.4V.
Regarding 25A, I suspect that's merely a fat finger error on someone's part so when you see this, my advice is ignore it.
- When you see this about 25A, it's likely an error
the reason I say this is because a closer reading of the specifications
shows the unit is rated at 6A (and likely where the 6 in Max6 comes from within the
Anyway, they mention 6A in several places, this is an
- Here the specs are more clearly stating 7.2V and 6A
if you're OK with the servo's performance at 7.4V, then the servo will be perfectly happy functioning at 7.4V because it's capable of operating at 8.4V, which is higher. Note; that they mention 7.2V in the specs - maybe another fat finger error? Could be is my opinion meaning they probably mean 7.4V (remember, English isn't their first language so cut them some slack).
Anyway, our servo is also capable of operating on 6V. The real question is; are you
willing to pay for our servo and not get 100% of what you paid for?
Does this strike you as a strange question?
Regarding the strange question
Would you be happy to receive 740oz-in when you paid for 845oz-in? I suspect not. Yet this is what you're telling me when you say you prefer a Hobbywing Max6 voltage regulator circuit (the BEC). Let me explain . . .
To begin, with regard to the DS635BLHV first, then the DS845BLHV, they're 8.4V servos, and we show you what performance you'll get on 8.4V, versus 7.4V, versus 6.0V, and all the way down to 5V. We disclose many things in the specifications but let's concentrate on torque and speed at various voltages.
Eyeball these specs for the DS635.
The first thing to do is scan across the top to the 7.4V column. Now scan down to torque-line and note it's 555oz-instead of 635oz-in. That's because we rate it on 8.4V where it's a 635oz-in servo.
But at 7.4V it makes less. And at 6V it'll make even less - where it'll only produce 485oz-in, and at 5V its producing just 420oz-in. Same servo, only change is voltage level 'in', understand?
However, the fact is our servo is perfectly happy on 5V, 6V, 6.6V, 7.4V, or 8.4V . . . but the voltage determines the performance. And this is basically true for EVERY single servo on the market regardless of brand, e.g. torque/speed varies with voltage input. But this isn't the whole story. You must also consider current, not just voltage. Two factors, so put another way, you have to both walk and chew gum!
And you're obviously aware of this because you note the Hobbywing Max6 is a 6A device. So now let's delve a little bit into current, measured in A for amperage.
Current is the real story
So here's how you use the information we give you. Within the 7.4V column, scan down to Current (stalled) and you'll see it says 5.1A . . . and with regard to what's actually important about this? Simply this . . . 5.1A is how much current it requires at 7.4V to give you 100% of what the servo can make at 7.4V, which is 555oz-in.
In order to to get 635oz-in, you must allow it to consume 5.4A but at 8.4V, which the Max6 won't do because it's a voltage limited device (max is 7.4V). Anyway, also remember how current works, you don't give the servo 5A, it draws what it needs. Just as you can't push water uphill without a pump, you don't stuff current into the servo, the servo sucks what it needs from the source.
So servos suck power, sources don't push power. Had a female customer observe servos are to sources (BECs and batteries) what babies are to mommies . . . meaning a consumer that demands something. Her point being, in the same way mommy doesn't determine how much milk the baby gets, the source (BEC or battery) makes available what the source demands but doesn't determine the flow rate, either!
Add to it this fact - this is true about all servos in the world, all brands - if the servo can only draw a certain amount of amperage and this is less than it needs? Then it will not produce the rated torque because you can't make torque out of thin air!
With a Max6 you're pretty much choking down most servos making more than 635oz be it ours, our competitors', everybody's servo because a Max6 can only feed enough current for a servo to produce maybe 555oz-in, give or take. So you were largely good with the DS635 (although at reduced performance) but then you expressed an interest in the DS845. Not a rosy picture with this one, sorry.
Note; by choking it down I mean starving a servo of current, which is like putting a sleeper hold on someone. Just as this will choke them out, the servo is starved for current instead of air. Take my meaning?
And note; this shit isn't theoretical because we test enough servos to get a good idea of what they make and how much current they're consuming to make it, and only then do we share the results in the form of specifications. So we know what a servo is going to make in the way of torque, and how much current it'll draw doing it. This isn't an opinion, understand? This is what's going to happen!
Anyway, at 7.4V, the DS635 won't generate 635oz-in, it'll only give you 555oz-in while consuming 5.1A. This is true if and only if the Max6 is actually making 6A. Dunno. Need to test it and see - and not at the 21°C (70°F) of a lab, but at the 35-40°C (95-104°F) of the real world.
Actually, we've measured worse than this in the real world as we stuck a thermometer beneath a white model helicopter canopy once and it was a scorching 135°F and honestly? I figure it'll be worse with a rig because so many have dark bodies (just like getting into a white car in the summer versus a dark colored car). But it gets worse because remember, the BEC-circuit is being heat-soaked due to the ESC making heat as a by-product of operation (reason good ones have fans).
Anyway, and quite basically, it's unlikely - in my opinion - a Max6 actually delivers 6A when it gets hot, meaning real world. Maybe it does, dunno. Have to test and see but this is my opinion. Will it work with the DS635? Probably yes but maybe marginal because this leaves no overhead whatsoever. Not good.
- Basic point is, in a perfect world a Max6 barely has the stones to run a DS635
Of course, I know you want me to blow smoke up your skirt and say it'll definitely work. I know what customers who tell me they want the convenience of a BEC really want to hear from me, but honestly? While the easiest thing in the world is for me to be agreeable and sell you a servo, call it done, and move on to what's next (especially because the average guy will never know the difference), the fly in the ointment is . . . I'll know.
So whether you can tell the difference, or not, the real reason I don't just shut up and sell you the f-ing servo is because I have to sleep with my conscience. And no offense, but I don't need your business enough to lie in order to get it. Lie? Yes, let me explain.
Lying through omission
In college you take a course on philosophy. One of the things you learn are the ways of lying. Or you can Google it and learn there are two primary ways to lie:
to conceal and to falsify.
In concealing, the liar withholds some
information without actually saying anything untrue. In falsifying, an
additional step is taken. Not only does the liar withhold true
information, but one presents false information as if it were true.
Delve deeper and you find out there are 4-ways to lie, some say 5-ways.
- Lies of Denial
- Lies of Omission
- Lies of Fabrication
- Lies of Minimization
- Lies of Exaggeration
To which I add, Lying to Yourself.
Regardless, omission - or not saying anything - is one of those lies on the list. And I know all about lying because my grandfather was a lawyer and as a little kid he taught me everything he knew about the subject because a) as a lawyer he dealt with a lot of liars (occupational hazard) and, b) he hoped I'd become a lawyer and take over his practice! Instead I followed my father into engineering and here we are, but I digress.
Bottom line? There is no point within the performance curve of the DS635BLHV servo where a 6A supply is going to cut the mustard. Best you're going to get is 555oz-in.
- Will the Max6 run the DS635 on the workbench? Yes.
- Will the Kraton 6S tool around the yard? Yes.
- Will it give you the 635oz-in you've paid for on a Max6? Nope.
There's not a chance in Hell you get 635oz-in out of our servo on a 7.4V supply (and that's being generous and presuming that thing really gives you 6A). Me? I have my doubts you even get the 555oz-in it's rated at at 5.1A but let's not go any deeper down the will-she/won't-she rabbit hole. We're deep enough in the weeds as is.
Especially since they (Hobbywing) don't share spec sheets for their device (nor do they state at what temperature the figures are obtained, and/or whether this is with or without additional cooling. These things matter, but moving on . . .
So next let's look at the DS845 servo where we're going to see pretty much the same thing, but worse (in a manner of speaking).
And as I know (because I designed it) and you will immediately see (and surely not be surprised to learn), the DS845 requires more current than the DS635 to reach it's maximum performance.
And once again, max performance comes at current (stalled), 8.2A at 8.4V, or 7.7A at 7.4V and at 6V, it might run it pretty good because it only needs 5.2A but this only gives you 625oz-in under the most optimistic of interpretations. 625oz-in is more than 555oz-in but still a far cry from a) what the servo is capable of outputting, and b) what you paid for. Basically, the Max6 simply doesn't have the grunt to power the DS845 to anywhere near rated torque - not really.
- Not saying the Max6 is a bad unit. Saying it's a 6A device and you need more.
So once again, even if you're fine with receiving less torque than the servo is capable of delivering, it's going to require north of 25% more current than the Max6 is capable of delivering (6A) to only get 740oz-in . . . but it won't make that because it can't give it the 7.7A it needs to make 740oz-in at 7.4V.
In fact, it's likely only really giving you 625-in at 5.2A (and that's true if and only if the Max6 is actually giving you 6A), which is about as much better than the DS635 as you'd expect. Me? I have my doubts you really get this because I've never seen a BEC that delivers what it's claimed to deliver. Especially once you bring heat into the equation.
How can I prove it? Simple, connect a servo to a Max6, get it to 105°F, then put it on the HP100 torque tester and see what the servo can deliver in the way of performance. If I were curious enough, I'd check and see but in point of fact, I know a 6A device can't supply my DS845 product at rated torque, so why bother?
Ultimately, and no offense,
but instead of believing you're lying to yourself in thinking a Max6 is 'maybe' good enough for a DS635, probably not good enough for a DS845, I'm actually of a mind to suspect you're not clear on the difference between voltage and current, or amperage.
That said, you're not alone in being confused. This is the principal reason I am expanding on my response to you.
- Voltage and current are two totally different things!
So what about the Savox SB2290SG-BE?
Since you've probably twigged to the fact I am answering/commenting in reverse order, I'll continue with this; initially your inquiry regarded the DS635 but now you're thinking the DS845 is more to your tastes.
And you've made the mistake of asking my opinion. This after judging for yourself you're willing to pony up a little bit more money. That's fine as long as you remember this;
- opinions are like bellybuttons - we all have them, and
- I've a dog in the hunt since the DS845 makes me more money
- And Savox is a competitor
. . . so since you mentioned the Savox, I'll try to give you a fair and balanced answer. And to save you time, I'll cut to the chase and just tell you who killed Cock Robin; the Savox won't run to capacity on a Max6 either.
How do I know? Simple, I went to their site and looked at the specs.
. . . and what immediately jumps out at me is that to make the rated torque, their servo requires 10.5A at 8.4V . . . and 9.2A at 7.4V and 7.5A at 6V so no way in Hell a puny little Max6 can operate their servo! Starting to understand why I guide people away from a BEC?
Buy a UBEC from ProModeler
You also asked about buying a UBEC from us. Yes, we sell them. The unit we offer is a Castle CC BEC Pro 2.0. Me? I'd rather run a battery - but - you already know this. However, if you must operate your servo off a voltage regulator, then that's the best one we know of. But why, you wonder, do I recommend against them?
To begin, and again, no offense but I probably know more about this than you. This is why I penned this little article called The Case Against Synthetic Voltage to help folks learn more about voltage regulators (and this is what BECs do, e.g. regulate propulsion pack voltage down to control electronics levels).
FWIW, they're called Battery Eliminator Circuits because they're designed to save the rig-manufacturers money by eliminating the cost of a separate receiver pack. But they have zero to do with high performance, they're strictly about saving money. If this were about saving money for you you'd be buying a no name East Asian import off Amazon, right? Anyway, read the article because you might learn something. Best part? It's free!
Please also take special note of the comment by a project manger at the bottom of the article - the guy at the US Navy Research Laboratory - who chimed in with regard to BECs in general. And remember, these guys have goverment-grade money to spend, eh?
Put another way, it's safe to say they're not using some hobby-grade BEC and yet they still revert to batteries instead of BECs because batteries are better. Trust me, there's a reason and it's to do with what you get from a BEC, any BEC no matter how much you spend designing it, is garbage. You can't see it with a $5 voltmeter but you can definitely see with with a lab instrument called an oscilloscope. Read the article!
Buy a capacitor (a glitch buster)
This is the first smart thing you've asked me. Facts are a capacitor can help mask some of the problems by releasing a jolt of juice when the servo needs it and recharge when the servo is loafing. Almost like something for nothing!
But at best one of these things is a BAND-AID for this purpose (a rig with a BEC that's insufficient or barely sufficient). That said, they do serve useful purpose because they protect the servo and receiver from spikes and give a squirt that may be helpful.
With the DS635, I'd definitely run one, maybe two. But with the DS845 or Savox? Won't help. Thus, having one is generally a good idea but if you need several, then you need to figure out that the root cause of the issue really is. Take my meaning?
Anyway, we offer a capacitor, called a glitch buster, or you can make your own. You can even put two on the receiver if you know where to connect them (at the servo ports, and if you don't have a spare port, then use one of these nifty Y-harnesses to make a place for it if all the channels are occupied with servo). Then just plug the Y-harness in where the servo is plugged in, and then plug in both the servo and the glitch buster into the block and easy peasy, you're done!
So why do you recommend a battery?
Aha, finally, what you didn't ask me! The reason to use a battery is they're capable of giving you 20A of the cleanest analog power on the planet. Compared to the digital shit coming off a BEC? It's no contest between the two!
Anyway, 20A is more than enough for any servo you're considering. Problem is, any ordinary battery you buy has just one lead. Thing is, a lead is worth 5A. So a battery with just one lead won't do the job, you need a pack with two leads, are we clear?
So to solve this problem (of getting more than 5A out of the battery that's capable of delivering 20A) we have packs made with two leads. Anybody can do it because it's off patent. And FWIW, this works for the same reason 5+5=10, or 10A.
Granted, 10A is only half the 20A a battery can deliver (batteries are a really, really good source of current and voltage, the best, in fact) but 10A is enough to solve your problem with a DS845. And that's ultimately what we're about doing, trying to sort your problem, e.g. helping you get what you paid for out of one of our servos!
So what about our DS1155BLHV servo? Even worse, right? Well . . . maybe not. This is an interesting servo. So let's see why.
Eyeball the specs for the DS1155
See anything interesting? The DS1155 is using a different family of motors from the DS635 and DS845 and as a consequence it's very, very efficient. It's in a league by itself at current draw and rated torque. At 1155oz-in it's only drawing 7.0A while at 7.4V it's still making 1030oz-in and only drawing 6.6A, and 6.0V? It's still making 875oz-in and drawing just 5.9A. This means a Max6 can maybe (if it really makes 6A) run this servo pretty well (which it couldn't with the DS845), and definitely couldn't with the Savox 2290SG. If 875oz-in is enough, then try using the Max6 and maybe you'll be happy. Depends.
Basically, the DS1155 is a freak because of it's motor. And we're secretive as hell about it and our Japanese source because take note of how much current the Savox is drawing to make significantly less power . . . it draws 35% more current (10.5A vs. 7.0A) and makes 250oz-in less torque. This is a big deal.
So back to batteries, our two-lead packs easily get 10A into your receiver to distribute to the servo. No fuss, no muss, and perfectly clean. Batteries supply analog current and BECs supply digital current and just like analog amps beat the snot out of digital amps in the audio world, batteries clean the floor with BECs. Fact.
If you want what you paid for, use a battery. It's the best alternative. Then there's no question whether the BEC is up to snuff, or not because the battery definitely is. Ours come with three leads instead of two because we also give you an XT30 (a 30A connector).
Look, we don't make batteries, we have them built to our specs. But the specs we have them built to are ones suitable for pros. Piece of advice? Stop thinking just because you have an electric powered rig, you can treat it like a toy. It's not a toy and best practice with high performance servos - ours, or a competitor's - is to power the control equipment the same way you would a high-end race car or truck with a dedicated pack. Think tool, not toy!
There used to be a breakfast cereal commercial on television where the tag line was, 'Silly rabbit,Tricks are for kids!' and I would substitute, silly modeler, BECs are for kids - except - I don't want to insult folks (but it's what we're thinking behind the scenes).
Our best advice, and again, this is true whether you're running one of our servos, or a competitor's, think instead of powering your rig's control electronics in the same way the guys who run nitro-buggies and gasser-powered giant rigs do it using a dedicated pack.
So instead of Mickey Mouse complications involving siphoning power from the propulsion system to power their control system (like the manufacturers supply with an all in one box combo where components only last a while before getting ripped out and replaced with good stuff) is don't treat it like a budget build. Instead, rely on a dedicated pack to do the job.
After all, it's not like it's much trouble to charge a small pack. And it'll run the rig all day (basically for 6-8 runs of your rig's propulsion pack) before needing to recharge the control pack. What's the big deal?
Hobbywing make available an extended warranty of sorts, what they call the Care Shield Plan. It's a really smart move on the part of one of the finest companies in the ESC-business because they know any product can take a dump on you.
Basically, it's insurance, meaning a numbers game where an actuary calculates how much you have to collect to replace dead units. It's based on their run 'rate' and because they are privy to the numbers, they set a price that protects them. And if you don't buy it? Too bad!
Doesn't make them bad guys, makes them smart guys in my book. But now look at it from our viewpoint. BECs fail. They typically fail in four ways;
- Fail High
- Fail Low
- Fail Zero
- Fail Intermittent
Obviously the problem with Fail Zero is nothing works - easy. With Fail Low things don't work well so servos lack grunt, LEDs are dim, fans are slow. Problem with Fail High it fries things (expensive too, like receiver and servos - anything connected to the device), Finally, Fail Intermittent is what it says, and these are a total pain in the ass. In the trade we call them 'Caspers' like the ghost because they're hard to figure out but Fail Intermittent can be shooting high voltage or low voltage, or zero voltage. Bad juju.
Point is, you feed our servo with a BEC and unlike a battery that CANNOT fry the servo due to high voltage, a BEC can release more than 7.4V or 8.4V to the control system.
And while receivers can withstand 12-14V briefly. Servos go poof at about 8.6-8.8V and release the magic smoke. Think we're the only guys saying this? Think again because the best servo company in the world, Futaba, gives the same warning!
Point being, when a servo comes in for service or repair, we can tell if it failed due to high voltage. Not going to cover you with a warranty repair.
Don't like it? Buy someone else's servos because we're going to be fair with you, but we're not going to warranty our product based on some BEC maker's product working like it's supposed to because, like Hobbywing, we also know things go teats up, sometimes.
It wouldn't be fair to us, our employees, suppliers, not fair to anybody. Not fair to you either because it would lead to higher prices to cover the practice because there ain't no such thing as a free lunch!
Oh, and another nice thing about a dedicated pack? It can't ever fry your servo due to over voltage - not ever! Physics (or chemistry if you want to be pedantic). Choose wisely.
In closing, if you have any further questions, reach out to me via email:
- or - if it's urgent,
you may always call;
407-302-3361 because I love bullshitting about models more than