Kraton Best servo money can buy?

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slick2500 said:
If you do not plan on driving your rc in wet conditions then no there is no reason to get the waterproof one.
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maybe not right now until i get bored. i do have a dust cover so should protect it from rain or snow. i know i wont be jumping on muddy puddles for sure.
 
Thumper33 said:
Okay all.... I've been looking at this for days. Simply looking at paper stats, not knowing anything else about these, here are some top options I've found in no particular order. My selection criteria were:

1) at least 400 oz-in of torque
2) at least .125 or less 60 deg speed.
3) No plastic gears
4) Lighter is better.
* price not a factor per OP

Spektrum S652 - The stock EXB servo for reference
Torque: 18.94 kg / 263 oz-in
Speed: 0.227 @6v / 0.184 @7.2v
Weight: 65 g
Price: $52

Pro Modeler DS505BLHV
Torque: 480 oz-in @7.4v / 505 oz-in @ 8.4v
Speed: .108 sec @7.4v / .094 sec @ 8.4v
Weight: 84 g
Price: $90

Pro Modeler DS630BLHV
Torque: 555 oz-in @7.4v / 630 oz-in @ 8.4v
Speed: .109 sec @7.4v / .097 sec @ 8.4v
Weight: 84 g
Price: $110

Pro Modeler DS385CLHV
Torque: 345 oz-in @7.4v / 385 oz-in @ 8.4v
Speed: .078 sec @7.4v / .068 sec @ 8.4v
Weight: 59 g
Price: $80

MKS HBL380
Torque: 541 oz-in @7.4v / 569 oz-in @ 8.4v
Speed: .092 sec @7.4v / .082 sec @ 8.4v
Weight: 73 g
Materials: Chrome Titanium Alloy
Price: $213

Reefs 444
Torque: 422oz @ 6.0V / 444oz @ 7.4V
Speed: .11sec @ 6.0V / .10sec @ 7.4V
Weight: 63 g - LIGHT!
Price: $116

Futaba S9177SV
Torque: 569 oz-in @7.4v
Speed: .11 sec @7.4v
Weight: 74 g
Price: $180

Futaba BLS172SV and BLS177SV
Torque: 514 oz-in @7.4v
Speed: .11 sec @7.4v
Weight: 74 g
Price: $230

JX Servo BLS-HV7032MG (from Banggood)
Torque: 451 oz-in @8.4V
Speed: 0.07 sec @ 8.4V
Weight: 70 g
Price: $66

Powerhobby 729MBL
Torque: 565 oz-in @8.4V
Speed: 0.08 sec @ 8.4V
Weight: 78 g
Price: $95

hitecrcd D955TW
Torque: 405 oz-in @7.4V
Speed: 0.12 sec @ 7.4V
Weight: 65 g - LIGHT!
Price: $105

ZOSKAY 35kg (amazon)
Torque: 486 oz-in @7.4V
Speed: 0.11 sec @ 7.4V
Weight: 60 g - LIGHT!
Price: $33 - CHEAP!

AGF RC A66BHLW (low profile)
Torque: 459 oz-in @8.4V
Speed: 0.065 sec @ 8.4V - FAST!
Weight: 66 g - LIGHT!
Price: $95

AGF RC A73BHLW
Torque: 556 oz-in @8.4V
Speed: 0.1 sec @ 8.4V
Weight: 73 g
Price: $66

*** Let me know if you'd like to suggest another for the list ***
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Nice post Thumpy
 
vindazzle said:
maybe not right now until i get bored. i do have a dust cover so should protect it from rain or snow. i know i wont be jumping on muddy puddles for sure.
Click to expand...

Well most servos are rather easy to waterproof, you just need some modified silicone conformal coating and marine grease. You can also use liquid tape and marine grease but you have to put the liquid tape all over the seams on the outside of the servo and it just looks hideous.

There are tons of videos on YouTube that show you how to do it.
 
I use the Power Hobby 729 MBL. I have 5 of these in my 6s rigs. Excellent servos. Been running them for years with zero issues. 500oz on 7.4 is more than enough for a Kraton. They’re fast, powerful, and for 95 bucks, it’s a no brainer. Easy to find on Amazon, amongst other websites. Same specs as the Savox 1212, except standard height. (1212’s are are little taller, and make noise, and personally I think the 1212 is a little slower than the 729). You don’t need an external battery or BEC. No glitching or anything extra. Plug into your receiver and go. One and done🤙🏻
 
Buckwhea7 said:
I use the Power Hobby 729 MBL. I have 5 of these in my 6s rigs. Excellent servos. Been running them for years with zero issues. 500oz on 7.4 is more than enough for a Kraton. They’re fast, powerful, and for 95 bucks, it’s a no brainer. Easy to find on Amazon, amongst other websites. Same specs as the Savox 1212, except standard height. (1212’s are are little taller, and make noise, and personally I think the 1212 is a little slower the the 729). 🤙🏻
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I considered one of those, went back and forth between that and a Bluebird BLS-4311 for a few days. Ended up with the Bluebird but I think it has too much torque for my Kraton :ROFLMAO: way better than any Savox I've had.
I want to try one of these next https://www.bluebirdservousa.com/product-page/bls-m52b-magnetic-sensor-helical-gear-servo
 
slick2500 said:
I considered one of those, went back and forth between that and a Bluebird BLS-4311 for a few days. Ended up with the Bluebird but I think it has too much torque for my Kraton :ROFLMAO: way better than any Savox I've had.
I want to try one of these next https://www.bluebirdservousa.com/product-page/bls-m52b-magnetic-sensor-helical-gear-servo
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That’s some mean specs right there! Never heard of them. Definitely gonna try one on the next build. I like that they use hall sensors. Next gen tech right there. We use them in helicopter gimbals.
 
slick2500 said:
Well most servos are rather easy to waterproof, you just need some modified silicone conformal coating and marine grease. You can also use liquid tape and marine grease but you have to put the liquid tape all over the seams on the outside of the servo and it just looks hideous.

There are tons of videos on YouTube that show you how to do it.
Click to expand...
+1

I disassemble all my new servos out the package, no matter the brand. I have gotten defective ones. DOA. They get returned ASAP. I Evaluate them, test them on my Servo testor and apply Conformal coating to the PCB's, spread grease around all the gears lightly. Usually you find one small blob of grease that sits on one gear and never touches the Teeth of any of the gears. And some have Zero grease (Dry) And I found some Servos with no Conformal coating at all, despite claiming to be WP.
I don't expect most to do this. But food for thought if you are so inclined.
Just that I have good luck with servos now, and most of them are AMZ cheapos.
:cool:
 
SrC said:
+1

I disassemble all my new servos out the package, no matter the brand. I have gotten defective ones. DOA. They get returned ASAP. I Evaluate them, test them on my Servo testor and apply Conformal coating to the PCB's, spread grease around all the gears lightly. Usually you find one small blob of grease that sits on one gear and never touches the Teeth of any of the gears. And some have Zero grease (Dry) And I found some Servos with no Conformal coating at all, despite claiming to be WP.
I don't expect most to do this. But food for thought if you are so inclined.
Just that I have good luck with servos now, and most of them are AMZ cheapos.
:cool:
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Like I've said a few times I love the red ones I still have some that are 3-4 years old now but for some reason the blue ones hate me every one of them that I have bought has turned out to be a dud.
 
Vulthraxis said:
@slick2500 was the questions not best servo money can buy implying that money is not a question in what were picking there for picking an amazon cheapo is the problem in this thread no?
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Some people can't possibly consider anything else but budget and value for your dollar.

In racing, like in life, we call these people losers because they will never compete with the best. Only fight over the discounted left overs. The scraps if you will.

If you want the best, you have to pay like the rest.

Sorry if I hurt your feelings 🥺
 
The problems not his opinion. Its that he has a post after every other opinion on here discrediting the other opinion. This is not a debate. Quoting my self "IMO" in my opinion.

Its ok to have and opinion its not ok to police others.
 
Hi guys, a customer pointed me to this conversation saying we'd been mentions both favorably and unfavorably, so allow me to add a little bit of details to the conversation.

To begin, SrC is 100% right, when he states we have limited experience with RC trucks. Hobbyists comprise about 8% of our business with defense and industry being our most important customers by a wide margin. As for me, I'm more of any airplane guy but I do own two T-Maxx rigs (nitro powered, old school), an X-Maxx, a TRX-4, an Infraction, plus three SCX24 so it's not like I'm a virgin.

That said, however, it's also true servos don't know in what they're being installed, e.g. whether it's a rocket, boat, truck, airplane, ordinance disposal vehicle, manipulator arm, focus assist device, laser guide, whatever. So to SrC I say this; agreed we don't know diddly about trucks compared to a ot of real experts like you, but we know a fair bit about servos - and - we have enough good customers to call on for advice to teach us about specific vehicles.

We, in turn, take this information, integrate it (meaning add to it what we know), and turn around and share it with others. Put another way, we know a bit, and we learn fast and thus, can actually provide a fair bit of help to those who own trucks. I will add this; I've looked you up on the Arrma Forum and have taken note - you - are one of those who provides a lot of help others. If you ever become a ProModeler customer, don't be surprised if I call to ask questions.

Next, to those with kind words for ProModeler, I am humbled our product is mentioned so highly. Thank you.

Regarding the Futaba CB700 - it's my opinion this is an awesome servo. To be mentioned in the same breath is an honor. As to why they state not to use a BEC? It's my opinion this is for the same reason I'm not fond of them, either. Will they work? Sure they work! Thing is, and as an engineer, what 'I' find more concerning regards;
  1. how do they fail?
  2. do they deliver what they say?
In reverse order, a little bit of reading is in order because we address this topic on the site, so there's no need to repeat. Examples include;
. . . and if you poke around on the site you'll find more useful information, but often within articles about other brands of products. Like X-MAXX standard servos and How to use an HV servo with a 6V radio and Will ProModeler servos work with NiCds? as well as Maxxing a servo's performance requires 8.4V, right? and there are other.

As to whether BECs deliver what they say, the real question is, under what conditions do they deliver what they say? If you poke around on the site of reputable BEC-manufacturers you'll find buried in the specs something along the lines of, 'Tested at 70°F with 15ft/s cooling breeze', or with language that indicates current output (flow) is dependent on voltage input. Yup, variable output based in variable input - hmmm.

BEC Specs
So here's the thing; your BEC may see 70°F on a cool autumn day but in the heat of summer? Nope! Moreover, that's only if it's a discrete component so what if it's built into the ESC? Then it's gonna be a lot hotter than that because speed controls get hot with operation, understand? It means the harder you run the rig, the hotter the BEC is going to get, and thus, the less current it delivers! Note I said current, not voltage. More later.

The other thing is the 15ft/s is about 10mph in terms of a cooling breeze. While maybe you see that if the rig runs without a body (unlikely because so many bits protrude into the airflow the boundary layer is distributed so essentially it's operating in stagnant air, meaning practically no cooling whatsoever). Worse, with the body installed there's less airflow than without 'and' if it's a dark color the sun heats things up even more. And ESCs with fans have them to cool the components to juice for the motor. The BEC? It's an afterthought1

So again, a BEC's not gonna give you what you think. Is it enough? We don't know. You don't either. Moreover, what if it's an East Asian import instead of a domestic product? Honestly? Isn't it more likely the reason they don't give you any BEC-scpecs is preceisely because they're not really very good, take my meaning? Moreover, if the BEC you depend on was free with the ESC (because so you didn't pay sqaut for the BEC, it was free), how good is it? Do you really think it's good? Anyway, to dive into a claim of 8A, or 10A, or whatever - but - with no specs to back it up leaves me suspicious. But it get worse.

Worse is the issue regarding how BECs can uniquely fail;
  • voltage high,
  • voltage low,
  • voltage, high sometimes,
  • voltage low sometimes.
Low isn't really a problem for the equipment (receiver and servo) unless it's too low and stops working altogether (but low voltage doesn't otherwise damage the servo or receiver). High voltage is bad juju no matter what because components may go poof and give up the ghost. But it's the sometimes-high or sometimes-low that are real buggers to diagnose. Think the servo guy should warranty the quality of the juice delivered by a 3rd party BEC? In what world is that even reasonable?

Servo motors have FETs inside. It's easy to blow them with a crawler by wanging the wheels back and forth over and over trying to dislodge the rig from a crevasse. Do it long enough and a FET (or all three) burn up. No, again, user error, not warranty. Can destroy any servo on this planet in short order doing that fool stunt. Basically, because a battery cannot possibly deliver too much voltage (enough to fry the servo) then when we see fried FETs it was either a) the customer being stupid or b) the BEC giving the servo too much juice because otherwise, the 2S-pack cant fail the FETs with too much voltage. Physics. Anyway, that kind of BEC failure is fail high (and high sometimes), remember?

So a BEC that's taking 8S and regulating it down to to 2S (call it from 30V to 8V) begins to fail something then there arethings in a servo or receiver that can go poof in the process. Lets out the magic smoke. Oops! Battery can't do that. Makes a battery as a power source better. Simple. Note, when a BEC is failing high sometimes, then how in Hell are you (or anybody) going to diagnose that? So if it fries the servo, is the servo maker on the hook for the failing BEC? Hardly fair to expect that, either. Just saying.

So a BEC, any BEC no matter how expensive, compared to chemical energy that always works (a battery) 'and' which can never be voltage too high (physics) and consists of just two cells and a lead (just 3-components meaning it's dead nuts reliable), then it's better. Cheaper too. Win-win. Remember, a BEC may have 30 components. Only one goes teats up and you begin to get problems - gremlins affecting power. Simply put, there's more to go wrong with a BEC compared to a battery. As an engineer I hate when there are more things to go wrong. Always.

Current - and - Voltage
Folks confuse the two. I'll say, the BEC doesn't deliver enough current, guy responds, but I set it to 8.4V. Two different things. Apples and oranges. I'll use a dirt-simple analogy. One that's often used with DC electricity because it works.

Ever seen a children's toy waterwheel? Little paddles on a spool. Set it in a stream and it spins like mad! Hook it up to a generator with pulleys and an o-ring and it makes enough electricity to power a light bulb. Great fun for kids. Educational. OK, so imagine this set out on the patio floor. Take a 5-gallon bucket and fill it with water. Drill a 1/4" hole in the bottom and watch it leak out. Get fancy if you like and time it. Bigger hole, drains faster, right?

However, if you make a mark exactly half-way up from the bottom (or from the top, half-way, right?) an interesting thing happens. Fill it to the top and time how long it takes until it's half empty. Now time it from from half-empty to completely empty. Same amount of water but it takes longer. Why is this? Turns out the water level creates more pressure at the bottom when the bucket is full versus when it's half-full. So here comes the analogy. Water level is like voltage and the size of the hole dictates current flow (bigger hole, the faster it empties). Ready to put this all together?

Waterwheel experiment
Back to our toy waterwheel out in the driveway (or on the back patio deck), e.g. somewhere water can spill with impunity. First, hang the bucket somewhere low enough to easily refill but high enough to place the toy waterwheel beneath it (to see it easily). Pretend we start off with a brand new bucket (no hole). So first you drill an 1/16" hole in the bottom, so it leaks out a steady pinner of a stream. Align the stream of water leaking out so the water lands squarely on the paddles. The purpose is to have the water turn the toy water wheel.

Thing is, a 1/16" diameter hole probably doesn't have the power to turn the wheel. So let's drill it out to 1/8" (so we get a stronger stream because more water is flowing). Maybe it tuns the wheel, maybe it still doesn't. So next we drill it out to 1/4" (again, in hopes this creates enough force to turn the water wheel). If that's still not enough force, then maybe drill it out to 1/2" diameter. See what we're doing? We're creating a stronger and stronger force of water using the increasing diameter of the hole to create a current flow of water draining out of the bucket to spin the wheel. Bigger hole, bucket empties faster - simple relationship.

Another word for draining the bucket is flow. The current of water 'flowing' from the bucket empties it, right? Remember I said voltage equaled level and a full bucket empties to the half-way mark more quickly than a half-full bucket empties to zero and that's voltage? Let's tie it all together.

Current - versus - voltage
The servo is the water wheel. When the stream of current is too weak to turn it, that's a current source, maybe a BEC that isn't flowing enough current to adequately power the servo. Doesn't matter if the bucket is full or half-empty (8V or 6V), the hole draining the bucket isn't large enough to power the servo, maybe delivering 3A but it needs 5A - bigger hole equale more current flow - same with DC electricity. Need a stronger source of current.

Current, in electrical terms, is measured in A (amperage, or amps). Voltage potential is measured in V (volts). The potential energy in a full bucket is greater than the potential in a half-full bucket (higher pressure, the basic reason it empties to half full faster than it goes from half-full to empty). It follows the best combination is a full bucket with the largest hole. Same ting with a power source, you want the highest voltage with the highest current flow . . . take my meaning? A 2000mAh battery rated at 10C 9common as dirt, even 20C is available easily). Anyway, that small battery pack will run a rig for hours and delivers 2.0A (same as 2000mA) x 10C = 20A (and for a 20C pack its 40A). Now do you begin to understand why a battery is better? Honestly? It's not even breaking a sweat delivering 8A to the servo when a BEC may be gasping for breath. batteries are better. Period!

Given; no matter how hard the little toy waterwheel is to get spinning, eventually you get a large enough hole in the bucket it creates a stream of water strong enough to turn it (or strong enough to wash it off the patio deck altogether), right? So if you add water to the bucket using a hose juuuust fast enough that it's always full, then that's the maximum voltage (8V) but add water to it so it stays half-full as it drains (a little bit lower rate of flow from the hose) and it's still producing water flow but slower than if it were full up (reason the same size hole drains the first half faster than the second half), that's 6V.

Both full and half-full are delivering enough current to turn the water wheel if the hole is big enough, but the full bucket's flow (same size hole) generates more pressure (higher voltage) because iot empties faster (so the wheel spins faster). Look at our servo specs. We give you data for 5V, 6V, 6.6V, 7.4V, and 8.4V and there's a current figure for each. Unlike other manufacturer's ProModeler give you enough information to make informed decisions. Put another way, information is knowledge and knowledge is power. As my Dad would say, 'Put the hay down where the goats can get it!

BECs suck
So back to the BECs, maybe they deliver enough current at the voltage you select, maybe not. Another word for maybe is sometimes. Me? I dunno but a battery always delivers more than enough current - always. And 100% of the time (always) is better than sometimes, are we, agreed? So I'll begin to wind this down with this. A BEC produces current at a voltage using a variable source (because you're constantly accelerating and decelerating the rig).

But every time you accelerate the rig, the propulsion motor puts a load on the rig's battery and the input voltage dips. Every time. No exceptions. Physics. Remember when I said a good BEC company shows you the specs and the current flow is dependent on voltage? This is what I mean, the BEC is fighting like Hell to deliver what is being asked while you're busy varying the voltaage driving your rig. Not good.

The BEC-circuit at heart functions using FETs (really fast switches) to generate electricity synthetically. It's on, or off. One or the other. On longer means 8V and on for less time makes 6V. That's how it works. on and off. Another word for this is digital because the FETs are either on or off, 1s and 0s . . . digital, you grok? A battery, on the other hand delivers chemical power and it's perfectly clean and smooth, analog.

Digital vs. analog
We see something like this in other electronics. Are you computer savvy? Would you rather have a square-wave battery back up or a sine-wave UPS? Square-waves are another way of saying digital and sine-wave is like analog and the latter costs a lot more (and higher cost almost always equates to better). Perfect analogy? Nope, but I hope you take my meaning. Here's another; what about car stereo systems, would you rather have digital amp drivers with their inherent choppiness or analog drivers that are more costly but really smooth? Same idea once again! Guys who really know a lot use vacuum tubes in their amps because of their analog delivery. Yes, vacuum tubes - like from the 1940s! Analog kicks digital's ass in many places.

Look, there are times and places when digital is better than analog, servos come to mind. Other times when it's worse - but - in terms of power for receivers and servos? An analog current source like a battery is 100% of the time better than the synthetic digital juice delivered by a BEC, no question. 100% is ever single time, remember?

Futaba
So let's circle back to Futaba, who are probably the world's premier servo manufacturer (they produce in a week about as many as we produce in a year). So they're not telling you to use a battery instead of a BEC for no good reason (and neither are we). But on the one hand you have some keyboard expert (whom by definition you only know as ButtyRocket, his handle), and he's telling you BECs are great because he's never stressed a rig enough to tell the difference. Who is ButtyRocket? What are his credentials? You don't know! But on the other hand manufacturers like Futaba are saying about servos, wait a minute fellas when it comes to BECs.

Anyway, for our part (and Futaba, too I suspect) we know it takes a real 8A to drive a servo like a DS1155. Put another way, some weak-sister BEC is almost to a certainty not up to the job. Not when there's a big load. On the workbench? Sure, the wheels steer just fine but when you're driving and then it's not cutting as hard as you expect? The answer is almost certainly insufficient current flow! Seriously, it takes a BEC with stones to pwer a big ass servo. Stones means BECs costing several thousand dollars. Military-class money, take my meaning? So are such BECs available? Sure, but how much money you got?

Don't want to take my word for it? OK, remember the article I referred you to about synthetic voltage, above? Brief article, make sure to review that one above all. Take special note how at the bottom there's one comment, and one comment only. It's by Steve Carruthers, a lead project manager at the lab, and he says . . .

When attempting to power sensitive electronics, i.e. receivers and servos directly from the propulsion battery we have had several major issues and they all revolve around the motor and controller. Several things are happening all at one time and can cause many different symptoms and makes it very difficult to diagnose the problem. The first thing that we noticed that cause a problem is the voltage spikes when loading and unloading the motor. We have seen voltage change as much as 3 to 8 volts with load and a great big spike when the load suddenly goes away. I do not have to tell you what happens to performance of most electronics with large voltage swings in short periods.

The next problem related to voltage is the continued drop in voltage and increase in current during the period of performance and the loss of power to the servos. The other problems we have encountered is the switching power supplies in BEC’s and the chopped power reaching the servos and receiver. We have had many unexplained gremlins in our systems when getting ripple in the power to our systems. Our solution is far too expensive for modelers and more complicated than most would be willing to proceed with. If there is sufficient space and allowance for an extra ounce, the best solution we have found is to use a separate power supply (battery) for the servos and receiver. That has increased our reliability many fold and reduced the overhead in both time and money.
- Project Manager, United States Naval Research Laboratory

Traxxas
Wrapping this up, let me mention how people love to hammer on Traxxas servos by saying they are poop because they fail after a while - but - there's nobody better on earth than Traxxas to take $1000 and give you an awesome toy to play with like an X-Maxx (fair's fair, they're really good at that game). But to do it means they must make compromises along the way.

The servo? It's not top drawer, nothing about the rig is, but the overall package is pretty darn good (until it gets abused). That's when you being to play the upgrade game. Thing is, their BEC-circuit is sized for a 250-300oz-in servo so when you put a +1000oz-in servo in the rig the BEC falls short. Well big whoop, is anybody surprised other than a rookie? Same thing is happening with aftermarket ESCs - the BEC? It was free. So how good do you really think the silly thing is?

Now do you better understand why reputable servo companies advise against using BECs? it's not that they don't work, because they do. And they save the manufacturer a ton of money (30¢ for the components in the circuit versus $20 for a pack). What part of saving money is mentioned along with high performance? Anything?

Bottom line? If you're gonna get off the porch and run with the big dogs, you gotta feed them something other than puppy chow!

Pots vs. Hall Effect sensors
I'll close with this; there was mention of Hall Effect sensors (as in better than potentiometers). True, but not true. What? Please review more on the subject with this brief article; About Pots vs. Hall Effect Sensors to learn more because everything fails.

Reason I get paid the big bucks is to decide the way something fails. Put another way; is one way better for the customer than another? Me? I'd rather something fail with plenty of warning, meaning a little at a time is better than all of a sudden. Like a bulb that starts to flicker occasionally gives me warning to swap it out for a new one is a whole lot better for most folks than the the bulb that just up and quits without warning, take my meaning?

In brief . . . you pays your money and you takes your choice!
 
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jbeech said:
Hi guys, a customer pointed me to this conversation saying we'd been mentions both favorably and unfavorably, so allow me to add a little bit of details to the conversation.

To begin, SrC is 100% right, when he states we have limited experience with RC trucks. Hobbyists comprise about 8% of our business with defense and industry being our most important customers by a wide margin. As for me, I'm more of any airplane guy but I do own two T-Maxx rigs (nitro powered, old school), an X-Maxx, a TRX-4, an Infraction, plus three SCX24 so it's not like I'm a virgin.

That said, however, it's also true servos don't know in what they're being installed, e.g. whether it's a rocket, boat, truck, airplane, ordinance disposal vehicle, manipulator arm, focus assist device, laser guide, whatever. So to SrC I say this; agreed we don't know diddly about trucks, but we know a fair bit about servos - and - we have enough good customers to call on for advice to teach us about specific vehicles.

We, in turn, take this information, integrate it (meaning add to it what we know), and turn around and share it out. Put another way, we know a bit, and we learn fast and thus, can actually provide a fair bit of help to those who own trucks. I will add this; I've looked you up on the Arrma Forum and have taken note you are one of those who provides a lot of help others. If you ever become a ProModeler customer, don't be surprised if I call to ask questions.

Next, I am humbled our product is mentioned so highly. Thank you.

Regarding the Futaba CB700 - it's my opinion this is an awesome servo. To be mentioned in the same breath is an honor. As to why they state not to use a BEC? It's my opinion this is for the same reason I'm not fond of them, either. Will they work? Sure they work! Thing is, and as an engineer, what 'I' find more concerning regards;
  1. how do they fail?
  2. do they deliver what they say?
In reverse order, a little bit of reading is in order because we address this topic on the site, examples include;
. . . and if you poke around on the site you'll find more useful information, but often within articles about other brands of products. Like X-MAXX standard servos and How to use an HV servo with a 6V radio and Will ProModeler servos work with NiCds? as well as Maxxing a servo's performance requires 8.4V, right? and more.

As to whether BECs deliver what they say, the real question is, under what conditions do they deliver what they say? If you poke around on the site of reputable BEC manufacturers you'll find buried in the specs something along the lines of, 'Tested at 70°F with 15ft/s cooling breeze', or with language that indicates current output (flow) is dependent on voltage input. Yup, variable output based in variable input - hmmm.

BEC Specs
So here's the thing; your BEC may see 70°F on a cool autumn day but in the heat of summer? Nope! Moreover, that's only if it's a discrete component but what if it's built into the ESC? Then it's gonna be a lot hotter than that because speed controls get hot with operation, understand? It means the harder you run the rig, the hotter the BEC is going to get, the less current it delivers! Note I said current, not voltage. More later.

The other thing is the 15ft/s is about 10mph in terms of a cooling breeze. While maybe you see that if the rig runs without a body (unlikely because so many bits protrude into the airflow the boundary layer is distributed so essentially it's operating in stagnant air, meaning practically no cooling whatsoever). Worse, with the body installed there's less airflow than without 'and' if it's a dark color the sun heats things up even more.

So again, it's not gonna give you what you think. Is it enough? We don't know. Moreover, what if it's an East Asian import instead of a domestic product? Honestly? It's unlikely the reason they don't give you any BEC scpecs is because they're really good, take my meaning? It was part of the ESC so you didn't pay sqaut for the BEC, it was free. Do you really think it's good? Anyway, to dive into a claim of 8A, or 10A, or whatever - but - nothing to back it up in the way of specifications leaves me suspicious. But it get worse.

Worse is the issue regarding how BECs can uniquely fail;
  • voltage high,
  • voltage low,
  • voltage, high sometimes,
  • voltage low sometimes.
Low isn't really a problem for the equipment (receiver and servo) unless it's too low and stops working altogether (but low voltage doesn't otherwise damage the servo or receiver). High voltage is bad juju no matter what because components may go poof and give up the ghost. But it's the sometimes-high or sometimes-low that are real buggers to diagnose.

So a BEC, any BEC no matter how expensive, compared to chemical energy that always works (a battery) which can never be too high (physics) and consists of just two cells and a lead (just 3-components meaning it's dead nuts reliable) that's another story. Why? Simple, it's because the BEC may have 30 components. Only one goes teats up and you begin to get problems. Simply put, there's more to go wrong. As an engineer I hate when there are more things to go wrong. Always.

Current - and - Voltage
Folks confuse the two. I'll say, the BEC doesn't deliver enough current, guy responds, but I set it to 8.4V. Two different things. Apples and oranges. I'll use a dirt-simple analogy. One that's often used with DC electricity because it works.

Ever seen a children's toy waterwheel? Little paddles on a spool. Set it in a stream and it spins like mad! Hook it up to a generator with pulleys and an o-ring and it makes enough electricity to power a light bulb. Great fun for kids. Educational. OK, so imagine this set out on the patio floor. Take a 5-gallon bucket and fill it with water. Drill a 1/4" hole in the bottom and watch it leak out. Get fancy if you like and time it. Bigger hole, drains faster, right?

However, if you make a mark exactly half-way up from the bottom (or from the top, half-way, right?) an interesting thing happens. Fill it to the top and time how long it takes until it's half empty. Now time it from from half-empty to completely empty. Same amount of water but it takes longer. Why is this? Turns out the water level creates more pressure at the bottom when it's full versus when it's half-full. So here comes the analogy. Water level is like voltage and the size of the hole dictates current flow (bigger hole, the faster it empties). Ready to put this all together?

Waterwheel experiment
Back to our toy waterwheel out in the driveway (or on the back patio deck), e.g somewhere water can spill with impunity. First, hang the bucket somewhere low enough to easily refill but high enough to place the toy waterwheel beneath it (to see it easily). Pretend we start off with a brand new bucket (no hole). So first you drill an 1/16" hole in the bottom, so it leaks out a steady pinner of a stream. Align the stream of water leaking out so the water lands squarely on the paddles. The purpose is to have the water turn the toy water wheel.

Thing is, a 1/16" diameter hole probably doesn't have the power to turn the wheel. So let's drill it out to 1/8" so we get a stronger stream. Maybe it tuns the wheel, maybe it still doesn't. So next we drill it out to 1/4" in hopes this creates enough force to turn the water wheel. If that's still not enough, maybe drill it out to 1/2" diameter. See what we're doing? We're creating a stronger and stronger force of water using the diameter of the hole to create a current of water draining out of the bucket. Bigger hole, bucket empties faster - simple relationship.

Another word for draining the bucket is flow. The current of water 'flowing' from the bucket empties it, right? Remember I said voltage equaled level and a full bucket empties to the half-way mark more quickly than a half-full bucket empties to zero and that's voltage? Let's tie it all together.

Current - versus - voltage
The servo is the water wheel. When the stream of current is too weak to turn it, that's a current source, maybe a BEC, that isn't flowing enough current to adequately power the servo. Doesn't matter if the bucket is full or half-empty (8V or 6V), the hole draining the bucket isn't large enough to power the servo, maybe 3A but it needs 5A - bigger hole equale more current flow - same with DC electricity.

Current, in electrical terms, is measured in A (amperage, or amps). Voltage potential is measured in V (volts). The potential energy in a full bucket is greater than the potential in a half-full bucket (higher pressure, the basic reason it empties to half full faster than it goes from half-full to empty). It follows the best combination is a full bucket with the largest hole . . . take my meaning?

Given; no matter how hard the little toy waterwheel is to get spinning, eventually you get a large enough hole in the bucket it creates a stream of water strong enough to turn it (or strong enough to wash it off the patio deck altogether), right? So if you add water to the bucket using a hose juuuust fast enough that it's always full, then that's the maximum voltage (8V) but add water to it so it stays half-full as it drains (a little bit lower rate of flow from the hose) and it's still producing water flow but slower than if it were full up (reason the same size hole drains the first half faster than the second half), that's 6V. Both are producing enough current to turn the water wheel, but the full bucket's flow (same size hole) generates more pressure (higher voltage) so the wheel spins faster. Look at our servo specs. We give you data for 5V, 6V, 6.6V, 7.4V, and 8.4V and there's a current figure for each. Unlike other manunfacturer's we give you enough information t make informed decisions. Put another way, that information is there for a reason!

BECs suck
So back to the BECs, maybe they deliver enough current at the voltage you select, maybe not. Another word for maybe is sometimes. Me? I dunno but a battery always delivers more than enough current - always. And 100% of the time (always) is better than sometimes (maybe), are we, agreed? So I'll close with this. A BEC produces current at a voltage using a variable source (because you're constantly accelerating and decelerating the rig).

But every time you accelerate the rig, the propulsion motor puts a load on the rig's battery and the input voltage dips. Every time. No exceptions. Physics. Remember when i said a good BEC company shows you the specs and the current flow is dependent on voltage? This is what I mean, the BEC is fighting like Hell to deliver what is being asked while you're busy varying the voltaage driving your rig. Not good.

The BEC-circuit at heart functions using FETs (really fast switches) to generate electricity synthetically. It's on, or off. One or the other. On longer means 8V and on for lwess time makes 6V. That's how it works. on and off. Another word for this is digital because the FETs are either on or off, 1s and 0s . . . digital, you grok? A battery, on the other hand delivers chemical power and it's perfectly clean and smooth, analog.

Digital vs. analog
We see something like this in other electronics. Are you computer savvy? Would you rather have a square-wave battery back up or a sine-wave UPS? Square-waves are another way of saying digital and sine-wave is like analog and the latter costs a lot more (and higher cost almost always equates to better). Perfect analogy? Nope, but I hope you take my meaning. Here's another; what about car stereo systems, would you rather have digital amp drivers with their inherent choppiness or analog drivers that are more costly but really smooth? Same idea once again! Guys who really know a lot use vacuum tubes in their amps because of their analog delivery. Yes, vacuum tubes - like from the 1940s! Analog kicks digital's ass in many places.

Look, there are times and places when digital is better than analog, and other times when it's worse - but - in terms of power for receivers and servos? An analog current source like a battery is 100% of the time better than the synthetic digital juice delivered by a BEC, no question. 100% is ever single time, remember?

Futaba
So let's circle back to Futaba, who are probably the world's premier servo manufacturer (they produce in a week about as many as we produce in a year). So they're not telling you to use a battery instead of a BEC for no good reason (and neither are we). But on the one hand you have some keyboard expert (whom by definition you only know as ButtyRocket, his handle, telling you BECs are great because he's never stressed a rig enough to tell the difference.

Sp on the other hand manufacturers of seros saying, wait a minute fellas when it comes to BECs and internet experts 9and the sellers of the tings) saying thse are great! Anyway, for our part (and Futaba, too I suspect) we know it takes a real 8A to drive a servo like a DS1155. Put another way, some weak-sister BEC is almost to a certainty not up to the job. Not when there's a big load. On the workbench? Sure, the wheels steer just fine but when you're driving and now it's not cutting as hard as you expect? The answer is almost certainly insufficient current flow! Seriously, it takes a BEC with stones to pwer a big ass servo. Stones means BECs costing several thousand dollars. Military-class money, take my meaning?

So are such BECs available? Sure, but how much money you got? Don't want to take my word for it? OK, remember the article I referred you to about synthetic voltage, above? Brief article, make sure to review that one above all, but note how at the bottom there's one comment, and one comment only. It's by Steve Carruthers, a lead project manager at the lab, and he says . . .

When attempting to power sensitive electronics, i.e. receivers and servos directly from the propulsion battery we have had several major issues and they all revolve around the motor and controller. Several things are happening all at one time and can cause many different symptoms and makes it very difficult to diagnose the problem. The first thing that we noticed that cause a problem is the voltage spikes when loading and unloading the motor. We have seen voltage change as much as 3 to 8 volts with load and a great big spike when the load suddenly goes away. I do not have to tell you what happens to performance of most electronics with large voltage swings in short periods.

The next problem related to voltage is the continued drop in voltage and increase in current during the period of performance and the loss of power to the servos. The other problems we have encountered is the switching power supplies in BEC’s and the chopped power reaching the servos and receiver. We have had many unexplained gremlins in our systems when getting ripple in the power to our systems. Our solution is far too expensive for modelers and more complicated than most would be willing to proceed with. If there is sufficient space and allowance for an extra ounce, the best solution we have found is to use a separate power supply (battery) for the servos and receiver. That has increased our reliability many fold and reduced the overhead in both time and money.
- Project Manager, United States Naval Research Laboratory

Traxxas
Wrapping this up, let me mention how people love to hammer on Traxxas servos by saying they are poop because they fail after a while - but - there's nobody better on earth than Traxxas to take $1000 and give you an awesome toy to play with like an X-Maxx (fair's fair, they're really good at that game). But to do it means they must make compromises along the way. The servo? It's not top drawer, nothing about the rig is, but the overall package is pretty darn good (until it gets abused). That's when you being to play the upgrade game. Thing is, their BEC-circuit is sized for a 250-300oz-in servo so when you put a +1000oz-in servo in the rig it falls short. Well big whoop, is anybody surprised other than a rookie? Same thing is happening with aftermarket ESCs - the BEC? It was free. So how good do you really think the silly thing is?

Now do you better understand why reputable servo companies advise against using BECs? it's not that they don't work, they do and they save the manufacturer money. What part of saving money is mentioned along with high performance? Bottom line? If you're gonna get off the porch and run with the big dogs, you gotta feed them something other than puppy food!

Pots vs. Hall Effect sensors
I'll close with this; there was mention of Hall Effect sensors (as in better than potentiometers). True, but not true. What? Please review more on the subject with this brief article; About Pots vs. Hall Effect Sensors to learn more because everything fails.

Reason I get paid the big bucks is to decide the way something fails. Put another way; is one way better for the customer than another? Me? I'd rather something fail with plenty of warning, meaning a little at a time is better than all of a sudden. Like a bulb that starts to flicker occasionally gives me warning to swap it out for a new one is a whiole lot better for most folks than the the bulb that just up and quits without warning, take my meaning?

In brief . . . you pays your money and you takes your choice!
Click to expand...
thank you for this great info mr beech.

i have a question. whenever i got to vietnam, i always ended up giving stuff to my less fortunate cousins. i have given away 4 game boys, multiple game consoles, clothes, cameras, you name it. I actually gave away an RC before and am thinking about building another one from scratch eventually. just reading your info makes me want to buy promodeler when it comes to the servo. but my question is, do you guys ever hold sales? lol. i think ill go everything stock except for a better/cheap tx and rx but want to "splurge" on a promodeler servo on my next kraton.
 
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