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Futaba BLS 451 Brushless Servos Review

Ian Bange reviews the future of RC servos, Futaba's new brushless digital servos!

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Introduction


Weight:2.11 oz. (60g)
Torque:118 oz./in. 6V: 147 oz./in.
Speed:4.8V: .13 sec, 6V .10 sec
Weight:1.6 x .8 x 1.4" (40.6 x 20.3 x 35 mm)
Manufacturer:Futaba
Available From:Tower Hobbies

Futaba has always been on the cutting edge of new technology in the world of RC electronics. From the days of (what seems like now) primitive proportional control systems, they have always been developing the latest and greatest in RC electronics. Now Futaba has done it again with the release of the world's first brushless servo for RC hobbyists.

Features

The Futaba BLS 451 Brushless Servo features:

  • Brushless motor lasts longer and operates at a lower temperature than brushed motors
  • Samarium Cobalt magnets and dual ball bearings
  • Lasts at least five times longer than brushed servos
  • 30% Faster response times
  • Same power consumption and centering as Digital servos equipped with Brushed motors
  • Exceptionally durable geartrain
  • Standard size.

The BLS 451 is an impressive servo even if you don't take its unique motor into account. With a speed of .10 sec/60 degrees and 147.2 in./oz. of torque, there are few servos on the market that can match its combination of speed and torque.

What the BLS 451 is for

Usually servos fit into a category that makes them easy to select for a given use, but the BLS 451 is an exception to the rules thanks to its specifications. Futaba and Tower Hobbies advertise the 451 as a premium steering servo for vehicles, and I have no doubts about its capabilities in that regard.

The 451's two limiting factors are its torque and its price. With these factors in mind, the BLS 451 would work well for control surface use where 150 in./oz. is enough, and when it is important to have the absolute best mix of speed and power available. These applications include single use on the elevators of aerobatic aircraft up to 33% and dual use on ailerons of aerobatic aircraft up to 35%. It would of course also yield excellent results for any smaller size aircraft in the .60-1.80 size. Finally, it would of course serve well for use in what it was designed for - competition steering servos for larger vehicles.

Installation

Installing the BLS 451s is now easier than your average servo install thanks to new, innovative hardware from Futaba. The new design of servo mounting grommets is much easier to work with than older designs, and while this may not seem like much of an improvement, the ease is much appreciated when it removes ten minutes of fooling with grommets out of your installation.

If you are not used to dealing with hi-torque servos, be sure to check and make sure that your mounting location is secure and that your mounting screws are tight. These servos generate a lot of force, and if your mounting is not correct, they could case in-flight failure.

Flying

The servos I replaced with the new BLS 451s were digital servos in the tail of my Razor Yak - a 60 size profile with extremely large surfaces. This aircraft is very responsive and is a good platform to see the differences between traditional mid-grade digital servos and the the new brushless digitals.

The first thing I noticed when I took off with the new 451s installed was that my surfaces were much more responsive, undoubtedly due to the extremely high speed of the 451s. A few trim passes and a quick landing to adjust expo settings, and I was ready to give the 451s a workout. I put the new servos through every extreme maneuver that I could think of: walls, snaps, blenders, spins, tick-tocks. In all cases the new servos responded with great holding power and instant speed. They were so fast that I could actually tell that I needed to be more careful with the timing in some maneuvers such as rolling harriers and snaps as the aircraft was more immediately responding to my inputs. This really demonstrated just how large of an improvement the new servos were over the ones they replaced.

Conclusion

If you are looking for the absolute best combination of speed, torque, and precision in its class, look no further than the Futaba BLS 451. While its brushless motor may not be an improvement in servo technology you can touch and feel, its capabilities speak for themselves. Its hardware and technology are innovative, and I think that it represents the future of servos. I hope to see more brushless servo releases in the future from Futaba and will be eager to test them as well.

Pluses:

  • Extremely high speed
  • High torque, especially for their speed
  • Innovative new hardware

Minuses:

  • Expensive
Last edited by Angela H; Oct 30, 2007 at 08:31 PM..

Discussion

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Old Nov 03, 2007, 09:27 AM
Registered User
Ireland
Joined Apr 2001
4,027 Posts
could you do some side by side test that are less subjective then flying your plane?
I woould like to see a clip where you show the speed and centering under load compaured to other servo's
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Old Nov 03, 2007, 12:22 PM
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daleksw's Avatar
Glasgow, Scotland
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Could I suggest that before writing reviews like this you at least take the trouble to find out the correct units for torque? AFAIK there's no such thing as an in./oz - certainly not for measuring torque. Makes it very difficult to know what you're talking about.

David
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Old Nov 03, 2007, 01:25 PM
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Old Nov 03, 2007, 04:18 PM
Can you spot the giraffe?
daleksw's Avatar
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look a bit closer yourself. The link you give is correct, and it does NOT list ounce/inch.
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Old Nov 03, 2007, 04:28 PM
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Old Nov 03, 2007, 04:40 PM
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Illinois
Joined Feb 2006
4,963 Posts
Nice article,id really appreciate some video also,maybe showing the same plane with the original servos vs the new brushless futabas during a preflight to show how smooth or fast they are as well as seeing flights with both servos,the test flight sounded cool.. It would rock to see it. Just an average rc pilot here but never heard of planes doing a tick tock just helis ?. You can compromise on servos but they can make a huge differance in flight performance.. both in crispness and response,torque and speed sound VERY good on these and they should fit many applications very well that call for full size servos .
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Old Nov 03, 2007, 04:46 PM
Can you spot the giraffe?
daleksw's Avatar
Glasgow, Scotland
Joined Jun 2005
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you do indeed see ounce inch - that is ounces multiplied by inches NOT ounce/inch - ounces divided by inches.

If you measure a force of 4oz a distance 2 inches out from the shaft that is a torque of 4oz * 2inches = 8 oz.inch.

It is not 4oz / 2 inches = 2 ounce/inch.

It's a HUGE difference as in one makes sense and the other is complete rubbish.

As an example which should have the '/', if you travel 60 miles in 2 hours, then you are travelling at 60 miles / 2 hours = 30miles/hour.

As a result, if you travel for 10 hours, you can expect to travel 30 miles / hour * 10 hour = 300 miles.

By the same token, if a servo really produced 100 oz/in, then at a distance of 10 inches, you'd expect to get a force of 100 oz/inch * 10 inch = 1000oz

If it's 100 oz.in, then at the same 10 inches you'd expect 100 oz.inch / 10 inch = 10oz, which I think most people would agree is more likely.

David
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Old Nov 03, 2007, 05:01 PM
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United States, TX, Kingsland
Joined Sep 2005
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Nice review Ian. Could you post a picture of the new grommet all by itself? It's a little hard to see the inside detail in the installed shots. How expensive is this servo?
Mike McD
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Old Nov 03, 2007, 05:39 PM
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electron_head's Avatar
New Zealand
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Quote:
Originally Posted by daleksw
Could I suggest that before writing reviews like this you at least take the trouble to find out the correct units for torque? AFAIK there's no such thing as an in./oz - certainly not for measuring torque. Makes it very difficult to know what you're talking about.

David
Even I know what he's talking about. But why some cultures cling on to these old imperial units of measurement is beyond me. Whats wrong with the metric system?
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Old Nov 03, 2007, 05:40 PM
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Old Nov 03, 2007, 06:00 PM
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Quote:
Originally Posted by mop26921
I understand now. Thanks for the explanation, I have learned something.
Well I'll assume you got the figures off the packaging then and didn't actually measure them.

Could you tell me where these servos are made. At a guess I'd say China and that would explain the inch/oz typo on the box? Or was that your mistake.
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Old Nov 03, 2007, 06:12 PM
Can you spot the giraffe?
daleksw's Avatar
Glasgow, Scotland
Joined Jun 2005
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Quote:
Originally Posted by electron_head
Even I know what he's talking about. But why some cultures cling on to these old imperial units of measurement is beyond me. Whats wrong with the metric system?
Honest, it's not a question of imperial vs metric units. oz.in is a measure of torque. oz/in isn't and neither is in/oz.

Apologies to mop26921 if I seemed to be getting at you, that's not what I had in mind at all. I happen to think that anyone who's going to present a review and give the impression of being in some sort of position of authority on the subject ought at least to know what they're talking about. The reader's don't have to understand every word, but the writer should - otherwise don't write it.

I can happily cope with torques in oz.in, kg.cm or preferably N.m. I can even cope with kg.m^2/s^2 or dimensionally equivalent units of energy like Joules, calories, electron Volts or even the incredibly obscure horsepower.fortnight and dyne.cubit - obscure as in I just invented them. But to repeat myself, oz/in and in/oz are not measure of torque or anything else I can think of.

If I told you I weigh just over 75 Fahrenheit, would you be able to tell me if you were lighter?

David
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Old Nov 03, 2007, 08:01 PM
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Quote:
Originally Posted by daleksw
If I told you I weigh just over 75 Fahrenheit, would you be able to tell me if you were lighter?

David
Getting pedantic now. You have quoted the speed as being:

Speed: 4.8V: .13 sec, 6V .10 sec

I know that this is actually the time to rotate thru 60 degrees but ...

These servos could actually go over 100mph in the right plane.

And for your information I weight about 68. Over on the US they would say I weigh about 150 and everyone would know it was pounds.
2.2 pounds to the KG.

68 KG is 68 000 grams but whats 152 pounds in onces? Its takes a bit longer to fiqure that one out and time is money.

You still haven't told me where the servos are made.

http://www.futaba-rc.com/servos/futm0550.html
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Last edited by electron_head; Nov 03, 2007 at 08:09 PM. Reason: Adding and correcting
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Old Nov 03, 2007, 08:35 PM
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Blah, blah, blah... and the beat goes on.
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