OhD

Anyone tried the BLS171HV? Looks like it might have all the right stuff. High voltage, brushless, programmable, fast and not too heavy. It will be very interesting to see if one sets the speed, if it will vary with battery voltage. If it doesn't it could be the end of the need for voltage regulators.

Jim O

can773

My Feedback: (1)

Hi Jim

I have one, but waiting for the Caelestia to try it out in. I have a Digiswitch that was set for 7V that I plan to use with a 2s lipo. Probably be a couple weeks before I get the plane and get it ready, and will let you know how it goes.

OhD

Chad, thanks for the feedback. You should be able to see if the speed changes as you set various voltage settings on your regulator. Did you get my PM?

Jim O

NJRCFLYER2

My Feedback: (42)

That would be a very nice feature, although not easy to accomplish. I imagine that coping with the dynamic changes in voltage delivered to it under varying load from it's own movements, as well as everything else connected to the power bus wouldmake ita little tricky to hold a constant max output speed. Think of the scenario when multiple servos aresimultaneously hitting the bus hard, each trying to maintain speed by drawing even more average current as they each contribute to the IR drops that they must compensate for. No doubt it can be done, and it will be interesting to see if this is what they actually have.

OhD

I noticed that the brushless motors in these servos appear to have position sensors by the number of wires coming out of them. This would suggest they could easily control the rpm of the motor if they had instantaneous info on the shaft position. Of course you'd have to set the speed at something less than max at 8.4 volts in order to control it to the same value at lower voltages.

Jim O

NJRCFLYER2

My Feedback: (42)

If they are using shaft position sensors, then it seems like there is the potential for some really good performance under load. It's a pricey servo, but if it delivers with better performance under varying load conditions, it might be worth it.

cmoulder

Do they have metal or nylon gears? Took a quick look on the Futaba website and didn't see the info.

OhD

It doesn't say MG so I guess they are nylon.

Jim O

can773

My Feedback: (1)

Will see if I can find a few spare minutes tonite to open one up and take a look.

nonstoprc

My Feedback: (90)

Just went through all Futaba hv servos at towerhobbies (http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=MAL) on weight attribute.

Was not able to see one in mini-servo category that is suitable for elevators.

Personally I would prefer to use hv servos in a pattern plane.

cmoulder

That's a good point. They need something the size of the 9650's to complete the "set". Seems like every model these days is designed for stab-mounted minis.

OhD

The S9070SB looks perfect for elevators on paper. It has the same features as the BLS171HV. I like the package where the mounting lugs are high on the case so the output arm is not too far above the bearings. I like the way the cable exits the bottom of the case so it is easy to install the servo in a perfectly sized hole. However, I do not recommend the S9070SB. I'd like to hear from someone else who has tried them.

Jim O

nonstoprc

My Feedback: (90)

Thanks for th info. At 1.13oz, s9070sb is slightly heavier than 9650 (.92oz). It will be an option.

Hope that we can get even lighter hv servos in the future.

Bill Clark

it says the servo screw size is 3x8mm which leads me to believe its a mg or atleast the spline is metal

OhD

I don't know where I got the idea the S9070SB was brushless but I took one apart today and there are only two wires to the motor so I'm sure they are not brushless and therefore don't have the same features as the BLS 171HV. I also found out why they don't center well. The feedback pot is on the circuit board and is mechanical coupled to the gear train by what amounts to a flat screw driver in a slotted screw. I was thinking about putting a drop of thick CA in there and buttoning it up, but I'd probably never get it open again. Anyway that tells me there is no reason the BLS171HV shouldn't be a great servo.

Jim O

OhD

I went ahead and put a drop of CA on the end of the pot shaft and the centering is now in the neighborhood of 0.1 degree at the servo which would be even less at the control surface in most applications.

Jim O

can773

My Feedback: (1)

Pic attached, combo metal/plastic. Output gear is plastic though.

OhD

Chad,

The servo mechanics look similar to the 9252. I tested its centering and it is in the neighborhood of .05 degrees at the servo wheel. That is really good so the BLS171 should be a great servo. What will you use on elevators?

Jim O

can773

My Feedback: (1)

Hi Jim,

Good to hear! I will use BLS 153 on the elevators, I was using them last year with good success and the BLS servos appear to be OK with elevated voltages as I plan to run 7V to everything.

OhD

I got a BLS171HV yesterday and ran some tests today. This servo is programmable so the first thing I did was check the settings as delivered. I changed the deadband from .35 degrees to .09 and set the speed to .1 sec. for 60 degrees. The servo centering is excellent at about .03 degrees. I set my transmitter trim up to get .1 degree steps for each trim click and it followed every click up and down. I ran it at 7.1 volts and measured the no load speed at .108 sec/60 degrees. Futaba specs it at .i sec/60 deg. at 7.4 volts. This is measured after it is up to speed so the speed from stop to stop will be slower. This is true of all servos. However it looks like it accelerates quicker than the non-brushless, but I will need some controlled comparative tests to see if this is true. There was some overshoot in the non loaded condition but one can adjust the damping if it is required. I also ran it at 6 volts and the speed did change so it looks like we will still want to use regulators.

So it looks very good and I plan on ordering a set. I can't believe what I am willing to pay in hopes of getting something that might make me fly better. How things change when you are getting old.

Jim O

Jon Wold

How do you program it?

OhD

Futaba sells a USB device called the CIU-2 and provides software that you can download from their site. I believe some functions can be programmed from another device they sell or from the 18MZ transmitter but I don't have either of those. The software leaves something to be desired and maybe when enough guys complain they will improve it. For example, when setting end point travel and neutral offset it only allows increments of .25 degrees. Transmitter Sub trim and ATV adjustments are much finer than that and I believe it needs to be better when aligning elevators.

Jim

OhD

To illustrate how fine you should be able to set the neutral and end points consider the following:

Assume your servo throw is set for a total of 100 degrees (+/- 50) with the full throw of the transmitter range which we'll assume is 2000 steps. It is capable of 2048 but we'll assume some is used for trim.
If you divide 100 degrees by 2000 steps you get .05 degrees per step.
This is 5 times better than the .25 degrees per step that the programmer allows you to set.

My assessment is you could probably match servos well enough for two ailerons but not for two elevators or two servos on one surface. It means you can't have interchangeable drop in servos if you replace one in the field. It is also a shame as it negates an advantage of the S.Bus that would allow you to connect multiple servos to one channel and eliminate Equalizers or Match boxes.

Jim

atul

Jim,

How bad is the centering problem with the S9070SB? I've just purchased some HV Servos for my first Futaba 18MZ project (a Naruke Aries, which I've just completed). Naruke's suggestion was to use the BLS 174HVs for Ailerons, BLS 175HV for rudder (though, IMHO, the BLS 171HV will be more than sufficient for the rudder as well) and S9070SBs for the elevators. I was planning on using a BLS 171HV for the throttle but decided to switch to an S9020SB for the throttle instead. If there's a centering problem with this servo, do you think its better to switch to the BLS 153 instead? I'm not sure whether the BLS153 can handle 7.4V though and all the other servos (BLS 174/175) required 7.4V.

Thanks,

Atul

[/quote]

I don't know where I got the idea the S9070SB was brushless but I took one apart today and there are only two wires to the motor so I'm sure they are not brushless and therefore don't have the same features as the BLS 171HV. I also found out why they don't center well. The feedback pot is on the circuit board and is mechanical coupled to the gear train by what amounts to a flat screw driver in a slotted screw. I was thinking about putting a drop of thick CA in there and buttoning it up, but I'd probably never get it open again. Anyway that tells me there is no reason the BLS171HV shouldn't be a great servo.

Jim O


[/quote]

OhD

The centering was bad enough that I decided not to use them for elevators. I selected the JR 3711HV for elevators as I couldn't find a small Futaba HV servo. I used the BLS171HVs on rudder and ailerons. The throttle servo is probably not critical.

Jim O