Futaba BLS172SV very hot with B2

[Steve Graham]

After installing the B2 units on my 700 helis I noticed increased energy consumption from my rx pack. Where before with both the skookum and vbar units it seemed I'd use 300 to 400 Mah per flight I am now using probably double that. At first I assumed it was the processor and possibly the accelerometers in the units using more power? I'm running 3 new pulse 2550 mah 2s lipo direct on both helis. This weekend at our fun fly one flight on my N7 took this rx pack down to about 40%. It was then that I noticed one of my cyclic servos was running very hot, like beat on electric heli motor hot. I spoke with a couple of the guys at the fun fly who were also running B2's and they indicated that they were not seeing any increased current consumption on their helis. I flew another flight, this time with my E-7 which has savox servos, and while I'm still seeing what I consider elevated consumption with this heli the servos were not more than warm. I have been running the servos on both my helis at a 200 hz refresh rate so I thought I'd try lowering that to 120 to see if it made any difference. None at all. On the last flight of the Nitro with the 172's in it I had a friend temp the servo cases. Several minutes after landing and shutdown the cases still averaged around 135 F. As I said immediately after landing the servo cases were nearly too hot to touch.

I also thought perhaps the gains were causing the servos to work overtime but I'm seeing no high gain type artifacts in flight so I really doubt this is the case.

Another thought is that even though I've got the vibration levels below the grey line and bailout is functioning well now perhaps the glow engine is generating some sort of harmonic that is causing the FBL unit to send extreme signals to the servos in an attempt to smooth things out. I really don't know if this is a rational possibility or not?

At this point all I know is before putting the B2 on this heli I had low current consumption and low servo case temps. Now I have both?

Any thoughts would be greatly appreciated. The 172's are overkill for a 700 class head. They are a 514 oz .11 second servo but they never ran hot or used the amount of power they are now with my first FBL unit.

[Steve Graham]

Unless any of the developers have any thoughts I'm preparing to swap all 3 cyclic servos. Just seems odd that all 3 $200 servos would go bad all at once? Next step will be to replace the FBL unit.

[abit late]

Have you checked for binding around the head, shafts and swash? Pull the blade grips outwards when checking. Tail servo running cool?

[OnTheSnap]

Probably it's the refresh rate. Drop it to 165Hz or so and check the temps.

[Steve Graham]

Thanks Alex,

I did try that last weekend. I took it from 200 down to 120 and the temps were not affected.

[Steve Graham]

No binding in the head. Recently rebuilt with new bearings, spindle, and Matt's updated rebuildable swash plate. Have pulled on the blades against the thrust bearings and can not find any binding.

Tail servo is running cool.

It is certainly possible all 3 servos are tired. They have not lived an easy life.

Still I'm kind of left wondering about the fact of greatly increased power consumption that seems to have coincided with the move from Skookum to the B2? I'm certain this is not right as others I've talked to have are seeing nowhere near the consumption I'm getting. The servos being hot is the only thing that explains in a reasonable way why I'm seeing this. The only thing left to resolve is if it's a result of the FBL unit or the servos going bad themselves.

[OnTheSnap]

It really boils down to refresh rates, and flight style. Maybe if you had the gain ultra low and loose on the SK I could understand. But with any reasonable gain, the amount of activity won't be greater on one system to the next.

The brain does have a much faster PID loop, but it's filtered by the refresh rate.

[Steve Graham]

Thanks Alex, That all makes sense.

[BrainDev]

Originally Posted by Steve Graham

..... Recently rebuilt with new bearings, spindle, and Matt's updated rebuildable swash plate. Have pulled on the blades against the thrust bearings and can not find any binding.....

Sorry if I ask you..........but you are absolutely sure that your thrust bearing are not reversed mounted?

[Steve Graham]

Well, It turns out that the simple, most likely if not confusing solution once again turns out to be correct. I threw in the 3 MKS 950's that I got for my Logo 550 and flew it about 8 flights this afternoon. Low power consumption, servos only slightly warm. I guess at some point the Futaba's just got old and tired. IIRC they're only a year or two old but they have been through a number of crashes. I was always amazed these things never stripped a gear but I guess over time the amps wore out? Don't know what else could cause a servo to start drawing so much power. Since their list is over $200 I may send them in to hobbico but wont really hold my breath that they wont want more than the servos cost to fix them

At any rate I am back to having the confidence to fly the N7 without melting down my servos Was a cooler fall day and the O.S. 105 was seriously hitting on all cylinders The VTX blades seem to work very well on this heli. Very quiet which tells me they're running efficiently. I run them on this heli at 1750, 1850 and 1950. Probably need to do a little governor tuning as I'm definitely getting some overspeeding. Was just enjoying the heli this afternoon among other things chasing 2 plankers around the touch and go pattern and doing long slides down the runway. I had to slow down and wait for them to catch up

Here's a couple pics that show my install and new blades. Don't know why HF rotates certain pictures.

Can anyone tell me what's wrong with my blade holder?

[Steve Graham]

Originally Posted by BrainDev

Sorry if I ask you..........but you are absolutely sure that your thrust bearing are not reversed mounted?

Thanks, I'm pretty anal about this but it's always a possibility. I think I found the problem ^

[etherbatxx]

Originally Posted by Steve Graham

seems odd that all 3 $200 servos would go bad all at once? Next step will be to replace the FBL unit.

$600 worth of servos went bad at the same time, right after you switched to a Brain2?

[myxiplx]

If they've had a crash I would suspect something mechanical in the servos. If you don't have a damaged gear, it could be a bent shaft, or damaged case (if the holes the shafts fit into get elongated it prevents smooth rotation).

Both of those will cause the gears to rotate less freely, and increase power consumption.

[abit late]

Another thing to check is whether the servo horns may have been binding on the casing,.

[Steve Graham]

Like I said they've lived a hard life but I did not notice the increased current consumption until I mounted the B2. The timing was an odd coincidence but having worked on avionics for 8 years in a former life nothing surprises me anymore. Don't believe the B2 had anything to do with it. It wasn't until about 15 flights in that I realized how hot they were getting. God knows how or why electromechanical devices fail but over time they do especially if you don't fly like the heli its a "glass slipper"

I'll do a post mortem on them before I contact Hobbico. Probably put them on a servo tester and let them run. I need some sort of rig that will do this while loading the output shaft. It may turn out to be something I can fix/replace myself.

[Baedarlboo]

Originally Posted by Steve Graham

I'll do a post mortem on them before I contact Hobbico. Probably put them on a servo tester and let them run. I need some sort of rig that will do this while loading the output shaft. It may turn out to be something I can fix/replace myself.

If you have a iCharger Duo it has a servo tester that you can set how many cycles you want to test and control how far they throw. Also measures transit speed and what not. Pretty useful diagnosing a good/bad servo. I had a tail servo go just like yours (getting hot and having some random erratic battery drain), I believe it was a worn pot. Once the pot is worn, the servo has no way of knowing its posistion in relation to center, so it's constantly fighting. Try test the servo by putting some pressure on the horn. Mine would give some and then at a certain point realize it's not centered and try and fight back.