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Old 02-24-2016, 09:00 AM   #21
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Quote:
Originally Posted by DCflyer View Post
Yea that's what I said. What are you saying
Chill...it supports what you said, since many people also state the opposite. I thought it would be helpful to the OP. In post 7 OP appears to still think HV will pull less amps
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Old 02-24-2016, 09:46 AM   #22
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Quote:
Originally Posted by vebbyson View Post
Chill...it supports what you said, since many people also state the opposite. I thought it would be helpful to the OP. In post 7 OP appears to still think HV will pull less amps
oh I didn't mean to imply that. I know that higher voltage servos (usually) pull more amps. I ran into that argument many times in my searching.
That's why I'd probably run the BKs at 6-7 v instead of the full 8.4.
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Old 02-24-2016, 01:11 PM   #23
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Ok thanks everybody. I think I will just get whichever goes on sale first.

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Originally Posted by Vinger View Post
It is not so much the fact that servos will draw high amps and brownout Spektrum sats, it is about the back EMF they generate while working, the better designed brushless servos tend not to be a problem, poorly designed servos will give you headaches. Choose wisely by searching this forum on which brands are good and which are bad at this.
I've read a little about back emf. I may be worried about the wrong thing (amp draw).

Quote:
Originally Posted by nwmtech View Post
Either of those servos will work perfectly fine with the internal HW BEC on the 160. The brushless BK's draw a bit more amperage than the coreless ones, but I have tested both with no issues. MKS servos are extremely efficient and I wouldn't hesitate running them on just about any BEC.

Personally, I'd run the BK 7002/7006, set them at 7.4v, and enjoy!
cool. I'm surprised the brushless draw more. By the way Nick, I've been re-listening to a lot of rchn lately as part of my "research" for this build.
Right now I'm listening to episode #106, where you cover a similar issue (hv electronics setup stuff). It's almost 2.5 years old now but I assume the info is basically still good.
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Old 02-24-2016, 03:15 PM   #24
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Quote:
Originally Posted by vebbyson View Post
Check out this thread supports that higher voltage on servo will pull more amps.
I don't see a thread link..

I've always assumed that higher voltage meant less amp draw, or at least not more, as in the case with pretty much everything else, like the main packs on a 12s machine vs a 6s machine, etc.


If I'm wrong, then oops. At least you guys were able to clear that up.
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Old 02-24-2016, 03:19 PM   #25
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All my brushless coreless high end servos draw more than their brushless counterparts. None, not a single MKS can be moved by hand without bending or breaking the arm that I fly? Nor my Outrages?
The KST coreless (Turnigy's) work extremely well for half the price of the rebranded (aren't they actually servokings?) BK's btw.
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Old 02-24-2016, 03:31 PM   #26
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Quote:
Originally Posted by Thestructured View Post
I don't see a thread link..

I've always assumed that higher voltage meant less amp draw, or at least not more, as in the case with pretty much everything else, like the main packs on a 12s machine vs a 6s machine, etc.


If I'm wrong, then oops. At least you guys were able to clear that up.
The argument is that with servos you get more speed/power with higher voltage, which takes more amps. If a servo had the same speed and torque at 6, 7 and 8 volts, then it would take less amp draw at 8v. But servos don't work like that. Put more volts in and they put out more power.
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Old 02-24-2016, 03:35 PM   #27
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So many variables at play. They simply don't work like brushless motors where HV rules. I do run all my HV servos close to max voltage. Why not take advantage of what they are capable of producing. Most good bec's now handle servo loads. I prefer separate flight packs myself or bec's such as the 3s sep battery pack ran Scott Gray bec's myself. I have had a few internal bec's fail. Cost me thousands. Also contacted by numerous others that have had the same issue.
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Old 02-24-2016, 04:28 PM   #28
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Guys

Sorry for the post length, but there are some important misconceptions posted in this thread that matter for us.

One is- you cant talk about servo voltage without talking about the servo’s rated voltage. It is more like motor kv than anything. So yea, conceptually, running any servo at a higher voltage vs a lower voltage can increase its power, that does not mean that an HV version of a baseline servo will pull more amps at 7v than the baseline will at 5v, with the same output load.

But this is not always true. Newer servos are very complex in terms of logic, where they use PWM, but also adjust power based on things like the magnitude of position-request change. But there is no reason a servo cannot monitor input voltage and adjust PWM to limit total power. Some limit power in a stall to prevent damage to the motor. So, you have to be careful about making absolute statements about this stuff- what may apply to your servos, and every type you have ever tested, may have nothing to do with some other brand/type/technology.

Another is, people are often under the impression that if they don’t see resets or alarms, their power supply is adequate. Strangely, these same people are probably very familiar with C ratings on flight packs, and how depletion/dropping voltage through the flight affects rotor power/RPM. The simple fact is that as current demand increases, voltage droops. And with that, for most servos, peak and average current draw reduces. That means, the system can be self limiting. Most servos are asleep at 3.5-3.8v. They cannot pull power if the bus drops to that voltage. And when that happens, the BEC can recover, and the cycle repeats. But in the interim- when the bus is 5% or 40% down during hard maneuvers- you ARE losing performance in the servo. Point is that you don’t size the BEC based on brownouts- you size it based on an acceptable droop in bus voltage.

And, that is not always easy- because often, it is anecdotal info from other users who are happy with their performance who guide your decision. But the question is- would they be much happier with a stronger power bus for the servos?

There is no inherent correlation between power consumption and motor type. I have seen an inexpensive brushless design pull more than 2x the peak AND average current, for less performance, vs a high-end brushless servo of the same rated performance. And, it may well be that some other even cheaper brand is more efficient than the better brand in that test. You don’t know unless you have proper test equipment.

I am tempted to just run these tests against current-gen servos. Unfortunately, brick/mortar shops are scarce, and don’t tend to carry a huge selection (i.e. multiple brands), so getting access to sample hardware may not be practical.
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Old 02-25-2016, 09:33 AM   #29
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Would an R2 buffer unit help with this or is that just for power failure?
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Old 02-25-2016, 04:07 PM   #30
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It can help here, but it depends on how well your BEC is sized to your servos’ demands. It comes down to averages, and I think people tend to forget with these buffer units that while they can help during peak current demands, they now become a load along with the servos that the BEC has to supply (to recharge).

Probably the most cost-and-mass-effective way to deal with this is to size the BEC appropriately, and add a small support cap to deal with servo inrush peaks.
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Old 02-25-2016, 04:28 PM   #31
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Back to the original thread:

The Castle Creations BEC Pro 20 can be wired directly to one of the 6S motor packs (PLAESE follow CC wiring diagram carefully) and does not require a separate receiver pack
It can be programmed (if you purchase the additional Castlelink USB adapter) to output any voltage from 5v to 25v in 0.25v increments.
I use it on my Trex 600E Pro DFC (12S) and it is fine.

You can use the BK (as long as the Brain FBL that was included has the latest software up that specifically addresses the issues it had with the BK 700X series of servos) or the MKS with that BEC

I use the Align BL-800H servos on swash and the BK DS-7005HV on the tail.
The BL-800H seem to really suck down the power.
But, if you set the Brain's refresh rate for the BK or MKS down to 200Hz, they will most likely consume less power for the same loads.

My Brain uses the Spekrum Sats (DSMX) and I've never had a voltage issue even with teh BL-800H and the DS-7005HV refresh set to 333Hz.

This is important - run a Optipower Ultra-Guard 430 backup power supply.
I fly with some very, very skilled pilots. I personally have seen at least 7 times where the Backup-Guard saved a heli / pilot from a catastrophic crash due to flight batteries coming unsoldered, ESC catching on fire, BEC coming unplugged.
Get an Ultra-Guard or something that is just as good.

I have the Spektrum TM-1000 telemetry reading the receiver voltage and an alarm set on the DX9 to warn me if it gets to 7.5v.
The BEC Pro 20 is programmed for 8v output.
The alarm only goes off when I unplug the flight pack and the the Ultra-Guard takes over.
Otherwise, I've never heard a peep from the alarm in normal flight.
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Old 02-25-2016, 05:11 PM   #32
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Quote:
Originally Posted by ticedoff8 View Post
I have the Spektrum TM-1000 telemetry reading the receiver voltage and an alarm set on the DX9 to warn me if it gets to 7.5v.
That is really the key to a back up solution and also why I can't really take advantage of one yet since I'm using a dx6 (the newer black version, not the i) and I'm not ready to upgrade yet. A dx9 is on my wishlist for the future though. Maybe next year.

Without telemetry you can't know when you fall back to the buffer pack so I don't see the point for me right now. However if that R2 thing can help protect against back emf (it's supposed to) and servo amp spikes (not sure about that), then I'll probably get one. I need to do more research on it though.
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Old 02-25-2016, 05:14 PM   #33
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Nevermind
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Old 02-25-2016, 06:11 PM   #34
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You would be completely wrong about that.

Check out the Ultra-Guard.
#1) Telemetry has nothing to do with the Ultra-Guard saving your multi-thousand $$ investment.
#2) There is an option SUPER bright white LED that starts flashing as soon as the voltage gets low enough for the Ultra-Guard to take over.
#3) Even without the LED, you know the Ultra-Guard is running the flight pack as soon as you land - there are two LED flashing when it is providing the power.

And...
#4) If you lose the flight batteries because they became unplugged or unsoldered, or the ESC or the BEC failed, you lose power to the motor.
Then the Ultra-Guard provides the control you need to auto to a simi-crash landing instead of the heli dropping like a rock to the ground.
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Old 02-25-2016, 06:15 PM   #35
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Ah ok I see. thanks.
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Old 02-25-2016, 06:23 PM   #36
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Quote:
Originally Posted by ultrataco View Post
The argument is that with servos you get more speed/power with higher voltage, which takes more amps. If a servo had the same speed and torque at 6, 7 and 8 volts, then it would take less amp draw at 8v. But servos don't work like that. Put more volts in and they put out more power.
This confuses a lot of people. the answer is sometimes they do AND sometimes they dont.


They Do - If you take one servo rated for say 150oz at 6 volts and put 7 or 8 volts on it it will draw more amps while generating higher torque. (this is like taking a heli motor and adding a cell)


They Dont - If you have a 6 volt servo rated at 150oz, and then you also have a "HV" version rated at the same 150oz but at 7.4 volts. then you apply the same load to both servos with 6 volts to the regular and 7.4v to the HV - the HV servo will use less amps. (This is like adding a cell but also swapping in a motor of higher KV)
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Old 02-25-2016, 06:26 PM   #37
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BTW - For what its worth I have 2 700's running full house Futaba brusless servos -451 cyc, 256 tail and 3072 throttle). Both setups have been measured at about 2 amps average load in flight.

Im sure some crazy coreless super high torque servos will use more, but certainly not 10 times more. Your setup should be fine.
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Old 02-25-2016, 06:37 PM   #38
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Quote:
Originally Posted by jharkin View Post
This confuses a lot of people. the answer is sometimes they do AND sometimes they dont.


They Do - If you take one servo rated for say 150oz at 6 volts and put 7 or 8 volts on it it will draw more amps while generating higher torque. (this is like taking a heli motor and adding a cell)


They Dont - If you have a 6 volt servo rated at 150oz, and then you also have a "HV" version rated at the same 150oz but at 7.4 volts. then you apply the same load to both servos with 6 volts to the regular and 7.4v to the HV - the HV servo will use less amps. (This is like adding a cell but also swapping in a motor of higher KV)
ok that makes sense thanks. I was just thinking about HV servos.
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Old 02-25-2016, 07:16 PM   #39
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It's already a long thread but I'll just add, for some real figures. I have the RJX 0521HVs, these are similar to the BKs, on a minicopter Triabolo, so it's a fairly chunky 700 size heli. I run them at the default voltage from the Kosmik BEC (I think it's 5.6 volts). In the logs I never see over 10 amps being drawn, the average is around 7 amps (even though the servos could, in theory, draw a lot more).

Having said that, I don't do aggressive crazy moves. I have an Opti ultraguard on it and it has never been triggered in flight.

I have JR8717s on the TDR powered by the much smaller BEC in the Jive 80HV and I don't know what the amp draw is but that setup has always worked great as well.
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Old 02-26-2016, 06:15 AM   #40
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Trillian-

Its interesting that your RJX servos draw so much more average current (7 amps) than my Futaba BLS (2 amps). I knew brushless where more efficient but I really would not have thought they where that much more efficient. wow
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