Wiring question

[splitboarder]

Im going to HV servos and wanted to know how you guys are hooking up your Jive ESC. Do you still use a nicad pack ? Or, just unplug the hot wire and run a 7.4 batt to your electronics?

Thanks

[R_Lefebvre]

Not Jive, but I run a separate 7.4V pack.

One problem I've found with the servos I'm using however, is that they aren't so happy at 8.4V on a fully charged pack. At least one of the super fast 0.03sec/60 servos I have. It's got some points where it buzzes really badly. But on 6V it's fine.

It's sort of like back in the day if you ever plugged a 5-cell NiMh pack direct to your servos. When it was freshly charged it made them behave badly, but when when drained a bit it was fine.

[FSAMedia]

I usually pull the hot wire, fold it back and secure it with some heat shrink so I can reuse it later. As for HV servos not liking a fully topped lipo, I agree...my servos get a bit noisy. I thought about running a bec, but that's just another failure point. JR advertises that they'll work, so I've put my faith, and a $hit load of money, on them. Great, now I'll be thinking about that the next few flights.

[pc3associate]

Just run the hv on a 7.4 pack. Less failure points. That is the nice point about spending all that money on nice hv servos. And if the ESC takes a crap better chance of a controlled auto.

[splitboarder]

thanks for the replies

So, here is my plan

7.4 2s pack strait into the JR 921 rx. Jumper from 921rx to the Ace One
HV servos into the Ace One
Ace one to the 921 rx

Sound right?

( I know what you mean FSA. Imswitching from a castle HV120 ESC to the Jive 80HV and really dont want to. I hate re-doing my Ace one throttle settings)

[FSAMedia]

You'll be happy with the Jive, it's got a much better governor and allows you to drop head speed down to the lower 70% range if you absolutely need to. Resetting the throttle curve is actually pretty easy...just adjust the curve until you're hovering at dead mid throttle stick....you know, easy

[splitboarder]

Yeah, I have been using the jive on my Maxi Joker 2 . Just got it on and set as far as throttle peak last night. Will fly today when I get home. Waiting for a 12 tooth 6mm pinion though. Im running a 14 with the KDE mod 1 115 tooth main gear and my head speed is way too high.

[R_Lefebvre]

When you guys say "a 7.4V pack", do you mean 2S Lipo? That's what I meant, but the problem is a 2S Lipo is really 8.4V.

Or are you suggesting to run it of a 7.2V 6S-NiMh pack. Or a 6.6V LiFePo4?

[pc3associate]

A 7.4v Life pack. The typical 2 cell life pack produces about 1v less than a normal lipoly battery. But of course as with all batteries no 2 are the same.

[R_Lefebvre]

Ok, cool. That's a good idea, I'll have to check if my charger can do Life.

I wonder, when the manufacturers created these "HV" servos and rated them at 7.2V.... what as the intent? Are they really supposed to be plugged direct into a fully charged 2S battery at 8.4V, as they are marketed? Or was the idea actually to use 6S NiMh at 7.2V?

The big problem with Life as I understand it is it's difficult/impossible to measure pack capacity based on voltage. You have to pay more attention to how much you use it and how much you put back in. There is no way to check the capacity mid-use?

[pc3associate]

Turning into a great discussion.

Great questions Rob. Doubt we will ever find out exactly. Battery technology and development as well as servo is such a closed door area. Would love to get some insider views on this stuff. Of course we are a small market for them.

As far as experience goes- i keep a log of all our batteries. Each battery is marked with a designation A1 A2 etc. We log the entire life of every pack. Flight times, mah used temp, and flight type. I can always tell the battery health by looking at the logs. Never had a problem with our Life packs. What i do see is when a lipo is discharged too much it will puff within the next 5 uses, usually the next charge. Had a Thunder Power 3s pack i use for gimbal control puff this week without being used.

Anyone have insider contact in any of these areas?

[R_Lefebvre]

So my charger will do LiFe. I'll probably get a few of these. I've actually got HV servos, running on 2S, but I am using a 6V BEC to avoid the problem. I'd like to get past that.

Do these have any voltage change at all that I can detect just before they dump? At least something so I can "land immediately!" ? Do they puff if overdischarged?

[splitboarder]

Your 2s lipos read 8.4 when fully charged because they are at a no load status. No battery can be read without a load. After you apply any reactive ( resistive) load the voltage will drop instantanouisly. So, a fully charged (8.4 volt lipo is realy at 7.4-7.2 as soon as it draws current). You only use it 30 seconds and hook it back up to your charger and it still reads 8.4 volts......but again thats because its under a no load situation. You would ned to measure true voltage with a meter in series as the load is draw. It wouls also need to be an analouge meter becasue digital meters are slower and wont be reading true instantaniuos voltage drop

[R_Lefebvre]

Hmmm.... I dunno. Yes, the battery voltage drops when it's under load due to internal resistance, but not that much for sure. I fly with telemetry so I can see the real voltage, and I would typically see about 0.1V/cell drop under load. ie: Using 4S on my quad or octo, it'll show 16.8V on the ground, then maybe 16.5-16.6V under load.

A 2S lipo will not drop to 7.4V under a light load.

[splitboarder]

A 2S lipo will not drop to 7.4V under a light load.

yes, it does if you are measuring voltage drop in series. That can only be done with a inline voltmeter,( think fluke) not your fpv equipment. we cant afford/nor do they make one small enough

[R_Lefebvre]

I have a Fluke 179, and a Pico Scope here. I'm not really sure what you mean by "inline voltmeter". There's only one way to measure the voltage output of a battery that I'm aware of, and I know quite a bit about electronics. So if I'm missing something, please let me know and I'll test it.

[splitboarder]

analog comparator is what you need to turly measure real time voltage, watts and amps. digital is too slow

[tech1]

Splitboarder. You are all over the map here with a lot of mixed information.

Most HV servo's are already rated for Lipo packs so if it says it is supported don't worry about the specific voltage. For example JR's specs for 8717 is misleading because it says good for lipo but only rates the input voltage to a maximum of 7.4V. This is what happens when marketing guys spurt information half cocked. They should have put the range from 6.0v to 8.4v to match their Lipo compatibility claim. Since these servos have been running great for years. I would have to assume that there is no issue at 8.4V.

To answer your question you need to split up your hardware depending on the rating for each piece. Items such as the receiver and normally ESC's and normal servo's need to run from a regulator. The HV servos will run straight from the 2S lipo. The ground (black / brown) wire will be the only wire that connects to all electrical parts.

Your Lipo vs Life comment is like comparing apples to oranges. The chemical makeup determines the cell voltage. These two chemistries cannot be directly compared for their discharge characteristics.

You could use either an analog or digital voltmeter with equal effectiveness to read pack voltages either loaded or unloaded.
If you have a pack that immediately drops by one volt when connected to a normal load you should retire it right away. A healthy pack should show minimal drop at first and then gradually drop as the load continues to run. The only time you could get that effect would be to put a load that exceeds the batteries maximum current. (ex. trying to draw 125 amps from a battery rated for max 100 amps) With the battery at its maximum current the voltage now becomes divided between the load and the internal resistance of the cells.

[Eric H]

To go back on topic, this is what I use on my gimbal equipped w/ JR 8917HV: http://shop.rc-electronic.com/e-vend...=6&c=541&p=541

HV regulator to 7.2v. Advantage is a constant voltage supplied throughout the battery discharge cycle. Servos will have the same feel and performance whether the battery is full or almost empty.

E

[nooobs]

Good to see the veterans chiming in.

Tech1 that's a "nice" way to explain it. ;-)
EricH I do the same on my setup.
I'll see you both soon!