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Old 01-06-2017, 09:04 PM   #21 (permalink)
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Originally Posted by mkovalcson View Post
mah is the best most accurate way to measure the power you've pulled from a battery.

Batteries sag differently depending on how new they are and their C rating.

A new high C rating battery won't sag much in the beginning. An old lower C rating battery will sag a lot and consistently read a lower voltage when it has more juice left in it.
Yea, but who cares, if the use of that metric is to determine when to land? You have what amounts to a fuel totalizer- a device which tells you have many gallons you have burned, but not how many were in the tank to begin with; you cant determine how much remains.

You want to kill a pack- run on an mAh sensor, with that pack at 3.8v on departure, or with too high a capacity defined for it. Heck, just a real change in temperature has significant effect on battery capacity, and that requires some testing.

It probably works OK for people who fly all the same packs on a given machine, at a consistent temperature, and who check their pack voltage before departing. But what do you do if you find a pack in the bag that shows 4.05v/cell? What do you set your mAh limiter at? There are a slew of ways to get in trouble here. If you use pack voltage- there are no ways you can get in trouble, so long as you fly a given cell count on a given model.
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Old 01-06-2017, 09:05 PM   #22 (permalink)
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I'd love to see a voltage reading that's averaged over a few seconds to clear out the dips. That would probably be simpler and more reliable than mAh, but I don't believe any systems offer that.
It is simple to implement that. I posted a couple of circuits that can do it for you, or for people with programmable transmitters- you can do it in code without much effort. But the point is to look at peak voltage as your resting voltage, and then also keep an alarm for peak dip, since there is a strong case for lipo cell damage from dips that exceed some minimum value (i.e. 2.8v or whatever, depending on chemistry).
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Old 01-06-2017, 11:35 PM   #23 (permalink)
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But I love my ol 9303
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Old 01-07-2017, 12:06 AM   #24 (permalink)
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Yea, but who cares, if the use of that metric is to determine when to land? You have what amounts to a fuel totalizer- a device which tells you have many gallons you have burned, but not how many were in the tank to begin with; you cant determine how much remains.

You want to kill a pack- run on an mAh sensor, with that pack at 3.8v on departure, or with too high a capacity defined for it. Heck, just a real change in temperature has significant effect on battery capacity, and that requires some testing.

It probably works OK for people who fly all the same packs on a given machine, at a consistent temperature, and who check their pack voltage before departing. But what do you do if you find a pack in the bag that shows 4.05v/cell? What do you set your mAh limiter at? There are a slew of ways to get in trouble here. If you use pack voltage- there are no ways you can get in trouble, so long as you fly a given cell count on a given model.
As someone who has flown with mAh telemetry for several years with heli's I can say it is the most reliable method available.

The issues you bring up are easily solved. I have a voltage alarm that activates when I first plug in the pack so I always know my packs are above 95% when I put them in the heli, I also always have a low voltage alarm set so if by some case something goes wrong with the mAh measurement I have a backup that should stop me damaging my packs.

For the multiple size packs I can setup a switch to take account of the pack capacity I put into the heli but now with LUA and the Jeti and some great work by Teros on his RC-Thoughts web page you can automate it so the capacity limit is set by the RFid tag attached to the pack that updates the application on the Tx via telemetry. The Vcontrol also has the capability to do this in an automated way with RFid tags.

You can tweak the capacity measurement to bring the packs down at a consistent level every time and adjust over time if you have packs coming down lower as they age. With the RFid method you can burn a new tag when required at a lower capacity so it is all automated.

With all of this it is a pretty foolproof system, I always leave a little in hand and alarm at 70% used so by the time I land I am well within 25% remaining and this little buffer takes into account any issues with small capacity differences between packs and temperature over the range I fly in.

Voltage measurement in flight might be fine for sports or scale pilots where the load is fairly consistent but it just doesn't work for flying 3D flight and especially when you fly very different headspeeds. Even with averaging of the voltage, if I set my alarm where needed when flying in my fastest head speed and throwing around the heli the voltage drops are large, so will need to be down in the low 3v range, then if I take my lowest head speed which cuts the current draw and load (i.e. voltage drop) on the pack down by 75% (even doing 3d) the cutoff will be way too low.

I could say the same thing about the voltage method in that this might work fine for someone who always flys the same head speed and style in a flight, but I can tell you that when flying very different head speeds (e.g. 1350/1650/1900rpm) and styles of flight within one flight the mAh method is by far the most foolproof and workable solution.

//Dennis.
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Old 01-07-2017, 12:08 AM   #25 (permalink)
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No issue with 9303 but its 22ms latency is slowed compared to the new jr control. And with dmss it splits important channels from semi important ones n spits them out faster. There is a utube review which has 3 parts on the XG 8 n the guy show n explains the rf coming n going inside n out. Once u see it. It will make more sense n see why jr has one of the best rf protocols on the market to day n xbus is great to. Using bus connection vs running servo wiring all over love it. Loved my 8103 too but I had to make the telemetry jump n 2.4 jump for club n piece of mind
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Old 01-07-2017, 12:58 AM   #26 (permalink)
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As someone who has flown with mAh telemetry for several years with heli's I can say it is the most reliable method available
....
I could say the same thing about the voltage method in that this might work fine for someone who always flys the same head speed and style in a flight, but I can tell you that when flying very different head speeds (e.g. 1350/1650/1900rpm) and styles of flight within one flight the mAh method is by far the most foolproof and workable solution.
//Dennis.
No, you cant, because it isn’t. Your approach towards measuring voltage in flight is not a good one- but that doesn’t mean good ones don’t exist, and aren’t every bit as capable as capacity-based systems. And more to the point, they function regardless of human error, and require no consideration for packs (no RFID, no capacity reset, no correction for state of charge or ambient temperature) other than the assumption of a fixed cell count for a given model. And if that changes and you dont realize it- you have bigger problems.
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Old 01-07-2017, 04:00 AM   #27 (permalink)
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I love it when these discussions turn into arguments of opinion.

I agree with TF

I adjust my MAH consumed until I land with 20-25% of my pack consumed. Regardless of my flying style. As the pack ages I will adjust my alarm. Simple.

Now keep in mind if I check it right after I land or after the pack has cooled it could vary 10-15%. Blabla

Do I care? No.

It's already on the charger at 5C. Don't worry, I'll fly again in roughly 10:00 minutes. While your continuing this pointless argument.

I say again, For Telemetry get a simple, reliable system. Your current transmitter is most likely not the best choice. You most likely will have to update your radio.

Try doing it by voltage alarms as it's been suggested & when your first pitch pump sets off the low voltage alarm you will be right back where you started. Keep it simple.

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Old 01-07-2017, 04:22 AM   #28 (permalink)
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As someone who has flown with mAh telemetry for several years with heli's I can say it is the most reliable method available.

The issues you bring up are easily solved. I have a voltage alarm that activates when I first plug in the pack so I always know my packs are above 95% when I put them in the heli, I also always have a low voltage alarm set so if by some case something goes wrong with the mAh measurement I have a backup that should stop me damaging my packs.

For the multiple size packs I can setup a switch to take account of the pack capacity I put into the heli but now with LUA and the Jeti and some great work by Teros on his RC-Thoughts web page you can automate it so the capacity limit is set by the RFid tag attached to the pack that updates the application on the Tx via telemetry. The Vcontrol also has the capability to do this in an automated way with RFid tags.

You can tweak the capacity measurement to bring the packs down at a consistent level every time and adjust over time if you have packs coming down lower as they age. With the RFid method you can burn a new tag when required at a lower capacity so it is all automated.

With all of this it is a pretty foolproof system, I always leave a little in hand and alarm at 70% used so by the time I land I am well within 25% remaining and this little buffer takes into account any issues with small capacity differences between packs and temperature over the range I fly in.

Voltage measurement in flight might be fine for sports or scale pilots where the load is fairly consistent but it just doesn't work for flying 3D flight and especially when you fly very different headspeeds. Even with averaging of the voltage, if I set my alarm where needed when flying in my fastest head speed and throwing around the heli the voltage drops are large, so will need to be down in the low 3v range, then if I take my lowest head speed which cuts the current draw and load (i.e. voltage drop) on the pack down by 75% (even doing 3d) the cutoff will be way too low.

I could say the same thing about the voltage method in that this might work fine for someone who always flys the same head speed and style in a flight, but I can tell you that when flying very different head speeds (e.g. 1350/1650/1900rpm) and styles of flight within one flight the mAh method is by far the most foolproof and workable solution.

//Dennis.
Well said.
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Old 01-07-2017, 05:27 AM   #29 (permalink)
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Green is telemetry-based pack voltage. Red is what a basic low pass filter many people have tried (and disliked) looks like to your TX alarm logic. Yellow is what a simple, proper filter looks like. You see massive dips in the yellow trace? You see any dips that are not representative of actual pack voltage reduction? That seem too difficult to use as valid telemetry data? There are 2 passive components, retail $0.50 to put together. But why do that, when you can invest in a current integrator, RFID tags, a database to dynamically update your TX model scripts for the pack capacity, and a backup voltage monitoring system (which makes no sense if you already believe the data is invalid…) with its own conditional tests…

Bad telemetry data is worse than useless; it leads to invalid conclusions. And that is the point- telemetry isn’t just about battery state- it is about a lot of things that matter- motor temperature, RX bus voltage, RSSI, etc. But if you implement data capture or processing badly (i.e. assume the motor can represents the coil temperature, or that a 10hz sample rate with a low pass filter on your RX bus will catch 2ms dips…), you end up believing things are great when they may be terrible. Not a lot of value in that.
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Old 01-07-2017, 06:01 AM   #30 (permalink)
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No, you cant, because it isn’t. Your approach towards measuring voltage in flight is not a good one- but that doesn’t mean good ones don’t exist, and aren’t every bit as capable as capacity-based systems. And more to the point, they function regardless of human error, and require no consideration for packs (no RFID, no capacity reset, no correction for state of charge or ambient temperature) other than the assumption of a fixed cell count for a given model. And if that changes and you dont realize it- you have bigger problems.
Well, I think I am entitled to my opinion based on the experience of 2 years and many hundreds of flights without a issue. I haven't seen a single documented case of filtered voltage being used with success in these multiple headspeed, multiple flight-style flights, so I'm not sure how you can say the method is better without showing evidence of someone actually using it.

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Originally Posted by extrapilot View Post
Green is telemetry-based pack voltage. Red is what a basic low pass filter many people have tried (and disliked) looks like to your TX alarm logic. Yellow is what a simple, proper filter looks like. You see massive dips in the yellow trace? You see any dips that are not representative of actual pack voltage reduction? That seem too difficult to use as valid telemetry data? There are 2 passive components, retail $0.50 to put together. But why do that, when you can invest in a current integrator, RFID tags, a database to dynamically update your TX model scripts for the pack capacity, and a backup voltage monitoring system (which makes no sense if you already believe the data is invalid…) with its own conditional tests…
So what happens to that yellow trace if I land and make an adjustment just before the alarm goes off at the end of my pack and have the Heli sitting on the ground for a couple of minutes? The pack voltage will recover and your line will climb back up, then I take off and beat hard on the Heli, how far past the safe pack voltage will it let me fly before triggering the alarm?

Most of the new ESC's are now including capacity measurement that is available to telemetry systems, if your solution is so bulletproof and simple why are none of the manufacturers offering it, even as an option?

//Dennis.
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Old 01-07-2017, 09:57 AM   #31 (permalink)
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Green is telemetry-based pack voltage. Red is what a basic low pass filter many people have tried (and disliked) looks like to your TX alarm logic. Yellow is what a simple, proper filter looks like. You see massive dips in the yellow trace? You see any dips that are not representative of actual pack voltage reduction? That seem too difficult to use as valid telemetry data? There are 2 passive components, retail $0.50 to put together. But why do that, when you can invest in a current integrator, RFID tags, a database to dynamically update your TX model scripts for the pack capacity, and a backup voltage monitoring system (which makes no sense if you already believe the data is invalid…) with its own conditional tests…

Bad telemetry data is worse than useless; it leads to invalid conclusions. And that is the point- telemetry isn’t just about battery state- it is about a lot of things that matter- motor temperature, RX bus voltage, RSSI, etc. But if you implement data capture or processing badly (i.e. assume the motor can represents the coil temperature, or that a 10hz sample rate with a low pass filter on your RX bus will catch 2ms dips…), you end up believing things are great when they may be terrible. Not a lot of value in that.
Hey EP, if its so easy to integrate a filter such as this, then why isnt this already being handled by our equipment today? Surely they are capable of this voltage dip filtration and smoothing if its as simple as you describe to do?

I too am one who abandoned the voltage method. On paper its the best because of everything you listed and no need to switch alarm values with different cell packs, but I spent more time fiddling with the alarm values in an attempt to get them low enough without constantly having false alarms every time I increased the collective, and even then it was causing me to come down too low, so I went back to timed flights which were just easier and come down at the the exact cell voltage I want every time.

I would love to use voltage if my system was actually seeing the yellow curve like you are showing.
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Old 01-07-2017, 11:26 AM   #32 (permalink)
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From what I read here it seems that no one knows the discharge curves of lipo batteries:



The voltage of Lipo remains almost constant until 95% or more of discharge and the last 5% of discharge, the voltage collapses very fast.
In a 3D flight with modern electric helicopters that lasts between 3 and 4 minutes, if it is decided to land ONLY when the voltage begins to fall, it would only have very few seconds to land and stop the engine before the battery is fully discharged below 3V per cell and thus irreparably damaged.
If you add to this a r/c or l/c circuit that delays the real voltage loss, at every landing based ONLY on the delayed voltage, you should throw away the lipo pack.

Side notes: who today start a flight without the battery full charged? As yet remember, today a 3D electric model doing 3D flight for only 3/4 minutes. Who today start a flight for flight only 2 or 1 minutes or less?
With a nitro I can understand that sometime instead of an usual 8 minutes one can start a flight with half tank and do a flight for 4 minutes, but here we are speaking of electric, not nitro (or gasser).
Is right to keep in mind the theories, but too often live far away from the usual practice.

Exactly as the correct theory that the phase lag on rigid heads must be adjusted to less than 90 ° but that, in the practical reality of the facts on 25,000 units (where the phase lag can be varied by software if necessary), has never been changed on any of the 25,000 units. Theory vs usual practice and reality of real rc-model.
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Old 01-07-2017, 01:40 PM   #33 (permalink)
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Your right that escaped us ...lol in all seriousness thou your right, voltage is very stable in a lipo and but also the voltage when looked at with a higher resolution would show a very consistent drop.
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Old 01-07-2017, 04:31 PM   #34 (permalink)
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For many of the reasons above, this is why I've used both voltage and capacity when running telemetry. Capacity is a good metric to establish a baseline cut, assuming a good pack that hasn't lost a non trivial portion of storage. Voltage is in place to monitor for any significant dips (could be a pack, could be a connector failing. Either way it means land).

The idea being, as extra pointed out, the heli doesn't know how much energy went into the pack. Voltage will give you a definitive cut off if set right, but you risk running your packs into the dirt (as noted by Thunder and BrainDev).

Ideally, you need to keep an eye on your packs when charging/cycling them. A laptop knows the wear on a pack because it knows how much it put back in from a certain voltage on the charge cycle. Running capacity alarms, you need to be aware of what 80% used really is.When new, it could be 2800mAh or something, but a hard year later, maybe only 2300.
That said, when I've had packs drop off that much, their IR has skyrocketed and they sag even with capacity left. Time to get new packs.

I'd like to think most people running Ah telem aren't sticking alarms at 80% of labeled cap and just leaving them there.
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Old 01-07-2017, 04:49 PM   #35 (permalink)
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I'd like to think most people running Ah telem aren't sticking alarms at 80% of labeled cap and just leaving them there.
FWIW I have a 40% announcement, a 30% announcement and at 25% It repeats "Land Now.." every 10 seconds.

I usually start thinking about landing at 30%.
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Old 01-07-2017, 05:04 PM   #36 (permalink)
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FWIW I have a 40% announcement, a 30% announcement and at 25% It repeats "Land Now.." every 10 seconds.

I usually start thinking about landing at 30%.
I do the same but have 50%, 60%, 70% with the last one repeating 3 times so I don't miss it. I find if I am doing a low headspeed flight if I haven't heard a call out from the telemetry after 5 to 6 minutes I start to think something is wrong, and the 50% used usually comes up around then and puts my mind at ease. It also works well to leave packs near storage charge, although I still usually put them on a charger when I get home to check them.

//Dennis.
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Old 01-07-2017, 05:30 PM   #37 (permalink)
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I have the same warnings, but also ahve a switch on ,my TX setup to read current pack consumption. That way if I have a doubt that it's reading correctly, I can get an instant read. I also have it read out every minute of flight. 1, 2, 3, 4 etc. That way if I get concerned, I can correlate.
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Old 01-07-2017, 06:09 PM   #38 (permalink)
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Thinking further on the filtered voltage method, there are other issues on top of what have already been described.

The voltage reading is dependant on load, even if integrated over time to average the load (and therefore voltage). So in a hard flight the average load (amps) will be higher and therefore give a larger voltage sag, even when averaged. So the alarm will be reached earlier than a very soft flight or low headspeed flight as the voltage drop under the lighter load will be much less so the result is more inconsistant than the capacity method.

So while the filter method can remove the spikes from a flight, it does not take into account light load versus high load conditions. For example if we set the alarm at a filtered 3.55v per cell, under a high load flight we might get a resting voltage of 3.75v saying there is a 0.2v voltage drop (1.2v on a 6s pack) from the load. With the same alarm set and a low headspeed flight which averages 1/2 of the amps we might get a 0.1v drop per cell under load (0.6v on a 6s pack) so leading to a resting voltage 3.65v per cell, which leaves a very different amount of capacity remaining.

With the capacity method it doesn't matter how I fly, or what headspeed I use so long as I start with a full pack, my resting voltage and capacity remaining in the pack is very consistent at the end of the flight. And it still doesn't stop me using specific voltage alarms to catch a bad cell or other issues.

//Dennis.
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Old 01-07-2017, 06:19 PM   #39 (permalink)
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Default FrSky Telemetry

To the OP - take a very close look at a Taranis X9DP. It has a form factor and switch layout very similar to your beloved 9303. If you were to go this route, here a shopping list I would start with:

Taranis X9DP - $200
Custom hydrodipped case - $45
XSR 16 channel Rx - $25
RPM + Dual Temperature sensor: - $20
6S Pack voltage sensor - $15

For around $300 you'll not only have a super bitchin' singularly unique powerhouse Taranis (each hydro-dipped case is unique), you'll have everything you need to record 2 temps (e.g. motor, battery, ESC,..), electrical RPM (from which both motor and rotor RPM are computed), total pack voltage, and most importantly (and pertinent to the current discussion), you'll also get the voltages of each and every LiPo cell in the system. Usefully, a: "lowest cell voltage" value is also reported. Note that all of FrSky's X-series receivers are 16-channel via the 1-wire SBUS connector - which is the simplest way to connect to the FBL and they all support FrSky's S.Port telemetry protocol. The XSR is the smallest and lightest (5g).

Every day is be kind to your LiPo day

It seems that if health of the LiPo is the primary concern, then the primary rule to follow is to: NEVER LET ANY CELL GET BELOW 3.0V. EVER! To me, this actually means to never let any cell get below 3.3V. But to do this we must measure each and every cell in the system. FrSky's SP-FLVS voltage sensor does just that and measures both the overall pack voltage (2S-6S), as well as the voltage of each and every cell in the pack. This telemetry data is reported back to the Taranis at a frequency = 3Hz. Additional FLVS sensors can be added to support additional multi-celled packs (but each sensor must be assigned a unique ID using the FrSky channel changer gizmo ($15), and you must be running OpenTX version 2.1.x or higher). With three FLVS sensors, you can (easily, cheaply and lightly) monitor every cell in a large model running 12S power (2 6S in series) and a 2S Rx.

Using telemetry for flight termination

With a Taranis and a model fitted with a FLVS voltage sensor and the RPM sensor, (but no current sensor), multiple alerts can be combined to provide all necessary ingredients for a practical flight termination procedure which is kind to your LiPos:
  1. COUNTDOWN TIMER: Conventional countdown timer that runs when the throttle channel output is > 0. This includes a voice bark at every minute followed by: "Ten", "Nine", etc final countdown barks at the end. The duration for this countdown timer would be manually adjusted using trial and error such that the battery ends up at say, 65% depleted (you chose this value). The pilot can ignore this alert and continue flying and will start getting nagged with warnings as the battery "runs out".
  2. BATTERY LOW: (Vave <~ 3.65V) - "You're battery is getting low!"
  3. BATTERY CRITICAL (Vcellmin < 3.3V) - "LAND NOW! You're nearly out of gas!"
  4. BATTERY DEPLETED (Vcellmin < 3.1V) - "WARNING WILL ROBINSON!"
  5. BATTERY TEMP HIGH (Tbatt > 120F) - "Battery is getting hot!"
  6. BATTERY OVERTEMP (Tbatt > 200F) - "LAND NOW! Battery overheating!"
  7. MOTOR TEMP HIGH (Tmotor > 120F) - "Motor is getting hot!"
  8. MOTOR OVERTEMP (Tmotor > 200F) - "LAND NOW! Motor is overheating!"

If the system does have a current sensor in addition to voltage, then additional useful parameters can indeed be computed: e.g. Instantaneous power (V*I) and total mAh consumed (a measure of energy). If the capacity of the battery is also known, then an additional useful parameter can be computed: "Estimated percent battery remaining". Additional voice alerts could be added to alert at user defined thresholds. Assuming you knew ahead of time exactly how much energy was actually in the battery to start with, then the "Estimated remaining" = "true remaining". But this is a very big assumption! But as long as the: "lowest cell voltage" is used and the threshold warning alerts heeded, any errors with "estimated" values will be harmless to the LiPos.

One other point worth mentioning; the current sensors are quite heavy. But do be sure to check out all the other cool telemetry sensors available. After using multiple Tarani for more than 3 years I can voice that FrSky quality is actually very good - and their stuff is unbelievable inexpensive! The only quality issues I've encountered are the switches on the X9D are somewhat cheesy. I'd look at the Horus and upcoming Q7X as well, but they got rid of a couple buttons that were near and dear to me

My $0.02

Yes I am a Taranis fanboy - (because IMO it is just that great - and get this - new hall effect gimbals for the X9D/X9DP are reportedly coming soon! )
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Old 01-07-2017, 07:19 PM   #40 (permalink)
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What I see is a LOT of futzing around with Voltage which seems like a real waste of time.

I'm never over discharged a battery since I started using mah timers and they have worked very reliably and consistently.

But if you guys know better, have at it. I have nothing more to add.
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