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Old Oct 07, 2012, 08:04 PM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
24,101 Posts
@ Pavlos - sounds like everything is working. Have fun.

Like mentioned by Aerocal, the reason you can't choose flap switch in the switch menu is because that's not where you select it.
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Old Oct 07, 2012, 11:04 PM
Need More PURPLE !!
Dejavu*Xion's Avatar
United States, NV, Las Vegas
Joined Aug 2012
3,703 Posts
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Originally Posted by crvnation View Post
Since you took it upon yourself to scold me, is this not OT content as well? You're posting and perpetuating it. Pot, kettle.
Lol...skidder87, sertav, kokopelli, mhunter always used the term " pot kettle" see ther. I told you it was him again with a shill acct yet again. Jim g. Asked me to keep an eye out for this guy. He always pops up in your dx8 threads.
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Old Oct 08, 2012, 02:07 AM
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Joined Oct 2012
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yes.. thank you guys..that makes sence...
as I said I needed fresh minds.. thanks for all the help again.. i think I'm ready for that maiden as soon as I find CG.. the first stumax at both of nicosia Fields..
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Old Oct 08, 2012, 05:29 AM
Ready to fly MRs
Sid3ways's Avatar
Swanton, OH
Joined Jul 2007
5,072 Posts
Quote:
Originally Posted by jj604 View Post
Honestly Andy, I know it's not your dept. but somebody at Spektrum needs to get biffed for the delay in getting a current sensor to the customers. It's not rocket science. Everybody else seems to be able to put an Allegro sensor in some heat shrink with a 1wire or I2c interface. And we even have people making their own.

The mAh used display on my FrSky stuff is the most useful bit of telemetry it has.

John
This is 100% truth. mAH used is by far the most important piece of info I want to see when flying my multirotors. I wish someone made an aftermarket one that would be compatible. I'm not up to building the circuit myself.
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Old Oct 08, 2012, 05:31 AM
Ready to fly MRs
Sid3ways's Avatar
Swanton, OH
Joined Jul 2007
5,072 Posts
Quote:
Originally Posted by Mukenukem View Post
You don't want a 150A sensor withouth the capability of measuring mAh. You want this: http://rctronix.steinonline.de/wp/?p=18 (sorry, German. But if you are good with electronics just have a look at the schematics, it is a piece of cake)

A diy capacity sensor, using the Powerbox menu. Also, the JLog (logger for Kontronik ESCs) speaks spektrum telemetry.
Thanks for the info Mukenukem. I'm not sure I'll have the time to put something like this together myself but if worse comes to worse I'll try to make one. I wasn't aware the Spektrum current sensor didn't display mAH used, live mAH ratings are next to worthless except for bench testings.
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Old Oct 08, 2012, 05:46 AM
Registered User
pgoelz's Avatar
United States, MI, Rochester Hills
Joined Oct 2000
946 Posts
Quote:
Originally Posted by Sid3ways View Post
This is 100% truth. mAH used is by far the most important piece of info I want to see when flying my multirotors. I wish someone made an aftermarket one that would be compatible. I'm not up to building the circuit myself.
Out of curiosity, why is mAH used important to you? I can see why people might want to see it while flying, but honestly, I find that battery voltage is far more useful. Unless you are trying to predict remaining flying time more accurately than using a timer, having an alarm at an appropriate cell voltage threshold works great for me.

I still use a timer but if the timer has expired and I have not gotten a voltage alarm (at 3.5V/cell), I can continue flying. And if I do get the alarm, I can avoid further high throttle excursions and make it back to the field and land without stressing the cells.

Paul
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Old Oct 08, 2012, 05:53 AM
Ready to fly MRs
Sid3ways's Avatar
Swanton, OH
Joined Jul 2007
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Originally Posted by pgoelz View Post
Out of curiosity, why is mAH used important to you? I can see why people might want to see it while flying, but honestly, I find that battery voltage is far more useful. Unless you are trying to predict remaining flying time more accurately than using a timer, having an alarm at an appropriate cell voltage threshold works great for me.

I still use a timer but if the timer has expired and I have not gotten a voltage alarm (at 3.5V/cell), I can continue flying. And if I do get the alarm, I can avoid further high throttle excursions and make it back to the field and land without stressing the cells.

Paul
Because when flying multirotors, when hovering you are using minimal amps. Since you aren't pushing the battery hard the voltage doesn't generally sag much like it would if you were flying a plane and moving the throttle frequently. I could be 6500mah into a 8000 mah lipo and the lipo will still hang onto a decent voltage. When the copter is far away from me it helps me judge how quickly I need to get it back. I don't have the ability to "dead stick" in like an airplane does. My deadstick means I have 9K worth of equipment falling to Earth like a brick.

Entire pack voltage doesn't give me the whole story to help manage battery life. My flights can be 14-18 minutes so a timer doesn't generally give me an accurate flight time. If I'm trying to frame a shot then knowing if I can take an extra minute or two to try and get it right is all worth it.

When it comes to flying my standard airplanes, I agree, voltage monitoring is sufficient.
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Old Oct 08, 2012, 06:10 AM
flitelab's Avatar
Canada, NS, Halifax
Joined Feb 2010
7,093 Posts
Agreed on multirotors I would much prefer mah used over voltage. Voltage is too flat with a quick dropoff so not easy to gauge remaining power. mah used gives a much better fuel level indication. Why Spektrum refuses to make such a sensor is strange but I've given up trying to figure out why they do anything.
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Old Oct 08, 2012, 06:19 AM
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United States, MI, Rochester Hills
Joined Oct 2000
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Originally Posted by flitelab View Post
Agreed on multirotors I would much prefer mah used over voltage. Voltage is too flat with a quick dropoff so not easy to gauge remaining power. mah used gives a much better fuel level indication. Why Spektrum refuses to make such a sensor is strange but I've given up trying to figure out why they do anything.
I would imagine because deriving mAH consumed from a simple current sensor involves computation (ie., integration of current vs. time elapsed), which is more involved than sending a simple analog value.

I see how a multi rotor might be a different case. In the mean time, can you goose the throttle once in a while when you are getting near the end of the flight and see if that drives the pack below a reasonable voltage threshold? OK for sport flying, but maybe not if you are flying a photo mission?

Paul
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Old Oct 08, 2012, 06:23 AM
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Canada, NS, Halifax
Joined Feb 2010
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Goosing the throttle isn't the best when trying to fly in a specific manner since on a multi all control is via motor control. You also have 4/6/8 motors pulling current so bursting the throttle causes a big pull on the lipo, not really a true indication compared to the power needed for hover and slow flight.

As for the complexity of a current sensor, just about every OSD around has this, it isn't that complex to do.
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Old Oct 08, 2012, 06:38 AM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
6,601 Posts
Paul, every microprocessor contains an accurate clock. mAh used is a trivial calculation. Multiply two numbers and add to the current value. And none of these current sensors send an analog signal, they all convert it to digital at the sensor.

Honestly it is simple to do with a Hall effect sensor. Quanum have had one that works just fine with their wireless LiPo cell voltage monitor for over a year for less than $20 from HobbyKing. The FrSky one also works well. I know there are several others, particularly from the European manufacturers.

I'm not a Spektrum basher but IMO they dropped the ball on this one.

John
Quote:
Originally Posted by pgoelz View Post
I would imagine because deriving mAH consumed from a simple current sensor involves computation (ie., integration of current vs. time elapsed), which is more involved than sending a simple analog value.
Paul
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Old Oct 08, 2012, 08:09 AM
AndyKunz's Avatar
Illinois
Joined Sep 2001
24,037 Posts
One of the small issues with mAh measurement is that with an ESC, power is delivered in pulses. To accurately measure current you need to be oversampling at a pretty good rate, much faster than the PWM frequency to your motor. Either that, or give up a little accuracy by having it averaged in hardware and then sampling at a lower rate.

The modelers who are most interested in this sort of thing are also the ones who are least interested in a device that goes inline in the power system due to the insertion losses. OTOH, a Hall-effect sensor is not nearly as accurate.

I've been down this path before I came to Spektrum.

Andy
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Old Oct 08, 2012, 12:04 PM
Radio? Screwdriver!
United Kingdom, England, Bristol
Joined Aug 2011
960 Posts
Quote:
Originally Posted by AndyKunz View Post
One of the small issues with mAh measurement is that with an ESC, power is delivered in pulses. To accurately measure current you need to be oversampling at a pretty good rate, much faster than the PWM frequency to your motor. Either that, or give up a little accuracy by having it averaged in hardware and then sampling at a lower rate.

The modelers who are most interested in this sort of thing are also the ones who are least interested in a device that goes inline in the power system due to the insertion losses. OTOH, a Hall-effect sensor is not nearly as accurate.

I've been down this path before I came to Spektrum.

Andy
I've found that a simple RC LPF does a good enough job to filter the current sense voltage out of a modern high sided current sense amplifier IC. This is what most of the watt meters on the market appear to do too now. The accuracy is more than good enough for modelling use (where +/-5% accuracy or so doesn't really make too much of a difference). Also having a small enough current shunt (1mOhm) will keep insertion losses to a minimum that is negligible.

From experimenting with mAh on telemetry (with Hitec gear but it still applies to others) with my own current sensing PCBs, I never found it that useful. It's interesting to see how a pack is performing, but tbh your charger can tell you that already from mAh charged (if you discharge to the same flight pack voltage every time). Pack voltage is far more useful, as it really tells you how much life you have left and when your ESC is about to cut off.

The problem with a mAH reading is that the amount of energy you can pull from a pack varies depending on cell degradation and current draw. As everyone knows, as a pack gets older it won't have the capability to store as much energy as it used to. So the problem is that one packs empty is another packs 30% left or if your pulling really high current draws for a flight, you could get less mAh out of a pack than when flying around gently. Hence, with a alarm set to a mAh, it may not be triggered as the pack ages or depending how the flight was flown. Then without a flight pack voltage alarm, you could find yourself out of juice with no warnings.

To make a mAh reading useful, you need to track the discharge capacity and the charge capacity over time. Then you can then accurately estimate how much juice you have left during discharge and also tell if a pack isn't holding enough charge. Now its possible to note this down manually every you discharge and charge, but apart from a small percentage of modellers I can't imagine anyone could be bothered! You could automate this, as Laptop batteries do with their on board fuel gauge ICs - however for RC use this would push the cost of the pack up considerably and also require a standardised way of communicating with the onboard IC. Both not desirable. For an example of this, look at the replacement cost of a Laptop battery!

Where as voltage will tell you that your about to run out of juice. Remember your ESC will cut out on voltage, so you want to land before you hit this cut off!

mAh is a nice thing to look at, much like looking at a ground track from GPS telemetry. However once the novelty has worn off, its not something you look at again. I've found this with the flight current readings too. Once I had played around with it and seen that current drops off in flight, and that your under the ESC rating I never really looked at it again. The only useful time was to know when a motors bearings were on their way out and thus the current draw went up significantly. However I could tell this from shorter flight times.

mAh measurement is way overrated imo.

That's my two pence.

Cheers,
Si.
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Old Oct 08, 2012, 12:15 PM
Stop scaring my donkey!
JohnathanSwift's Avatar
Greenland
Joined Mar 2012
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Simon says...and I believe it!
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Old Oct 08, 2012, 12:23 PM
Suspended Account
Joined Sep 2012
428 Posts
Quote:
Originally Posted by AndyKunz View Post
One of the small issues with mAh measurement is that with an ESC, power is delivered in pulses. To accurately measure current you need to be oversampling at a pretty good rate, much faster than the PWM frequency to your motor. Either that, or give up a little accuracy by having it averaged in hardware and then sampling at a lower rate.

The modelers who are most interested in this sort of thing are also the ones who are least interested in a device that goes inline in the power system due to the insertion losses. OTOH, a Hall-effect sensor is not nearly as accurate.

I've been down this path before I came to Spektrum.

Andy
That does sound hard. A properly calibrated DX8/10 voltage reading should be much easier and not have a 0.3V error said to be "within specs".
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