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Old Jan 05, 2013, 07:34 PM
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Batteries don't last long at that level, and most can't do it at all.
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Old Jan 06, 2013, 12:23 AM
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San Jose, California
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I called Aeromicro, the guy at my LHS told me that to him it seems that the FMS ESC that I am using possesses a current limit capability. This hypothesis actually lines up with my observations... and here is why. I did mention here on this thread that all my other FMS mini warbirds with the same motor has no problem generating full power...only difference is the FMS 2 and 3 blade props are no as big and I think no as pitchy as the Top RC 3 blade Hurricane which was originally designed for 2s power to compensate. Perhaps there is some differential threshold between the Top RC and FMS 2 and 3 blade props when drawing full power....

So with the bigger and pitchier top rc prop on a 45C to 90C....as acting power supply the capability of sourcing at best 90C burst current .... min current = 45 * 850mah = 38.25A
max current(burst) = 90* 850mah = 76.5A

This means we have a window with a minimum current of 38.25Amps and a maximum burst of 76.5Amps...which is completely out of range of the given 35Amp Esc

which also then correlates with the known working 25C to 50C 850mah 3s which gives a minimum window of 21.25Amps and a maximum(burst) of 42.5Amps

So with the above given calculation...how do we explain the 3s 45C to 90C 850mah sag down to 10 amps at WOT??? giving only 80 to 100 watts give or take?

The answer is quite simple the min and max window for the high discharge rate is completely out of range of the ESC rating...even at WOT assuming that the ESC can hold 45 amps for 10seconds grace period...which I think is accurate for the FMS and hobbyking blue series escs...which all use the same programming algorithmic procedures.

Lesson learned... now I am going to buy a 25C battery....maybe even a 20C.....

Thinking back this is why some of the manufacturers specify what discharge ratings to use for an ARF kit...to ensure proper performance of the model given an ARF setup.

tengarang
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Old Jan 06, 2013, 12:35 AM
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United States, AK, Fairbanks
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Quote:
The answer is quite simple the min and max window for the high discharge rate is completely out of range of the ESC rating... Lesson learned... now I am going to buy a 25C battery....maybe even a 20C.....
Entirely wrong

The discharge rating on the pack doesn't mean anything about how much current the battery will actually deliver. Current is DRAWN by the motor and prop, not pushed by the battery. If the motor only needs 3A to swing the prop, then that's all that'll flow in the system even if the battery is rated for 500A of output.

ESC "current limiting" isn't the problem here.

Now, you said running the system with your "good" 3S 850mAh pack is showing 30A and 240W on the meter. Something is MASSIVELY wrong there, because that indicates only eight volts at the battery. A 3S lipo ideally shouldn't go below ~10.0V in normal use.

Frankly, with the data and conditions you've laid out, your problem makes absolutely no sense. Are you sure you've got all your numbers right?
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Old Jan 06, 2013, 12:41 AM
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San Jose, California
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Quote:
Originally Posted by C₄H₁₀ View Post
Entirely wrong

The discharge rating on the pack doesn't mean anything about how much current the battery will actually deliver. Current is DRAWN by the motor and prop, not pushed by the battery. If the motor only needs 3A to swing the prop, then that's all that'll flow in the system even if the battery is rated for 500A of output.

ESC "current limiting" isn't the problem here.

Now, you said running the system with your "good" 3S 850mAh pack is showing 30A and 240W on the meter. Something is MASSIVELY wrong there, because that indicates only eight volts at the battery. A 3S lipo ideally shouldn't go below ~10.0V in normal use.

Frankly, with the data and conditions you've laid out, your problem makes absolutely no sense. Are you sure you've got all your numbers right?

Thank you for your deductive reasoning...my data is proper to the integer....and it is repeatable.
out of desperation and frustration I thought I had a solution to run with ... but seems like Im mistaken. Perhaps I can make a video illustrating what I described...

so are you saying...all but one of my batteries are bad...and that its a coincidence that the one and only 25C to 50C which so happens has the lowest discharge is the healthy guy? But how do I reason with the fact that the less pitchier and smaller diameter FMS props setup with same motor can draw the expected performance?

All setups are using the 3128 1550KV bell motor with the prop being the variable...with the 35C to 90C discharge packs

at this point in any event I think it is worth my while...to entertain this issue by making a video....
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Old Jan 06, 2013, 12:45 AM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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30Amps and 240 Watts is 8V surely?

On a 3S that is about 2.7V/cell under load. Not good but still likely in practice if the battery is heavilly loaded and has high IR.

30 Amps from an 850 mAh pack is a huge ask. Most if them have nothing like that continuous C

Quote:
Originally Posted by C₄H₁₀ View Post
Entirely wrong

The discharge rating on the pack doesn't mean anything about how much current the battery will actually deliver. Current is DRAWN by the motor and prop, not pushed by the battery. If the motor only needs 3A to swing the prop, then that's all that'll flow in the system even if the battery is rated for 500A of output.

ESC "current limiting" isn't the problem here.

Now, you said running the system with your "good" 3S 850mAh pack is showing 30A and 240W on the meter. Something is MASSIVELY wrong there, because that indicates only six volts at the battery. A 3S lipo ideally shouldn't go below ~10.0V in normal use. To drag the voltage of a 25C 850mAh pack down to 6V would take a HUGE amount of current; I don't think you'd even be close with 30A.

Frankly, your problem makes absolutely no sense. Are you sure you've got all your numbers right?
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Old Jan 06, 2013, 01:24 AM
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San Jose, California
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Originally Posted by jj604 View Post
30Amps and 240 Watts is 8V surely?

On a 3S that is about 2.7V/cell under load. Not good but still likely in practice if the battery is heavilly loaded and has high IR.

30 Amps from an 850 mAh pack is a huge ask. Most if them have nothing like that continuous C
Im not going to deliver a video tonight but in the next few days yes...

im using this to take my data...I bought it, never calibrated it, but I trust it because none of my birds have fallen out of the sky due to over amperage...and I test all my birds

http://www.hobbyking.com/hobbyking/s...Analyzer_.html

For now based on the feedback I am getting from colleagues in here....my watt meter is not all that accurate? I mean...I plug the thing in between my lipo and the load and I push the stick all the way up!

videos to come...soon


I just came back from the basement....with the setup in question...I thought I try this time a 2s 1000mah 15C ...and guess what? I am getting 14Amps at 92 watts....3 identical packs verified.....

How do I compare this data with a 3s 45C to 90C 850mah drawing only 10 amps at wot? no video to prove this now...but soon to come
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Old Jan 08, 2013, 09:58 AM
just Some Useless Geek
Chicagoland
Joined Oct 2008
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Wow. Yeah, I'd sure like to see your setup and test data on a video capture. But I'm with Butane here; something is totally upside down for you to be getting these results. Perhaps we can help you spot it if you capture everything in a video and show us. After all, we're all trying to collect and share consistent, repeatable data that has universal meaning and usefulness. Results like this threaten the usefulness of any data we collect.
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Old Jan 08, 2013, 10:32 AM
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Originally Posted by A Useless Geek View Post
Wow. Yeah, I'd sure like to see your setup and test data on a video capture. But I'm with Butane here; something is totally upside down for you to be getting these results. Perhaps we can help you spot it if you capture everything in a video and show us. After all, we're all trying to collect and share consistent, repeatable data that has universal meaning and usefulness. Results like this threaten the usefulness of any data we collect.
Yes I understand, I will make the due date sometime this week. Night times here in the west coast will work best for me. Videos will come soon.

I did order some 3s 850mah 25c-40c lipos....last night from hobbyking. Those will also add to my data collection

regards

tengarang
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Old Jan 08, 2013, 05:50 PM
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United States, AK, Fairbanks
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Those packs could take weeks to get to you... If you start feeling impatient () HobbyPartz and ValueHobby are both US-based with similar battery prices and quality to HK, and shipping time is on the order of two or three days.
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Old Jan 08, 2013, 06:07 PM
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San Jose, California
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Originally Posted by C₄H₁₀ View Post
Those packs could take weeks to get to you... If you start feeling impatient () HobbyPartz and ValueHobby are both US-based with similar battery prices and quality to HK, and shipping time is on the order of two or three days.
Thanks friend,

They are coming out of the US warehouse.....still that doesn't mean it wont take several weeks lol from hobbyking

The video presentation will not be contingent on the arrival of the new packs...they will serve as a confirmation...and plus I need a few new ones anyhow.
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Old Jan 11, 2013, 12:25 AM
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Guys

So no video yet, Ill be able to get a film up this weekened to document the things that we have been talking about. BUT good news! my batteries have arrived, and I tested all 5...yea...they all worked

http://www.hobbyking.com/hobbyking/s...dProduct=20417

these are 25C to 40C discharge rates....and not fully charged either. 48% out of the box on average.

all drawing 21A 221watts
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Old Feb 02, 2013, 08:42 AM
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Denmark, kbh
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Quote:
Originally Posted by jj604 View Post
...(edit)...30 Amps from an 850 mAh pack is a huge ask. Most if them have nothing like that continuous C
+1

I wouldn't be comfortable bleeding anything in excess of 8A from a battery this tiny.

If you manage to pull 600mAh out of the battery, that would correspond to a flying time of 1 minute and 12 sec at 30A...
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Old Feb 02, 2013, 02:48 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by tengarang View Post
Guys

So no video yet, Ill be able to get a film up this weekened to document the things that we have been talking about. BUT good news! my batteries have arrived, and I tested all 5...yea...they all worked

http://www.hobbyking.com/hobbyking/s...dProduct=20417

these are 25C to 40C discharge rates....and not fully charged either. 48% out of the box on average.

all drawing 21A 221watts
Are you using those with those red JST connectors? I think those are only rated at 5A.

Jack
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Old Feb 05, 2013, 10:49 AM
just Some Useless Geek
Chicagoland
Joined Oct 2008
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Yeah, on all my nano-tech packs over 10A or so capability I am changing the connectors to XT60. HK is starting to get wise and do it themselves.
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Old Feb 10, 2013, 01:48 PM
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Sydney, Australia
Joined Jan 2007
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In-plane Motor Thrust Testing

This describes an easy method of measuring motor thrust with the motor, prop and ESC in the plane. I am publishing it in the threads of the planes that I own, and in the Power System forum. I have searched for, and not found, a method such as this. If it already exists, I’m sure someone will let me know . I hope this thread is an appropriate post for this post.

I have looked at various techniques used for motor thrust testing and most of them seem to use some sort of test bench, where the motor, prop and ESC are removed from the plane (e.g. this thread). I have constructed a test bench for myself in the past, where the motor was attached to a pivot arm resting on a digital scale and pushed downwards. This was both fiddly to set-up and felt dangerous, as the prop blades were whizzing horizontally near my eyes as I tried to read the scale, so I have hardly used it (in fact, I forget where it is now!).

While looking at my digital kitchen scale the other day, I realised that there could be a way to measure motor thrust accurately and safely, without removing anything from the plane… and literally on the kitchen table! The test set-up is shown in the photos. Since a digital scale is based on strain gauges, it can operate from any orientation (correct?). I made up a simple “L” bracket so that the scale could hang from it while not touching the table top. A string with two loops at the ends is then taped to the middle of the scale and the loops passed around the horizontal stabiliser. Planes without u/cs must rest on rollers to reduce friction as much as possible - I used 150mm lengths of plastic cable conduit. The “L” bracket is clamped to a table top so that the prop clears its end, and the plane is rested on books if necessary.

Attach the loops, power up the plane (with Wattmeter attached if required) and then switch the scale on and hang it on a the nail on the “L” bracket. Note the scale reading if it is not zero. Spin up the prop, slowly at first to verify everything is Ok and then give it WOT and note the maximum thrust (less the zero thrust if present). Takes about 1 minute, and you can change props and get another reading quickly and easily.

I would suggest that this could be a more accurate measurement of actual motor thrust than a test bench, since it allows for any blockage of airflow by a large fuselage frontal area (e.g. FW-190), it is certainly much faster to set-up. The accuracy of the rollers was checked by comparing the thrust for my FW-190 wheels down vs wheels up with rollers, which varied by only 5gm at 525gm. For testing of more powerful motors, I would use a padded strap to attach to the h. stab, and would add a safety line or strap attached to the clamp.

I use the FC 28-22 1200 kV motor from HK in most of my park flyers – it is light, powerful and easy to swap out. I measured 670gm thrust with a 10x3.8 prop and 525gm with a 10x5. This compares to a published max thrust of 710gm with 10x5 and a user review of 660gm for a 10x4.7. The FlyBrushless website shows max 385gm for a 28-22 1100kV motor with a 10x6 prop. These figures are fairly close, and in any case I am more interested in comparative, rather than absolute, thrust figures, to work out which is the best prop to use. My Art Tech Spit has a stock 4038-15 700kV motor and gives 730gm of thrust with a 10x5 prop. Since it’s AUW is 650gm with a 1500 mAh 3S pack, I have decided to not move it to 4S at the moment.
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