Very slow build from France


#101

That is awesome consuptuon overall, especially for 8s. Remember when we talked before actual builds, numbers were 3kw+ on 12s. Also congrats to wc win. We will get u next time :wink:


#102

Congratulations for your nice project.
Am I correct if 205A is the MAx.Current value written on the top line:

As your plane/flight/glide times are going to be longer and longer, could you tick the red voltage (in addition to the green current scale) so that we get a volt scale on the right in order to get P = UxI in real time.
In search of the optimum Hydrofoil/BLDC motor/propeller, as future steps, with same board, it will be interesting to compare the input power for:

  • a change of propeller (Flying Rodeo vs rest of the world),
  • a change of front wing (thin kitefoil speed wing 600 to 900 cm2) to measure the needed power at constant speed therefore the front wing drag. The Takuma has a giant 1500cm2, renowned to facilitate the learning curve but known to saturate at 22/25 knots in kitefoil that is 40kmph. Yes, a speed that is scary for most of us. Even if I don’t want to go faster that 30km/h, a thin low-drag 600cm2 front wing (standard in kitefoils) will mean smaller motor and longer battery duration.

[Off-topic Mode = ON]
My grandma has a saying “Time of jubilation = time of taxation”. Nice match though. :wink:
[Off-topic Mode = OFF]


#103

i don’t have the voltage display because it’s of the scale , recorded this time 38v … that is why i get 7705w , sometimes the voltage is correct somethimes it is way of…

i will try to make better log, longer fly, change rate to 1ps, and stop before it eraise because it is recording in loop

and the amp number has needs to be double check, but it gives a idea

this one before: 110A, not full throttle, pics was propeller going out and back in the water

205A is what the esc hefei says (it might be lower than that), and it is for very fast take off, i can do it without the 205a pic, it is interesting to see that with the solas propeller this pics was “165A” and going from 190mm diameter to 135mm i get more rpm “205A” pic and feels the same about thrust

i have a 860kv, i will try to see if i can go 35km/h with the takuma wing and the 40mm motor


#104

Hum…

I don’t know what to do … Just cooling them in water in a alloy box right now


#105

Oh crap. Sorry to see that.


#106

What happend?

Please be careful with them! They are like bombs when they blow up!

Scroll to 3:10

This is how I charge my lipos:

As seen in this clip:


#107

Looks like none of them are safe. I only charge outside on my driveway and store them outside too.


#108

my setup 4 lipo 4S 16A multistar; 2in parallel mounted in serie : 8S 32A

the first 2 lipo always discharged a litlle more them the one on + esc

usually i stop around 3.8v @ 60%, this time i went for a last ride (my fault ) … , i knew when i get below 3,78V i having trouble to lift the board, that happened i was a bit far and i didn’t want to swim, so i laid down and went 3min at low speed to get back

esc recorded 80A for the last 3min

lipo 1 cell 4 swelled and burst in the box, and fire started, didn"t melt anything, just took the smoking lipo and put it i the water.

lipo 2 as well sweel no burst no smoke very hot , in water as well

lipo3 and lipo4 are ok a bit of balance swell a lot less

usually i put 22A on in the 32A pack so, i guess if this time i had 10A left , at 10C that 100A , i pull 80A and burst the 2/4 lipo

that the max for multistar, got them on a deal for 40€ each, last me 12H of playing and riding

BE CAREFULL

if you use a 16A multistar at 3.77V by cell it will bust at 48A in less than 3min

hobbyking specifications are correct , just need to know how to read them , burst will occur at 10C of the left capacity in the lipo


#109

Thank you very much for your detailed data. Make sure you dispose those beasts responsibly soon. We have a special waste truck visiting every few months in the next city, they take all kinds of dry (i.e. no lead acid) cells. Maybe there is something like this in France, too.

So this is a thermal issue? A thermal sensor on each battery and thermal throttling or even cutoff should be a recommended addition to every build then. I always thought of the battery fires as extereme examples of servere abuse, as liions in university did not show thermal runaway with even a nail straight through them. But your example was not extreme. I have sometimes thought about my BMS development as „overcautious and expensive overengineering“. A minimal monitoring of currents or a good fuse and thermal cutoff are mandatory for myself now. I recently blew a 300A fuse on my 12S liion battery myself, I have not even isolated the fault completly yet. I would argue that a reasonably engineered liion battery with generous distances for saftey between cells would not show such big faults. But cells do age and then thermal monitoring and a shutoff mechanism when cell voltages differ too much would prevent eventual failure.
Do you already have a conclusion for yourself about what caused it and how you would detect/prevent this in the future?


#110

When you look at larger Cs batteries, the weight and volume is increasing tremendously. 1 kg for 5000 mah 6S 60c.


#111

Oh terrible. Glad u are ok. And rest of equipment.
I am still confused today with some people in RC world (mini cars, smaller multirotors, mini boats) usually they dont balance discharge or protect the batteries and escs. I guess electronics are well, not that super expencive so they dont think about damage that much. I was surprised also, a lot of them dont know the amount of amps they pull. They just overengineer batteries and escs.
Some Li ions (18650) have fuse inside for this kind of things but lipos definitly need fuse at least per pack since its a bit more complicated per cell. BMS is rly a good thing here. Not that expencive but, hows the quality of pcb’s :confused:
I did see few videis on yt where ppl disasemble lipos and connect bms to each cell.


#112

yes this is a thermal issue for me, and the esc with the settings:" active free wheeling" and" auto lipo detect", did not cut at 3.3v , i recorded a voltage drop to 20v on the 8s pack, probably “voltage sag” because the voltage went up above 3.3v after for the cells left , just too much for the multistar

my solution:

  • going on 12s to drop the amp: just order the fulcrum pro+ 300A
  • new case with battery display
  • new lipo graphene 15C a pack 12S 24A (after i go 18650)
  • will test with the same pod first, with the solas propeller (lower pitch than FR)
  • new motor after with lower kv, depending on results, stay with 40mm or go 56mm
  • new pod with o-ring and cable glads
  • finally new board but i don’t want the battery under me, so i need to re work the design…

probably lcd temp gauge for the battery or alarm, water cooling no sure yet, depending on the board configuration

the battery safety and BMS, i could go with the tattu plus:

http://www.gensace.de/tattu-plus

a little bit expensive yet … but if it is the price to pay…


#113

New box , fit 8s 48a or 12s 32a … Waiting for the new esc …


#114

that sounds pretty good, how do I know even how many Ah my esc supports?
Or the esc can put any AH respecting only Volt esc


#115

My hifei 8s take 200a and burst at 280a , that is what is written , it worked pretty Well not heating issue
The new one takes 15s and 300a , probably Will use it around 100a

You can put a wattmeter to Check the max amp , usually 1/2 what is written depending on brand

one way to know:
use a small propeller low pitch and good cooling for esc, if it is working fine, you can increase propeller size if you want more speed , and if the esc starting to get to hot, you are probably maxing it out…

It is better to use it at 100% , they don’t like partial load around 75% , better if there is the active free wheeling option

In the case i can put 12x12 vtc6 …for the same price…


#116

Thank you for all the detailed info and performance provided in the forum, you are a very valuable contributor!

I am curious why you originally went with 6 packs and 8S as its a TON of cells to be balanced, wired in parallel, and then in series. Seems like a of extra failure parts when you could go 12S, fewer batteries, amps, and wire connections?

Was it that you were trying to lower motor RPM with 8S?

Also, any videos or links on why you say ESC’s prefer to run a full throttle? My ESC has settings to lower throttle to 75% and 50% so it should not be an issue, but possibly throatle settings change the way the ESC works so full throttle on the trigger is still making ESC run like its at full throttle for high current flow still?

I will be testing ESC with 75% throttle and 50% throttle just to see how current and motor perform for interest sake.


#117

in the begin i choose to go 8s because a good deal for the esc 8s and multistar lipo:
i got 8 16a 4s for 42€ each

in my case i have 2x16a 4s on each side and the esc, i don’t think there is to many cables and this step up hold nicely so far

-20A was to big in size and not enough so 2x16A fit nicely

  • I prefered to split amp and voltage in 4 lipo, yes i could have use 2 big 28a 4s tattou
  • on the last run, 1 lipo brust and over heat the one below

i prefer that 16a burst than 20a or more

now i have 6/8 lipo left so i can use than to test a 12s pack

since i will go 12s, i need to lower my kv to not over spin the propeller as i went to use it at 90-100% throttle

why?
i just follow the user manual of Hifei, “how not to blow your esc” for the 75% throttle is the worth
i will look for the pdf :wink:

on heli forum as well, reading about governor mode, keeping the same rpm for a long time, active free wheeling…

since i go full throttle from the beginning, and i had not overheating esc, motor still running, i guess i will keep it this way:

i want 30km/h even at 3.3v / cell
i need 3100rpm on load
i need 4300rpm off load with a 40mm motor and my big wing
i will need a 600kv for the 12s setup probably


#118

the problem with constant rpm on partial throttle (same as governor mode), it is better to re-gear or change kv apparentlyin my case

old one from castecreation : explaining why there is more heat at 1/2 throttle

http://www.modelaviation.com/inside-esc

another link : https://www.rcgroups.com/forums/showpost.php?p=10945889&postcount=14

i had found some better tests , still looking for the " don’t run 75% if you don’t want to blow up your esc"


#119

new stuff : m10 cable glad, insert m3 diameter 4mm perfect to hold the screw in the sls


#120

Game over :cry::cry::cry:
Motor spined in itself , may be because it is a left propeller … Wires touched and melted , and a good swim back …

I have another motor but not with me , going on vacation for 3 weeks …:cry: