HI EVERY BODY I NEED HELP FROM ALL THE MEMBERS FOR THIS PROJECT..........I STARTED THIS PROJECT AS MY COLLEGE PROJECT.I AM A GRADUATE IN AERONAUTICS.

THE MAIN AIM OF THE PROJECT IS DEVELOP A SMALL UAV (15 KG) FOR SURVEILLANCE PURPOSE CAPABLE OF AUTONOMOUS FLIGHT

ABOUT THE UAV

Confugration

shape: Shadow uav type(not v type tail)
wing span: 3m
length: 2.5 m
maximum weight:15-16 kg
aerofoil:*******b
l/d:30


motor: Kontronik tango 45-13
esc:jazz 55 a
reduction gear: Mega 4:1
propeller:apc 20*13 pusher
power system: Lg li-ion(6s 8 pack 21.6v)

autopilotaparazzi twog
gps:ublox
modem:2.4 gz

construction:composite and alluminum mix

mission:
Slow flying for survillance and monitoring
normal ground take of and noraml landing

STATUS

all the systems are with me and i tested it all are working properly.....
i complete a ground run successfully....
autopilot is tested with ftdi driver and working fine with paparazzi GCS

now i am getting this problem:

when the battery are new the motor was running nicely.......i ran the motor for many times .....i did the ground run and display it in my college project........

but now after 3 months i am facing this problem
while doing the experiment for static thrust measurement with a load cell

1. the battery pack got discharged to 19 volt
2. after recharging it the motor gets off after some time......
3. the battery volts comes down slowly even after few seconds of run of motor


any suggestion from any body

Why the box tail?

Originally Posted by pritam_ashutos

now i am getting this problem:

when the battery are new the motor was running nicely.......i ran the motor for many times .....i did the ground run and display it in my college project........

but now after 3 months i am facing this problem
while doing the experiment for static thrust measurement with a load cell

1. the battery pack got discharged to 19 volt
2. after recharging it the motor gets off after some time......
3. the battery volts comes down slowly even after few seconds of run of motor


any suggestion from any body

Sounds like you are pulling more amperage than the battery will allow. You might want to look into better batteries.

sounds like your battery could be the culprit, possible that a cell or two may have gone bad or discharged below 3.2 volt/cell, check each of the individuals cells
When you recharge how much of mah does it take in ? and what is the charged voltage of the pack?
What capacity was your battery, Do you have any current draws under load before and now?
Try a different pack and see if you get the same problem

hi prashant thanks for your suggestion

before testing all the battery i checked all are above 3.5 and after the test in some battery voltage dropped..

i am charging with .5a by GT CHARGER........till 240-300 capacitance

the battery i am using is LG LI-ION of 2400 mah and 3.6 v
so together (6s 8p) i am getting 21.6 v and 19.2 Ah which can give maximum 48 A current to the motor

I have not heard of an LG Li-ion 2400 Mah Battery, are these laptop batteries? or lithium polymers or li-Fe ? can you post a picture of your battery, or a link from where you got your batteries

I am lost as to what you mean by till capacitance is 240-300, certainly thats got nothing to do with charging
A fully charged 6S pack should have about 4.2X6=25 volts but yours before testing is only 3.5v/cell and an empty li cell is 3.2v/cell so when you are testing the reason your motor is going off is probably the low voltage cut off on the esc is kicking in

lg li-ion
If you intend to build or rebuild a pack with 18650 cells we highly recommend purchasing these cells WITH TABS already welded on.

Features:
• 3.6V 18650 size Cylindrical Li-Ion Cell made by LG Chemical.
• The highest capacity in the market : 2400mAh
• No Memory effect and longer storage life than NiMH Battery
• Lighter weight and higher energy density than any rechargeable battery
• Perfect for building Laptop battery and other portable power devices
• Dimension: 18 mm diameter and 65 mm Length
• Weight: Max. Charging current: 1C ( 2.4A ), Max.
• Discharging current 2.5C ( 5A )
• Cautions: Li-Ion Battery may explode if charging or discharging inproperly.
• User must have knowledge how to charge and discharge Li-
• Ion battery before making a Li-Ion Battery Pack Strongly suggests that you use a protection IC to keep battery from over discharging and over discharging.
• We are NOT responsible for any damage that is caused by the misuse of the Li-Ion Battery.
• Capacity Nominal 2350mAh, Minimum 2300mAh
• Dimensions: Diameter 18.3 mm (Max 18.4 mm)
• Height 64.9 mm (Max 65.1 mm)
• Weight (Typical) Approx. 46.5 g
• Nominal Voltage: Average 3.7 V
• Internal Impedance: less or equal to 90 mohm (with PTC)
• Cycle Performance: 80% of initial capacity at 300 cycles
• Charge: Current = 1150 mA Voltage = 4.2v End Current = 50 mA
• Discharge: Current = 460 mA End Voltage = 3.0V

that explains your problem, these are probably laptop batteries and not suited for high discharge applications as is required for your UAV,

You will need batteries that can discharge atleast 25-30C, these cells that you are using can only discharge 2C so under load the voltage drop can be significant to cause the LVC to kick in.

Move to lipoly say 6S2P 8000ma 30C pack (actually for your plane you will need even bigger packs) and you should have no problems...
Handle such high capacity lipo packs with care...any shorts and you sure would have fire, i have seen college students not taking these cells seriously and ending in fire....

i need current of up to 15-50 A and 22.2 v max for my motor
and my battery pack can give 21.6v and it can deliver maximum 48 A current(total 19.2 ah with discharge capacity 2.5 c)

"i need current of up to 15-50 A and 22.2 v max for my motor" where did you get these numbers from?
from the spec of your motor, it can take from a min of 6 cell to 20cells and the 15-50A range that you are saying is the current draw on load (for a given prop) should be around or below 50A) and for a few seconds you can go upto 70A but if you draw continiously at 70A u will sure burn this motor.

you are assuming that your battery pack is capable of providing 48 amps as given by the battery data sheet, I suppose it is not,

what is the measured current under load in your system for the prop you are using?

what is the measured current under load in your system for the prop you are using?

i did not get wat are you asking........

ok if i will add 2 more pack i think it will be ok wat about your opinion
and i am not going to give 70 A i want to run it for 75-80% of maximum power

with a multimeter measure the voltage and current drawn while you are running the motor with the prop
adding two more packs will not solve your problem...sooner or later these cells will give way...and you will be adding more weight into your 15kg uav....

dump that pack and get decent lipoly's you have a great motor there but not sure if it can haul 15+kg's
do you have any thrust figures on that motor prop combo

ya it can produce a thrust of 3.5 kg........

and if you will go through this link i think it is sufficient for a normal slow flying wat i need

http://www.rcgroups.com/forums/showthread.php?t=594526

i think you will be heavily underpowered......Redo you math on this...