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first off...allways been a sloper (40years)

i have recently cut the nose of one of my slopers (50", thin flat wing section, rudder, elevator flaperons) and stuck an electric moterin it

I have a 7.2v battery to power the motor but when i connect everything up i notice this battery also powers the radio (receiver, servos)

question

 

what happens when this battery falls flat enough to no longer power the motor, wil it also be too flat to power the radio and therefor "crash"

or

if i have two batteries, 1 for motor and the normal one for the radio, then you get the problem of two batteries in parrallel charging each other up

or

do i have the normal battery for the radio and "cut" the red core from the speed controller to the receiver letting the motor battery power the speed controller

 

god, slopeing is much less problematical

 

help

please

taa

bob

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Most ESCs cut the power at a safe value (be aware this may be selectable so check it's programmed appropriately) and this is well above the point where the inbuilt BEC stops providing regulated voltage for the receiver/servos (assuming 2S or above).

 

Plan to land soon after the motor cut as you will be in the region of fairly steep voltage drop-off and subsequent battery exhaustion but there will be more than enough capacity to plan a leisurely approach.

 

7.2v?  Is this a LiFe or NiMh pack?  LiFe do have a fairly dramatic voltage drop at end of discharge so be conservative with the cut-off point if they are the former.  Default settings will probably assume LiPo.

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There's not really enough information to answer how long the battery is likely maintain the to  rx & servos after LVC (Low Voltage Cut).
In pre lipo days I regularly timed glide duration at over 20 minutes from LVC when using a 7 cell 600mAH nicad battery in a model with with only 2 servos but I would never deliberately run a lipo or LiFe battey down to LVC.  

Re using a separate 4.8v Rx/servo battery - cutting the red ESC to Rx wire as you suggest is the normal method.  

 

What type of motor are you using, brushed or brushless ?

What type of battery & what capacity is it ?

How many servos ?

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You really don’t want to run any lithium chemistry battery (especially lipos) down to the ESC cutoff voltage as you will inevitably shorten the pack life, especially in cold conditions. Consider it as a backup safety device, not the primary means of gauging when your flight is over! Aim to land with the pack at 3.5-3.7V/cell; set timers and/of use telemetry to get to this point. The only by one I ever hit ESC LVcitoff is during very cold days, and even then I consider that a pilot error - at anything lower than 5 degrees I take off 25% of the run time, at 0 degrees 50%.

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Bob, a typical 2.4 receiver will consume < 80 ma in normal operation, so after that it's how much work the servos are doing.

 

Note also the LVC will normally cut in when the motor is under load, which is at a way higher current than the rx and servos on their will consume, but it's much kinder on Lipos not to run them down to the LVC cut out.

 

All my electric gliders, inc an 3.3m ASK 11 and a Vegas warm liner, run off the main lipo via the ESC and I've never run the battery down, such that even after a period of extended gliding that the glider has landed with the Lipo discharged below 3.5v per cell, resting voltage.

 

As far as I am aware all the electric glider competition guys use the BEC and they tend to use small lipos and high power to get to height.

 

If you don't have a telemetry, then set a timer to run off the throttle so the Lipo still has 20+ % capacity when the timer goes off, in a 50 inch soarer I doubt that you use more than 50-60 mah in 20 mins of unpowered gliding.

 

To put it into perspective my pure glider mini blade glider (ailerons, flaps and V-tail) runs off a 700mah 2s LiFe and I can fly that for hours on the slope and still have bags of capacity left.

Edited by Frank Skilbeck
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hi

thanks to all who replied

in most cases i have no idea what you are talking about.

LVC.timers, telemetry,BEC,ESC..

think i will stick to throwing it of a hill

thanks everyone

 

p.s. built myself a new 'plane over the christmas holidays. a dave hughes soarcerer, with flaperons and i still use 35mhz

sorry guys    i guess i'm still stuck in the old school

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3 hours ago, Robert whitaker said:

thanks to all who replied

in most cases i have no idea what you are talking about.

LVC.timers, telemetry,BEC,ESC..

 

  • ESC - Electronic speed controller. This is the component that sits between the flight battery and motor and gives you throttle control. In most instances it also outputs a lower voltage (normally between 5-6V) to drive the RC gear so you don’t need a separate receiver battery.
  • BEC - Battery eliminator circuit. The bit of the ESC that chops the voltage down for the receiver and servo supply. Has a constant and peak amps rating (normally in the 3-5A constant range) so BECs are not generally used in large models; they will normally have a separate power supply. 
  • LVC - Low voltage cutoff. This is a function of the speed controller that prevents the motor being used below a certain voltage, usually configurable between 3.1-3.5V per cell. This prevents over discharge of the pack, but shouldn’t be used as the primary means of doing so.
  • Timer - Pretty self explanatory, in electric models you normally set a timer on the TX activated by the throttle stock to ensure you don’t over discharge the pack in flight.
  • Telemetry - Sensors are connected to the RX which transmits the data gathered back to the TX to monitor onboard parameters such as altitude, speed etc. In this case pack voltage, cell voltages and/or current draw would be monitored to monitor the charge state of the pack in use, with audio alarms set to go off at preset levels of discharge.
Edited by MattyB
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Wow...

It appears that I live in a different world to everyone else.

 

"Sensors are connected to the RX which transmits the data gathered back to the TX to monitor onboard parameters such as altitude,"

"a timer on the TX activated by the throttle stock"

 

I have a rudder, elevator, ailerons and sometimes flaps.

 

somehow I think my age is showing, the world is moving too fast and i want to get of

 

so. thanks to everyone but i'll go with this idea

            "Re using a separate 4.8v Rx/servo battery - cutting the red ESC to Rx wire as you suggest is the normal method".

and when the motor doesn't spin anymore i will know that battery is flat but i can keep flying as long as the wind blows.

 

 

 

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I am not a glider guider nor am I particularly interested in electric flight but I keep an electric foamy trainer for use by beginners and the following story may be of interest to you.

 

A few weeks ago, on St Valentine's Day, I left a LiPo, a 2200 3S, to charge up unsupervised. One of the three cells was showing far less charge than the other two when I put it on charge but I thought that the balance function of the charger would take care of that, then I carried on doing other things in the house and garden. It was only when I smelt burning plastic that I opened the door to the cellar to be confronted by thick black smoke! The LiPo had exploded and had set fire to My Big Guff vintage model and my to WOT 4 XL totally destroying both. The Big Guff had taken me fourteen months to build. Pictures of before and after below.

 

My point is that if you run your LiPo flat it may be difficult to recharge it. It will certainly shorten its life and you may be faced with an explosion if you are not careful. I make sure that I'm always around when charging batteries these days, either that or I charge then outdoors on an iron plate.

 

 

Maiden Flight 3.jpg

Maiden Flight.jpg

Remains of Big Guff.JPG

St Valentine's day Massacre (1).JPG

WOT 4 XL Restored (4).JPG

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NiCads are no longer available and NiMHs are a pretty poor solution for high current powertrain applications compared to lithium chemistry packs. As a result performance of your model is likely to be somewhat lacklustre (in line with the early days of electric flight), especially if you are using a brushed motor. I humbly recommend you get an electric expert in your club to sit down and explain the basics to you, and at least set up the timer on your TX - it is normally very easy to do. What TX do you have?

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You also have the option of Lithium Ion for your motor drive cells, these are available in cylindrical metal packages of various capacities, though not so many options as LiPo.

They are purported to be safer than Lipo's, I have used a few 18650 sized cells sourced from https://www.fogstar.co.uk/. They would need making up into packs of whatever size you need

 

Cells are 3.6 / 3.7 V nominal and 4.2V fully charged, I have seen some advertised as able to supply 30A other sized cells have capacities up to 5000mAh

Edited by FlyinBrian
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MattyB

two Tx  Futaba T6EX  and a Skysport 6.  Both 35

 

i am no longer in a club. the one I used to be in has all but given up on sloping. it used to be it's main stay (competitions, scale, everything) but no longer. it doesn't  even 

have a dedicated slope anymore.

 

i go to the slopes i have known for years and more often than not mix with the hang glider crew..I guess i've been a "loner" for about 10 years now (i'm 64}

.

FlyinBrian

 

cells are 4.2v charged, so i have to go 4.2v or 8.4v

i've stuck an old electric motor and speed controler from "somewhere" in the front of an old sailplane.

it's got a 5 cell nimh battery

this combination will pull the 'plane of the table (i'm old school,,,build em light) and will run for about 7 to 8 mins.

 

i just thought i'd give it a whirl but i had concerns about the battery as this all started as above

 

 

everything charged up ...motor battery (red wire to Rx cut)  Rx battery and Tx battery all ready to go.

now wait for a nice 10 to 15 mph from south to west and i'm out there

i shall also take my faithfull phase 5 sport and my new (old) soarcerer

 

fingers crossed eh?

 

cheers everyone for the help

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David Davis

 

after your fire i had a thought

i keep my pc, server, cctv system and various other computers running in the celler (remote access, bit of a geek in computers)

and i have an automatic Halon fire extinguisher above them. if it detects a fire if dumps the halon into the celler to starve it of oxygen. 

no water etc so no damage

 

 

a word of warning... you MUST isolate the system everytime you go in the celler. if it goes of when you are there YOU WILL SUFFOCATE

 

just an idea.

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10 hours ago, Robert whitaker said:

David Davis

 

after your fire i had a thought

i keep my pc, server, cctv system and various other computers running in the celler (remote access, bit of a geek in computers)

and i have an automatic Halon fire extinguisher above them. if it detects a fire if dumps the halon into the celler to starve it of oxygen. 

no water etc so no damage

 

 

a word of warning... you MUST isolate the system everytime you go in the celler. if it goes of when you are there YOU WILL SUFFOCATE

 

just an idea.

Sounds awfully technical to me! ?

 

I've just settled for installing a smoke alarm and a CO2 fire extinguisher.

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