[secant0give]

If they are plastic props you want to take a bit of the rake angle off the drill so they don't grab and do a helicopter on you. Can be a bit of a nasty suprise. It also happens when you drill things like brass, and it's especially bad when your opening up an existing hole

Here's a link with a pic

http://www.listoftools.com/grinding_oper...brass.html

[Flying fisho]

I bought a step drill from Bunnings. Hold the step drill in my little vice & spin the prop on it from both sides. I then use the 8mm drill bit for the finishing touch.

[wingtipper]

new lipo battery .
i have a new Turnigy Lipo battery 3s 4000mah . which i changed the plug on . ( warranty void ) .
On it's 1st charge one cell wont charge past 4.04 volts . the others chargs to 4.2 volts .
i tried it on 2 seperate chargers which both confirm .


my question is . is it outside of acception ? ( obviously the charger wont complete the charge cycle) .
DO I THROW THIS BATTERY IN THE BIN ?

[Raptorfly]

Hi Frank

I had a Lipo like that. 3S 2200mha and from new it had 1 cell was lower than the others. I used it for testing, charge it up and then run it down a few times. Now when I charge it, it's balanced but I'm too worried to use it when I'm flying, it might or can drop a cell, I don't trust it. So I only use it for bench testing and setups and on my RC car.

Hobby King could replace it for you even if you changed the connector. Sometimes they just send you a new one and you don't need to return the old one back. Try them out.

Don't bin it...use it on setting up

[Skidz]

Frank, discharge it (store mode) on your charger and recharge it again and check the balancing. It might come good. George is paranoid . Fly it. Check your balance at end of flight and after recharging if you are still concerned.

[Claudius]

Frank, if it was mine, I'd give it a few discharge/charge cycles on the charger, and see if the end of charge voltage difference starts to get smaller. If it didn't, it wouldn't see a flight.

Thanks for the suggestions on prop reaming guys - smuzz, might have to pay you a visit shortly.

[wingtipper]

ok i did discharge and cycle the battery a few times . the difference is getting smaller , its now 0.10 volt down at full charge . also after 5 minutes in the plane on a static test , the 3 cells were 3.82 3.84 and 3.85 . so my guess is it is a borderline cell, however it lasted the time . also discharged on the charger at the same rate as another battery . so it might be ok .
claudio , i'd like to give you advice on the drill . it's a dodgy thing to do , seeing that so may scenarios can eventuate , worst case being a sliced tendon .

[Claudius]

ok i did discharge and cycle the battery a few times . the difference is getting smaller , its now 0.10 volt down at full charge . also after 5 minutes in the plane on a static test , the 3 cells were 3.82 3.84 and 3.85 . so my guess is it is a borderline cell, however it lasted the time . also discharged on the charger at the same rate as another battery . so it might be ok .

That is encouraging. It could be that this cell has a slightly higher internal resistance than the other two cells, and so fell deeply out of balance since the initial conditioning charge post-manufacture. The good news is that this is not a necessarily a terminal (no pun intended) problem; the less good news is this cell will likely always be the runt in the pack.

You could confirm this somewhat by repeating the static test with a cell checker attached - a cell with higher internal resistance will show a larger voltage drop from its starting voltage while under the same load (although it is more reflective when the cells all start at the same state of charge, which may not yet be the case with your pack).

If this is the case, that cell will likely get slightly warmer than the other two under load, further accelerating its premature aging. If it's not the centre cell in your 3S, and if the battery placement in the airframe gives you the option, consider marking the battery so that the weak cell is not face-down/velcroed etc (i.e. keep it exposed if possible) to give it the best chance at living as long as its neighbours.

claudio , i'd like to give you advice on the drill . it's a dodgy thing to do , seeing that so may scenarios can eventuate , worst case being a sliced tendon .

No, would definitely have the prop well secured, regardless of how it is reamed (no desire to have my drill start generating thrust! ).

Was just wondering whether there is a trick I don't know to accurately drill concentric holes without a drill press, core drill bits, etc.

[secant0give]

Claudio,
The best way to get it concentric is to drill it wiht a drill press. If you try and do it with a pistol drill you won't get it square and if it's not dead square it will never be concentric.
I have a nice drill press at work I'm more than happy to drill out a few props for you. I've done heaps of them, Like I said before the trick is to sharpen the drill so it doesn't grab.

You could use a step drill as wayne suggested I think these are made so they don't grab, they are often used for opening up holes in sheet metal. You'd have to by one tho' and make sure it has a step the right size.

[Flying fisho]

I will have my step drill with me at the field on Saturday. One of the steps is 8mm and while it only drills 1/2 way through the prop from each side, I normally hone the hole with an 8mm drill to finish it off. All can be done at the field conveniently

[wingtipper]

ok i did discharge and cycle the battery a few times . the difference is getting smaller , its now 0.10 volt down at full charge . also after 5 minutes in the plane on a static test , the 3 cells were 3.82 3.84 and 3.85 . so my guess is it is a borderline cell, however it lasted the time . also discharged on the charger at the same rate as another battery . so it might be ok .

That is encouraging. It could be that this cell has a slightly higher internal resistance than the other two cells, and so fell deeply out of balance since the initial conditioning charge post-manufacture. The good news is that this is not a necessarily a terminal (no pun intended) problem; the less good news is this cell will likely always be the runt in the pack.

You could confirm this somewhat by repeating the static test with a cell checker attached - a cell with higher internal resistance will show a larger voltage drop from its starting voltage while under the same load (although it is more reflective when the cells all start at the same state of charge, which may not yet be the case with your pack).

If this is the case, that cell will likely get slightly warmer than the other two under load, further accelerating its premature aging. If it's not the centre cell in your 3S, and if the battery placement in the airframe gives you the option, consider marking the battery so that the weak cell is not face-down/velcroed etc (i.e. keep it exposed if possible) to give it the best chance at living as long as its neighbours.

claudio , i'd like to give you advice on the drill . it's a dodgy thing to do , seeing that so may scenarios can eventuate , worst case being a sliced tendon .

No, would definitely have the prop well secured, regardless of how it is reamed (no desire to have my drill start generating thrust! ).

Was just wondering whether there is a trick I don't know to accurately drill concentric holes without a drill press, core drill bits, etc.

regarding the battery pack that sounds like the most likely situation Claudio . thanks . i guess i'll look at it as a 95% battery with a shortened life .

[smuzz]

I was talking about this stuff on the weekend (Bob, you were asking me about it).
Available from Bunnings, inexpensive, very light weight and easy to sand when it's dry.

   

[wingtipper]

OK ..
HAVE AN ESC in the Corsair , when setting up , everything works , however it wont detect minimum throttle position until i put the travel adjustment to -74% . that means it wont idle untill the stick is 1/2 way up . any thoughts or suggestions on how to fix it ????

[Raptorfly]

OK ..
HAVE AN ESC in the Corsair , when setting up , everything works , however it wont detect minimum throttle position until i put the travel adjustment to -74% . that means it wont idle untill the stick is 1/2 way up . any thoughts or suggestions on how to fix it ????

Did you try the standard throttle reset by keeping the TX on unplugging the plane. Push the throttle 100%. Connect the battery to the plane and as soon as you hear the first beep pull throttle back to 0%.

[smuzz]

Yes, George's advice is worth a try - reset the ESC (this will calibrate it).
Frank - I think there was a separate manual in the box for the ESC too, wasn't there?

[wingtipper]

it's all good , i tried this several times after i got the sub trim and everything right . IT didnt work .
The trick was to go back to minus 74% where the throttle would work , even if it was at 12 stick . then do the reset . then everything was great .
BY THE WAY SMUZZ , it's a simply beautifully built plane , very impressed with fms design and build quality .

[smuzz]

Pleased to hear that 'Tipper - I look forward to seeing you rip across the field for a high-speed low pass!

[Flying fisho]

Have been reading Steve C's link to "How to Determine the Power Requirements of RC Electric Motors.docx" (introduce yourself here thread)and querying the reference to "The average voltage of a 3 cell Li-Po pack is approximately 9.9 volts." and how it affects the equation. I believe the average to be 12v (max 12.6v min 11.4v ie 4.2v & 3.8v per cell ) Am I misguided?

[secant0give]

You can take them down lower than 3.8 V per cell but it's not great for the loggevity of the pack
I think your figures are quite reasonable Wayne.

What you will see, If you put a watt meter on and run your motor, is the voltage will go lower as the pack comes under load. If you start pulling enough amps to get the pack to it's C rating then you will see the voltage drop quite a bit below 3.8V per cell but as soon as the load comes off, the voltage will come straight back up again.

[Flying fisho]

As I time my flights to reduce cells no lower than 3.8 v to preserve battery longevity, under load what could I expect a battery voltage to drop to at the end of my flight. Theoretically speaking of course . And would that verify a 3.3v average?

[secant0give]

As I time my flights to reduce cells no lower than 3.8 v to preserve battery longevity, under load what could I expect a battery voltage to drop to at the end of my flight. Theoretically speaking of course . And would that verify a 3.3v average?

That is a very good question Wayne and it depends on the amount of current your drawing and what the internal resistance of the cells are. Sometimes one cell has higher internal restance than the others and it will drop the voltage of the whole pack (because it's in series) I have a few packs that I purchased at the same time from the same place and they are different from each other under load.

What you can do is put a meter on them and test tem on the ground. I usually bring my meter down to the field when I'm there. Samste nearly allways has one with him as well. Do it with a fully charged pack and after your normal flight and you can see the difference and get a feel for what happens.

That's basically what happins with my radio beeping, I have the telemitry set to alarm at a certain minimum voltage around 3.6 V per cell first alarm 3.4 V per cell urgent alarm. You will have noticed it on the flight line. Beep beep beeep ect as soon as I back off the throttle the alarm stops, because the pack voltage goes up again. I can draw enough current to urgent alarm a fully charged 12S 3000 pack with my big Yak but this is in "10 second burst" mode and I only do it for a few seconds usually less than 5 seconds.

[Flying fisho]

I have meters too. Was more trying to validate the 9.9v average 3cell battery for the purpose of motor selection. Have a stuffed Pitts Special motor & hoping to come up with a suitable replacement. Could have learnt to rewind it but considered the original underpowered.

[gbanger]

I think you will find that just about every ESC, Motor and battery builder in the RC world use a base rate of 3.7 volts per cell to do their cals when you are talkin average power available under normal flight load. (We are talking Lipo's here)
This voltage varies considerably depending on the current draw of your motor and as Jason suggested how close to the C rating you are working the battery.
In almost every article I have read they all use 3.7 volts for working out everything from props right through to Max amps etc. etc. etc. as the standard loaded flight voltage.
Gazz

[Flying fisho]

Thanks Gazz will substitute 3.7v for 3.3 on the posted calculator.

[Skidz]

Wayne,

Be careful in your understanding of the battery final voltage after a flight. When you measure 3.8v per cell at the end, it may have dropped to 3.5 or 3.4v while you were in last phase of flying with the motor on full throttle. Batteries present their best voltage when there is no load. If you look at the graph below (which is on an LiFePO4 battery so the voltages are slightly lower than LiPo), you will notice where the current draw (red) is high, the voltage (green) drops. Also note than when the load was reduced to zero (motor throttled back), the voltage comes back up again. This final voltage is what you measure at the end of the flight. The motor calcs will always consider the voltage with a motor under powered conditions.
   

[Flying fisho]

Point gratefully taken, so 3.3v is correct in the calculations? You mentioned 3.4 -3.5 volts under full throttle at end. Presume that means higher mid flight which would represent the average. Not familiar with LiFePO which stated 10.2v max presumable under power & average 8.9v avg. That graph & measuring power under load would dispute Gazz's 3.7v comment (no disrespect intended Gazz as I always value your opinion) Back to being unsure as to what average voltage to use for calculations but if Gazz stands by his comment so will I.

[gbanger]

I am only relaying the information that I have learned during my flying career.
I am well aware that voltage drops as load increases over time, and that is amplified as the battery loses power... christ... thats electric flight 101. I was simply saying that when you are doing your setup cals to work out what you need in a power train for an electric aircraft that 3.7 volts per cell is the industry norm.

[wingtipper]

hi Wayne . i had some discussion with Claudio about this .
heres what he suggested , and i have found it quite good .
you ideally want to land with 20% left in your battery pack .
so if you have a 4000mah battery pack , you dont want to use more than 3200 mah .
if your landing with 3.8v per cell , after a fully charged flight . . put your battery on charge and see how many MAH IT TAKES TO FULLY CHARGE AGAIN . WONT TAKE LONG TO WORK OUT what your volts are on stanby as to how many mah it takes to charge .
using this formula several times and getting as close as possible to it , by adjusting flight times ( mixed flying ) i have found with 20 % left each cell is around 3.75v to 3.80v. incidently the lowest i landed with was 3.34 v per cell thats almost dead flat and the plane showed no sign of weakness , it was ready to fall from the sky . once you go below 3.7v per cell it will drain quickly . but as claudio suggest cells can sustain 3.8 volts under load for some time . hope that helps .
safe 3.8v per cell after landing with some to spare . 3.7v per cell is game thats what id expect to land at after 2 failed approaches or 1minute coasting . HOPE THAT HELPS .

[gbanger]

You guys are talking about 2 completely different things.
Wayne is asking about flight setup,you are talking about flight timing.
Flight timing is critical to 2 factors, how long you say up there and how hi your throttle percentage is.
Stay up there to long at high throttle and see ya...
What you are doing is destroying the longevity of your batteries.
Fly all the time to well under 3.7 volts per cell and you might get 100 to 150 flights and your battery will be dead...
Fly all the time to 3.8 volts per cell and you will get 250 flights out of the battery... or more.
The figures I have used above are just ballpark examples, the fact of the matter is... Look after your batteries and they will look after you, abuse you batteries and guess what... they will abuse you.
Educated conservative flying will always prevail over the YEEEHAAA cowboy fly by night she'll be right approach.
And if anyone that flys electric aircraft cant see or understand that, they should seriously consider taking up flying I/C's, then they will really now when their time is up.

[Skidz]

Sorry, I wasn't referring to flight timing but rather why 3.7v is used for set up calcs and not 4.2v or 3.3v.