need to go slower to go faster??

[stum]

Originally Posted by rootar

thats really what im after linc, i dont have a 4s to run id like to stay, I can ALMOST make a 20 minute main with it, but its a 50% chance of if my pack my start to dump right there on the last lap or next to last lap.... just need to squeeze a little extra are teh Y winds of nue motors more effecient?

im looking at a 1512 2Y????? its 1400 kv

You need a good 5% buffer when racing, after a couple months of racing your pack will start to hit LVC's with less mAH run through it and then where will you be? If you want to fix this you need to think longer term iMO. That is unless you can get lipo's for 20.00 a pop or have more money than god in that case hook me up!

A good 4s 25c to 30c 5000mAH will easily last that with some buffer so as the pack wears you don't have to replace it as soon. My SMC 28c 5k packs started out taking 5200mAH before hitting LVC and after 3 months of racing are down to about 4850-4900mAH, this is just fact and will happen to all lipo's in all system no matter who makes them. My polyquest (enerland), SMC's, Neu Energy, Maxamps.. they all do the same thing. You will actually be killing those 4k packs even quicker due to taking them down to the bottom that often as well... if you don't send them to LVC every time out they do tend to last longer.

#1 you don't need more than 40mph to win against anyone on any track
#2 4s is more then enough voltage to keep a 1:8 scale in good temps if you have decent equipment.
#3 the 4s 5k packs will last longer every race vs a 5s 4k pack, it may only be 2 minutes but that is often all the buffer you need.

[Dafni]

Originally Posted by stum

#3 the 4s 5k packs will last longer every race vs a 5s 4k pack,...

are you really sure about that?

[stum]

Originally Posted by Dafni

are you really sure about that?

If you test on equal grounds yes.. mAH is mAH so unless you are pulling more C's than a battery is capable of it will hold its voltage through the entire mAH of the pack and the 5000 will win every time. Higher voltage doesn't change how much gas is in the tank (mAH). Higher voltage will reduce the amps needed to perform the same wattage which is nice if you have weaker cells, but again unless you have a 4s lipo not capable of the demand you are after it's not going hit an early LVC. Anyone who gets different results didn't do the test on equal grounds. Higher voltage w/ less amperage or higher amperage w/ less voltage, the trick is if both packs can handle the amp draw there is no advantage to the higher voltage setup other than a potentially cooler system as voltage is normally your friend. If you have a battery that cannot comfortably meet the amperage demand (low “c” rated 4s pack) you will hit a early LVC and at that point a smaller mAH high voltage battery could beat out a larger pack. But with today’s 4s 30c lipo's being the standard you won't see what you saw just a year or two ago when 12-20c 4s lipo’s couldn't handle the amp load and would go into early LVC leaving the higher voltage system running even with less mAH.

This isn't like comparing a 8s system to a 4s sytem where other things do come into play that change the relationship a bit more, we're looking at 4s to 5s.

I'll use these specs as they are most a like in size/weight

14.8v x 150a = 2220 (5000 30c)
18.5v x 100a = 1850 (4000 25c)

but to show even a 5s 4k 30c that does weigh more and again changes the relationship in the car (heavy = more work for the motor & higher avg amp draw) you may net the same output but again the weight is now a factor as it is an even larger battery so the favor would still be to the lighter 4s 5k pack. Also keep in mind if you go just off these numbers you have to reduce gearing to match the actual MPH of the 4s system to even start to compare for run time. If you run the same gearing or are geared for more MPH than the 4s system what I was saying above is what you need to pay attention too.. to figure out run times. So again you have to gear for the same MPH for this to have any effect even on the 6s + setups.. to match or exceed run times.

18.5 x 120 = 2220 (4000 30c)

Originally Posted by stum

Higher voltage doesn't change how much gas is in the tank (mAH).

You should measure how much energy is in a battery using this formula. Ah x V = how much energy there is. (Watt/hours)

4S 5Ah
and 5S 4Ah have exactly the same amount of stored energy.


Are you saying that a 20s 8k pack has the same amount of energy as a 2s 8k pack?

[stum]

Originally Posted by bensf

You should measure how much energy is in a battery using this formula. Ah x V = how much energy there is. (Watt/hours)

4S 5Ah
and 5S 4Ah have exactly the same amount of stored energy.


Are you saying that a 20s 8k pack has the same amount of energy as a 2s 8k pack?

It's not that simple boss.. a 20s 8k pack would not only be impractical in RC the weight would be ~1480grams vs ~365ish.. I could outrace you with any 1:8 setup me on 2s 8k and you with 8s 8k :P I can imagine how efficient your truggy/buggy would be with that much added weight :P don't forget about the wind resistance calculation for a brick that size and the balance issue you now have and the fact you can't hit any jumps, or at least land them.. lol :) how much did that ESC cost to run it?

And as noted above it has a lot to do with where the motors peak effeciency is as well if you are under the 30k rpms or way over it you will have negative effect to calculate as well.

mAH = gas tank, AMP rating (c rating) = fuel line, Voltage = Octane

You have some cars capable of 40mpg, while some only do 12mpg on the same size tank, you have slightly better operation and mileage with higher octane fuel vs low grade in the same car but if you burn too hot you can destroy the motor at the same time, you can't take the car that does 40mpg and expect 100mph but the car that can do 100mph won't get you 40mpg.

Same with rc's and setups.. way more to calculate than a simple 'same amount of energy' statement and that isn't even true, as you have to factor in the batteries capable amp draw not just voltage x mAH, you have to use your mAH and c rating to figure out amp draw and multiply the amp draw by your voltage to get a usable watt/hour (as I did above). And that doesn't even start to tell you which is going to be more effecient with out looking at all the other items. The fact that you can do over 45 w/o heat issues tells me your motor has a slightly higher kv rating, thus more than enough RPM's to not have to worry much about the little votlage from 4s to 5s, again this was a change to speed up your lap times.. and get you beyond 20minutes. I have raced 20minute mains w/ my 4s 5k 30c packs w/o any issues with a few warm up laps to boot, no 50% chance of not making it.. lol.

EDIT: YA know.. I just noticed you have a 2.5d reading back, and only geared for 43.. I was reading two different configs and lost track, for some reason I thought you had the 1.5d (2700kv) and were pumping it w/ 5s.. hehe my bad on that end and it will change how effecient it is, with a the 2.5d you will be at a fairly low RPM on 4s, usable as I race the 2.5d on my erevo truck now geared for about 40 on a 4s config and it's perfect (I have run a 20min main w/ it as well). Took 3rd in the last a-main of the year behind the two local pro's (pro series pro's).

So ya with that low of RPM you'll want to stick w/ 5s and gear down, heh :) I'll just shut up now :P