Efficiency?

[brijar]

My friend and I have similar trucks, but he always gets more runtime than me, even though I have much higher capacity batteries (mine are 5200mah, his are 3850mah, same voltage).

My truck:
Revo 3.3 converted to single speed with RRP steel trans gears geared 25/40
Castle/Neu 1518 1800KV
Castle MMM (older one with bullet plugs on the battery terminals, perhaps version 2 or 3)
6s Turnigy 5200mah 30C hardcase (three 2s packs in series)

His truck:
E-Maxx with newer chassis, but older 2 speed transmssion
Castle/Neu 1515 2200kv
Castle MMM (newer with battery wires soldered to the board, version 4 or 5)
6s Thunderpower 65c 3850mah (two 3s packs)

Could it just be driving style? He usually gets at least 5 to 10 more minutes than I do. My Turnigy packs are getting fairly puffy and I had to go to 5s because one cell was always lower than the others. My charger will usually put 4800mah to 5000mah into the packs after a run with the MMM set to 3.1v/cell. Thinking about changing it to 3.0v/cell.

[devious1]

Running a voltage that low will damage them from my understanding if it hasn't already...
Which in turn could be your problem...

Someone will step in here shortly with more accurate information
to see how far off i am with my understandings.

I have my cutoff at between 3.5 and 3.8v
Its been a while since i checked the voltage on my MMM.

I honestly wouldn't have run them that low

[brijar]

wow really? The default on the MMM is 3.1V I think. Used to be 3.0V in older firmwares. A lipo cell's nominal voltage is 3.7V, so I'm not sure how you're getting away with running a 3.8V cutoff. I have always been told not to discharge them below 3.0V per cell and that stopping them sooner will prolong their life. Perhaps I am mistaken, though.

[E-Revonut]

3.1 is fine for a cutoff. 3.2 gives a little more safety and doesn't push the batteries as far. A cutoff of 3.5-3.8 is nonsense, I can easily put enough draw on a pack, even a good pack to drop it down that low during a run. Driving style plays a big difference in runtime. For starters, is he flipping over a lot. A poor driver can have more play time just as easily as a good driver. If he's upside down more than he's driving he could get more time. Without running the numbers I'm nmot sure but your gearing seams pretty high. Also you don't have his gearing listed. He could be running his more efficiently than yours with optimal gearing.

[josh9mille]

honestly there is nothing similar between the 2 trucks besides having 4 wheels. you are both using different motors, different truck, most likely different driving styles also. Tire/wheel combo plays a big role as well. Try trading trucks for a few runs and see what happens. That would eliminate driving style from the mix

[brijar]

I meant that they are similar in that they are both 4wd monster trucks and weigh about the same. We are both using Castle motors and running the same voltage as well. It seems to me like a Revo and an E-Maxx should theoretically require similar amounts of power, unlike, say, a Revo and a Rustler.
He doesn't flip a whole lot. Forgot to mention that he is using Monster GT tires (really tall) and I usually use stock Traxxas Talons. He also likes to drive in 1st gear most of the time, so that could make a big difference. I'm unsure of his gearing. I know he is using a Savage X spur gear (47 or 49t) and either a 21t or a 25t pinion.
I was thinking about just switching packs. My Revo breaks nearly every time someone else drives it haha. I have run a 21t pinion, but my runtime seemed about the same and was still shorter than his. What is a typical gearing people run on a converted Revo?

[pinkpanda3310]

Originally Posted by brijar

He also likes to drive in 1st gear most of the time, so that could make a big difference.

Another thing that hasn't been touched on is controller settings. Using punch control and slightly lesser epa settings will reduce peak amps as well.

[coolhandcountry]

You should ask how he has his esc set up.
I find rolling on the throttle and off to coast more helps battery life too.
I would expect your 1518 to maybe draw a few more amps. (could be worng without looking)
First gear running would take a load off the amp draw.

[bruce750i]

Emaxx appears to be geared sky high. First would be more ideal with even average size tires.

Revo packs lost there c rate but still hold most the capacity. High Ir?

Typical gearing I would say something like 16/40 4s 2000kv. Do you ever reach top end? Was it because of lack of gearing or lack of power?

[devious1]

Originally Posted by E-Revonut

3.1 is fine for a cutoff. 3.2 gives a little more safety and doesn't push the batteries as far. .

Wow i didn't think i was that far off, That's what i get for not running an rc for over 6 months.

Wait, Just checked my settings list, whatever auto lipo is on the MMM is what its set on.
as i don't have a monster link.

[BrianG]

Originally Posted by brijar

wow really? The default on the MMM is 3.1V I think. Used to be 3.0V in older firmwares. A lipo cell's nominal voltage is 3.7V, so I'm not sure how you're getting away with running a 3.8V cutoff. I have always been told not to discharge them below 3.0V per cell and that stopping them sooner will prolong their life. Perhaps I am mistaken, though.

+1. A 3.8v/cell cutoff is simply insane. Unless of course, you actually want to only discharge about 15% of your pack before having to charge it again. Sure, it'll last longer, but short runtimes aren't fun. Besides, many lipos are cheap enough these days that I'd rather "ruin" a pack by using ~80% of its capacity per run consistently than extend it a little by babying it.

Personally, I like a 3.2v cutoff. When the pack is removed from the load and sits for a couple minutes, the voltage drifts back up to 3.6-3.7v, and that's where I like it. The only time I'd run a higher cutoff value is if the load was very light where there will be less "drift up".

Anyway, back to the original post.

Assuming gearing is set "right" in both setups and ESC settings are similar, I would say drive style is a huge factor. Someone who brakes and takes off hard will use a lot more energy than someone who maintains a fairly constant speed with fewer changes in throttle. It would be pretty simple to test if it was indeed a drive-style issue; just swap systems and see if you get the same runtime results. If so, then it's drive style. If not, then it's either a setup or component issue. A data logger may help too here. Hook it up to both systems and compare the results.

Efficiency is simply the ratio of output power (power getting to the tires) vs input power (from the battery) expressed as a percentage. A system with low efficiency means that lost power is going somewhere, and would be easily indicated by heat dissipation somewhere, either the battery, wires, ESC, or motor. The power could also be lost on worn bearings, tight mesh, etc, so check those too. I would compare the temperatures of the various components of both systems. Chances are the low-efficiency system will have more heat build-up somewhere (which represents the lost power) than the other. It's just a matter of figuring out if it's a setup issue, drive style issue, or a faulty component.

[crazyjr]

Is it possible that the batteries are responsible for the efficiency? The poster is running turningy 5200 30c 6s and his friend has a Thunderpower 3850 65c, and the poster says the cells in his are getting puffy. I think it could be the higher c rating and the higher quality packs used adding to the efficiency. Looking at the c rating alone, I see it as sort of a resistance to discharge, as well as a show of handling of the load. higher c rating, to me, means to some extent longer runtime per mah, 156 amps(30c) verses 250.25 (65c) shows me the 3850 should run longer than the 5200 anyways

[brijar]

I know it seems wrong, but he runs less punch control than I do. I have mine set to 75% and I think his is closer to 30%, if any. I do like to go fast, and with the 25t pinion, I cannot reach full throttle without a very long and flat street.

I remember that my packs wouldn't change temperature at all when they were new, but now they are warm to the touch after a run. Maybe 80F, depending on how hard I drove.

I know his is geared crazy high, but since he uses 1st gear a lot, it isn't awful. Somehow his motor has put up with it. My ideal speed is 60mph on 6s, so I geared it to hit about 70 on paper. Not sure if that is unreasonable or not.
My friend is always going on about how he can put his radio to 120% and actually make it go faster. I'm quite sure that he is only changing the endpoint and that simply makes him reach full throttle faster which makes the last 1/16th inch of throttle travel useless.

Lately we have taken to playing tag with the trucks, so we tend to travel about the same distance.

All the factors point to him having a shorter runtime, but I guess I just have a heavier finger. I do think that my batteries have something to do with it. How could I go about measuring the IR of them? Find a big resistor? We have fancy oscilloscopes and other meters here at school, but I don't think we have any ESR meters.

[Maxxman]

Could it not be that he simply has better batteries so are less stressed and last longer?

His Thunder Power G6 65c batteries seem to capable of supplying 250A continuous and 500A burst (65x3.850 and 130x3.850 respectively) whereas yours seem to be able to supply only 156A continuous and 208A burst (30x5.2 and 40x5.2 respectively) assuming that there are 30/40C Turnigy batteries like these linked below:

http://www.hobbyking.com/hobbyking/s...dProduct=10277

[brijar]

Those are them. Except the cases are cracked badly and missing the front. I have also noticed recently that sometimes the truck will seem to slam on the brakes for a hundredth of a second whenever I'm accelerating at high speed. This worries me that my MMM could be going out. But it doesn't get terribly hot or anything. Might have just been a loose pin on a rear driveshaft. I thought it was the LVC kicking in, but the LVC doesn't apply the brakes. Only cuts throttle. I'm using firmware 1.24 I think, btw. Newer firmwares cause heavy cogging and startup issues.

Just because his batteries can supply more amps doesn't mean that they can supply current longer than mine, does it? If anything, his should drain quicker if he is drawing more current from them. Wouldn't a battery that can only supply 1A last longer than a battery that can supply 10A, if they have the same capacity?

I'll see if he will let me try his batteries tomorrow.