Efficiency?

[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.

[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.