6s vs. 4s?

[jsr]

Instead of thinking of how much mA your setup consumes per time period, think about Watts. So instead of looking at mAh, think Wh and do your calculation that way. Here's an example:

5000mAh 4s pack gets you 15min runtime
5A * 14.8V = 74Wh
This means you're consuming about 74Wh (not really as the LVC cuts it off before that) in approx. 15min.

Now, to get the equivalent runtime with a 6s setup, you want the same Wh capacity:
74Wh / 22.2V = 3.3Ah = 3300mAh

So choosing a 3300mAh 6s pack will get you equivalent runtime as a 5000mAh 4s pack.

Theoretically, the lower kV setup provides more available torque, but because the lower kV motors have more internal resistance and build up rpms slower, the torque is applied a bit slower thus you don't feel that additional torque as quickly as the torque provided from the higher kV motor (which gives the smoother feel). Also, the higher kV motor should theoretically have more top end speed, but because all these motors are way overpowered for the vehicles they're run in, we're not using all the available torque and power from the motors and the difference on the top-end is dampened so they how quickly they reach that top speed is not as noticeable.

Higher voltage is better for heat, however there are other items that wear a bit faster (such as the ESC caps as their life is shortened with higher voltage, but operating life should still far exceed your usefulness of the ESC). For me, I get 2000-2300kV motors for considerable lower price than the lower kV motors from Neu, Neu-Castle (their 1800kV motor is nice), and Tekin, so I'm sticking with 4s until the lower cost 4s motors are no longer available or lower cost 5s and 6s motors are available. Plus, my other RCs are set up to run on 4s also, so the compatibility is useful for me. Otherwise, I would run 5s or 6s.
For those concerned with the price of the Neu-Castle 1600kV, it's a monster sized motor that IMO is too big for buggies and truggies (you'd be using a small percentage of it's potential, which is why it runs so cool). The Neu-Castle 1800kV 1512 motor is a nice option that's similarly priced to Tekins and would run well on 5s (6s is a bit too fast and you'll lose most of that runtime advantage).

Oh, forgot about your battery question...
Don't go by the ESC amp ratings...they're all BS. They usually go by the rated FET capability at 25C instead of derating for operating temps or design limitations.
The higher voltage you go, the lower current capability you "need". I say "need" because most people get more than they "need" because the higher discharge packs have lower resistances (which is why they can discharge more current), so they feel punchier. There's a difference between "need" and "want". You don't "need" a 150A discharge capability pack, but you may "want" one. Also, higher discharge packs will run a bit cooler (again, due to the lower internal resistance). It's up to you.

[kingdomracer]

It's always so nice when someone comes along and clears up the fog in front of me, thanks. Now if you will explain to me the formula that you used to know that a 5000 mah 4s runtime is 15min. I already own a bunch of Enerlands that make up 2 sets of 4s and 1 set of 6s and they're 6000mah and using you formula they will be just 400mah under so they'll do just fine and should give me the same run time as my TP 8000mah 4s. I tend to stay away from 6s due to my share of fried MM ESC's but I cured that problem with xtra caps so I'll probably run a couple of laps with 6s just to see what it does but plan to run 1800kv 5s 47/12 setup on my 8 2.0

[georgec]

Thanks jsr, excellent information. Helps to put it in perspective.

[jsr]

The 15min runtime was just a number to make the math simple. Whatever runtime you get on your specific setup (which includes your motor, battery (capacity and discharge), vehicle weight, track size and design, and driving style) on 4s, if you want to keep that same runtime, then use the calculation I did in the previous post to find out what capacity you need in a 5s or 6s battery to make the same runtime.
Good luck and have fun!

[kingdomracer]

Originally Posted by georgec

Recently there have been some guys from Kentucky and Georgia coming to race with us at our local track (great bunch of guys) and all of them have ran 6s with 1400kv motors. A couple of them let me drive their buggies (MBX6) and they did seem to be noticeably smother than my 4s/2000kv setup and their motors all ran 5 to 8 degrees cooler. They didn't seem to be any faster than my setup just smother. All this has made me second guess my setup. Could it be that running higher voltage with a lower kv motors is that much more efficient than lower voltage with higher kv motors??? The overall cost is about the same because the batteries they were running were only 3300mAh as opposed to my 5000mAh and getting the same run time. As for motors they all ran the Tekin 1400kv, witch I don't know much about other than the price isn't bad. The funny thing is all but one ran the MMM esc and only one ran the RX8 esc.
Any input on this

Just curious because I'm looking at getting batts for a 5s/1800kv setup, what runtime are you getting with the 4s/2000kv setup?

[jzemaxx]

Ok....I'm puzzled guys. I got my MBX6 buggy done. Running 6S 4400mah batt, motor is a 1512 1380KV motor. Running 15T pinion on it and after a 5min heat I'm using 1100-1200mah. WTF??? That puts me almost the same usage and runtime as a 4S 5000mah batt. I figured the 4S being only 74 w/h and the 6S being 97 w/h I would see pkenty of runtime. That calculates out to be only 16mins with a 6S 4400?? Doesn't add up. The buggy weighs 30 grams lighter now then it did with the 4S MMM 2200KV setup.

[suicideneil]

Is that geared for the same speed or more/less?

I think part of the issue here will be that you can get the same runtime with a lower kv motor + higher voltage and lower mah lipo, but to see an increase in runtime you need to keep the same mah capacity & lower the current draw ( HV and lower kv again ). Having a lower mah will reduce weight but lessen the advantage you get from lower current draw = same overall runtime.

[jzemaxx]

Originally Posted by suicideneil

Is that geared for the same speed or more/less?

I think part of the issue here will be that you can get the same runtime with a lower kv motor + higher voltage and lower mah lipo, but to see an increase in runtime you need to keep the same mah capacity & lower the current draw ( HV and lower kv again ). Having a lower mah will reduce weight but lessen the advantage you get from lower current draw = same overall runtime.

I figured the total capacity of the batts would be the determining factor. The 4S 5000mah only has 74amp/hours. The 6S 4400mah is 97 amp hours. I figured that is a larger "gas tank" per say. So it should give me more runtime. The speed is the same.

[suicideneil]

Hmm, good point. Buggered if I know then

I think you'd need an Eagletree hooked up top get some more meaningful numbers to crunch.

[jzemaxx]

Originally Posted by suicideneil

Hmm, good point. Buggered if I know then

I think you'd need an Eagletree hooked up top get some more meaningful numbers to crunch.

Trust me, its got me scratching my head.

[BrianG]

So, let's recap:

- Old system: MM2200 (1515) 2200kv on 4s 5Ah. Total rpm=32560. Weight=X.

- New system: Neu 1512 1380kv on 6s 4.4Ah. Total rpm=30636. Weight=X-30g.

Can we assume both systems are geared for the same approximate speed?

Otherwise, the only thing that stands out to me is the new system has a smaller motor pulling a taller gearing for not much difference in weight.

[jzemaxx]

Originally Posted by BrianG

So, let's recap:

- Old system: MM2200 (1515) 2200kv on 4s 5Ah. Total rpm=32560. Weight=X.

- New system: Neu 1512 1380kv on 6s 4.4Ah. Total rpm=30636. Weight=X-30g.

Can we assume both systems are geared for the same approximate speed?

Otherwise, the only thing that stands out to me is the new system has a smaller motor pulling a taller gearing for not much difference in weight.

That is correct. Wondering now if I should have gone with a 1515 instead of the 1512. The gearing though did not change. I left the same pinion on, so speed might have dropped 1mph....but not much.

[DCastaneda]

I too am looking for a viable 4s/20minute runtime setup. Seems like the best bet would be a Tekin 1700kv truggy motor to keep the amps down? On our medium sized track the CC 2200 gets just about 17-20 minutes but we need a reliable 20 minute main setup. Any input as far as the tekin motors go?

[jsr]

Are all the settings in the ESC and radio the same? Changing throttle curves, punch, etc will change runtimes.

Also are you driving the same? The buggy might be more controllable now in 6s so you're on throttle sooner/harder than with 4s thus consuming more average current.

there are other factors to runtime to consider. But if truly nothing chnaged then that's odd. But look at all variables first.

[jzemaxx]

Originally Posted by jsr

Are all the settings in the ESC and radio the same? Changing throttle curves, punch, etc will change runtimes.

Also are you driving the same? The buggy might be more controllable now in 6s so you're on throttle sooner/harder than with 4s thus consuming more average current.

there are other factors to runtime to consider. But if truly nothing chnaged then that's odd. But look at all variables first.

All the settings have remained the same. I did swap though from a MMM to a RX8, but I set the RX8 the same with zero timing, low punch and current limiter on full to limit any amp spikes. The driving hasn't changed as my lap times are still the same.