First of all I am with Brian on this. Any heat is wasted power and lost efficiency. Might not make a big deal in run time but I do think that it has to make some. Is that worth the bigger $$$ outlay of a HV system??? Not for some and for me neither. Why I do like HV is the fact that my ESC runs cooler and has easier life for the same amount of power. This should mean that it should also have a longer life. Batteries too. So there has to be some money saved there to go some of the way of paying for the HV setup. Any of that make sense to anyone or just in my head?

Also I can swear that my motor runs cooler too. I remember my CC 1515 1Y getting rather toasty on 6S but my 1520 geared for some speed runs much cooler. Maybe because the can is bigger and can dissipate more heat????? Either way all of my MT's and Truggies will end up running 8S eventually with the buggies running 6S.

Nobody is saying that as your wattage needs increase, you shouldn't go up in voltage. But none of my systems average even 20 amps. Yes there are points that go much higher, but on average between 12-17 . So I'm sure someone can throw the math to it, but assuming a 15amp average draw in my E-revo on 4s, for 45mph, What would really be the gain going to 8s? Is it fair to go by the average amps?

Not really a fair comparison with those motors. One is smaller and higher kv the other large and low kv and running the same voltage.

Totally normal, the longer motor has less magnetic losses because it spins at lower RPM and the can is longer so it dissipates more... This is not the compairison we talking about, here it is :

1515/1Y 2200Kv on 4S
1515/2Y 1100Kv on 8S

2 motors of same length and weight. I don't know the neu specs but I am pretty sure that the internal resistance of the 2Y will be ~4*more than the 1Y

You try the both setup, geared for the same speed, you will find ~ same temps for both motor, although the ESC will be cooler.
To keep the runtime equal, you need for example to run 4S 5000mAh and 8S 2500mAh, 2 batteries of same weight and price.
So the battery discharging rate is also divided by 2 ==> the 8S will operate at ~ same temp too.
That's why I said earlier that the efficiency gain in HV setup will be mainly in the wires and the ESC, not necessarily in battery and motor...
Just my 2$ :yes:

If you don't need to go up in voltage why consider it? Is that revo for racing? Sounds like you have a smooth finger so the gains will be less than if I were to race that setup and move to hv.

Hv setups usually have more grunt right? Is it possible some people learned to be lighter on the trigger as a result?

Hum... No, HV and low Kv have less grunt, because the motor has higher inductance, so it limits amp spikes too.
A LV setup need a smooth finger to spare some mAh and limit amp spikes.

Honestly, I'm mostly after knowledge. I have seen many a great thing claimed from higher voltage systems, but have never seen data logs, or anything else, showing it.

My brain hurts when I try to understand inductance. From what you're saying Nuz I understand higher inductance means less magnetic pull?

That's not how i understand wiki's explaination -

Inductance=magnetic flux/amps
When a conductor is coiled upon itself N number of times around the same axis (forming a solenoid), the current required to produce a given amount of flux is reduced by a factor of N compared to a single turn of wire. Thus, the inductance of a coil of wire of N turns is given by:


The formula didn't paste ^ ??? Anyway, more turns means more magnetic flux per amp. Higher resistance in the winding wire but less current being drawn through it. The voltage is just to reach a desired rpm.

Sorry if this seems basic but just trying to understand. So a LV setup produces heat from amps to reach the same inductance and a HV setup produces heat from higher resistance.

A higher value of inductance means the more it will resist changes in current flow in either direction. Under the current impulse of sudden WOT (ie. full voltage applied to motor) it will initially not have much power due to the coils building up their magnetic fields and resisting a change of current flow.

Howstuffworks has a great analogy of how inductors react with changes in current. http://electronics.howstuffworks.com/inductor1.htm

edit: pinkpanda3310, Wikipedia uses images for the functions to keep it looking the same without having to bother with IE/Firefox/Chrome/etc. specific formatting issues.

My experince with HV vs LV was mainly with the feigao 2 pole xl motors.

An 8xl motor on 4s and a 14xl on 8s spin about the same rpm, and thus would run the same gearing in the same rc to get the same overall speed. The 14xl ran cooler (it actually did not overheat in a 30min bash) vs the 8xl (20 mins was about all it could handle).

Also, going from 4s to 6s made a big difference too. a 1515 sized motor on 4s always seemed to have issues (like a 1515 1y) with a heavy truck, but dropping to a lower kv motor and going to 6s worked fine with the 1515 size.

Any reason why I saw this?

Must have been the super ma packs you were running! It's contradictory to some of the above posts but my hv low kv setups have always had way more snap and power through the throttle band over my lv high kv setups.

Thanks Shonen, my brain didn't hurt on that one:smile:

I had a look at Brian's car set up guide and compared a stock e-revo geared for 45mph on 2s and 6s.

6s result was 15a, 333w average draw and 98a, 2175w burst
OMGWTFBBQ result was 45a, 378w average draw and 292a, 2453w burst

I went a step further and made my own hyperthetical using Asheck's revo as target power. Trying to assume the same driving style etc.. Average 15a on 4s = 252w average guessing 1680w burst (100a burst * 16.8)

HV setup-

Motor- Neu 1515 3D, 1360kv, 0.012ohms, 30200rpm (on 6s)
Battery- Hyperion 6s, 2200mah, 35c, 0.014ohms
Esc- MMM, 0.0003ohms

Power-

22.2v * 11.4a = 253w average
22.2v * 76a = 1687w burst

Losses-

11.4a * 11.4a * 0.0263ohms (combined resistance) = 3.4w average
76a * 76a * 0.0263ohms = 152w burst

3.4/253 = 1.34% power loss to heat average
152/1680 = 9% burst

OMGWTFBBQ set up-

Motor- Neu 1515 1D, 4100kv, 0.003ohms, 30340rpm (on 2s)
Battery- Hyperion 2s, 6500mah, 35c, 0.0021ohms
Esc- MMM, 0.0003ohms

Power-

7.4v * 34a = 252w average
7.4v * 227a = 1680w burst

Losses-

34a * 34a * 0.0054ohms (combined resistance)= 6w average
227a * 227a * 0.0054ohms = 278w burst

6w/252w = 2.4% power loss average
278w/1680w = 16.5% burst


Those 2 setups do not take into account losses from wires or voltage drop which would affect the LV setup more than HV. On top of that, the rate of temperature increase will be more on the LV setup due to higher amps which of course affect all components leading to more resistance, heat, voltage drop.

I did this for my own curiosity but figured I would post it since I took the time to work it out.

Panda: FYI, the setup guide algorithm takes vehicle weight and target speed and produces a "required power" figure. Then, calculating the current draws (average and burst) is a matter of joule's law based on the voltage used. As such, this is not exact, so keep that in mind.

I realize that real world testing will have different results. I was just showing heat loss as a calculation. I could've added further losses from a nominal 200mm of wire but I forgot and today I don't have time.

BTW the sliders used in the car setup guide is a handy tool :great:

Thanks. :smile:

BTW: There is also a tool to figure wire losses: http://www.scriptasylum.com/rc_speed...esistance.html

Yes, of course, I saw that too. There seems to be no end of growing uses on your calcs page, from newbs to pedantics. But I won't look at it tonight, it's 8:15pm and I'm still in the office. The last post was 4:00am this morning before work :sleep:

You are comparing two setups. Do the batteries have the same C rating and the same amount of energy content (say, same peak power)?