longer run times?
 

i had asked some questions re 4s/5s/6s lipos in the general electric section but had the thread hijacked and got very little info out of it so i will try here. i am currently running a mmm v3,2200kv motor.powered by 5000mah 4s 30c lipo with 14-18t pinion 46t spur in my mbx5t. i currently get about 13 minutes running out of each pack. i am after 15+ minutes as we are starting to see 15 minute finals pop up at a few evemts here.
does any one have and suggestions? maybe decreasing motor size to 1600kv? will that be a noticeable drop in power and speed?

Hi! Threadjacker here. I'll try again. (It's alright, I'll forgive you 'cause your kiwi)

Motor kv does not refer to it's size. It is how many revs per volt (e.g. 2200kv motor on 1 volt = 2200 rpm). This page lists some motors of various sizes and kv. A point I would like you to note is the power ratings. Different kv's but still the same power output [e.g. 1515 1y has 2500 watts max power (Your castle motor is the commercial take of this motor), and a 1515 1.5y 2500 watts max power]

Power is volt times current (Volts x Amps = Watts). Higher kv motors draw more amps to produce the same power. 2200kv motors are suited to 4s - 2500w / 14.8v = 169 amps. 1500kv motor on 6s - 2500w / 22.2 = 113 amps.

So if you change the motor and battery in your setup (same size lower kv motor, higher voltage battery) you could expect to draw less amp draw, hence less heat, and over all a more efficient setup.

You will not see a decline in responsiveness or power when you trigger it. In fact you will have more power at your fingers because the lower kv has more torque.

Hope I helped this time :smile:

would a 6s 20c pack last a little longer than a 6s 30c due to a lesser burst rate?

Actually the oppposite. The 30C pack would last a bit longer because it can hold voltage better under load, and would hit the cut-off later.

dropping to a lower kV motor and the same gearing will give you slower speeds but longer runtime, less work is being done. With the lower kV motor if you gear for the same speed the same amount of work is being done and runtime will be about the same. The power that your motor is rated to handle and output is useless for figuring your runtime as was mentioned ( sorry for stepping on your tows PinkPanda) Hook up an Eagle Tree and you will see what kind of power your actually using. I have a few graphs of the 1515 2.5D in my RC8T and you may see very short bursts of about 2000watts but your average is much lower. I had a peak amp draw of 168A I think but my average draw was about 25-30A. Your driving style, throttle control, and gearing will play the biggest role in your runtime. You said you have 14-18T pinion, how is the speed for you with the 14T versus the 18t? If the 14T is enough speed on the track you will get longer runtime than with the 18T. I will be running a 50T spur and 15T pinion on my truggy to start the year running a CC/Neu 2200kv on 4s, speed should be pretty close to the 1515 2.5D (1650kv) on 5s, it might be a touch faster and I may drop to a 14T. As for batteries 4s 14.8V x 5000mah gives you 74 watt/hrs (voltage x amps) So a 5s pack of 4000mah should supply the same amount of power and give you the same run time, however running higher voltage will decrease the amp draw and create less heat, the lower amp draw will not yield longer runtimes though because the 4000mah battery has less mah to supply you power. If your in need of longer runtimes and you change nothing you need a bigger battery, like 6000mah+. Make sure everything moves smoothly in your truck, no binding anywhere. Tire choice affects runtime, lighter tires take less energy to rotate and will give you longer runtime, any thing that can be lightened up on your truck will help. Learning throttle control and rolling into the throttle rather than stabbing it and blipping the throttle like a nitro will help a tremendous amount!

I ran smaller batteries than another electric guy at the track, yet I could easily get 3-4 minutes more than him. He was better than me overall but he didn't have the throttle control and his idea of gearing up and then turning down the epa on his radio to get the speed down doesn't help either, the motor is still doing more work to get up to that speed.

Any other questions? Maybe talk to BrianG, he's the guru on here for giving you all kinds of formulas for figuring out amp draw and such

Not stepping on any toes:lol: Matter of fact it's nice to have a different perspective. I was referring the table of motors to show different kv does not mean different size or power, 'tis all.

[QUOTE=E-Revonut;356560] You said you have 14-18T pinion, how is the speed for you with the 14T versus the 18t? If the 14T is enough speed on the track you will get longer runtime than with the 18T.

-i notice the difference in acceraltion between the 14-18t and the 18t feels like it has longer legs than the 14t.so would running a larger pinion make the motor wrk less?

As for batteries 4s 14.8V x 5000mah gives you 74 watt/hrs (voltage x amps) So a 5s pack of 4000mah should supply the same amount of power and give you the same run time, however running higher voltage will decrease the amp draw and create less heat, the lower amp draw will not yield longer runtimes though because the 4000mah battery has less mah to supply you power. If your in need of longer runtimes and you change nothing you need a bigger battery, like 6000mah+.

-so larger mah packs make things more efficient?



Learning throttle control and rolling into the throttle rather than stabbing it and blipping the throttle like a nitro will help a tremendous amount!

-i am still search for that perfect throttle curve setting to give me a steady throttle 'roll'

Mah = milli amp hours, this is how big the fuel tank is, nothing to do with efficiency. The bigger the mah the bigger the pack, the longer the run time (with the same setup).

Learn to use a steady finger instead of flat out.