4s vs 5s and gearing

OK so i,ve a big question. I,ve sell my RC8 to my brother but i,ve keep my brushless system and i,ve put it back in my Mugen truggy yesterday night, and the setup is, flightpower 5000mAh, 4s, Neu 1515 1Y and MGM16018.
I,am geared 15/46 on 4s, but i,am plan to buy a 5s or 6s this week.
I want to know, if i run my truggy on 5s or 6s, can i leave the same gearing (15/46) or i must absolutly go down on the pinion

I,ve keep the mechanical brake on my mugen, and i,am limit to a 15T on the pinion, i can,t go down. If i want to go down on the pinion, i must remove the mechanical brake and use the controller for braking, and i realy don,t want to do this.

I know if i go 5s or 6s with the same gearing, the top speed will be realy to fast, but my goal is not to be realy faster but it,s to go down on the current.
So if i keep the same gearing, is my current and the temperature will go down and the efficiancy will be about the same or i will reduce the runtime, raise the current and temperature

Thank you!

[othello]

>or i will reduce the runtime, raise the current and temperature

This is exactly what will happen when you increase voltage without changing gearing. So yes, if you increase voltage and you don't want to go faster and want to benefit from lower currents you have to change gearing. Why do want to go down on current? Do you have heat issues with your ESC, motor, battery?

I would like to have harder acceleration. For sure, little more top end would be nice too
My friend have a Jammin CRT truggy with the new OS .28XZ and i want smoke it on the track.

so if i well understand, if i go 5s or 6s, i must to gear it down to stay in the 40mph range, like on 4s setup???
But if i keep the same gearing, i'll pull more curent??

[othello]

First thing i would try at your place:
If your electric components do well on 15/46 and you see some headroom temperature wise, try 16/46. With good batteries (flightpower for sure are) you will see an increase in top speed and acceleration won't really be any worse. But check your temperatures.

A friend of mine runs his Mugen MBX5T like you do with a 1515/1y and MGM 16018, but he uses 6s2p A123 which can be compared to 5s lipo. This translates to good top speed and more acceleration then the car/tires can handle. But the motor does reach 70°C at the end of a 7-9 minute run with 25 degrees outside temperature. Still on the safe side but this tells me, that 6s Lipo would simply be too much -> too much power and every component would run at its limit.

With 5s your voltage increases by 25%. With a good 5s battery your top speed could increase by 15-20% (when you do not change gearing) as your new 5s battery will most likely be heavier then the one you are using now, air drag increases ....

You will definitively use more current, as going faster and getting to higher top speed requires more energy. So runtime will decrease when you choose a flightpower 5s 5000mah (compared to your 4s 5000mah) without changing gearing.

OK i,ve look for the Flightpower 4350mAh, 5s. The weight is about the same, and i,ve try a 14T pinion and i,am to the limit but i can use it. On BrianG speed calculator, with my actual setup i,ve a top speed of 40mph, and if i go with 5s and 14T pinion, i have 46mph.
Do you think that i,ll see a big difference with this gearing and a 5s, and for the runtime and temps, i think it should be about the same

What do you think

[othello]

Theoreticaly with 5s 4350 (78300mWh) you will have 8% more energy on board when compared to your 4s 5000mAh (72000mWh) battery pack. But on the other side your car will need more energy (higher top speed ...), therefore i would expect the temperatures to rise somewhat. Runtime will go down somewhat too. But as you said not by far.

But what's the advantage to run high voltage

Maybe that i'll be better to change my 1515 1Y (2200kv) for a 1700kv and run 6s????
Or simply try to run a pinion gear that will put my speed on 6s at about 40mph, like on my 4s setup?

[tc3_racer_001]

any way tat you could run a slightly bigger spur?

hv is only good when your aiming for the same speed. a 6s which goes 35-30mph will be much more efficient than a 3s which does the same speed... id suggest trying without brakes, adding a smaller pinion and go from there... easier and much cheaper than putting more money down for a motor which may not be warrented (if you do change the motor, your 4s pack will be slower, whereas if you keep the same motor its as easy as changing out the pinion beofer your next race!!

this make sense?

[lutach]

Higher voltage = lower AMPs used to get the same power of a lower voltage set up. Lets say your properly geared vehicle is making 1200watts peaks with 3S then the system is peaking at around 108A+- a few. Now on 6S your system will peak at 54A+-. Now we all know a lot of system will peak much higher, but the average A will be lower with the 6S then with the 3S (In my case it is ). I still haven't run my 1521/1.5Y with 10S in my BPP truggy as I'm having some fun with the 1521/1Y with 6S, plus I'm still testing how good the Kong Power 5000mAh 3S packs are.

Originally Posted by tc3_racer_001

any way tat you could run a slightly bigger spur?

hv is only good when your aiming for the same speed. a 6s which goes 35-30mph will be much more efficient than a 3s which does the same speed... id suggest trying without brakes, adding a smaller pinion and go from there... easier and much cheaper than putting more money down for a motor which may not be warrented (if you do change the motor, your 4s pack will be slower, whereas if you keep the same motor its as easy as changing out the pinion beofer your next race!!

this make sense?

Yes it's a good idea, but i real want to keep the mechanical brake. I don't want to brake with the controller, because i want to remove more stress of possible on the controller (and you know like me that MGM controller seem to be very fragile) and more, use the controller to brake pull lots of curent of the batterie, and cut on the runtime.

But, if i've not choice, i'll remove brake and use motor to brake, and use smaller pinion to run on 6s.

But a last question, if i use 6s but i'am geared to keep the same top speed than my 4s setup, is the 6s will be more powerful, with harder acceleration???

[othello]

I think it is a good idea to keep mechanical brake with the MGM ESC. My buddy uses the brakes of his MGM ESC, but experiences braking problems in his MBX5T.

>use the controller to brake pull lots of curent of the batterie, and cut on the runtime

Actually, braking with the ESC regenerates energy back to your battery pack, thus runtime will be longer. During braking with the ESC current flows back to the battery and therefore you see some amp spikes resulting in a rising voltage (can be compared to charging your battery pack). This puts additional stress to your ESC and it will run hotter.

I would not recommend running your Neu 1515/1Y (2200kv) with 6s. RPMs could exceed 50000rpm. 5s is more then enough and would give you around 40000rpm. This seems way more reasonable and as i already posted does work in a MBX5T and gives you very good acceleration and top speed (with a good battery).

With a good battery 5s could definitively give you better acceleration (if you have enough grip). Let's assume your actual 4s flightpower pack is able to pump out 150A@3,5V x4s = 2100 Watt. The same 5s battery pack would be able to generate 150@3,5V x5s = 2625 Watt. More Power means you could gear it for higher speed and you won't accelerate any slower as you have more power at your fingertip. On the other hand if you use more power, runtime will come down and your components will run hotter.

If you want to benefit from higher voltage (and thus using less amps) you have to gear accordingly. Meaning: If you switch from 4s to 5s, you have 25% more voltage (theoretically 25% more motor rpm), therefore you have to change gearing by almost 25% (for example from 1:14 with 4s to 1:17,5 with 5s). The car will have about the same speed. Amps will drop, as will temperature of your components. Thus leaving more room to gear it for more top speed (if you want to).