Darksand

Hello all,

I am new to the brushless RC's cars (had some cars with the mabushi 540S and 540SD and some nitro cars.)
But now with the brushless engines and the other new electronics (esc, 2,4ghz etc) i picked up this hobby again.

Nothing fancy, not racing. Just bashing and running on mixed terains.

I bought myself a cheap short course truck with a 540 sized 3300kv brushless system (i couldn't find any other specs of the engine.)
I want to buy an exact same (2nd hand/ broken roller for spare parts) and will do some upgrades on the truck.

The truck is a 1/10, 4x4, brushless from Amewi wich is the exactly the same as some models from Himoto, Redcat racing, Amax and HSP

Now my question. The runtime on a 2000Mah 6 cells NiMH feels low (about 5 minutes. Ok, i do like to punch the trigger), and i wouldn't mind to increase this.
I have ordered a 3000mah and a 4600Mah battery. My goal would be of running this truck at cool temperatures for an hour or more. If this would cost me some topend speed, I wouldn't mind to cut it by 25%. The same goes for power.


So i need to upgrade (actually downgrade) the engine.
All the engines i see outthere are like crazy stuff, even giving 1/8 scale trucks wheely power. I dont need this. I just want a descent speed on it, nothing fancy.
All the stuff about kv/turns/winds/poles/sensored etc just brings a waze over my eyes. I am beginning to become clueless here.

What do i need to do to get this runtime, while still maintaining enough power/speed to have some fun with it?

Thanks in advance

Robotech

An hour? I'm assuming on ONE battery pack? Five minutes of runtime on 2000Mah NiMH is about right...hence why races used to always be 5 minutes long. (use to be 4 in the NiCd days)

Mah=capacity=runtime. Batteries here are your key since there won't be a huge difference in motors. (BTW, electric power plants = motor, internal combustion power plants = engines...sorry, pet peeve)

Right now I think the highest capacity batteries I've seen are 5000+ LiPos. To get close to an hour you'll probably need to take 2 5000mah LiPos and wire them together in parallel and figure a way of securing both of them into your vehicle. In parallel means your going to get a 2-into-1 Y adaptor so that you plug both batteries into the Y adaptor's 2 male plugs and then take the adaptor's one female plug and plug that into your speed controler. This doubles the capacity but maintains voltage so 2 5000mah packs become 1 10000mah pack. Obviously you'll need to make sure both batteries are identical in Mah and number of cells (2S).

NOTE I've never done this with LiPos and would definately ask someone who has a lot of questions about this before you try it!!!

Your other issue is the vehicle you're putting it in. A 4x4 Short Course truck is heavy and it's drivetrain takes a lot of power to spin up to speed because you're trying to accelerate 4 tires instead of two, overcoming the friction of two gearboxes rather than one, and are spinning those heavy metal driveshafts. So a high turn low torque motor (which is going to be the one that gives you the most run time) isn't necessarily going to work in your truck unless you want to replace burned up motors often or have a truck that moves just slightly slower than something from Tyco.

So you need a decent motor to move the truck first off. A 17.5 540 would do the job but would be stressed. A 13.5 540 would still be very underpowered but would work. I run a 8.5 540 in my SC10 4x4 and there are much faster trucks on the course. I'd guess a 13.5-10.5 is where you want to be. A 550 size motor would be prefered because the extra size will give you more torque and thus keep the motor/speed controller from working too hard and building up a ton of heat. More poles also equals more torque and lower operating temps so a 4-pole 540 sized motor would be a better choice than a 2-pole 540.

If you're going to shoot for an hour though you're going to want a fan and heat sink on your motor and ESC...that's probably going to be manditory.

Even with all this...I DOUBT you'll get an hour of run time out of it. My SC10 4x4 gets about 10-15 minutes out of a pack (3400mah IIRC) So going to two 5000mah packs MIGHT get 30-45 minutes out of it.

Darksand

Thank you very much for all the explanation.

Let me try to recap if i understand everything and mix it with my bad understanding of all the stuff i found on inet .

As far as i understand high turn engines (oops motors :P, sorry i am Dutch) have more torque and lower kv (usually higher operating voltages).
I also read that higher turns pulls less amps (but maybe more watts because of the higher voltages)

So these motors would run hotter in my heavy 4x4. Would this also be the case when I get, lets say, a 2750 or 3000kv 15T with 14-16 volt (or more, just trying to understand ths ) rating and let it run on 7,2/7,4volts with the same gear ratio? the 3000kv would run 10% slower then the 3300 (theoretically) right?

Ooh, when all this just sounds stupid, please say so

Robotech

LOL...not sounding stupid at all. A lot of this stuff with brushless I'm still new to as well. You are correct though for most of this.

I'm just not sure what you're reffering to when you say: "when I get, lets say, a 2750 or 3000kv 15T with 14-16 volt rating" Are you talking about running it with a 14-16 volt battery pack?

If I remember correctly, the kv rating is the RPMs the motor will turn per one volt of electricity. So yes, a 3000kv motor will turn fewer RPMs than a 3300kv motor if both are running off the same voltage.

KV ratings versus motor turns is where Brushless motors get confusing. My understanding (and again, this is just from what I've been able to understand) is that the motor's kv rating is more of a tell tale performance mark than it's number of "turns". Motor manufacturers still refer to motors by the number of turns they have because users of brushed motors are use to that term when dealing with an electric motor's "speed potential".

Darksand

Thanks for all the answers ,

I have to agree this is a bit confusing, i had to think about it myself too .

Let me try to make it a bit more clear.

When i get a 3000kv motor, with the same gear and the same battery, it would theoretically run 10% slower.

Now, with the current (unsure but probably low Turn 3300kv max 12v) motor, it will take more amps then a high Turn 2750 - 3000KV max 16V motor with the same gears and battery, Right?

My idea was to get a motor like this. Give the battery more endurance by really undervolting the 16V motor with just 7,2v. Figuring the Watts of this engine will only gome into play when you use it at max voltages.

If both engines are 500 Watt, the high turn won't get there until I use 16V (or overgear, not sure)

This way i have a car wich runs slower and probably cooler on 7,2v, has more endurance on the battery but still has the option to go faster by using more volts when i want to.

Is that a smart choice?