Rc18T ran for 40+ minutes.

[ducati777]

Yup you read right. First time I got to really try out my new setup and I decided I'd walk the neighborhood till the battery died. It never did and I finally just went home, 40 minutes later.

I'm still learning about Lipo's but it came outta the truck at 10.86 volts, so it was probably starting to wear down.

I think a lot of my run time had to do with the gearing. I put a 10 tooth pinion on the 60 tooth spur. Top speed was probably high 20's, but get this, if it found traction it would wheelie. Acceleration was pretty much instant onroad.

I'm still in disbelief, 40 minutes of good strong running. There's pictures in the mini forum if yall wanna see my setup.

http://forums.radiocontrolzone.com/showthread.php?p=1750125#post1750125

[standard_63]

I ran my Emaxx last night in my backyard for 41 minutes using dual TP6000 packs. Batteries were at 6.4v when I stopped. Hacker C50Maxx and Master Comp controller -- they were cookin' when I was finished!!

[ducati777]

Dang, I used to think I'd be a nitro guy forever. Then mini's got me into electrics and now lipo/brushless makes me think nitro is outdated. An E-Maxx would be a lot of fun, I'll admit the lil 18th scale can't go all the places I'd like it to, but I'm sure happy with its performance.

40 minutes is by far the longest I've ever driven an rc car nonstop. My buggy gets maybe 10 minutes on a tank, and the stock 18T got maybe 20 minutes... Just nuts, I'm glad I made the switch.

[TimisTim]

You have an rc18 right? What do you have to do to make the drivetrains bulletproof on those? I'm very interested in getting one. Did you get the 5400kv mamba?

Those minis look like a blast, and ya can't beat 40 min run times.

[ducati777]

Yup Mamba 5400. That was a big choice, it seemed like everyone around me was going with the 6800 and the 8000. I asked some questions around here and bomb-proof suggested high voltage and low kv. He was completely right. I went with the 5400, and 3 cell Lipo pack.

On the drivetrain I shimmed the diffs, and added brass compression sleeves to the outdrives. My rear diff is doing well but I think I hear some clicking from the front. I'll have to reshim it. I used shock spaces for shims, but next time I do it I"ll just buy the shim kit.

The fun part about mini's are how durable they are. With the mamba you can get up to some stupid speeds, and occasionally you'll lose control and the little truck will go cartwheeling end over end for 50 feet. Oddly they take this abuse just fine.

I figure I'll probably go through dogbones, they seem to be under the most stress and are exposed to all the sand. My whole town is sand which is just brutal on exposed parts. But yet another benefit, parts are cheap. New dogbones are 3 bucks a pair, compared to maybe 35.00 for 2 CV's on the buggy.

If you're thinkin Mamba, I can't recommend the 5400/3cell enough. Its totally controllable and you can gear it for whatever speed you want.

[OptimaMan]

I can see that. I ran my Mini T for over 30 minutes - I just gave up because I was bored. I was running a HiMaxx 5400, 12.97, and 1900 TP 3s pack geared with 12 tooth pinion.

I've also ran my TC over 30 minutes on a charge... my new pack, the 5s 4400 should take my TC4 to over 1 hour run times!!! I'd go bug-eyed before the pack is actually used up!

[TimisTim]

A 5S PACK!!!! Geez, does the car even hook up! How many volts is that 21?

Must be amazingly fast. Wish I could see it run.

[OptimaMan]

You don't always have to use a high KV motor you know. Using a basic 2100 on 18.5 volts, we're only talking about 36,000 rpm or so. So, decent performance - but REALLY long run times. Now, if I WANTED to make it insane, I simply can swap it out for a 4200 motor and rev that sucker beyond 70,000 and it'll never hook up. :)

BTW, I actually haven't gotten around the actually USING the 5s pack yet - it's just sitting in my box brand new and ready to go.

[TimisTim]

Even though it is only a 2100 isn't the power still there when using higher volts? Or in other words how does the troque compare to a higher kv motor like a 4200 on the same voltage. It should have more right? Just less top end so it has to be re-geared.

[OptimaMan]

Yeah, kinda. 36,000 rpm is 36,000 rpm. Only thing is that it'll be a VERY torquey 36,000 rpm so you CAN gear it wayyyy taller if you want.

A 4200 motor will spin 2x faster than the 2100 motor but only have 1/2 the torque. However, because it's 1/2 the resistance, it'll draw 2x the current and hence make up for the lost torque by using up more amps. Now, this is assuming the battery and controller have no internal resistances. This is up to a certain point however. I can go on and on, but I don't feel like typing up a LONG essay nor hijacking this thread.

[ducati777]

Thats okay. People keep saying that lower kv=higher torque and I just don't see that happening. For example lets run a 2000 kv motor on 10 volts for 20k rpm. If we throw a 4000 kv motor in at 10 volts and hold it to 20k rpm, it will develope more torque than the slower motor right?

Simply because it'll draw more amps than the lower KV motor. However if try and compare a 2000 kv at 10 volts to a 4000 kv at 5 volts, I'd expect the lower kv higher volts to have more power. But I'm guessing on that one.

One way I like to look at things is how much energy I can hold in the battery pack. For example the biggest pack I could get into my 18T is the TP 2100 I think. But I could only get 2 cells. So I like to think of it as 2100x2=4200 of energy. I instead went with a 1800x3=5400 of energy. Thus with a lower kv motor, and higher volts, I can fit the 3s battery and get more run time.

[bomb-proof]

4200 motor will spin 2x faster than the 2100 motor but only have 1/2 the torque. However, because it's 1/2 the resistance, it'll draw 2x the current and hence make up for the lost torque by using up more amps.

And by using more current, it will lover the voltage. By lowering the voltage, it will lower the RPM.

So, more heat, more voltage drop, less runtime, etc.