Gearing, Voltage, KV - OH MY!

I recently got a Duratrax Raze for a great deal, it has a RCM motor mount and battery tray. I want to build it up for my 5 year old son. He does pretty good with his brushless slash on 2s but I sometimes limit his top speed with EPA's. I know Castle does not recommend this but it seems when I gear it very low, he spins the tires too easy, and I dont think less voltage is possible.

I have a spare Mamba Monster ESC that I want to use in the buggy. I dont yet have a motor or battery for him. Can you guys recommend a motor/battery/gearing setup that will keep temps down and top speed under 30 (probably under 25 is better for the 5 year old)? I dont want to jeopardize the ESC.... as I have had my share of problems with the MMM. In my buggy, with MMM/2650, on my small backyard track, 2s (4000 25c) on 15/48 is perfect...temps are low, power is perfect, speed is perfect. But I fried an ESC and when I contacted Castle, they were concerned with me running 'only 2s'. so now I only run 4s, even on my little track and havn't had a problem since.

I just want a reliable setup for my son to practice with. Any suggestions on a low top speed setup?

[BrianG]

It's odd that CC said 2s was too low. I can understand if the user geared to the moon to compensate for the slow speed, but if geared "normal", there should be no problem. 2s or 3s on the 2650/MMM setup would be pretty good for a beginner. Then, as they get better, 4s would be an easy upgrade for more speed.

So, for a buggy, I'd get the 2650/MMM setup, 2s or 3s, and then gear for about 20-25mph. That should be a lower speed setup without having to gear down too low to limit speed, and also would reduce torque.

[eovnu87435ds]

mabye it was just me, but the last time I tried 2s with my mmm/2650 in my hyper 7, which is very similar to the raze, but it cogged alot. i'm not sure, but that MMM has since detonated. either way, 3s can be a good midpoint between slash and full speed racing. I used to run 4s for my qualifying races and then 3s for my mains. it opens alot of possibilities for you

So Brian, you'd say that the ESC smoking when I ran 2s was a fluke? It happened in the first 2 minutes run on a brand new esc. I ran plenty of 2s packs through a different esc after that, and never had a problem but I changed my habbits when I finally talked with (I forget his name) at CC. He didnt say it was an absolute NO but he said 'Why only 2s?, your pulling lots of amps that way'. So I went with 3s or 4s.

eovnu... I didn't experience cogging on 2s. I ran 8000 12c and 4000 25c 2s packs. When a bunch of us on my track would run 2s, it made for some really tight races, almost like a spec class.

Maybe Im a bit paranoid but rightfully so... I own 3 MMM's and have had 4 warranty claims. (well 3 through Castle and 1 from HPI). I have always tried to do the right thing, never abusing my stuff.

Thanks for the replies guys.

-Frank

[BrianG]

The "lots of amps on 2s" statement is not totally true. Amperage is dependant on a lot of factors; gearing, vehicle weight, voltage, motor size/kv, etc. So, let's say you have a typical buggy setup: ~8lbs, 2650 motor, MMM ESC, 4s lipo, geared 46/12 (geared ~40mph). That's a pretty common setup. If you reduce the voltage and leave everything else as-is, current will go down. Of course speed will go down too. That's just common sense. Maybe the CC rep thought you were geared higher while using 2s? Many people may make the mistake of using too low a voltage and then gear up too high to compensate. That can certainly pull a lot of current.