brushless xxxt and gearing
 

Thanks mike for your help with this setup. I took it out last night and it flew, even on cheap six cell 3300 nimh stick pack and had excellent run time. The amount of dust it threw when I got it do doughnuts was v. cool.

Anyway the point of the post was to ask about knowing what the right gearing would be.

I am running 17/88 at present and at the end of the run the 4200 was warm (could leave my finger on for good 5 secs). I was pulling 37 amp peak using my 'watts up meter'

Whilst I am running 6 cells, I will mainly be using 7 cells (GP 3300), so will I need to go up or down in pinion size?

Is using a temp gun a good way of checking the right gearing?

I run 19/86 and that seems pretty good, I actually ran in 95 degree weather, and real hard off-road and it seemed to handle it fine. I've heard people go as high as 21/86.

The weird part about brushless is gearing up sometimes causes less heat. If you can pass the 5 second test and are happy with the speed, then you could stay there.

I also found 19/86 to be a good place with the xl4200 and MGM 12012 in my XXX-T MF.

thanks fo the comments Re~mix and Batfish.

I'll watch the 5 sec test and see how it holds for a full discharge and change as necessary. Good to know other possibilities though. :D

I noticed that you ran 88, which is fine too. I run 86 because I bought the kevlar spurs and thats all they had, and 88 tends to rub against the rpm gear cover.

Myself, I ran 86 because that's the stock spur on the XXX-T MF and I have a full range of pinions so I had no specific need to get more spurs.

Either way, you're sure to be happy with how it performs with the setup you're running (sounds like you already are), and you could easily gear up or down a couple teeth as long as you keep a good eye on temps.
You should consider a cheap infra-red temp gauge. I use the Duratrax Flashpoint (I think that's what it's called). If Mike can get that (or a similar IR gauge) for you, I'm sure it would be less than $30. They're very easy and quick to use and provide temp readings within a couple degrees of actual temp. Just point at what you want to measure, press the button, and see the temp.

I looked at the losi site and the rtr ver (what I have) has a different gearing to the kit. The internal ratio is different as well as the spur gear (kit - 86t, rtr 88t).

@ batfish. I will certainly consider a temp gauge espec when running 7 cells soon. what should the temps be for the basic 4200?

Someone can correct me if I'm off, but a good rule of thumb for motor temps is to keep them below 180F all the time. A good, safe running temp is 150F or below. The magnets in the motors start breaking down at 220F, from what I've heard here.

I personally strive to keep the temp of the motor below 150F and the temp of the speed controller below 140F for the entire run. This generally means that I gear for running at a track (max speed of 30ish MPH) instead of speed runs or 'extreme' bashing. This usually means more conservative gearing and temps when compared to someone trying to push their vehicle closer to the sound barrier :)