MM5700 in Losi XXX-T

I'm running a MM 5700 in my Losi XXX-t and have it geared 20-pinion and 86-spur.

Does this sound right ? I see some guys saying around 14-15 for the pinion and 86 for the spur (this is probably for buggy's but would it also be for trucks ?). Wouldn't this slow down the car (If 'im correct when you gear down the ratio goes down meaning a higher number).

I also see messages about BEC/UBEC !!!??? Is this something I need on top of the MM ESC and Motor ?

Thanks

[BrianG]

Can't answer your gearing question as I'm not familiar with that vehicle, but whether you need a UBEC or not is determined by the main battery pack voltage. If you are running over 8 cells or 3s lipo, get a UBEC.

And in case you don't know; a BEC is basically justy a votlage regulator which converts the main batter pack voltage to 5 or 6v for your receiver and servos. The BEC in most ESCs are linear, and will heat up a lot if using higher cell counts. The UBEC is a swithincg device so it runs much cooler and more efficienty.

Forgot to mention it : I run the truck with Team Orion's Platinum lipo's 4800 (which are 4 cells 2S2P). Which means they are considered 2 cells not ?

So I do not need a BEC/UBEC ?

[jollyjumper]

i'd use a 18T pinion.
and no need for ubec on 2s lipo.

Thanks jollyjumper, so using an 18T on a 86 spur wouldn't that limit the top speed ?

Is see you're also from Belgium. I race in Arendonk, maybe you know the track.

If you do know it would 18T get me up to top speed at the main straight ?

BTW, were do you race ?

[glassdoctor]

You have to try it and see... the speed may or may not actually go down. That depends on whether the motor is revving all the way out with the 20. Sometimes speed actually increases if you drop a tooth or two.

I think I was running a 19t in my T4.... not sure how the gear ratios of the trucks compare. I'm sure you are close at 20 but you should try going down 1 or 2 teeth and see what it's like. Gears are only $3 and take 60 seconds to change. ;)

For what it's worth, imo the MM can handle overgearing a little. I run my 4600 with a 24t pinion in my buggy.

Thanks glassdoctor,

I was reading through the Mamba Max Tuning Guide today (didn't notice it before :dft001: ) which basically says not to approach the gearing the same way you would do with a brushed motor. Wtih a brushed motor you have to combine torque with speed. A brushless only needs to be approached in terms of the time it takes to get to full speed. So this indeed implies to use a tooth or two less like you and jollyjumper say.

[jollyjumper]

how long is the back stretch on arendonck?

I think its about 20 meters following is a 180° high turn. There's a small tripple, a big double and a washboard (i think this is what its called) and lots of turns. Its rather technical, so not just speed minded.

[jollyjumper]

that is short, you will have to see if you can even use all the speed the 5700carries.

[glassdoctor]

Sounds like a small track... i doubt a tall gear or super top end is really what you want. If you can find a sweet spot where the temps are the lowest on motor and esc that's what you want.

There will be plenty of speed all the way around if you ifnd it's "happy" gear. :)

Your truck should be crazy fast fro racing with this setup.. my T4 looks like the fastest truck on the track with 6 cells... and your running lipos hee hee.

[Mr.lst]

a 5700 in a xxxt is going to be to strong! You will be doing doughnuts all day. I have one in my rustler and that is all it is worth and that is with everything turned down. Good luck.

I am running a MM5700 in my XXX-T. With my 3s lipo I like to gear it at 15/86 and when running my 6 cell IB4200 pack I like to gear it 17/86. This gearing keeps my motor temps down around 180 degrees. I am sure that I will have to make some changes once summer gets here and things warm up. Just take a stab at the gearing and then check your motor/esc temps until you find your sweet spot. Good luck!

[Mr.lst]

do you have issues with doughnuts though?

Yes I do spin out quite often if I don't have the punch control turned way up and my throttle curve adjusted. Even then I still have to be gentle with the throttle. I mostly only run my XXX-T in the street outside my house. When I get out to bash in dirt I prefer my E-Maxx. I normally run one pack through the Losi and two or three sets through the Maxx.