E-maxx w/ Feigao 540C 8XL pinion selection

[gizzmo79]

I wonder if i run with 8xl on 4s lipo and gear it with 51/16 will that be okey?

[mickeymoose]

Hi guy's, I don't have an E-Maxx but I have built a custom brushless lst2 that uses a quark 125b, Feigao 8XL, E-MAXX tranny with 2nd gear only, Proliine 40 series Ground Hawgs 6.5" dia, and the LST2 diff ratio is 3.30:1, I am currently running a 20t pinion and 64t spur. with 12 GP3300 batts top speed was only about 28mph. The batteries only lasted about 8-9 minutes and at the end of the run temperature's were, esc 115, motor temps were getting into mid to upper 140's, and the batteries low160's. I just got some maxamps 6000mah Lipo's ( 2ea. 7.4v packs in series ) and the truck is sick. it has so much torque it's hard to keep from flipping it over, run times are about 25 minutes and top speeds are about 35mph or so. It's alot of fun now that I've gone lipo. the motor temps are also down to 135-140, the batteries are only 100, and the esc is still 115-120. I know this is a little long winded but I hope it helps. Oh yeah you might want to ask Mike, or some of the other more experienced guy's here what they think about possibly going with a L size motor instead of an XL. The XL has a ton of torque, might be to much for an E-Maxx?

[refusalspam]

I know this is almost a year later, but I wanted to give an update.
I did get the Feigao 8XL (C, finned can) and the BK 9920 from RC-Monster. I'm running it with 16 cells nimh cells now. I got some cheap batteries from all-battery and I goofed up the soldering job on them (needed a more powerful iron). Nonetheless, the batteries still keep a good charge. I do get a bit of cogging at slow speeds and braking seems to be very weak. I'm not sure if its because of the controller or the batteries. I am using a separate receiver pack (disabled the BEC) and I've programmed the controller as best as I could using the stock radio.

In response to mickeymoose, I think you should make your motor selection based on what batteries you plan to be using (or choose your batt. based on the motor you want to use). In general, its better to compare motors by seeing how much power they can consume (wattage) and calculating whether your batts and esc can deliver it. For example my 8xl can use up to 83 amps so 83 amps * 16 cells * 1.2volts/cell = 1,593.6 watts. You also want to make sure that your motor doesn't spin faster that it is spec'd for. Again, my 8xl has a ~2000 kv rating with a max rpm of 40k so my batteries shouldn't deliver more than 20 volts. L motors tend to have higher kv ratings so you won't be able to use as many cells before you hit the rpm limit. You can get around this by using a higher turn motor, but this has a side effect of lowering the max amp draw. Once you calculate it out, you'll see that the L motors are just not as powerful as the XL's.

One more thing to consider is that higher voltage & lower amp is generally more efficient than lower voltage higher amp (for the same wattage). So if you have a choice between one or the other you should opt for the higher voltage system.

If you feel that the XL's are too torquey then you might need a taller gear ratio.