Lipo 11.1v ???

[whiteman]

I noticed on Traxxas website, they advertise if you have 11.1v 4000mah, the rustler would go 50mph, and if you have 11.1v 8000mah, it can hit 70mph. Why would the different in Mah would increase the speed when it is the same voltage?

Thanks for taking the time to answer this

[ElectricThunder]

More current means more torque (higher capacity packs at the same discharge rate mean more current). More torque means a higher gearing (larger pinion or smaller spur) can be used.

Another benefit to a higher Mah pack is that it may very well hold its voltage better than the lesser capacity pack (in the case that you have, say, a 5000mah pack and a 10000mah pack; both rated at 20C).

In my little example, the 5000mah pack is putting out 100 amps at 20C, while the 10000mah pack is putting out 100 amps at 10C. The 10000mah pack will hold its voltage better because it does not have to have as much voltage sag to discharge the demanded current, and the pack is WELL within its current rating limits.

That help?

[SS Pede]

I'm familiar with C ratings but I'm surprised that Traxxas predicts a 20 mph difference between the two packs. Sure one of them is rated for twice the continuous current, but that doesn't mean all that current will be used. I guess the higher-capacity cells will support the current better so they remain at higher voltage, which means more speed. But 20 mph? Yikes. I guess if you gear up to take advantage of the higher current rating...

[vashon10]

This chart doesn't show 20mph difference, it looks more like 5mph.

http://www.traxxas.com/products/electric/rustler3708/images/rustler_speed_chart.jpg

Do you have a link to what you saw ?

My mamba stampede can do 39-40mph with 7.2V 6 cell 3600mah, so it would seem strange for 50% more voltage would only get 10mph more in rough numbers with a rustler velineon.

[rccardude04]

The reason is that they changed the pinion for the 8000mAh battery speed run. The box even tells you this.
If you ran the larger pinion on the 4000, you'd have a very hot, possibly nuclear battery. The 8000 will handle the excessive current much better than the 4000 pack and, yes, hold its voltage better. But it also just simply won't destroy the pack like it would the 4000.
-Eric