6, 7 or 8 cell battery packs?

[Philistine]

I've a couple basic questions about batteries. What is the advantage of more cells? Is it more run time or more more power to turn the wheels? Is there that much of an advantage going from 6 cells to 7 or 8 cells? What do you recommend?

 

[Badd]

I've a couple basic questions about batteries. What is the advantage of more cells? Is it more run time or more more power to turn the wheels? What do you recommend? Is there that much of an advantage going from 6 cells to 7 or 8 cells?

If you volt up , you can gear down , more wheel speed with more power . But like with any setup you will need to test gearing to get it right. Most people that are running Ni-Nh are running 7 or 8 cells . There is even poeple running 4 cell Lipos .

 

[Philistine]

So if I understand you, by uping the cell count I can go to a higher gear ratio (more torque) with higher wheel speed?

 

[chrisjlittle]

More cells gives you higher voltage which gives you more speed, not more runtime. Technically speaking, more voltage is more "power" (more watts at full throttle) but not necessarily more torque. Speed controls work by varying the amount of voltage to the motor, but a higher voltage pack will not supply more amperage to the motor unless your old pack was underrated and not able supply the needed amperage, which is unlikely. A battery can be wired to supply longer runtimes, but I've never seen anyone do this in a crawler, and the extra weight of the needed number of cells (at least 12 nimh/nicad or 4 lipo) would be outweigh the advantage of the extra runtime, imho. The main advantage of having higher voltage is that you can gear down more (giving the motor a greater mechanical advantage over the tires, giving you more torque) while still retaining your wheelspeed. Yes it is worth it. The only ways to make a motor make more torque at a given RPM is to alter the motor design, such as heavier brush springs, better armature or magnets or switching to brushless.

 

[Philistine]

Thanks chrisjlittle! That helps alot. I'm not intrested in modding the motor, but I'm intrested in "gearing down". Is that related to the spur and pinion gear? If so how is it related?

 

[chrisjlittle]

Thanks chrisjlittle! That helps alot. I'm not intrested in modding the motor, but I'm intrested in "gearing down". Is that related to the spur and pinion gear? If so how is it related?

"gearing down" is reducing the gear ratio to a lower (numerically higher) gear ratio. Either a larger spur, a smaller pinion or both. It really works the same way as a prybar, use a longer one and you can move more weight. See mechanical work in wikipedia, that article defines the whole concept better than I can in my current sleep deprived state.