SnapRoll92

I Am About To Get A Stampede XL-5 Finally But What Is The The Biggest NiMh Pack I Can Put In It. Thinking Of Buying From www.cheapbatterypacks.com

gulio

iTrader: (32)

Any sub C size will fit (be a tight fit) and are avasilable up to about 4600 mah now.

SnapRoll92

I Bought An 8 Cell 4500 mAh Battery Off Ebay, Says It's 25 mph Faster Than Normal 6 Cell.

gulio

iTrader: (32)

sounds like a winner, make sure you gear it down because increasing the voltage in a sense "gears it up" .

SnapRoll92

Ok, ya uh.. how do i gear it down??? i feel stupid for askin but im kinda new to rc cars and trucks, used to planes.

jimmythebarrel

iTrader: (6)

Ok, heres the long explanation.

Ok, the gear ratio is the number of turns the motor has to take for one rotation of the tires. The lower the ratio, the more acceleration and the less top speed you have. The higher the ratio is opposite.

The equation is I(S/P)=R. Where I is the internal ratio for the transmission, the Pede has a 2.72 (you can find that info in your owners manual most times). S is the number of teeth on the spur gear, and P is the number of teeth on the pinion gear.

A stock Pede has a 2.72 internal ratio, an 86 tooth spur, and a 19 tooth pinion.

So the formula is 2.72(86/19). 86 divided by 19 is 4.52, and multiply that by 2.72. Which works out to 12.3.(all rounded off to make it easy) So your motor turns 12.3 times for every time the tire rotates. Or a 12.3:1 ratio.

Now, to change gear ratio, you adjust the pinion and spur gear size. A smaller pinion or a larger spur will produce lower gear ratios. A larger pinion or smaller spur will produce higher ratios. BTW, the pinion is the gear thats mounted directly on the motor shaft, the spur is the gear the pinion meshes with.

In general, a lower ratio produces faster acceleration and longer run times. Its also easier on the motor since it doesn't work as hard. A higher (or taller) gear ratio produces higher top speeds, but puts more strain on the motor and shortens run time.

What gulio was saying about increased voltage refers to the fact that more volts to the motor make it work faster. Not sure exactly how much, but it in a sense changes your ratio to taller gears. So if you don't "gear it down" you can put some serious strain on your motor and drivetrain. Especially with plastic gears.

If you figure an 8 cell produces a third more power to the motor, then gear up by a third, or figure maybe a 16:1 ratio (this is purely guess work, but close enough). Great for top speed, but some strain on the engine. And probly some heat issues.

Anyway, long winded, but hope it helps.

jimmythebarrel

iTrader: (6)

Oh, and the gear up by a third thing, thats not acually whats happening. Your ratio is still 12.3:1. Its just to show how much harder your motor is working to get an idea of whats going on. And like I said, its mainly a guess.

gulio

iTrader: (32)

My guess is to install a pinion with about 3-4 less teeth than stock.

jimmythebarrel

iTrader: (6)

Bah, I screwed that up, my bad. LARGER pinion and SMALLER spur will produce lower gear ratios. SMALLER pinion and LARGER spur will produce higher.

So get a pinion with a few more teeth. Of what I would acually do is buy a steel spur gear, maybe a 83t gear. It would stand up better to higher speeds.

Of course, you dont have to change anything if you dont want. And spur and pinions are cheap, so its not hard to play around with ratios. I bought a Robinson racing Pinion pack with 6 different pinions for like 15 bucks, and spurs are like 5 bucks. And thats steel.

AND MAKE SURE YOU CHECK THE PITCH OF THE GEARS! Thats the angle of the teeth. They have to match. Pedes use 48 pitch gears.

If in doubt, go to your local hobby shop and talk to them. I find that is they are worth a damn, they are more than willing to help you out.