ChrisP

iTrader: (11)

Wouldn't you normally use a longer rollout with a P2K and a shorter rollout with an MHS?

I thought it was generally true that the P2k is a torque motor, giving it the power to turn taller gears vs the MHS which is an rpm motor, which would need shorter gearing to have acceleration?

Geppetto

iTrader: (35)

You're right! Excellent point! The characteristics of the motor must be taken into account when selecting which pinion to select, however, the formula for determining rollout remains the same.

I've raced the MVP and the Monster motors, and with a given rollout, the pinion choices are very different.

The good thing is that there only seems to be two characteristics... High Torque or High RPM. Gear accordingly!

ChrisP

iTrader: (11)

There's normally only one or the other...but looking at the dyno numbers on a P2K2pro at the LHS last night their numbers were crazy!!

Seemed to be producing as much or MORE torque than my Fantom 410 (P2K) as well as turning 2,500 RPMs MORE????? P2K torque with MHS revs????? That sounds dangerous...but fast

I was goign to pick one up to try....but then reconsidered as I've recently geared my P2K DOWN to try and limit some of my top end and force me to drive within my limits...(12th scale beginner with a car that's WAY too fast....C/D-main driving with a car that has A-main speed)

safaridog

iTrader: (1)

oppss your right, i got mixed up

scootr117

Knowing the formula is one thing, but how does a person who is new to a track decide which way to go? I missed the gear at cleveland this year and got walked away from...(still had fun though)....I suppose if the length of a track or part of a track is known you could gauge off that or is based on motor temp? How do you determine if your gonna run a 1.7 or 1.8 rollout??

Gitsum

iTrader: (1)

Just send it in the corner turn and send it again....lol

ChrisP

iTrader: (11)

Wow.....brought back from over 4 yrs ago..

Unfortunately, Scootr, I don't know if there's an easy answer, since the rollout you can get away with running is going to depend on the characteristics of your motor, batteries, track layout and driving style, etc...

Basically, pick a starting point and go by performance....do you have enough acceleration out of the corners, are you topping out too early on the straights?

Keeping in mind that the smoother you drive, the taller you'll be able to gear as you carry more corner speed so already have a jump on the acceleration...the other cars may not be that much faster than you...but they have a head start since they're carrying more speed into that given section...

scootr117

Thanks.....I guess that it would be dependent on driving style... I need to work on the corner speed with 1/12...it is way different than 2wd offroad and 4wd touring...which was my normal classes before this winter. I need to get the nerve up that it is going to stick at a higher speed in the corners.........

Tron 101

iTrader: (23)

I have been learning on rollout for touring and now I read up on 12 scale .
What I learned from touring is that depending on the motor I want a rollout between 0.91-1.1.
BUT with the 12 scales Im seeing you guys talking rollouts of 1.6 and even higher.
What am I missing.? Is there a diff between touring and 12? I know there is no internal gear ratio, so in 12 scale should I be gearing higher?
Before I learned to do the equation for rollout I was running a 100-116 spur with a 25T pinion, 64P, and my temps were great and just where I wanted them, but after doing the rollout I found out that my rollout was over the 0.90 and even over the 1.1-1.2 range?
WHAT GIVES???????

Trips

iTrader: (16)

The differences in rollout are due to the 1/12 cars much lighter weight and 4 cells versus 6 cells.

In the touring car you're trying to move a much heavier car... With gearing as tall as a 1/12 scale car, the motor wouldn't have the torque to get up to speed (unless you were on some ridiculously long track, or a banked oval)

Also the extra cells in the touring car will push more current through the motor... given the extra weight of the touring car and the drag in the drivetrain, you'd fry the motor in one run or so.

Trips

iTrader: (16)

I think I posted this a long time ago, but here it is again... If you have a Texas Instruments programmable calculator, here's a program for rollout that might come in handy... It can calculate your rollout, or if know what rollout you want it can calculate what pinion you should choose to get there. You'll need to know the final drive ratio of your particular car, (for a 1/12 pan car, it's 1.0) Here it is:

()
Prgm
ClrIO
Lbl rm
Disp "1-Rollout"
Disp "2-Pinion"
Disp "0-End"
Input m
If m=1 Then
Goto r1
ElseIf m=2 Then
Goto r2
EndIf
Goto r3
Lbl r1
ClrIO
Input "Spur",s
Input "Pinion",p
Input "Tire Size",d
Input "Final Drive",f
Disp d*¶/(s/p)/f
Goto rm
Lbl r2
ClrIO
Input "Rollout",r
Input "Tire Size",d
Input "Spur",s
Input "Final Drive",f
Disp s*r*f/(d*¶)
Goto rm
Lbl r3
ClrIO
EndPrgm

James35

iTrader: (1)

For pan cars, there is a very easy way to calculate rollout without needing to write anything down, or starting/stopping with the calculator. You can do this formula all in one shot on a calculator.

Diameter x pi x pinion / spur