XRAY - Model racing cars

The webside contains a lot of info.
Some digging brings almost all answers

For the diif you find some info.

But for gearing I've built a excel spreadsheet to determine roll-out. And the right pinion / spur combination is so specific that there is no general model for it.

Greetings,

Joep

This is probably a stupid question, but then they all are if you dont know the answer - is there a specific rollout figure for each make of tyre - or is it calculated some other way. I've heard rollout mentioned a lot but never really fully understood what it does or how you calculate for diferent tracks to get your gear ratio.
Many Thanks
Phil.

I never heard of stupid questions. Learning is done by asking and making mistakes. I'm still doing that.

The definition of roll-out is:
The amount of mm the car travels per revolution of the motor.
The formula to calculate roll-out is:
(tire diam. in mm) * pi * (# tooth pinion) / (# tooth spur) * (# tooth pulley duff) / (# tooth pulley central layshaft)

And (# tooth diff) / (# tooth central layshaft) = also called 'internal gear ratio'
For the FK'04 it is 1.77
And for the FK'05 it is 1.7

Ok example:

Tire 64 mm
pi = 3.1416
pinion = 25
spur = 84
car = fk'05

roll-out
= 64*3.1416*25/84*1.7
= 35.2 mm / motor rev

Now practical:
- motor too hot-> lower roll-out
- Good batteries to quickly empty -> lower roll-out
- motor does not reach max rev's before half of the straight -> lower roll out
And of course everything the other way around also applies.

I always calculate with 64 for rubber tires. But in theory every brand has a deviation....

I hope this helped a little.

Gr. Joep

lol hey us honda/ rc fanatics use mm a lot lol!