t4mania said:
I'm a little confused about this rollout thing. Say I wanted to find my rollout then I need to know my pinion size which I'm not sure which to use. If I want to find my pinion size I need my rollout which I don't know either. Do guys know the rollout automatically by the size of the track or what.
Hit or Miss... and or experience and knowledge of what a motor can do..
I can tell you I was a LOT BETTER with it in the old days...because I knew MORE of what a BRUSHED MOTOR did - (winds & voltage)
The BRUSHLESS ESC and MOTOR deal changed a lot of that - because now every Motor / Esc combo will be different...sometimes HUGELY different in rollout.
Things I personally look for
Pretty precise TRACK SIZE
Estimated Lap Time
Tire Diameter
so say a 165 ft track
est. lap 4.80 sec
= 34.375 ft. per second (this would be 23.43 MPH)
so using a 2.12" (diam.) tire (which would be .555 ft ) the tire would spin approx 61.94 times per second (or 3716.4 RPM's at the axle)
If you know your motor will spin a certain RPM under load at a given voltage - you can set your ratio from there.
say a 17.5 = 2200 Kv (RPM Per Volt) Unloaded, but loses 40% of it's RPM under load....
at say 3.7 volts you could be looking at about 4900 loaded motor RPMs
4900 (motor RPM's) / 3700 (axle RPM's) would be approx a 1.32 RPM Ratio
Say I'm running a 88 tooth Spur Gear...I'd be looking at a 66 - 67 tooth pinion just using basic crude numbers. *88/66 = 1.333 88/67 = 1.313
I believe if you run the ROLL OUT formula that comes to a 4.995 roll out.
Pinion (66) / Spur (88) * Tire Diam (2.12) * Pi (3.1416)