I am new to gearboxes and gear ratios. I need some help understanding the Vex versaplanetary gear kit information. For example, if I look at the Versaplanetary gear kit ratio identification guide for the VP 5:1 gear kit (217-2819) I find the following info. There is a 18 tooth sun gear driving four 27 tooth planet gears. The planet gears fit into a 72 tooth ring gear. Thus, the gear ratio would be (72/27) * (27/18) = 2.666 * 1.5 = 4.0 but this is listed as a 5:1 gear kit. I see that the planet gears are on a plate with a 28 tooth input and the sun gear is attached to a 28 tooth output gear. Does this matter?
Following the same approach, I calculate a gear ratio of 3 for the VP 4:1 gear kit and a gear ratio of 9 for the VP 10:1 gear kit. Each gear ratio seems to be one less than the stated value.
What am I missing? Do I have something inverted?
Any guidance for a novice would be greatly appreciated.
I am definitely