Throwing Problems/Motors

[EricH]

Originally Posted by stretch851

So besides changing the pulley ratio, how much would the numbers change if we changed our gearbox ratio to 5:95? I'm sorry but I couldn't follow how you produced all your calculations.

5:95 is 1:19 gearbox, which is an overdrive gearbox (increase speed, decrease torque) and will not help anything.

I think you meant to say 95:5, or 19:1.

Let's walk through the math (I'll try to keep it simple).

You have 8.45:1 and 1:1 ratios. These combine by multiplication to a 8.45:1 overall ratio. Note that a 1:1 ratio just means that you're moving the same power to a different place (ignoring efficiency losses). Take the CIM free speed (without load), and divide that by the ratio (8.45) to get the current theoretical RPM of the shooter. (Torque gets multiplied by the same ratio.) Using circle math, you can compute a linear speed for the tip, as well as force on the arm (and ball, by Newton's First Law) and the torque applied.

But, we know that an 8.45:1 reduction just isn't enough. What BBray suggested was to change the 1:1 reduction to a 3:1 or a 5:1, something like that. Using a 3:1 reduction (3x the teeth on the pulleys where the arm flips) results in (8.45*3): (1*1), or 25.35:1. Run through the numbers again for that reduction.

I'm sure someone can go more in depth at another time with gearing theory, but this should get you started.

[chigskonkwo]

Our team also had our catapult shooter powered by motors and it seemed to be powerful enough, but with the ball it didn't have enough power to get it high or far enough. The team decided to change the entire design to pneumatics (with one week left ) but got everything on and working in 3 days, and it works great , better than the motors.