Quote:
Originally Posted by stretch851
Yes our pivot is three foot off the ground. our arm is curved so that it's height/length(frame to pivot, dy) is about two feet. Oh what does the 1:1 ratio do? We figured a 1:1 ratio was good.
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You are already running a net reduction of 8.45:1, from CIMs to arm, which is lacking torque needed to throw the ball reasonably.
If you changed one of the pulleys in the setup by factor of 2 (doubling the highest pulley, or halving the lowest pulley, you will change the ratio to a 16.90:1, halving the "top speed" but doubling the torque. You are never making it to the mathematical top speed anyways, because the arm is unable to accelerate to that number in the 120 degrees.
What you want to do is optimize the ratio of top speed to torque; having enough torque to reach the top speed, while having enough speed to throw the ball effectively.
Let's get into the math: You want to shoot for roughly the 4000RPM range on the CIM side of the gearbox. With your current setup, that would (in physics land) get the arm moving at 475rpm, with the tip of the arm (2' long) moving at 100 feet per second. Now obviously that would never happen and is basically completely impossible. Now the ball is not at the arm tip but is probably about 18 inches from the fulcrum (let's assume this). I don't know what speeds you were looking for, but the 15-20 feet per second range would definitely make it a competitive shooter (depending on the launch angle).
To achieve this speed on the arm, you will likely want to adjust the ratio on your pulleys from 1:1 to between 3:1 and 5:1. Of course I am working from a mathematics perspective so it may be best to buy 2 or 3 different ratios worth of pulleys and swap them in and out to get the best ratio.