Free throw robot.

How about something using a crossbow mechanism. Take an old car tire cut it to the size needed to fit the ball and make the tubing large enough. Now it's just a matter of angle and pull strength.
You could shoot it from one side of the court to the other if you wanted.

I found the numbers.

Previous aerodynamic analysis has shown that the optimal release angle is in the range of 51 to 56 deg, and velocity is in the range of 20.5 to 25 ft/sec. Biomechanical analysis has shown the importance of bent elbows and knees, and a snap of the wrist at the moment of release. This imparts the spin and consequent Magnus force that adds lift to the trajectory, increasing the range and the angle of entry.

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Krumlink said:

What other ways could you do it?

Flywheel
Pneumatic Cylinders to shoot it
Catapult/Trebuchet
...

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Air Cannon.
Coil Spring. think human cannon ball.

A Catapult/Trebuchet is to bulky. A crossbow/slingshot would be smaller but not easy. Imagine what a beast the robot would be with each method.

Based on what your link is showing when the ball is raised a human back is doing a pivot of the trunk then the ball is is flipped by the hand and the arm. what if you were able to use a leaf spring from an old truck and flip it like a plastic spoon. You would need a pivoting hand acting as a wrist about 8" from the top. ?

killivolt said:

Based on what your link is showing when the ball is raised a human back is doing a pivot of the trunk then the ball is is flipped by the hand and the arm. what if you were able to use a leaf spring from an old truck and flip it like a plastic spoon. You would need a pivoting hand acting as a wrist about 8" from the top. ?

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Sounds both possible and inexpensive. A small electric winch to reset the spring. Maybe a strain gauge to determine when to stop the winch.

What you want to do is have a have a short cylinder, slightly greater in diameter than the basketball, to rifle (roughly speaking) the ball. To power the ball, place it in a mounting that compresses a spring. The mounting will be compressed into the spring with a cam/latch. As the cam rotates, it compresses the mounting, until such a point that the cam-latch slips from the mounting, thus releasing the mounting/ball. The cam could also have a release point to set the loading of the next ball.

Spring suggestions:
- other inflated balls
- surgical tubing (using elasticity as oppose to compressed springs)
- mattress springs

Krumlink said:

A catapult/Trebuchet would be dangerous, since it would require a spring/stretchy to pull back and fire it, besides it would be more prone to breaking.

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Actually, it shouldn't be too hard to design one, using not much more than a counterweight for propulsion. Some sort of jack mechanism(maybe just a stepper and linear screw for up and down?) could cock it, and an adequate solenoid could release it.I can envision some sort of stepper motor setup in order to move the counterweight closer, or further away from the fulcrum, thereby giving you a measure of velocity control. It could even automatically move the counterweight, so that each time it needed "cocked", it would be very light on your "cocker", and just have the stepper return the counterweight back to where it needs to be, in order to make the shot. Quite repeatable, I would imagine. Now that I've thought about it a little more, I believe you could probably transition(after each shot) the balance point of the counterweight to the other side of the fulcrum briefly, thereby doing away with a separate "cocking" mechanism altogether.

Krumlink, wiki the difference between a catapult and a trebuchet. Catapults used elastic materials. Trebuchets used counterweights and were "more advanced". One of the things they did better was they could fire much heavier louds because they weren't limited by elastic materials. If you watch the Return of the King, you can see the defending humans used trebuchets and the attacking orcs used catapults.

A trebuchet is also very repeatable because the energy applied to the projectile is always exactly the same Potential energy =mgh

Thanks for the ideas.

I floated the idea of the free throw robot to teachers in various departments today. So far I have buy in from ag, votech, and the principal. We will be getting a science teacher who is said to be "scientific". He should be interested too.

The plan is to have students from each area collaborate on the design and construction of the robot. The students in the ag shop are very good at metal fab and will build the frame and related parts. The people in it votech can fabricate parts. Together they can work on the launcher, be it springs, pneumatic, hydraulic or whatever. My class will do the electronics and programming with some help from the science teacher and his students, who at the very least, will keep us honest.

I will present all your ideas to the students.

Thanks.