3v0

The students at the school have caught on that robotic (electronics+CS) can be fun. Now I would like to build support in the community.

For some time I have been thinking about building a free throw shooting robot to entertain during halftime at our local high school basketball games.

Most everything will need to be scratch built or scrounged/re-purposed. There is no budget to speak of other then my pocketbook at this point. We may get some small donations but have no plans to go begging. Our community is small and the merchants are too frequently asked to donate to school programs.

I see the project in two parts. First the mobile platform. Then the gizmo's to locate the robot and shoot the ball.

The school has fabrication tools to build the framework. welders, plasma torch, and a lathe. We even have a small CNC mill. We can design the frame and hand it off to the students/instructors to have it fabricated. Getting other departments involved will help make it a school wide project rather then one from my class.

If the platform is stable we can use common lead acid batteries for power. They are not my first choice but they are free. Need to figure out where to scrounge the drive motors. An H-Bridge to build.

To shoot the ball I am thinking of using an automotive air-shock connected to a small air filled tank.

This is a long term, possibly multi year project. I am quite open on most everything but the budget, and that the robot needs to shoot the ball. It would be nice if it could make the shot.

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HarveyH42

Hmmm... Sounds like an ambitious project. I'd get the physics class to do some math and see what you would need to shoot the ball. Don't remember how far the free throw line is from the basket, but the basket is 10 feet. You will need to go higher, least 6-8 inches just to clear the rim. The arc and velocity will depend on the height you will be launching from. Don't know the weight of the ball either. Does the shot style matter? We you use to play a little after school (25-30 years ago), mostly just messing around. There were several straight arm shots, that were surprisingly effective. Thinking some type of catapult.

Know you aren't asking about budget help, but you could sell endorsements (like the pro players), small signs or stickers from local businesses. I'd wait until you've made some progress, and have a clear design. The kids at school will of course keep their parents informed of the progress. Should be an interesting project, should spark a lot of talk in a small town. Endorsement should sell themselves, no need to beg. Just put out the word at the appropriate time, that you are considering it. No pressure on you to complete it. Not sure about the school's position on advertising though. Our school allowed it, but that was a long time ago, and a very small town, which depended on the local businesses to help out occasionally.

Have you search the web? I remember several ball shooting competitions in the past, nothing big like a basketball though. Should turn up some ideas for mechanisms, maybe some math help.

3v0

It is ambitious, especially on the cheap. Both help make the project interesting.

If there was a physics class I would be teaching it! I am more worried about repeatability then getting enough power out of an pneumatic system. If I have to I can put 100+ psi in a 20lb propane tank. One of the advantages of making the robot large. Balls weight about EDIT: 600 or 20 oz. For me style does not matter. Maybe it will to the basketball coach?

I may get some local help but the kids/school hit the locals up so frequently that I only plan to take was is offered without asking. The goal is to not spend a lot of anyone's money. It would be a lot faster to buy things like the H-Bridge and such we can make them for a lot less. Since we have not motors at this point thinking about the H-Bridge is getting ahead. It would be great to find an electric wheelchair. In the end we will use whatever can be made to work.

Monday we are scheduled to give a short presentation to the school board. Mostly the kids will talk about what they learned and demo their little Walter class robots. I may be able to talk to the board about the idea after the presentation.

A quick check of the web did not provide anything that was useful. One school started out to build a similar robot with a 6K budget, They ended up with one that launched T-shirts into the crowd. Did they wimp out? Do not know.

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Leftyretro

Very ambitious indeed. I would first work on a proof of concept of the ball launching subsystem. Pneumatic would certainly have plenty of power (air pressure PSI X area of diameter of ball in square inches) but capacity of tank Vs number of launches would need to be checked for practicality. Also how to activate the air pressure (it has to be large volume and quick acting solenoid valve or you have to figure out how to seal the ball in a tube against proper launching pressure and yet be able to release it quickly? Repeatablity would have to be tested before going on to a full scale Bot, as requlation of air pressure and friction of ball to launcher may be too variable to score any points at all I bet some kind of spring loaded mechanical launching system would be more practical. You could have a motor reset the launching spring for each shot.

Lefty

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Nigel Goodwin

Basically what you're looking at is a cannon - air power is commonly used for such designs - should be no problem repeatedly firing nice round, same size, same weight, balls accurately.

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3v0

This is all in the head scratching stage at this point. I am looking for the options which are the most do-able given the restraints. It will make sense to build a proof of concept for the ball launcher and other systems when I find designs that have a decent chance of working.

Unless I want the robot to resemble a small pickup truck I do not think the air cannon will work. The spring may be a workable idea. I was thinking about spinning a flywheel that would engage the throwing arm. ISounds too heavy and the gyroscopic effects would be horrid.

The air cylinder could still work but I have not done the math. The one problem I have seen so far is that most are not intended for fast action and have small lines running into them. But that could be fixed. There is this. http://www.drillspot.com/products/41...0_Air_Cylinder

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dknguyen

Does it have to be full-sized basketballs? I imagine the crowd would be just as pleased if the mini 8" balls were used. Would make things easier as you could use trebuchets or smaller air cannons and loading devices.

Personally, I like the trebuchet idea as it doesn't require a high-speed, high-torque motor- just a decent-torque motor to set it up. And whenever it pulls back, the "palm" could just be aligned with a bin with a hole at the bottom, on the side so a ball just rolls into it.

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Marks256

why not make something like this? Except re-engineer it to use basketballs instead. Also, it will have to shoot it in the air at the right angle and velocity.


EDIT:

Also, how do you get free lead acid batteries?

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Pommie

Try to get a look at a clay target launcher. They have a crank which drives a free spinning arm on the same shaft. The free arm has a strong spring from the end of it to a fixed point. Once the arm passes the point where arm, pivot and spring anchor are in line, it completes the following 180° without hindrance. This is difficult to describe in text. I could draw a little diagram if needed.

Mike.
Edit, I quickly drew it in Autocad.

3v0

Most of the stuff on the web is scaled down. Here are 3 of my favorites. The robotic arms are by far the most interesting. I do know how difficult motion of this sort is. Think of it as lust.

This is not powerfull enough but it show grace which is way cool. Perhaps hydraulic?
http://video.google.com/videoplay?do...48129910481180

This one is very close to what I was thinking about using an air cylinder, but is scaled down to about 1/2 size.
http://video.google.com/videoplay?do...43965815400900

Full size and does the job, but it mega overkill
http://onecityatatime.wordpress.com/...in-pittsburgh/

As much as I would love an arm I think the air cylinder is more within our reach.

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futz

Have a look in your local junkyard at windshield wiper motors. Dirt cheap, lots of power and all geared down already. Since you're using lead-acids, they'd be a good possibility. Worth a look anyway.

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Krumlink

You can get 12V18aH Lead Acid Batteries (the ones that we use in our robots) that pull up to 100 amps at times for about 25-35$

http://www.mkbattery.com/index.php

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Krumlink

The robotics team has used a launcher like this before with great results. It was on the 06 robot, and it could fire 20-45 balls per minute, and was configured so it could autonomously aim with the CMU camera.

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3v0

Replies to posts follows math blurb.

How much energy will it take to shoot the ball. To get the ball to go through the hoop it has to come in from the top. The hoop is at 10 feet. I need to know what the trajectory of a good free throw looks like. That would be angle and velocity. It seems the main goal is to find the velocity/energy needed to acomplish the trajectory. I think a measured number would be better then a computed one.

A quick look at the web shows that there is info on the subject. Some people even put an accelerometer in a bb but I did not see any data. I did find this about how to shoot a good free throw. The same page talks about spin which needs looking at.

Shooting a Free Throw

I started the thread by saying "I am quite open on most everything but the budget". I still am, but if possible I would like throw or toss the ball rather the shoot it out of a cannon, gun, or machine gun. If you take a look at the three videos from a few posts back I think you will see the human like motion of the arm equipped robots is much more fun to watch.

In then end we may end up building what we can rather then what would be nice or most appealing. So keep the ideas coming.

I would LIKE to use a full sized basketball. I have seen this sort of machine on either junkyard wars or mythbusters (maybe both). If we were shooting golf or tennis balls it would be a good choice.

This sounds like a possibility.

Futz: I love using old car parts but I do not think a wiper motor wold have the torque to toss the ball. It would work if it was used to spin up a flywheel.

This is pipe dreaming but it is what sounds good this morning. Build a two wheeled balancing robot. To the unit with a vertical air cylinder and ball holder. To shoot the ball the robot has to lean over at the correct angle for the distance from the hoop. Crazy but fun and I am sure it would get attention.

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Krumlink

Why not use a ball launcher that you make? Just have a top wheel and a bottom bike wheel or something and have the bottom one with a big motor on it. I can maybe get you some stuff, gotta ask robotic's team (motors, wheels, etc)

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