Shooting a ball over a wall

[bloody-orc]

Hi there.
My objective is to build a bot capable of collecting and shooting a ball over a 10cm high wall at a distance of 5-150cm. Balls are squash balls (44mm in diameter) and made from rubbery material (painted blue). As this is a competition the shooting of the balls must be as fast as possible.

So what have i come up with so far:
My first idea wast to use 2 rollers spinning fast and when the ball gets betwean them, the ball gets shot out and pow over the wall it goes... but after some tests i figured, that i need a quite powerful motor to do that (my toy motors just chunked when the ball got betwean the rolers and this even with pretty high gearing). so this idea is roled out for a wile (until i get a better motor).

Second idea was to use an air cannon. oh well it has the power, it's fast etc but it's quite hard to make. well you can make a one shot cannon easily, but to make a cannon capable of shooting 20 balls in 90 seconds and this for at least 3 rounds is a bit tricky. as my cobuilder is working on that i don't know how this thing is oging to work exactly.

Third idea was to use a manioulator (or a grabber or an endefector) to grab the balls, move to the wall and just drop them over. But as you all guest it may be 100% eficient but it's damn slow...

So is there any other ways? i'm open for all ideas.

PS This is for a bot and must be autonomus. and the size is 30x30cm

 

[dknguyen]

I think the rollers is a good one if you can get it to work. Dropping is easy, but then you require a really fast bot. ANd pneumatic...that's just hard and it may exceed your weight limit and working with compressed gas is not as safe.

I am not entirely sure how the spinner things grip onto the ball and gain speed before it goes flying, but you probably need to get stronger motors (that aren't geared down so much) since speed of the rotors is what sends the ball flying farther. Maybe one of the motors here...
https://www.superdroidrobots.com/
Maybe a spring powered catapult wound up by a linear actuator or something. Or a trebuchet.

 

[HarveyH42]

The rollers could work, but you need a larger diameter like tires or wheels. Look at a baseball pitching machine. The trick is to adjust the rollers so that it just has enough grip to grab the ball. The rollers should be soft or atleast spring loaded. It's not neccesary to sqeaze the ball flat, that just strains the motor

 

[bloody-orc]

i had like 5cmrubber lego wheels for the rollers but it seems that i squeezed it a bit too much yes... must find a way to adljst that squeeze...

 

[akg]

which is more important , ball speed or ball rate ?
what about a centrifugal type configuration ?

 

[Pommie]

Try to find a diagram of how a clay pigeon launcher works. It's a fairly simple device and will launch balls continually from a hopper.

I'll try and describe it.
There is a motor which drives an arm with a lug on the end of the arm.
There is a second arm on the motor shaft that is free to rotate and gets driven round by the lug on the first arm.
These two arms are in a horizontal plane with the motor below them and the motor is turning clockwise as you look down on it.
There is a spring from the second arm to a fixed point to the right of the 3 O'clock position.
The motor drives the second arm around until it reaches 9 O'clock at which point the spring takes over and it flies rapidly through 12 O'clock and to 3 O'clock. It is this rapid movement that launches the projectile.

HTH

Mike.

 

[Pommie]

I've tried to draw it.

Mike.

 

[bloody-orc]

pommi great idea but it's hard to get a ball on that (robot must do it itself) and it also requires reloading (pulling the arm back in position one...) great idea though.

AKG: important is that balls get over the wall ASAP (there atre 2 bots facing eachother and shooting balls at eachother. whoever gets rid of his balls first is the winner.

 

[Pommie]

The arm doesn't need pulling back, it just goes around and around. The balls can be gravity fed in a tube at the 6 O'clock position. Should be buildable in technical lego. I may try later.

Mike.

 

[Nigel Goodwin]

The arm doesn't need pulling back, it just goes around and around. The balls can be gravity fed in a tube at the 6 O'clock position. Should be buildable in technical lego. I may try later.

I've seen it done in Lego Technic (on the TV).

 

[Pommie]

I couldn't resist. My son has just started playing again with lego mindstorms and so it's all over the floor. Perfect to give this a try. So, here's my initial attempt.

The zip is an AVI of it running. I had to zip it as AVI is not an allowed file type for upload.

Mike.

 

[Nigel Goodwin]

I couldn't resist. My son has just started playing again with lego mindstorms and so it's all over the floor

I tried to convince my daughter she ought to have Lego Mindstorms for Christmas - but she wouldn't do it

 

[Someone Electro]

Try making it shoot somthing.

I know i made a lego catapult once.It would be hard to automate it becuse i used very strong elastics.When fired you had to hold it to the base plate or the catapult jumped right off it.

I think the best way is 2 wleles that grip the ball.Its easy to make,easy to load balls in and can shoot very rapidly.Speed is all that maters so you need a motor whith high RPM.They made one of those on mithbusters and worked very well.

 

[bloody-orc]

actually Pommie i really like that idea a lot. thanks a bunch... now i need to make this thing myself and try how will it do... only bad thing is i cant regulate the strenght of the throw wery much (i know i could move the rubber bands other end with a worm gear but still...)

 

[bloody-orc]

although a genious idea, it has some design faults. Try to make it with a little bit longer arm wich could hold a ball. The arm tends to be longer and reach out further than the pole holding the rubber band's other end...

and like all catapults without stopper it shoots slam on the ground 10cm infront of it...

My prototype of it:
www.minupildidonsiin.blogspot.com

 

[The Mad Professor]

One idea you might like to experiment with is the "venturi effect", this would make the weapon self loading without any additional mechanical mechanisms.

Gravity may also be employed to move the projectiles into the barrel , both methods are employed on a smaller scale for paint-ball weapons.

Lastly, if supplies of compressed air are limited , a small fuel-air explosion may suffice with tremendous results, albeit rather dangerous to implement for the amateur. A wealth of information can be found using the search rubric "Spudgun"

 

[dknguyen]

Miniature artillery? That's gotta be against some rule in the competition. Personally, I like the idea of a spring loaded gattling gun, but the squash balls are probably too big compard to the size of the robot for the motors be big enough to cock strong springs fast enough. (You said 1 foot x 1 foot maximum size? What about height?)

 

[Marks256]

Hmm, what about CO2? Or the "Air in a can" that is used to clean computers? Then you could have a motor activate a valve, or something? Or you could have a servo activate a valve? You could grab a cheap paintball gun off from eBay, and then rip out the firing assembly.

 

[AllanBertelsen]

bloody-orc said a 10cm high wall not 10m. Would a solenoid be able to do it?
Charge a capacitor to get enogh power. The book "Mechatronics for the evil genius" describe the technique. There you find formulas to calculate the nessesary energy.

 

[Marks256]

bloody-orc said a 10cm high wall not 10m. Would a solenoid be able to do it?
Charge a capacitor to get enogh power. The book "Mechatronics for the evil genius" describe the technique. There you find formulas to calculate the nessesary energy.

Oh! My bad. Ok then i would suggest the "Air in a can". Here is a diagram of my idea.

**broken link removed**