Side vs. Top Shooter

[darkMatt3r]

Based on prototypes we've seen many people are going for the bottom and side shooters with either 2 or 4 wheels. Not to state the obvious but I just wanted to make the topic clear.

I just want to get everyone's opinion on these different Designs. If there are other similar designs to the side and top rollers bring them up in this thread too.

What are the clear advantages of having a bottom vs. side roller, and vise-versa?

In our team we've been discussing the fact that a side shooter will have less backspin and thus may be less forgiving when either hitting the backboard or basket. We've thought about the possibility of having a third wheel on either the top or bottom that was idle, with no power, and would just be the provider of spin on the ball as it goes through the shooter.


On the other hand, a bottom shooter has only one side of the shooter itself being powered, the bottom wheel, and thus instead of having wheels on each side of the ball to propel the ball either a curved piece of metal or lexan or even just a bar of metal must be on top in order to provide friction for the ball to exit the shooter. Thus, the ball is not propelled as far.

There are clear advantages to both options but in terms of accuracy it seems that that depends on the angle of the shooter itself, not the style of it.

What are everyone's thoughts? Regarding not just both of these types of shooters, but all methods of getting the ball into the basket?

Thanks,

-Matt

[Tom Line]

A bottom shooter can have another set of wheels on top and get the same distance. It has the added advantage of not curving your shots like a side-shooter will. After all, it's pretty hard to get two motors to spin the exact same speed. A top/bottom shooter will simply result in some top spin (or better) some back spin.

Of course, a top/bottom shooter will be taller.

Other than that, there isn't really a whole lot of difference.

[MrForbes]

We are working on a single wheel shooter to give the ball backspin, so it will bounce downward and go in the basket when it hits the backboard. We'll aim for the backboard. We also are hoping for a relatively flat trajectory, since in our experience it's not too hard to aim side-side, but it is pretty difficult to accurately judge distance, so we're trying to minimize the effects of how far the robot is from the goal.

We haven't got there yet....this is all still theory! but it's based on watching 2006 robots play Aim High

[farmersvilleRob]

Well... I think it has more to do with the context of the shooting. Firstly, spinning wheels to shoot a ball are always unpredictable based on:

1. Spinning wheels, as that on a pitching machine, rely on deformation of a ball in order to get the desired friction to shoot the ball. (even baseball pitching machines deform the ball!) And this deformation is different from ball to ball, let alone balls that are quishy in general!

2. Spinning wheels need to speed up to the desired RPM before a ball can even be placed into it, and the balls then put into it slow it down enough to where you again have to wait to put the next ball in

3. The efficiency of a wheel powered shooter is probably very low considering the power is distributed by friction (which also means more compression of the ball would be needed to make the ball go further thus affecting points 1 and 2)

4. Every single ball shooter that operates by wheels has either been right up to the goal hugging the side of the fender, where every robot will try to shoot from as well if they go with a shooter and even there the balls in youtube videos has scuffs on it which means its only a matter of time until something gives.

5. When shooting a fastball from a pitching machine, there's a reason why the wheels are different speeds for the slope of the ball. When shooting a crazy basketball that weighs more than twice as much, the slope will be incredibly hard to tune to the wheels speed and compression of the ball and even THEN the distance will play a HUGE role in the speed of the wheels as well which means the wheels would have to be tuned while moving which requires a lot of time, just like a pitching machine warming up

Now for a horizontal v. vertical shooter:

Horizontal shooters basically are side spin magnets meaning if you even have the motors a little off the somehow magically set speeds, there will be a curve left and right. That curve isn't and will never be enough to get around objects like a boomarang either since the curve on a ball is actually made by a low pressure system on one side.

You also cannot shoot a ball with a slope since the horizontal motors means there is no y component. Then shooting at a basket becomes dodgeball, and the ball's compression would make a nice bounce right back, and never make it from more than 5 feet away because the speed would need to be too high to make it the right distance in a straight shot.

Vertical are basically the same, however, they, being vertical, means they have little affect on left and right movement. That's good, but then like in the first 5 points on wheel shooters, there is so much unpredictability, that it's better to go a more direct mechanism to ball shooter such as a catapult. However, the effect of a tension/spring method weakens with every shot which means its impossible to tune as well without the fear of fatigue affecting shot.

We went with a rotational shooter. Direct, and doesn't have fatigue.

[DjMaddius]

With our teams prototypes we have found that if you power both the top and bottom and supply 30% power less to the top then the ball gets the perfect backspin. Though these change with different designs and such. This will power enough for distance and backspin though so its what we are going for.

[Alpha Beta]

Originally Posted by Tom Line

A bottom shooter can have another set of wheels on top and get the same distance. It has the added advantage of not curving your shots like a side-shooter will. After all, it's pretty hard to get two motors to spin the exact same speed. A top/bottom shooter will simply result in some top spin (or better) some back spin.

Of course, a top/bottom shooter will be taller.

Other than that, there isn't really a whole lot of difference.

What Tom says matches our research.

I think farmervilleRob's prediction of 5 feet, fender only capability for spinning wheel based shooters is a gross underestimate of what the concept is capable of. When looking just at 2009 examples one could get a false impression of what is possible because we were aiming at moving targets. Close shots where a practicality of the game. In 2006 we saw much longer shots hit with consistancy. It is interesting though to consider how chewed up these balls will be allowed to get before they are replaced between matches.

[Brian Ha]

Okay, so the reason we chose a bottom rotational wheels and then just a bar over top was for back spin. Adjusting speed and bar location give more spin vs more distance. Back spin is definately wat u want.

Now some reasoning behind why I think u shouldnt have a wheel unpowered on top, wheels have much more friction over a bar. The bar is used for back spin, thats why it works. The wheels that r underneath it are use for propulsion.

Thats wat I think atleast.

[dtengineering]

Hmm... an interesting thread. Buried in here we've got a rookie clearly and confidently stating what can be done, and a veteran making a conservative estimate based upon observation of the 2006 game play, and carefully limiting his comments to the "subject to further testing" clause.

I've posted a link to this video of our 2006 robot before, but I'll do it here again just to show that a single-wheel shooter is more than capable of hitting from half-court.

http://www.youtube.com/watch?v=jggKd...5&feature=plcp

But I'll also point out that just because you can hit the target from half-court in practice, doesn't mean that you should count on being able to do it during the game. We were resoundingly whupped by a a few teams who made it their goal to get close fast and score with every ball.

Jason

P.S. I should also point out that properly designed shooters will not damage the balls. In fact, I'd expect that to be part of the tech inspection process. Although a week or two into the '06 season I didn't believe it was possible to build a shooter that wouldn't damage the ball, it turns out I was wrong about that... our 2006 poof balls have been fired hundreds of times and are still in pretty good shape.

[farmersvilleRob]

But how heavy were the nerf balls? This year's are 11.2 ounces. Thats very heavy and will make a HUGE difference in the torque to rpm ratio gearbox. Especially when watching these threads go through and the prototype shooters are barely making the 8 foot shot. Which is also a big change in distance considering that gravity cannot play a part in the full slope like it could in 2006. As well, there is a compression difference pointed out in my previous point that also is a huge affect on the needed torque to compress the ball while taking it in. 2006 was a rpm game. This is a torque game

[MrForbes]

2012 ball weighs 50% more than 2006 ball.

Our first test had a lot of gear reduction...not much distance. But I did get a slow-mo shot of it, it's fun to watch

http://www.youtube.com/watch?v=-imnfSSOta4

[farmersvilleRob]

Originally Posted by squirrel

2012 ball weighs 50% more than 2006 ball.

Our first test had a lot of gear reduction...not much distance. But I did get a slow-mo shot of it, it's fun to watch

http://www.youtube.com/watch?v=-imnfSSOta4

So it seems there is a huge difference by only 50% weight difference. I'm not against trying a new shooter, but based on these, it's hard to gear down to the desired torque and keep rpms. I suggest instead of looking to the past for solutions in the 2006 and 2009 games, look into a new design for the new challenge. Who wants to see some 2006 and 2009 remakes? I'de rather watch new prototypes of flying cars fail than watch dependable wagons slowing go in circles.

[Donut]

I'll echo the previous comments in that the main difference between side vs. top shooters is the potential spin on the ball, and the height of the shooter. We are leaning towards a top shooter because of the ease in imparting backspin.

As for skepticism on the design working at all, mine is gone after testing a prototype of ours today. We built a vertical shooter (2 wheels above, 2 below, all 8") with 2 CIMs through CIMple Box transmissions direct driving the wheels and placed a basketball hoop such that it was the equivalent of firing at the top hoop from the key. I was concerned that there would be too much variation in shot placement with all speed/angle variables being the same, and in our initial tests where we fed the ball in by hand the results weren't too pleasing, with some shots flying over the backboard while others fell short. We saw ball feeding as a big issue and added a guide chute behind the shooter to consistently feed the balls in the same spot, then fed them in by pushing with a PVC pipe during our second test. This made an enormous difference as we tested about 30 shots and made 50% of them into the basket. All the missed shots landed on either the back or front of the rim as well so even for the shots that missed there was relatively little variation in ball placement. Considering that we were shooting at less than a 45 degree angle and had no spin on the shots I'm sold on the feasibility of a shooter working this year.

[Alex.q]

Originally Posted by farmersvilleRob

But how heavy were the nerf balls? This year's are 11.2 ounces. Thats very heavy and will make a HUGE difference in the torque to rpm ratio gearbox. Especially when watching these threads go through and the prototype shooters are barely making the 8 foot shot. Which is also a big change in distance considering that gravity cannot play a part in the full slope like it could in 2006. As well, there is a compression difference pointed out in my previous point that also is a huge affect on the needed torque to compress the ball while taking it in. 2006 was a rpm game. This is a torque game

Do I read this as I should use my cims for a shooter, or can multiple FPs or RS-775-18s provide the necessary torque? We don't yet have a finished prototype of this system, but our goal is 20 ft (hopefully). We do not however, wish to lose our cims from the drivetrain unless absolutely necessary. And in regards to copying 2006/09 I don't mind copying it if* it works.

*conditionally of course.

[farmersvilleRob]

Originally Posted by Alex.q

Do I read this as I should use my cims for a shooter, or can multiple FPs or RS-775-18s provide the necessary torque? We don't yet have a finished prototype of this system, but our goal is 20 ft (hopefully). We do not however, wish to lose our cims from the drivetrain unless absolutely necessary. And in regards to copying 2006/09 I don't mind copying it if* it works.

*conditionally of course.

Well, it's very difficult to do the math on motors without the stress, without the launch parameters (angle, number of motors and wheels), and rpm relative to a urethane foam basketball lol but I would say definitely more torque than any 2006 or 2009 bot. And based on prototypes, I would say test both. The 775 Banebot probably when geared down to the appropriate torque doesn't display enough rpms. At 20 feet and 45 degree launch angle you need ~30.008 feet/sec of muzzle velocity. Based on our excel spreadsheet of glorious math!

ps. That takes into account for distance and hoop height from launch (in our spreadsheet its set to 6 feet) and ball weight

[MrForbes]

It's pretty easy to get close numbers....find the no load rpm of the motor, find the wheel diameter, decide if you want a wheel on each side of the ball or just one side, and figure out the gear ratio needed to make the wheel(s) spin that fast, or just a bit faster.

If the motor speed drops too much when shooting the ball, add another motor, or add mass to the wheel and wait longer for it to spin up