How is your team doing it?

[Cody Carey]

Ok, so we have gotten to the point where we need to figure this out NOW... we would appreciate anybody giving us a little input on how their team is aiming their ball from different distances, or how they are changing the arc that the ball travels in. One way is to change the ammount of power behind the ball and to keep the angle from which it launches the same... and the other way is to keep the power behind the ball the same, while changing the angle from which it shoots. If you could help us out... we would really appreciate it

Thanks in advance,
-Cody

[Rick TYler]

I don't have a drawing for you, but what we are doing with our one-wheel shooter is to vary the angle between the wheel and the pressure plate. The wheel is mounted on a live axle between two vertical posts. We built a simple U-shaped piece (but picture a square-bottomed "U") over the same live axle, with bearings holding the ends of the "U" over the same shaft that spins the wheels. By moving the "U" up and down we can vary the height of the shot. The ball shoots by the wheel squishing it against the pressure plate and then releasing it.

I think this is enough to get you going without doing all your design work for you. For instance, figuring out how to move the "U" back and forth is a nice little design project. Good luck.

[Cody Carey]

Tank you very much.

However, we have a base design already done, we are going to have our two-wheeled launcherat the bottom of our robot, and redirect our ball through a spout like a snowblower's.

We were just wondering weather or not we should vary the angle of the spout, or vary the speed of the wheels on the launcher.

[Jonathan Norris]

through empirical means we have been able to find a ideal angle of launch which will work every where from on the ramp all the way back to about 15'. We are planning on not having an adjustable angle on the shooter. We found that there is little need to adjust the speed if the angle of your cannon is correct, and you plan on firing the ball in strait.

[Donut]

Originally Posted by Jonathan Norris

through empirical means we have been able to find a ideal angle of launch which will work every where from on the ramp all the way back to about 15'. We are planning on not having an adjustable angle on the shooter. We found that there is little need to adjust the speed if the angle of your cannon is correct, and you plan on firing the ball in strait.

Our team found a similar thing through some fun equations. Every angle has a speed where the ball will stay in the goal area for a much longer range than you might normally get; you just have to find this speed and angle, and decide what angle to set it at to be most advantageous for you. We are still modifying the speed of our shooter with a constant angle, but this big range features gives you the nice ability to not have to worry much about shots from a certain area. We are also considering giving our shooter the ability to have the departure angle (from a barrel) modified between matches. It would do us nothing in game, but if we find the current angle is not working well, we may be able to change it by a few degrees in hopes of making things easier the next match.

[Cody Carey]

would that angle happen to be 39.7 ? It was mentioned to me by a math teacher once, but I don't remember what significance it has...

[Donut]

The special angle would vary depending on the speed you're willing to fire the ball at. Lower speeds would require a higher angle, and give you a shorter range closer to the goal (for example, 3ft. to 10ft.). Higher speeds allow you to use a shallower angle, and give you a longer range farther from the goal (like 12ft. to 30ft.).

Which one you want to use depends on your strategy, how much power you're willing to give the shooter, and the angles you can actually get on your robot. For example, you may want a somewhat higher angle if you intend on always shooting from close in, that way this range is close to the goal and you can save power. Shooting faster obivously gives you more range, but drains more power, and might stick you with a problem of being too close to shoot.

[Alekat]

Originally Posted by Cody C

We were just wondering weather or not we should vary the angle of the spout, or vary the speed of the wheels on the launcher.

I believe varying speed it much easier. it requires fewer moving parts. As for which is better, it may remain to be seen with competition.

[Donut]

Originally Posted by Alekat

I believe varying speed it much easier. it requires fewer moving parts. As for which is better, it may remain to be seen with competition.

Varying speed is easier (in our opinion). The only problem is that it gets affected by draining battery voltage, so you have to monitor the actual speed of the wheel (not just the pwm value) and make sure it stays the same.

[Spindash54]

Our team is going to be using a fixed angle launcher (if you can call it that). Although I can't divulge everything, our balls will be shot onto a track of sorts and fly into the center goal while standing on the alliance platform.

No cannon aiming, robot aiming, or camer use required.

[Cody Carey]

Thanks to everyone who has replied so far... you have been very helpful

[CircularLogic]

My team thought that even though varying speed is easier to do (less to build), the acceptable margin of error in varying speed was not enough for us. Consequently, we have decided that we need to vary our angle for the job.

We're doing this by only articulating the very end of our shooter and using a simple system of gears to move it, with a 2 or 3 turn potentiometer to keep our angle measured (although we may be replacing that method with a simple slow moving motor and a feedback loop to stop us at the angle we need and then some simple driver know how figure out if we are below or above angle).

Another way that we were thinking of articulating angles was a ball screw with two fixed points, one at the bottom of the socket and one attached to the end of the shooter. THen you simply spin the screw and it moves up or down. We ended scratching this idea after looking at the cost of it, but it still is a pretty good idea.

[Jared Russell]

We are just varying motor speed. Set the shooter up from different ranges, find a speed that works, and repeat until you have pretty good coverage of the field. Make that data into a table and set the motor to the power that corresponds with the given range (found by the camera or other means).

To compensate for battery variations, you will want to use a feedback loop to keep a constant velocity. We took a banner sensor and some reflective tape to make a primitive binary encoder. If the speed (ticks/sec) is too low, increase PWM value. If it's too high, decrease PWM value. The math is a little more complicated than that in actuality, but you get the idea (see the programming section; search for PID).

As a nice side effect of varying the power, the ball shooter recovers from the velocity drop after firing a ball more quickly (it detects that it has slowed down and gives the motor a higher PWM signal for a fraction of a second to compensate).

It is FAR simpler in hardware to build an adjustable speed shooter than an elevating one, even if the software is more complicated.