Balls Hitting Midair

VEX Robotics Competition Discussion VRC
#1

Our team is having trouble performing double shots into goals, when we shoot the 2 balls collide midair causing only the first to go in. This only happens when we have both balls next to each other inside our robot, if both balls have some space in between then they do not collide and they both go in. Our success rate is around 40% of shots going in, and dont even get me started on triple shots.

Currently, our hood is supporting a curved design with no extra accessories like a mobile backboard, with the balls being shot by a 1200rpm rubber band roller. Have any of you been experiencing the same issue and did you find any way to solve it?

#2

When my team ran into this problem, we tried tweaking the hood by small amounts to adjust the trajectory of the balls. We didn’t have much success though, so we decided to do a backboard instead.

3 Likes
#3

this is probably the biggest issue that a high speed hoodbot will have. you can make it better by fiddling with your hood, but tbh the best solution is a 180 hood or a portable backboard, to smooth out the path of the ball and prevent any collisions from slowing it down.

7 Likes
#4

Besides having a long hood or portable backboard (which are more ideal), you can use your indexer (assuming you have one) to feed the ball into your top roller slower

1 Like
#5

I slowed down my middle roller to help control the speed at which the balls are fed into the main roller. This completely fixed the issue.

My top roller is 1200 rpm, middle 300, and bottom 600. and my cycle speed remains very fast despite the middle roller’s drop-off in speed

edit: didnt mean to reply specifically to @Xenon27‘s post

4 Likes
#6

So simple yet so effective, I need to consider adding this.

#7

I’ll pm you our solution which works very consistently for us

#8

Interesting, I would assume it would affect cycle speed but I guess by your experiences it doesn’t. I’ll have to try this for myself, however how consistent is this solution and can it go beyond 2 balls being shot?

#9

We are already considering plans of adding a portable backboard and other counter measures incase we are unable to solve this problem. Have you had a chance to try this out for yourself?

#10

I haven’t personally experimented with a backboard or a 180 hood, but I do know they’re a very good upgrade to a hood that will make shots smoother and allow for faster cycle times with a lot fewer misses. If I were actually to compete this season I would definitely use one.

2 Likes
#11

I myself have experience with using a backboard, having built one on my most recent bot. It definitely improves cycle time if your ball shoots too far since it transfers forward velocity into downward velocity. However it did not fix our 2 ball shooting issue.

I am suspecting the problem is due to the lack of torque on the top roller. Top rollers are usually geared / chained to be faster than the bottom rollers, therefore there will be less torque. When the balls are getting shot, top balls might actually be shot at a lower velocity compared to the lower balls, since there isn’t enough torque for the top roller to spin up to its max velocity. The second ball is then shot at max velocity since the top roller will have time to spin up to max rpm once the first ball leaves. Therefore, since the second ball has a higher velocity than the first ball, they will definitely collide.

3 Likes
#12

this is definitely one reason the collisions occur.

another is when the first ball does not enter the goal cleanly, it might hit the inside of the rim when entering the goal, which slows it down long enough for the second ball to hit the first before it can enter the goal fully. this is what the backboard mostly helps with, making sure the balls go smoothly down into the goal without ricocheting off the inside of the rim.

5 Likes
#13

Make a macro so that the balls shoot after a certain period of time

3 Likes