If you are shooting into the high hub, do you think a flywheel is sufficient? Or do you find a top roller adds a large benefit. Particularly for teams who have been to a week 0 with an official goal and or who have an official goal for practice, how do you minimize bounce? I was really disappointed to find that the official field acted very differently than the team version, particularly with regards to balls bouncing out, and am looking for ways teams have mitigated this.
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I’m considering putting loose spacers on the shooter hood standoffs that will spin freely when the ball slides past it. Hopefully that helps eliminate backspin.
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we’ve had success with what i believe was schedule 40 PVC over the 1/2 churro on the back of our shooter, definitely flattened our shots a good amount
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While I can only comment on our experiences but any kind of spin on either extreme (forward or backward) makes the bounce/roll out likely. There are ways to reduce spin on the ball without adding a top roller however the fastest and most effective way is to add one. Keep in mind the following videos are before tuning wheel speed and PID’s to best case. We are also messing with squish spacing.
No top roller
With top roller
On a side note, ball pressure plays a lot in accuracy as well. We noticed that when the ball dipped below 3psi our shots had to be from a lot closer to the hub. We also noted the balls lose pressure pretty quick and the fill port (the rubber thing on the ball where you air it up) is pretty weak and can tear easy.
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We have flywheel only. Backspin is definitely impactful but I would consider our shooters pretty good. Do we get bounce outs? Absolutely. Are we going back to the drawing board? No.
We have the AM replica Hub and an agitator and we get weird ricochets and bounce outs but we make a lot of shots too.
Our team does not have the full AndyMark version of the upper hub - we only have the ring, we have the ability with our shooter to control backspin - but we were under the impression that some backspin is good. What I’m getting from this thread is that teams with experience on an actual field are saying any backspin is not good. Is that correct?
Here is my summary of what seems like the most common opinion:
If you can specifically control what part of the hub you are hitting then spin isn’t bad. Near backspin / far topspin cause the ball to actually go down into the hub. This is hard to do especially when the easiest side to hit (far) wants top spin which is the opposite spin that most teams have (backspin).
If you just remove all spin and try to reduce speed as much as possible it is the catch all way to make the ball in most situations (still have odd interactions with the wheel at the bottom and other balls, but those are hard to prevent).
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Can you elaborate on why you think forwardspin (aka topspin) makes the bounce out more likely? I made a thread about it but never got a good answer
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Yeah sure. I kinda worded my answer a bit carefully. I said on the extreme ends of either forward or back spin. Before we had our top roller our back spin was like 400-600 rpms (sorta a guess with the slo-mo). If you have extreme forward spin the ball likes to hit the near rim and skip over the back part of the rim. If you hit the mid center of the cone you have bounce out depending on your distance to the goal. It is very dependent on how tall your robot is and how far you are shooting from.
The ball will want to bounce with the edges of the hub as it comes in. The polycarb walls of the hub can only dampen the impact so much. The top roller reduces the spin of the ball, giving it a lower kinetic energy for a relatively close exit velocity. So when the ball shot with top rollers bounces against the walls of the hub for the first time, it doesn’t bounce off with as much energy, and falls closer to the exits. The low energy shot is key this year.
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Our first and second prototype shooters were single axle only. When we built our polycarb cone, we found that the backspin was causing many bounce-outs. If the ball hit the “back” of the cone, it would accelerate downwards and bounce wildly off the agitator wheel. Shots in most other locations that hit polycarb also had significant downward acceleration. We were probably getting more than 50% bounce-outs.
Adding a “top roller” to our 3rd and 4th prototypes which creates a form of 2-axle shooter resulted in a huge reduction in bounce-out percentage. With our comp shooter we still get the occasional bounce out, but it’s usually from a direct hit on the axle/collar of the agitator wheel. We’ve set our distance targeting to be just a bit past the middle of the cone and our angular targeting to be just left of the middle of the cone to try to minimize direct hits on the agitator axle and increase the chance of contacting the cone first.
We do not attempt to remove all backspin. A little backspin seems helpful for stable flight.
Shooters that are able to significantly reduce spin compared to a standard single-axle hooded shooter are going to do much better this season than a high-spin shooter. If you aren’t in a position to add a second counter-rotating axle (or multiple), you might as well try anything that might reduce friction of the ball on the hood. Rollers as a hood, teflon backing, or any other ideas to help the ball slip on the hood will be better than getting full backspin.
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I had an interesting debate with some of the other mentors on our team about this idea. My initial thought was the same as yours that free spinning rollers on the back would reduce backspin, but they believed it would actually increase the backspin or even just make the ball spin in place if there wasn’t enough initial momentum. After thinking about it a bit I’d have to agree with them. Have you tested this?
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Just want to clarify, when you say counter spinning axle you mean spinning the opposite way of your flywheel right?
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I haven’t tried anything. I’m just throwing words on a screen and hoping something sticks 
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Yes. When viewed from the same end, if the main shooting axle is rotating clockwise, the axle(s) on the hood side of the shooter would be rotating counter-clockwise. This results in forces on opposite sides of the ball trying to propel it in the same direction.
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If you want a little data on what front spin shots look like, here’s some video from our week 0, yesterday.
Lead to bounce outs:
- hitting the rim
- hitting the agitator
- shooting with too much energy
Help with bounce outs:
- shots that barely clear the rim
- landing on the sides of the cone, especially the far side
To generalize, no matter what the shooter type, longer, higher shots bounce out more than shorter, lower shots. And hitting the agitator pretty much guarantees a bounce out.
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Assuming you are using two powered axles, did you happen to test which motor power ratios for topspin worked the best (particularly from longer distances)? Or does topspin not seem to have an effect on bounce out?
We are not. You can see how our shooter works in our release video.
From our observations, spin direction mattered less than shot energy. Higher, longer shots have a greater tendency to bounce out.
We have a top roller, but we’re having trouble getting it dialed in. Is yours spinning faster, or slower, than your flywheel?
Ours is spinning faster, but the top roller only has 2" wheels and the shooting axle has 6" wheels. The surface speed of the top roller wheels is significantly less than the shooter wheels, somewhere around 50%.
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