Shooter Mechanism isn't firing ball far enough

The mechanism uses two compliant wheels powered by a 775 redline motor. It fires the ball only a few feet.

1 Like

Try more compression for sure. We had the same problem to start with. We are now at almost 3 inches of compression.

7 Likes

Right off the bat I don’t think you are compressing the ball enough. For a hooded shooter my team is running 1.5" of compression for reference.

Next, compliant wheels aren’t a good choice for a flywheel. Colsons or stealth wheels are a much better choice.

Additionally, the hood seems a little flimsy. Can you make it more ridgid?

You can also add more mass to the flywheel to get a better moment of inertia. We added 4 72 tooth alum gears and it made a noticable change.

Finally, what ratio are you running those 775 pro(s) at? How many 775pros? You definitely want more than one.

Specs for our prototype:
2 NEO overdriven 48:18 (w/ belts & pulleys)
4" farelane 60A w/ pressed hex hub
4 72 tooth gears to add mass
1.5" of compression
Don’t have release angle, and can get this later if needed

Here’s some pics/videos of our setup: https://drive.google.com/folderview?id=1zihcAObjHTf17158VB-DEvLK89sTFsaK

11 Likes

Lots of variables here you need to play with:

  1. Compression of the ball
  2. Type of shooter wheel
  3. RPM of shooter
  4. Release angle of the hood/friction from the hood

Many things you can play with. I’d start with #1 right now as it looks like you barely have any compression on the ball. You’ll need a more rigid hood for backing to keep compression, especially since you’re testing with compliant wheels.

For more help I recommend reading this thread from the start

And the many other build threads going on right now on CD, included teams like 95, 3847, etc.

2 Likes

Adding on with the compression, you ideally want to keep compression along the curve until the release point. If the ball loses contact with the wheel but is still contacting the hood, it can create consistency issues.

Are both of the neos running your shooter wheel or just one neo?

Our current setup is 2 NEO with a 42:18 overdrive.

We were having this problem too, so we added a second wheel 6.5 inches away from the other. I don’t know if your robot design allows enough space for this, but we are able to hit the high goal from ~10 feet out. Good luck!

We are using 2 falcon 500’s with 1:1, about 2.5" of compression, and 4" wheels and are shooting a constant center shot from 32 feet currently.

I would try 1. add more compression for sure and 2. either use a higher power motor that can work through the compression and keep inertia of the wheel up or use 2 redlines at least

Edit: I also see that the plexi glass material is wobbling at the top when you shoot. Try to make sure that curve s completely stationary or your shots will be super super inconsistent.

3 Likes

:flushed:
Holy smokes. How much RPM does that take out of the system? It seems like you are using more energy to compress a 7" ball to 4" than to actually shoot the thing.

If I recall correctly we are dropping about 500 rpm. Running 2 neos on 6 inch wheel, 54:36 overdrive. Shooting about 40 feet right now. We are still playing with different hood angles/rpm/compression to have the “flattest” trajectory to shoot from 34 feet.

A quick suggestion:

(1) Replace those two wheels (look like 4" wheels) with the 6" wheels from your drivetrain. See if you can get at least 3, if not 4, wheels next to each other on that shaft.
(2) Let your motor come up to speed before putting the ball in.

With those two changes, I can almost guarantee that you’re going to see better results.

Also, how do you have that geared? Those wheels just don’t seem to be turning that fast. This is one place where you want a low ratio like 3:1 or 7:1 or similar.

The thing that a lot of people miss is that it isn’t your motor that shoots your ball. Your motor is just there to move energy into your wheels – the ball shoots because you have a crapton of energy stored in the wheels and some of that energy is transferred to the ball.

This seems to be common advice, implying it’s difficult to get 4" wheels to spin fast enough to shoot far enough with these game pieces.

Question for anyone who knows: Let’s say there are packaging constraints leading a team to really want to stay with a 4" shooting wheel. How could 4" wheels be made to shoot far enough (30 - 40 feet)?

  • Just add power & wheel/flywheel mass, and adjust to faster spinning gear ratio? Is it that simple?
  • Or are the typical forgiving FRC bearings a spin speed limiter & better, faster bearings should be sought?
  • I saw someone (one of the blogs - can’t remember which) suggest a low friction hood material can help with exit velocity - maybe use UHMW tape or PTFE sheet?
  • What else? Is anyone shooting 30-40’ with a 4" shooting wheel?

We are using 4" colson wheels with a Falcon motor geared 1:1 and at 90% speed we have shot it to where it lobbed it to about 28 feet. Once we get our angle correct and bump it to 100% we should be able to do at least 30’. Our hood is lined with FRP wall panel currently and our compression is currently at 1.5". I’ll put an update on here once we assemble our more sturdy prototype and get the angle set correctly.

Looking at your video there’s also a fair bit of flex in the lip of the hood which is losing you some distance as well.

But overall it’s the mass / radius of the flywheel that’ll affect how much energy you can transfer to the ball.

My team can nail 35ft shots with our prototype with near 100% accuracy with 4" wheels. It’s definitely possible. See my post above to specs/pics/videos

Do you mean the basic wheels you get in the drive train kit for rookies?

Yes. Not suggesting that for the production machine. But, for the prototype, it’s a fast way to increase compression, increase speed and rotational inertia.

Was not trying to imply that. In our experience, 4-in wheels work just fine. The main reason for that suggestion here was that it was a very quick way of increasing compression.

How many RPMs on the shooter wheel? are the neos at 100% speed or something less for long shots?

What does your fairlane wheel hub look like? was it easy or hard to make?

We have a similar testing setup but with falcons and will probably alter it by incorporating some of your specs to get more range.