Help needed with chainsaw hooded shooter

My team is doing a redesign of our shooter, and recently made our first attempt at a hooded one.

We’re currently running 2 direct drive neos with 4in Colson wheels.

The prototype is made of polycarbonate, and is quite rigid as far as I can tell.

Before the motors spin up, everything feels really solid.

Once the motors start spinning however, the whole thing starts vibrating fiercely and sounds quite like this:

https://youtu.be/2CoS5MrRGO4?t=24

It still manages to shoot balls about 15-20’, but given our 2" of compression that seems a bit lackluster.

Any suggestions to help with either problem would be appreciated!

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Your YT link instead links to just “sound/”. May have your link setup backwards.

We had similar results shooting with a similar (only a single neo) setup. We got more distance going to a 1:2 upduction(? ive heard a few different words for this) , and we had plans to move to 1:3 for better PID overhead before covid hit.

V1 shooter:

Attempting a 40ft shot with the setup

V2 shooter:

35ft(ish) shot pre-pid

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Don’t expect rigidity from polycarbonate. It can work, but default to aluminum.

It’s fine to run a 1:1 ratio, but don’t mount your motors like that. Mount them to the plate and use a belt or chain to the shooter shaft.

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Here is a picture of our shooter:

Polycarbonate is perfectly fine, so long as you use 1/4 inch thick and have lots of cross supports between the two plates of the shooter. Rigidity will come with proper material-specific build practices. We ran a shooter with polycarbonate all (of the short) season and had no problems. In fact, all of our major mechanisms other than our drivetrain and climber were made of polycarbonate and 1/4-20 tapped churros.

The sound does not work for me.

As for the vibration:
•I agree that a side mount of the motors with chain or belts would be better.
•Are you using hex bearings? Hex bearings are not spec-ed for concentricity so we used round thinderhex bearings.
• Are your shooter wheels balanced? Not sure what wheels you are using but I know many people have to rotate them in relationship to each other to minimize vibration.

We did not get much more distance than what y’all are getting until we did an up-duction. Our final was ~1:1.3 with two F500s and could shoot in the 30-35 foot range if I’m not mistaken (don’t quote me on that because it’s been a couple of months but that sounds right)

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With the hex couplers it appears you are using, it’s really easy to install them such that the resulting hex “shaft” is not perfectly straight. At 6000 rpm, anything other than an axially straight shaft will cause substantial vibration. Also, the Colson wheels are likely not to be perfectly dynamically balanced. Again, at 6000 rpm, slight imbalances will cause vibration.

I’d recommend that you try a redesign to belt drive a straight Thunderhex shaft in round Thunderhex bearings. It looks like you have CNC capability so it should be pretty easy to design and cut some new side plates. See how much that change reduces your vibration. I expect it would be a lot.

If there is still some or even a lot of vibration, you might try rotating one Colson wheel relative to the other to see if a different alignment improves dynamic balance and reduces vibration. If you have more wheels, you could also try different wheels along with different relative alignments. I’ve heard of people using a go-kart wheel balancer to dynamically balance shooter wheels, but I have no experience with that. If you have any connections with a local racing scene, you might be able to get good dynamic balance with less trial-and-error.

One more suggestion that you didn’t ask for…it might seem like having the gap between the Colsons could help the Power Cell track straighter through the shooter, but it likely would want to move to one side or the other like a wide belt would if you put it on a roller with two crowns. If you have the capability, you may want to turn down the hub on the inside of each wheel so they are very close to seamlessly touching. You might also want to turn down the slight crowns on both wheels so the surfaces are perfectly flat. You might improve your shooting accuracy with those modifications. Of course, if your accuracy is just fine as-is, there would be no need to fix what is not broken.

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I clearly need to write faster and watch less Netflix while responding. When I started writing, there were no replies. When I finished, there were 3 in front of me with much the same advice. At least it’s good to see a lot of agreement in ideas for improvement.

One more thing to add is that if you can design for 6x2" Colsons and can find any of the VEX live hubs for Colsons, you won’t need the upduction that has been recommended for the 4" wheels. I’m a big fan of slower rpm for safety (even though 1:1 direct drive from Neos is still very fast) and for improved shooting consistency as the Power Cell has less abrupt acceleration and potential for slippage as it enters the shooter.

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Balance the Colson assembly.

If you balance it as an assembly, and you take it apart, it needs to be re balanced. Actually a better suggestion is don’t take it apart once balanced. The collar clamps are not symmetrical for sure and frankly neither are the wheels.

Balancing is easy and pays off in spades! Takes a simple fixture and a little time and patience.

We actually balance the tires by themselves then as an assembly.

In the end of this video, after everything else shuts off you can barely here the shooter spin down. Also the shooter didn’t start up until the camera lights came on.

Balance

Edit: Sorry Paul, I meant to hit reply to all.

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@Mark_Wasserman is absolutely right. Colson wheels can be pretty ‘out of balance’ right off the bat. Plus they have a rounded profile. We cut them flat and even on the wheel outer diameter AND the sides! Mr. Miyagi said life is all about balance! :slight_smile:

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Sorry if this has already been addressed:

Just noticed the motor to Colson shaft. If that rigidly clamps down on both shafts then that’s not good. Too many things constrained that have to be perfectly on center. That interface needs to act like a Lovejoy vs. a solid shaft. The sole reason Lovejoys exist. A hex coupler left loose could act as a Lovejoy just to try…

Our initial shooter design used two Colson wheels in a similar layout to yours, we later found that AM Stealth wheels with no gap in the middle were MUCH more effective. Initially, we had assumed that having a gap in the wheels would help with centering the ball, but when we investigated the wear pattern on the wheels, we determined that we were actually getting very poor contact with the ball (even under compression), which resulted in shorter shots and worse accuracy caused by the ball slipping on the wheels as it went through the shooter.
We also are gearing our motors up to roughly 1:2.5 and we switched from using 2x NEOs to Falcon 500s for the better torque and higher RPM.

As for the noise, as others have pointed out, this is likely due to vibration caused by a lack of rigidity. Our shooter (which is almost entirely 3D printed) had this same issue initially, and we resolved it by reinforcing the motor and shaft supports and by switching from chain to belt drive.
Even now, we generally don’t run the motors higher than 80%, as it still will make a terrifying sound, but even so, it can easily shoot basically the full field. Our design philosophy was “Trajectory doesn’t matter if you’re shooting so fast the ball travels in a straight line”. :laughing: