Drum shooter?

[viggy96]

Does anyone here think it would be reasonable to shoot balls using a spinning drum, rather than a wheel, so that you could shoot 2 or 3 wide?

Our current plan is more or less inspired by 148's 2009 bot, Tornado, (though without the fancy ball storage) (https://www.youtube.com/watch?v=aCVLZFyEI1Y) and we were trying to see if we could put a shooter on it as well, to shoot for the high goal. Being able to empty the hopper faster would be very beneficial.

[SenorZ]

Nothing wrong with a drum to process balls. But they're much smaller than the 2009 balls. So there is a risk or jamming, or having a very narrow helix.

Trick is getting them to a high speed shooter.

[viggy96]

Originally Posted by SenorZ

Nothing wrong with a drum to process balls. But they're much smaller than the 2009 balls. So there is a risk or jamming, or having a very narrow helix.

Trick is getting them to a high speed shooter.

I guess my original question wasn't clear. I was thinking about using a drum as the high speed shooter, in order to be able to shoot multiple balls at once, rather than a single wheel, which can only shoot one ball at a time.

[Boltman]

Drum could work .

[SenorZ]

I'd love to see a continuous stream of balls flying out of a drum!

Consider the power consumption. The balls are pretty light, but trying to pull several up from the bottom of your hopper with enough speed to propel them 5+ feet in the air, all using the same mechanism is going to be challenging.

[Cothron Theiss]

Originally Posted by SenorZ

I'd love to see a continuous stream of balls flying out of a drum!

Consider the power consumption. The balls are pretty light, but trying to pull several up from the bottom of your hopper with enough speed to propel them 5+ feet in the air, all using the same mechanism is going to be challenging.

I might be wrong, but I still think you're misunderstanding the OP's intentions. I think the OP is asking about just using a large, wide flywheel capable of launching more than one ball at a time, not using the drum that contains the Fuel to also launch it.

[viggy96]

Originally Posted by SenorZ

I'd love to see a continuous stream of balls flying out of a drum!

Consider the power consumption. The balls are pretty light, but trying to pull several up from the bottom of your hopper with enough speed to propel them 5+ feet in the air, all using the same mechanism is going to be challenging.

I was more thinking along the lines of having a drum after the loading conveyor. The conveyor would be low speed used for loading the hopper and transporting the balls up to the high speed shooting drum.

[Kevin Sevcik]

Originally Posted by SenorZ

I'd love to see a continuous stream of balls flying out of a drum!

Consider the power consumption. The balls are pretty light, but trying to pull several up from the bottom of your hopper with enough speed to propel them 5+ feet in the air, all using the same mechanism is going to be challenging.

Okay, 74g ball. Call it 8 m/s muzzle velocity. Let's assume rolling without slipping out of the shooter, we'll call it a ring so I don't have to look up inertia of a wiffle ball. So 1/2mv^2+1/2mr^2(v/r)^2. So r cancels and mv^2. Each shot has about 5j. Yes inefficiencies and all that. Say 10% efficiency, so 50j per shot. A properly geared CIM would put out 334W, so 6.5 shots per second without slowing. So with those assumptions, a 2 CIM drum shooter could put out 13 shots per second without slowing.

[pipsqueaker]

Drum shooter is absolutely the way to go (unless anyone can design a high-capacity catapult, 1678?)

[rick.oliver]

I agree, a drum, roller, wide wheel, what ever you call it that accepts and discharges multiple balls should work. There will be a trade off between accuracy and width. So, 2, maybe three wide is about the limit is my guess.

[Eric Scheuing]

Originally Posted by pipsqueaker

Drum shooter is absolutely the way to go (unless anyone can design a high-capacity catapult, 1678?)

I for one would love to see a robot that launches the entire contents of their hopper with one shot of a catapult.

[JamesCH95]

Drum/roller shooters work pretty okay I guess...



Especially when coupled with a constantly-recycling hopper.

[RoboChair]

Originally Posted by pipsqueaker

Drum shooter is absolutely the way to go (unless anyone can design a high-capacity catapult, 1678?)

You leave us out of this! Just because I am well versed in catapults does not mean we can build any catapult.

[BeardyMentor]

Originally Posted by Kevin Sevcik

Okay, 74g ball. Call it 8 m/s muzzle velocity. Let's assume rolling without slipping out of the shooter, we'll call it a ring so I don't have to look up inertia of a wiffle ball. So 1/2mv^2+1/2mr^2(v/r)^2. So r cancels and mv^2. Each shot has about 5j. Yes inefficiencies and all that. Say 10% efficiency, so 50j per shot. A properly geared CIM would put out 334W, so 6.5 shots per second without slowing. So with those assumptions, a 2 CIM drum shooter could put out 13 shots per second without slowing.

That math works out but we have to think of things in terms of instantaneous vs average ROF. Back in the bad old days of paintball before the more sophisticated hoppers and good, high flow regulators we would run into this all the time. Your math would run very similarly to what you just did. You then try and implement that solution and you have problems of inconsistent shots or misfeeding. Then you would realize that you only have so much control over your ROF. Very rarely would you be able to get the feeding so that each shot is evenly spaced in time. If your goal is to be able to handle a real world 13 fps average over a load of fuel, you need to be able to push quite a bit more than the theoretical numbers for 13 per second. The reasoning is while your average may be 13 per second over 2-5 seconds, you may see spacings between fuel characteristic of much faster rates of fires. Say, the first 3 might be actually 1/20th of a second between the fuel while the last 3 might be 1/6th of a second between shots because the system feeding the shooter loses efficiency when the hopper gets low.

What I just said starts to fall apart if you have a completely linear indexing system for the fuel where it will not have to go from bulk storage to single file. This means we can index the feeding uniformly throughout the firing cycle. Unfortunately for us, this will reduce the number of fuel a robot can carry per unit volume which is not good for cycle efficiency.

[rich2202]

Originally Posted by viggy96

Does anyone here think it would be reasonable to shoot balls using a spinning drum, rather than a wheel, so that you could shoot 2 or 3 wide?

The Fuel is 5" wide. The opening 17.5-21.5" wide depending upon how you look at it.

IMHO, you will be challenged to get a 2 wide stream into the opening.