electrically-powered centrifuge weapon

[gorobei]

So watching the mythbusters episode with the civil war era steampowered machinegun reminded me about the DREAD gun.
http://www.defensereview.com/m...ews&file=print&sid=526

There have been some "vigorous" debates on the defense forums on the creator's claims of little to no recoil, no gyroscopic effects, and general suitability for combat. [The current proposed model is a single spinning disc/chamber with a heavy center axis component.]

Part of the recoil and gyro torque precession attacks come from the assumption that there is only one spinning component. Another article commented that a second spinning disc/chamber rotating in the opposite direction of the the first would neutralize the torque and some of the recoil issues.

I don't remember enough of my high school and college physics to figure out what happens to precession when you have two contra-posed angular momentums. Anybody able to shed some light on this?

 

[Mark R]

My understanding is that gyroscopic effects can be cancelled by counter rotating masses - as long as they have equivalent angular momentum.

However, I simply don't see how rotation recoil could be dealt with. You have to accelerate the balls in a rotational fashion, which means you have to apply a torque to them. While linear recoil is cancelled by shooting 2 streams at 180 degrees - the rotational recoil is not.

How significant the rotational recoil would be, I don't know.

 

[jbzx86]

I couldn't tell you conclusively if the recoil would be neutralized by a counter-opposing force. It sounds like a more complicated version of the nail grenades in Team Fortress Classic. Push a button and unleash a torrent of large, metal balls... understanding the gyroscopic effect and precession, wouldn't the axis rotate in a fashion describing a cone? If this is true, then I suppose it would depend on the amount of force being applie to the projectiles to determine the amount of recoil and stress on the structure of the weapon.

 

[Nathelion]

1) You can't have a recoilless gun unless it propels a mass "backwards" as well. Bazookas are recoilless because they're basically rockets, not rifles. I suppose you could rather easily make it fire a bullet "backwards" at the same time it fires one "forwards", thus eliminating the recoil, but i could see some other problems with that approach.

2) You guys remember that thread about high-powered centrifuges a couple of days back? I don't know about you, but I'd personally rather not be in a Humvee with this thing on the roof when a stray bullet hits it and it goes WHAM-SLAM-KADUHNK and 10 000 little centrifuge fragments go flying across the landscape.

 

[Nathelion]

Concerning the rotational recoil, I figure you could probably have two of them rotating in opposite directions firing simultaneously. My mechanics skillz are a little bit too rusty to really know for sure though.

Hmm. It occurs to me, that since angular momentum is always conserved, shooting a bullet really shouldn't result in any rotational recoil. I mean, think about it like this: Ignore the whole centrifuge apparatus and just imagine a bullet tied to the helicopter with a string, and imagine the helicopter-bullet system in rotation (the displacement of the helicopter due to this rotation would be small due to the mass ratios, but still there). Now cut the string. The helicopter would go flying one direction, the bullet would go flying in the other direction, but neither would rotate. The same thought experiment should apply to the centrifuge gun; you'll end up with linear recoil, but not rotational recoil (as in recoil that will rotate the helicopter).
To make the scenario more intuitive, imagine two bullets bound together by a string rotating about each other. Now cut the string. The bullets will go flying in opposite directions. The angular momentum inherent in the system will still be there, but it will manifest in the paths of the two bullets being offset from each other by the length of the string, rather than actual rotation. Further, in this scenario, no force would be exerted on a hypothetical helicopter holding on to the middle of the string (ie. the central axis of the centrifuge).