Flutterby™! : Gauss Rifle 2002-03-04 18:05:39+00

Gauss Rifle

2002-03-04 18:05:39+00 by Dan Lyke 19 comments

Zack came over on Sunday to add my experience in working with chocolate to what he'd read in the book (which we'd given him for Christmas). While we were waiting for the chocolate to come to temperature we worked on a Lego quadruped (I learned a lot of things about gait, I'm not sure a quad is going to happen with that few sensors and motors, but I think I know how to build a hexaped now), and I showed him the plans for a gauss rifle that I'd seen on /.. The instructions say:

When the gun fires, it will happen too fast to see. The ball on the right will shoot away from the gun, and hit the target with considerable force. Our one foot long version is designed so the speed is not enough to hurt someone, and you can use your hand or foot as a target.

Both of us said "what fun is that?". So I've ordered two kits so we can build a longer one that you can't use your hand or foot as a target for...

Umm... If you do this with those ceramic magnets, they'll get busted before you can get the balls to travel with any decent velocity. I'd suggest using electromagnets around steel cores instead.

I think we'll start with these 'til we bust the ceramics. If we start going to electromagnets it's time to start making active systems rather than passive ones...

Naw. The timing for the active system is rough, while one based on the same set-up can use simple DC.

I've stayed away from having to worry too much about how to calculate magnets and current draw, but I figured we could work out timing issues with conducting rails. Obviously there are some manufacturing issues because we'd have to make those gaps as smooth as possible, but that seems to be a place to start.

Well having made one of these is high school, I would suggest you be carefull. We used a 3 foot long wound emag coil and about 400 Watts of power. Our test shot went across the room and punch through the cinder block wall. We were using simple bar magnets for the ammo which worked great. You would put them in one end with a little bit sticking out and they were perfectly stable, then you gave them a nudge and they raced forward. I know know enough that I could probably work out the equations involved in that design but it would be fairly complex.

Aaron, how'd you switch the magnet? More details? I'm always looking for cool ways to put other people's kids in mortal danger...

Hey Dan, Tom & I are thinking about going away for a couple nights--you want to take care of my 13 year old? He needs help picking out a science fair project, too.

Dori, I don't have energy to do this for two kids. I mean, if you really really need a weekend, maybe, but the last thing I need is more commitments.

Sorry, Dan, I should have put the <fe> tags in. I figured that asking for childcare right after your "looking for cool ways to put other people's kids in mortal danger..." comment would make it obvious enough.

Yep, those magnets are darned fragile. And strong. Leap across the table if you're not careful strong.

Dori, I've hung out with enough parents to know that "would you put my kid in mortal danger?" is always asked in a "ha-ha only serious" manner...

Hmm.. Thinking... a small series of coils, a stepper motor controller. .. It's time I started playing with electronics again.

hey i really need a fesable plan for making a strong guass rifle. and i have no idea how to get enough power saftley for those electro magnets. i also thought about making a solenoid or wat ever but its a huge pain to get all that timing right. please send me any ideas.

hmm, you have an emag with a core of some sort. How do you set it up so that the projectile would go through a tube or something? Is the projectile the core?

In the one we were building we just hit the magnets and transferred the energy through them physically. But for much more than a coffee table demostration this means you destroy the magnets, 'cause those ceramics just aren't that strong.

I'd need to play with this more, in talking with my dad this weekend I've realized that one of my issues with building things that have an effect on the physical world is that I think in milliamps, and it's time to start thinking in at least tens of amps, but I think doing the windings around steel tubes should be a good place to start.

I'm sort of working on something like that on my own. It's a totally passive magnet setup, and I don't plan on going electronic. There is a way to use passive magnets and get the balls' speed higher than the magnets could normally allow. I'm toying with the idea of using some sort of non-conductive material (probably wood) as a sort of "bridge" across the magnets. It would be an upside down U shape, so that it is vertical on both sides of the magnet, and horizontal across the top. I haven't actually built it, but it's on my to-do list. I'm also really new at this, so if what i'm saying is totally wrong, please forgive me.

Also, I was wondering what kind of spacing works best? Something like 2.5 or 3 inches? Thanks!

I had best results when I followed those instructions with the 2.5" spacing. And the final speeds (before you start cracking magnets) aren't in the "wow, that'll hurt someone" category, they were in the "oh, that's fairly cool" kind of range.

Remember that with the passive setup what you're really buying is that extra ball-bearing's worth of energy at each magnet station, so you still have to have a relatively inelastic collision at each magnet.

Hrm. Ok, thanks... I think I'll give this a shot and see if enough energy is transferred across the bridge without cracking anything. How many magnets did you string together? I'm trying to build something that'll be about long-barrel rifle size... something around 4-6 feet in length.

We just went for the foot long version. If you're not colliding with ceramic, longer should be very possible.