Leftyretro said:
Or a short cattle prod
Hey a taser should work, just paint it like a knife
Ow. My sister and I used to chase each other around with the cattle prods back on the farm. Many healthy zaps from those things (nothing like the fencer though). *sigh*---the good ol' days.
Shortest one we had was about a foot long; longest one was maybe 3 feet long.
When I was studying ju-jutsu (Hokutoryu, in Hämeenlinna, Finland) we just used rubber knives and bo sticks. I had to move back to Canada and turn my life upside down again though so I never even made it to my orange belt; ergo, I have no idea what the higher classes used to train with (but I never saw a shock knife).
Anyway, to try to inject a little on-topicness into my post:
Maybe Nigel has a suggestion? Don't know if it would involve a shock knife though.
What is the spec for what the knife should accomplish? I mean, it's probably going to need to have an effect upon contact with any part of the blade, right? Will you be practicing with or without your gis? I'm pretty sure our farm shock prods wouldn't have much effect through my gi unless it was really (REALLY) sweaty; it's pretty heavy cotton.
Hm. Another idea from the farm. If the point is just to be able to tell whether the "blade" scored a hit, could you maybe stick a narrow stiff tube on a hilt, wrap it in some fuzzy material (say, thick felt) and cover that thoroughly with coloured chalk powder? That should show up pretty well (I'm assuming you're wearing white). A limitation would be that you might get too few hits before needing to reapply the chalk.
Otherwise, maybe actually take apart a cattle prod (or a bug zapper racquet, as someone else mentioned). You could perhaps put the batteries into a belt pack if they are too big. Put the circuit into the handle of the knife if it fits, then take a rubber knife blade and wrap a pair of electrode wires up the blade, making sure they never touch or overlap. If they are thick enough gauge, I would try carefully melting them partway into the rubber so they don't slip. They'd have to stick up enough to make solid contact of course.
I myself wouldn't try making the zapper circuit from scratch for general use; I would feel much better cannibalizing something known to be relatively safe. That said, I don't actually know exactly how dangerous bug-zappers can be.
Torben