Thinking about Berzerker
Feb. 2nd, 2008 06:44 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
johnridleyLast time was a good first attempt at the trebuchet. Our biggest problem was pulldown. We did a lot of fooling around with various tackle and wasted a lot of time, eventually coming up with something vaguely workable. A couple of pulleys allowed the hank-cranked winch to be mounted out of the danger zone but still pull down. Problem is, it was needlessly complex, required some pretty good pulleys (which we did not have, we had junky pulleys and they scared me, luckily breaking without hurting anyone) and it still put someone in the danger zone for a few seconds while the pulleys were changed halfway through the pulldown (though we did put on safety ropes before getting in there).
This time I'm completely eliminating the tackle. An electric winch will be mounted at the primary pulldown position, no pulleys will be used. Since it's remote operated the winch can be directly in the danger zone without problems. At the beginning of the pull, the cable will be parallel to the beam so tension would normally be quite high, so we will prop a stick in there to divert the force to the side. I think it will have outriggers in case there is a tendency for it to rotate away from the center.
Harbor Freight had this on sale so I picked one up today. 2000 pound capacity, so it should do the trick.
OK folks, I'm just throwing bowling balls. Think of other stuff you want to throw. I should think anything up to about 30 pounds would be easy, up to 60 should be doable with less range. I suppose one good experiment would be to see how much we can throw.
I bought 300 feet of yellow "caution" tape so we can keep vehicles out of the backthrow area this year.
Also, I picked up an ignition coil to use for the shower heater ignitor at Murrays today. I think I broke the parts guy's brain; I went up and said "I need an ignition coil." "For what car?" "No car, I just need a coil. Just any old plain cylindrical ignition coil." He had no idea how to find an ignition coil unless I gave him a make and model. So I said "OK, fine... uh, 1973 Chevy Suburban." There were about a dozen, two of which were in stock, one of which was $20, so that's my choice. A quick check here shows that ignition coil fits about 1000 models, probably anything with a spark plug and a distributor made at least up through 1980.
I probably could have gotten one for $5 from a junkyard, but it would have taken an hour to save $15, and I probably would have gotten my jacket pretty dirty. I just need to figure out whether I actually need to use a ballast resistor for my application (it is stamped "external resistor required").
The other major part, a 10-amp NPN driver transistor, was liberated from an old 250 watt AT power supply last night while watching Good Eats. I was hoping for an N-channel MOSFET, but whatever. A 555 driver and I should be good to go. I guess it should be well isolated and waterproofed (though the part in the shower will be 12v only, the ignition part will be right on the burner).
This time I'm completely eliminating the tackle. An electric winch will be mounted at the primary pulldown position, no pulleys will be used. Since it's remote operated the winch can be directly in the danger zone without problems. At the beginning of the pull, the cable will be parallel to the beam so tension would normally be quite high, so we will prop a stick in there to divert the force to the side. I think it will have outriggers in case there is a tendency for it to rotate away from the center.
Harbor Freight had this on sale so I picked one up today. 2000 pound capacity, so it should do the trick.
OK folks, I'm just throwing bowling balls. Think of other stuff you want to throw. I should think anything up to about 30 pounds would be easy, up to 60 should be doable with less range. I suppose one good experiment would be to see how much we can throw.
I bought 300 feet of yellow "caution" tape so we can keep vehicles out of the backthrow area this year.
Also, I picked up an ignition coil to use for the shower heater ignitor at Murrays today. I think I broke the parts guy's brain; I went up and said "I need an ignition coil." "For what car?" "No car, I just need a coil. Just any old plain cylindrical ignition coil." He had no idea how to find an ignition coil unless I gave him a make and model. So I said "OK, fine... uh, 1973 Chevy Suburban." There were about a dozen, two of which were in stock, one of which was $20, so that's my choice. A quick check here shows that ignition coil fits about 1000 models, probably anything with a spark plug and a distributor made at least up through 1980.
I probably could have gotten one for $5 from a junkyard, but it would have taken an hour to save $15, and I probably would have gotten my jacket pretty dirty. I just need to figure out whether I actually need to use a ballast resistor for my application (it is stamped "external resistor required").
The other major part, a 10-amp NPN driver transistor, was liberated from an old 250 watt AT power supply last night while watching Good Eats. I was hoping for an N-channel MOSFET, but whatever. A 555 driver and I should be good to go. I guess it should be well isolated and waterproofed (though the part in the shower will be 12v only, the ignition part will be right on the burner).
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no subject
Date: 2008-02-03 03:43 pm (UTC)no subject
Date: 2008-02-03 04:15 pm (UTC)I don't see how it matters how much current the thing draws. If you're concerned about people getting a shock between the switch and ground, it's irrelevant how much current is going through the switch; the entire energy capacity of the battery is available to shock someone even if the thing isn't running at all. And grounding the metal box should deal with that.
For that matter, how much current does the LP solenoid draw? I bet it's more than a few milliamps. Same issue there.
I think the whole thing could be put behind a sheet of visqueen and grounded, and there'd be no significant chance of shock. You could easily operate the pushbutton I have in mind right through even a quadruple sheet of visqueen.
If you think it matters, we can just switch on the 555 part of it and leave the rest running; with the 555 not driving the transistor, I don't think there will be significant current draw to kill the battery, and the switched current to the 555 will be a few milliamps at most.
But even wired like that, you still have the hot side of the battery coming in to the switch, and it would be fully capable of delivering 20 amps if you gave it a path to ground, even if there weren't a circuit at the other end at all.
We could set up something like a 5v relay in the 12v circuit with a limiting resistor to the hot side; that should limit the max current delivered to the switch to whatever will pass through the resistor at 12v, which would be little more than would be needed to trip the relay, maybe 20 ma.
no subject
Date: 2008-02-03 05:24 pm (UTC)Point. OK then. I just worry about power and water. I think my mind was on the fact that the sparker is running up the voltage, and those things HURT even if you're dry.
But even wired like that, you still have the hot side of the battery coming in to the switch, and it would be fully capable of delivering 20 amps if you gave it a path to ground, even if there weren't a circuit at the other end at all.
Wrong transister then. IIRC, you use a PNP with a pull up resistor. The system is activated by pulling the gate to ground, so there's no way to pull much power through the switch. I could do that with the valve too.