Entry tags:

circuits, halloween, howto, machining, steampunk

Steampunk Cane, Part 1
Or, how to craft a keyed flux channel for your aetheric jumpship
(This is part one of a how-to series. Continue with Part 2, Part 3, or Part 4!)

Credits

• Cane concept from Girl Genius, by Phil and Kaja Foglio (best seen illustrated here)
• Highly Efficient 0-100% LED Dimmer © 2006 J.A. Bezemer. Schematics for this circuit are open source, licensed under GNU GPL 2 or later. Therefore, so are my exceptionally minor modifications.

Every well-dressed gentleman requires a cane, and the retrofuturist is no exception. Since this Halloween's outfit has been heavy on the "Victorian" and really light on the "Time Traveler," I accepted Ann's gracious offer to finish my shirt for me while I spent the last week working on my cane. It's almost complete—the paint is drying, literally—but the project is so large that I'd like to split it up over a couple posts, anyway. As I'm sure you all know by now, I'm really bad about stopping what I'm doing to take pictures, but I hope I'm getting better. Thumbnails link to full, and there are more shots in the set.

Basic Design

I don't have any pictures laying out everything you need, because I bought things and made it up as I went along. The basic idea is this: shape an acrylic tube to look like a huge vacuum tube, open at the bottom. Make a non-conducting base (I chose more acrylic) to hold brass rods. The brass rods fit into the tube, and both support the dimmer circuit and act as the power rails—they give it the look of a vacuum tube instead of some sort of crude pleasure device. The base of the cane is wooden, as it should be, and it is fitted at the top with a plain metal pipe of some sort for the batteries and controls. The tricky part is mating the acrylic tube on top to the metal tube. I got really lucky and found exactly what I needed at Home Depot.

Prototype the Circuit

I first wrote about this circuit way back in February. Since, I've discovered that moving it off the breadboard supply and on to 9V batteries solved just about every glitch I had. The start-up pulse that I was getting when quickly switching off and on appears to have been some sort of capacitance issue with the 808, not the dimmer circuit. I bought enough components to make this circuit three times - one prototype, one real circuit, and one in case I massively messed up. I didn't want to disassemble the prototype as I made the real one, and the components (with the exception of that damnable inductor) were all really cheap, in any case. Finding a choke of the necessary rating (5mH) was hard enough—finding one that also fit inside the tube ended up being a real challenge. The coil cost more than the rest of the circuit combined.

Qty	Digikey Part Number	Unit Price	Extended Price
3	497-2983-5-ND	0.86000	$2.58
3	BC547BTACT-ND	0.11000	$0.33
9	BC560CTACT-ND	0.12000	$1.08
3	1N5822-E3/51GI-ND	0.34000	$1.02
3	490-3830-ND	0.23000	$0.69
3	490-3811-ND	0.16000	$0.48
3	P13460-ND	0.11000	$0.33
3	P13465-ND	0.11000	$0.33
6	P13464-ND	0.14000	$0.84
3	DN4755-ND	11.88000	$35.64
3	CT2205-ND	2.71000	$8.13

I got the LEDs from theLEDlight.com - I've bought from them before, and I love their site and selection.

Qty	Part Number	Unit Price	Extended Price
1	LED5-30-40DG-WW-12	$17.88	$17.88

Now having some experience with the circuit, I first had to divide it in two parts—the part in the tube, and the part in the handle. I wanted to split it up so that you didn't have batteries floating around in there, for instance. I decided against a switch for simplicity - I'll just pull the batteries out when not in use. So the batteries (V_LEDS, V_logic, GND) and the potentiometer (GND, V_ref, V_T4) go into the handle. I knew I wanted it to have rails soaring inside to give it the look of a vacuum tube on steroids. So combining those nodes gives five rails. V_LEDS, GND, V_logic, V_ref, V_T4. Ground is by far the most used, so it goes in the center. I made V_ref and V_T4 shorter than the back three. I thought it looked better, gave a sort of frame or shelf for the LEDs to float above, and gave me extra room to fit the inductor.

Make the Base

Five rails inside a tube that's 1 1/4" OD is a pretty tight fit, but it can definitely be done. The thing to watch out for isn't just the placement of the rods, but making sure that you still have enough room to turn the nuts on to tighten them down. I had originally planned on two rows, three in back and two in the front. Fortunately, I abandoned that early and went for a pentagonal configuration. This gave me a lot more room to work with, as I could put the rails far to the outside and give myself a nice cage to work in.

I was really stumped on how to get the rods equally spaced until I remembered how to use a compass. Looked up the formula for length of sides of a regular polygon and approximated that with the compass. If you start at the odd point and then do the two vertices on either side of it, working out from there, it doesn't matter that the last two aren't exactly the right distance from each other. The placement is still symmetrical, which is all that really matters.

I ended up making the base three times. The first time, I just didn't have my head wrapped around the mechanics, and I made the base the same as the OD of the acrylic tube I'll be using for the shell. Unfortunately, I forgot that I would be flaring the bottom of the shell to fit the inside of a 1" cast bronze union for copper pipes (expensive, but the best connector I could find). Both Lowe's and Home Depot have unions in this size, but only Home Depot's was useful to me. Theirs was threaded to the same gauge as black pipe is, and with copper so expensive and not sold by the foot, I had to go with black pipe for the main body. Figuring out this junction literally took me an entire Saturday of shopping at every hardware store and home improvement place I could find, and was the one part that made me really wish I had access to a metal lathe.

So, the second time I made it, I used some acrylic I had laying around from the last time I put a window in a PC of mine, back when that was a new and different thing. That ended up being too thick, letting me only grab a thread and a half of pipe when I put it all together. The third one came out best (practice, practice!), and is actually a little too thin (from window-acrylic, again, from Home Depot), but I bought an O-ring this morning that I hope will help deal with that.

Cut and Thread the Rods

Deciding how long the rods should be took a little while. On the one hand, I had no idea how the circuit would fit along them, and I didn't want to run out of room. On the other hand, the whole vacuum tube section goes above where you'd hold the cane, and I didn't want my cane turning into a staff—it'd muddy the impression of the character. In the end, I decided on 8" from the acrylic base to the end of the long rods, and it ended up being a really good choice on both counts.

I picked up a dirt cheap tap and die set at Harbor Freight. It's imported crap, but I'm only threading brass, and I didn't know what size I'd need. I should've done some more research, but just ended up going by trial and error. I got 1/8" rods of 360 free machining brass, and tried #6 and #4 taps. The former worked, but felt sloppy. The latter I think was too deep a cut, but it held the nut a lot better, and the #4 nuts are also a lot smaller, so I went with that. It ended up being a good choice, except that it was hard to keep the threads straight. When using a die, you're supposed to taper the end of the rod first, so the die as something to 'sit' on before its teeth have a chance to grab. I think my tapers were uneven, which got me off to a bad start. Regardless, while it's not machinist-quality work, it's serviceable. I tapped the end, threaded a nut on, and marked 8" from the thread side of the nut. Then I used my angle grinder to cut off the rod and clean the end up. Sand off the burrs, and put the next rod in the vice.