Category Archives: Electronics and hackery

Rescuing a mill from the skip

Managed to get hold of a rare old mill – an Emco F1. It’s a beast. Here’s what they look used to look like when they were first sold (gotta love that jacket, huh?):


Here’s mine:

Before getting mine into the house I stripped off all the metal casings to leave just the essential working bits. No way to get it into the secret-workshop/attic otherwise. The control box was huge too:

… but with luck I’ll be able to ditch it and control it completely from a computer. Before trying to get the thing to move, though, the mechanics of the thing needed overhauling. I stripped it down completely:

And cleaned and degreased all the bits:

And that’s when I found that the leadscrews were a bit knackered. The lead screws are almost the most essential parts of the mill – they’re the mechanisms that move the head up and down, and move the piece you’re milling back and forth under the milling head. They’re supposed to move smoothly but these ones felt … crunchy.

Taking apart leadscrews is not for the faint hearted. Although they look like a simple screw and nut, there are a line of ball bearings running around the thread between them.

To stop the bearings from just falling out when they reach the end of the thread, there’s a little return tube that carries the ball bearings back to the start of the thread again.

Some of the ball bearings in this mill had shattered and jammed the nuts, stopping them from moving properly up the leadscrew. Nothing for it but to dig ’em all out and re-ball the thing.

Trouble is, when the leadscrew’s assembled you can’t access the ball bearings – can’t even see them. The only way to ‘refill’ the nut with bearings is to stick them into place inside the nut, one by one, with tweezers. I found that coating them in gloopy lube let me stick them into place inside the nut thread, where they held for just long enough to screw the nut back onto the screw again.



Once the nut is loaded with bearings again (not forgetting that the little ball return tube has to be filled with them too), you can gently thread the nut back onto the leadscrew. As you screw them together, the ball bearings get pushed up the thread toward you, but you can use a toothpick to nudge them into the little return tube.

I couldn’t get all the nuts working again – there were two nuts on each leadscrew, with a setscrew to let you put some tension between them, which lets you tighten the nuts to the screw such that there’s no slack or wobble. One of the nuts was completely knackered so I decided to ditch it and go with a single nut on the Z-axis (the axis that lifts and drops the milling head) figuring that gravity would help counter backlash.

I assembled it all again – this time with new stepper motors.

The new motors didn’t quite match the old ones – the shafts were too long – but I managed to get them to fit by spacing them with spare washers and nuts.

Finally, I carried the thing upstairs to the attic. Not something I’d want to do again 🙂

Next stage: milling some stuff!

Tiny stepper motors

If you’re ever in a posh car or on an expensive motorbike, you’ll sometimes notice that when you turn the ignition on, the speedo and rev counter dials do a quick self-calibration, moving their indicator needle all the way round the dial and back to zero again.

Instead of using a traditional meter mechanism (a simple coil and magnet), they use a tiny computer-controlled stepper motor. Here’s one removed from a dial:

The metal shaft sticking out used to have a little plastic indicator needle on the end. Inside, they’re more like a watch mechanism than a traditional stepper motor:

The tiny black cog in the middle is magnetic, and sits in the round gap in the metal frame just to its left.

Power up the two coils in the right sequence, and it drives the tiny cog round, in turn moving the other cogs which move the indicator needle.

These are more traditional stepper motors, though still very tiny:

I dug them out of a tiny camcorder. The shorter one controlled the focussing lens, while the longer one controlled the zoom. The little chip on the left is an Atmega168 – similar to the chip in an Arduino. With luck the chip’ll have enough power to drive the motors directly. Not sure yet what I’m gonna get the motors to do, exactly, but whatever it is it’ll be tiny and very cool. Yeah.

Secret Project #16638

20121009-141501.jpg

Ever since I found you could get little SMD jumpers (zero ohm resistors) it’s made laying complicated circuits on single-sided circuit boards much easier. Normally if you need a signal to cross over other tracks without touching them, you have to solder little wire jumpers in to form bridges, which means a lot of careful wire measuring and stripping (you can see the red ones above). For little jumps I can use the SMD resistors – the little black oblongs with 000 printed on them. If you’re careful they can jump over 3 other tracks…

LED Boost driver

A friend found a stack of discarded LED assemblies in a skip, and threw them my way. Amongst the other bits, there were several Dialight Lumiled strips – nicely machined aluminium backplates with 6 bright white 1-Watt LEDs mounted on top. They’re designed to be run from a proprietary power supply that delivers around 19.2 volts at a tightly controlled 350mA. So, not the sort of thing you can wire up to a car battery.

I figures this was as good a time as any to start embarking on analogue electronics – gotta dip your toe in the water at some stage. So, after several hours of wading through various “solutions” on Farnell’s website, I came across a tiny little chip that claims to be designed specifically for driving blocks of 6 LEDs like this. The datasheet showed an example circuit along with the specifications of the extra components needed, so I ordered the bits and designed a little board.

It’s a boost driver, which means it can produce a higher voltage output than the voltage you put in. Power in and out are roughly the same, though; so it takes more current input than the current it can provide at the output.

I designed the PCB in Eagle, and used a free plugin/script to convert the pattern into G-code for my mill to understand. Gotta write more about my mill another time – for me, this is where it shines. It took about 5 minutes to carve out this little circuit, much much faster than etching a board in acid, the old way.

Soldering the components on was a little bit fiddly but doable. I find it helps, when soldering multi-legged components like the little SOT3-6 driver chip, to wet all the pads on the board with solder first, using solder wick to remove all but the thinnest little layer.

The board worked first time. Which shouldn’t have been surprising, given that it was the manufacturer’s design, but I never seem to imagine things will go that easily… And the little driver circuit is small enough to mount inside the lights’ cases, too, so I’m going to have to make up a batch of them.

Solar power for emergency use

I’ve had lots of questions from friends about how to set up their own emergency solar system, so that if there’s a power cut / apocalypse / etc they’ll still be able to have lights, radios and phones working. So I’ve put up a page with FAQs and a few example solar setups, from around £250. Cheaper if you already have a car battery lying around – the bare bones is really only about £150. It’s all stuff bought from eBay, and it’s a tiny fraction of what most people charge for a solar starter kit. Check out http://www.shopwiki.co.uk/l/Solar-Technology-80W-Solar-Panel-Kit—Starter – even Maplin are trying to charge £600 for a £110 panel plus a £20 charge controller. And there are shops asking for upward of £800, relying on the fact that people don’t understand how simple they are to use.

So, do it yourself! Don’t get ripped off by buying a kit (unless you buy it from me, in which case why not buy two?).

Check out http://howiem.com/solar for more info. Any questions, drop me a line and I’ll add it to the page.

New project: h’s Lights controller

[Update: 3D render of the board! Woo]
 
3-chan-ardu-v1
 
I’ve been putting LED lights up around the house, driven by solar panels. Free light. Yummy. To save precious power, and because they look cool, I like the lights to be automatic – fade up automatically when you enter a room, fade out when it senses you’ve gone. It’s a simple thing to build a circuit to control it all, but it gets a bit tedious building the same circuit over and over again, so I’m getting some PCBs made up.
Continue reading