Rudyard Kipling wrote a poem called ‘The sons of Martha‘ which is a gentle hymn of praise to those in society whose graft keep things going while others enjoy themselves. I like to think it’s about engineers. It contains a line which I really like: ‘They do not preach that their God will rouse them a little before the nuts work loose‘. If I’d paid a little more heed to that, I wouldn’t now have a pile of wreckage rather than a working drone. I failed to properly tighten the propeller nuts, and sure enough one came loose at altitude. It makes for an amusing video (I hope I haven’t given away the ending), but it may be a little while before the drone flies again.
I recently acquired a woodturning lathe. Unfortunately, it was missing a rather important part – the centre drive head, which grips the wood being turned. It’s not huge or complex. It just looks like an elongated nut with spikes on one end which grip the wood being turned. At the other end is an internal screw thread, which fits on to the drive shaft of the lathe:
Because the lathe is old (you can tell from the black and white picture), the manufacturer doesn’t sell the spare part any more. They don’t seem to appear on eBay, presumably because anyone with a lathe isn’t going to sell such an important component. If I had any significant metalworking machinery, I could make one – but I don’t (yet). I do have a 3D printer, however.
I didn’t do any stress analysis on the component, but my instinct told me that a printed part wouldn’t going to be strong enough for this job. The centre has to hold a largish lump of wood spinning at up to 3000rpm. It has to do this while the wood is carved by a chisel, and most importantly it has to do this while I am standing very close to it. It’s not allowed to break. The body of the part needs to be reasonably strong, and the spikes on the end doubly so. It’s not really printable unless you have a SLS metal printer. If I could afford one of those, I wouldn’t be buying an old second-hand lathe.
My solution was to cast a new component, and to 3D print the mould for it. Some years ago I came across Plastic Padding Chemical Metal, which is a two-part polyester resin filled with metal powder. It’s designed for repairing things, and it’s very strong when it sets. I’ve mended various things with it over the years, and none of them have ever failed. I thought I might be able to use it to cast a new part. My wholly unscientific feeling was that it ought to be strong enough for the body of the thing, but probably not for the spikes. For that purpose, some hardened steel masonry nails might do the job. Casting would allow me to embed the nails in the part, and to create the required femall screw thread by simply casting around the male one.
This is actually the Mark III version. The first two did not have a separate end piece, and I eventually realised that once I had filled the mould with resin and put the nails in, I would not be able to separate it. Doh! One thing to bear in mind is that Plastic Padding is sticky. It’s designed as a repair material, so it’s intended to stick to things. I didn’t want it to stick to the mould, or to the screw thread on the drive shaft. To stop this, I lined the mold with sellotape, and covered the shft’s screw thread with a layer of PTFE plumber’s tape. You can’t beat a good bodge. Here’s how the mould looks, half assembled and almost ready for filling:
And here it is fully assmbled and filled with sticky goo, waiting for it to set:
After 20 minutes, I opened up the mould (you’ll have noticed the carefully-planned slots on the mould join line, for levering it apart) to reveal this mess:
Which eventually delivered a component which clearly needed a bit of cleaning up:
But it works! Just for entertainment, I mounted a 2″ square section block of cheap pine, and turned it into one of the roughest spindles you’ll ever see – but the Plastic Padding component worked fine:
Now I just need to learn how to turn wood properly…
Incidentally, I’m not sponsored by Plastic Padding. I’m not averse to them sending me a free pack, either 😉
I’ve not posted much about 3D printing for a while, largely because I haven’t ben able to get my printer to make a decent print without a lot of fiddling. Prints were rough, structurally weak, and generally unsatisfactory. I Tried all sorts of kludgy fixes, but nothing seemed to work reliably. I was beginning to think that the filament I was using was beginning to degrade (some of it is a year or more old). Then I had a conversation with a colleague about the 3D printers (Ultimaker II’s) at work. They were suffering similar problems, and were returned to good operation by replacing the print heads. It turns out that with sufficient usage, the tiny hole in the hot squirty nozzle (that’s a technical term) becomes both worn and partially blocked with overcooked filament residue. It’s a bit like the virtually indestructible stuff which accumulates on the the tins in which you roast vegetables. You do roast vegetables, don’t you? This (blocked nozzles, not ineffectually-cleaned roasting tins) results in a number of problems:
- Low extrusion rates
- Filament feed skipping, because it can’t push the filament hard enough
- Erratic extrusion
At work, we’ve started to think of the print head (or at least the extrusion nozzle) as a consumable item, to be replaced routinely after an as-yet undetermined quantity of filament has been extruded.
Why, I thought, couldn’t I try this at home? No reason at all. Apart from anything else, hotend technology has improved since I bought mine. It seems the generally-accepted best DIY print head is the e3dv6. It’s cleverly designed to separate the hot part from the rest by as small a thermal bridge as possible, and also has a built-in fan to keep the cool part cool. And unlike my old hotend, it’s got a separately-replaceable nozzle. So if (when) it does clog or wear out, it will be cheap to replace.
I bought one. Naturally, it needed a new part printing to fit it on to Richmond, but that was easy. And guess what? It works brilliantly. In a stroke, I’m back to creating smooth, accurate prints. Indeed, I’m tempted to say that the quality is better than the J-Head generated when it was new. I’m really quite chuffed.
It just goes to show that perseverance sometimes pays off. It turns out that the reason I couldn’t get the Olimex esp8266 to work properly was that my USB/serial converter was faulty. The replacement one arrived today, and now I can program the wifi module using the arduino IDE with no problem. Five seconds after programming it, it had connected to my home network and was sending temperature readings via MQTT to my raspberry pi server. There are plenty of IO pins exposed on the Olimex module, so I can do lots more with it than with the wi07c module I was using before. Watch this space.
I found a very promising new ESP8266 module, from Olimex (a Bulgarian company).
It’s a breadboard-friendly board with an ESP8266 and 512k of flash memory on it, and it’s dead cheap. There’s even a carrier board for it, with a relay and a reset button, also dead cheap. I bought a couple, because it exposes all the pins from the microcontroller, so I can (a) use more than one I/O, and (b) hook up the reset pin so that I can put the device into (and, more importantly, wake it up from) deep sleep mode to extend battery life. There are videos on line of how simple it is to program these devices using the new arduino IDE.
The (insert strong adjective here) problem is that I can’t (insert strong adjective here)-well get it to work. I can connect it up to my PC fine. I can even put it into flash mode perfectly well. In neither case will it respond coherently to anything sent to it from the PC. In ‘normal’ mode, it just repeatedly sends the word ‘Error’ over the serial link, and does not respond to any AT commands.
In reflashing mode, it simply fails to respond to the reprogramming commands. I’ve tried two of these modules, and both behave the same. I’ve contacted Olimex both by email and on their forum
, and had no response. It’s a shame, but I think these modules are destined for the rubbish bin. At least they weren’t expensive.
Update: Olimex have got back to me, and have made some helpful suggestions. They don’t know what the problem is, though, and it’s not one they have seen before. It may well be something to do with my serial adapter. I have another on order, so I guess I’ll find out in due course.
For a while now, I’ve been playing with the super-cheap esp8266 WiFi module. It’s been a bit of an uphill struggle, mostly because of the poor documentation (actually, that’s not fair – the documentation may well be excellent, but my understanding of Chinese isn’t) and the lack of easy programming tools. Until now, there have been essentially three ways of using the module:
Serial for breakfast
The initial method was to control the module via a serial link. As supplied, it can communicate with an arduino (or anything else) using a simple serial connection, using AT-style commands which will be familiar to anyone who has worked with modems, especially GSM ones. It works, but it’s a bit clunky. By and large, I think people have stopped doing this.
C for elevenses
Pretty soon after it became available, smarter people than me figured out that the module is powered by a general-purpose microprocessor (and a pretty powerful one at that). It also became apparent that you could reprogram this directly, and use its spare capacity (and spare I/O pins). Thanks to the manufacturer’s release of an SDK, it became possible to write code directly on the module, without the need for an arduino or any other processor. For less than five pounds, you could have a general-purpose microcontroller with build in WiFi.
Of course, there’s a catch. The tool chain required to do this programming is hard to set up and complicated to use. It also means programming in C and understanding a pretty complex SDK. It’s not particularly friendly. There were some valiant efforts to make this easier, notably Mikhail Grigorev’s bundling of everything into the eclipse IDE. This works well, but it still requires you to program at quite a low level.
lua for lunch
More recently, there has been nodemcu. This is a new set of firmware for the esp8266, which builds in an implementation of the lua language, with the SDK functions wrapped and easy to use. Nodemcu allows you to write programs in lua, upload them to the esp8266 and run them on it. This works pretty well. I’ve had temperature sensors in my house using it for a while, It has some drawbacks, principle amongst which is that the nodemcu firmware takes up quite a lot of the available memory, leaving fairly little for your programs. Add to this the fact that your programs are sent to the device as source code, and interpreted (or compiled) in place, and you find that there really isn’t much space to write more than simple programs. This shouldn’t be an issue for small sensor nodes, but I found myself scratching around trying to save a byte here and a byte there just to get my code to run.
Arduino for dinner
What everyone has been secretly waiting for, of course, is the ability to program the esp8266 like an arduino. And now we can. There’s a new version of the arduino ide 1.6.1 which gives you the ability to program the esp8266 using familiar arduino code. The wifi functions are easily available, as are most other arduino functions. It’s insanely easy to write something which connects to a wifi router, gets an ip address and sends data to a server. Or indeed to run a server on the device. Because the arduino language is compiled to native code before being uploaded, there’s loads of space for programs. Some of the normal arduino libraries have not been ported yet, but I’m sure they will be in the coming weeks. I won’t be going back to any of the other methods. Long live the king!
It’s worth repeating that the esp8266 gives you a tiny board with a 32 bit processor running at 80MHz, at least half a megabyte of memory (my recent olimex ones have 2MB), multiple IO pins and wifi for less than five pounds. If I were arduino (whichever half of arduino you care to pick) I’d be worried.
Since I posted a video of my 3D printed lathe on YouTube, the video has now been viewed over 100,000 times. If a typical working day is 8 hours, and the working year is 250 days or so, then it’s the equivalent of about two solid years of someone watching it. That’s not a job I’d want.
Anyway, a number of people have asked for the STL files so they could make one themselves. I’ve finally got them in some sort of order, and you can now download a zip file with them all from here [wpdm_package id=’423′].
If you haven’t seen the video, here it is:
So far, only one person I’ve told about this project thinks it’s a good idea. Everyone else looks at me wtih a mixture of pity and puzzlement, neither of which emotions seems to be mitigated by my explanation. Clearly, the best thing to do with the project is to bury it quietly, and where better to commit something to obscurity than on my blog?
A little bit of background
My eyesight is rubbish. With glasses on, I can see perfectly. Without them, I’m as blind as a bat. When I go to bed, I take off my glasses. If I wake up in the middle of the night, I am unable to find out what time it is without putting my glasses back on and looking at an illuminated clock. The problem is, that by the time I’ve done this (and waited for my ageing eyes to focus properly), I’m fully awake. If it turns out that it’s far too early to get up, it can take ages to get back to sleep.
The usual suggestions
Most people say “Can’t you get a clock with a big display?” It’s a logical suggestion, if you can see well. For me, the digits on a bedside clock would have to be about a foot tall for me to be able to read it without glasses. Others say “Can’t you turn on a light?”, but doing so brings me to full wakefulness (and runs the risk of disturbing my wife). Fools suggest “Can’t you just use an alarm clock?” I do. But if I wake up before it goes off, I want to know if it’s three hours before, or only one. If it’s only one, I’ll get up and do something useful.
Here it is, in all its glory:
No, it’s not the internet. It’s the Buzzclock. To use it, you press and hold the button on the top. It then tells you the current time by silently vibrating: one pulse for each hour, then one shorter pulse for each ten minutes past the hour. There is virtually no noise, no light and best of all no need to put on glasses. The time is not accurate to the minute, but it’s good enough to make the decision whether to get up or to go back to sleep.
Don’t laugh, it hurts my feelings.
Inside the box
It’s a bit of a squeeze. The brains of the device is an arduino Nano, connected to a battery-backed real time clock. The Nano is a very useful device – more or less the same functionality of an arduino Uno or Leonardo, but in a much smaller package. It’s also dirt cheap (about three of your earth pounds). You can plug it directly into a breadboard for prototyping, and then when you want to build the final device, you can solder it in to a PCB or stripboard, or you can plug it in to a terminal block breakout board, as I did.
The real time clock (RTC) module I used came from ebay, and also cost about £3. It uses a DS3231 chip, has a rechargeable backup battery and (unnecessarily) has 32k of flash memory on the same board. I guess the flash is there in case you want to use it for datalogging. The RTC chip also has a built in thermometer (I don’t know why).
The RTC and the arduino communicate over the two-wire I2C interface. This makes the wiring really simple. There are handy arduino libraries available to do all the heavy lifting. Thsi is a good thing, because the RTC chip has its own protocol for getting and setting the clock time, and the libraries wrap this into a nice simple set of commands.
The final component in the build is the vibration motor. This is one designed for mobile phones. As usual it’s from ebay and cost about a pound. This is a thing of beauty. It’s a small dc motor (it runs off 5V – the arduino can power it directly from an output pin) with an eccentric weight on its output shaft. When the motor spins, it vibrates. There is nothing special about that, except that it is tiny. The whole assembly is only about 10mm long. The engineering that goes in to mass producing those must be just staggering.
How it works
THe button is just a push-to close switch. As long as you hold it down, the arduino gets power. Let it go, and the power is cut. This way, the arduino uses no power at all when not in use. The RTC has its own backup battery, so it keeps track of time without using the main battery.
Every time you press the button, the arduino boots up. It then contacts the RTC to get the time from it, and sets its own clock. The output pin connected to the motor is brought high for half a second then low for half a second for each hour in the current time. After a full second pause, shorter pulses are used to indicate the tens of minutes after the hour. And that’s all it does. At four o’clock in the morning, when all is pitch black, its a very quick way of working out it’s too early to get up.
Setting the time
At the moment, you can only set the time by connecting the arduino to a PC and sending a string over the serial port. This is not a big deal, because the RTC keeps time over a long period. It’s only an issue when the clocks change to or from daylight saving time, and I can cope with the effort twice a year.
I can’t take any credit for this.
Earlier this summer, I built a Rubik’s cube solver from a Lego Mindstorms set. I simply followed the plans for the Mindcuber design. It seemed to work quite well, but my Rubik’s cube had one face which was much stiffer to rotate than others, and the power available from the Lego motors was insufficient to reliably turn it. So it’s been sitting in my office for a while doing nothing. Today, however, Rob lent me a speed cube he bought from Amazon. It’s designed to take as little torque as possible to rotate, and has nicely chamfered edges so it doesn’t jam if it’s slightly out of alignment when you try to turn it. In the picture, the speed cube is the one on the left.
The cube-solver robot loves it. I’ve posted a video of it on the YouTubes at http://youtu.be/iDMrePmmNA0 .
The whole thing is a supremely pointless exercise, but it is rather hypnotic to watch.