Freesteel Blog » Machining
Monday, April 18th, 2016 at 4:43 pm - Machining
This has taken a lot of effort fighting through the device trees on the Beaglebone to make it access the PWM and Quadrature encoder services at the same time, which is the minimum required to effect a stimulus response observation from a DC servo motor powered by an H-bridge.
What happens when you apply a fixed voltage to the DC motor for an eighth of a second, then reverse the voltage for another eighth of a second, and then set the voltage to zero (and try it for many different voltages and directions):
Here’s the graph of motor positions (in Y) over time (in X) for 20 different trials:
Tuesday, April 5th, 2016 at 1:04 pm - Flightlogger
On this second day of heavy rain in the Pyrenees I think I might have the time to catch up some ancient history from all of last week. We waited five hours on El Bosque for the wind to come right, and were then rewarded with this flight with vultures.
These birds came much closer than they ever showed up in the pictures. They fly with hunched shoulders.
Unfortunately the GPS for that flight is inexplicably jagged, so here’s a flight above Teba from a day later where the data is cleaner.
The yellow cube is 1000m on each side for scale from a flight that took off at the point on the frontmost vertical cube edge
Here’s a zoomed in section of the left most section of the path, shown looking down, with 100m XY axes in yellow. The track comes in from the bottom right goes to the top left (against the wind direction), then turns left to make four anticlockwise loops that drift back with the wind
It happened towards the end of the flight before last when my wings became my own, and I just wasn’t thinking about it any more. I stopped having those intervals where I lose concentration and fall out of the sky because there was no concentration to lose. It was all about the feeling.
Above the town of Teba watching the cars scooting along the grid of streets like busy beetles in a rotten log
Low on same rocky hill just after take-off where I struggled to survive for some minutes before I found a bubble of rising air
If you need to learn hang-glide, there’s a English school down here called Lejair where you could get it all done in two weeks (instead of the average two years of weekends back in England) because the weather is better and they use tow trucks with gliders tethered above a trailer so you can learn how to fly it without having to run up and down the hill and learn how to steer in short difficult bursts. (If you have to ask why you need to learn hang-gliding, then you don’t need to.)
We were woken by all this nice birdsound. Then we spotted that it was from three tiny birdcages in the courtyard below and it seemed so cruel. Why can’t they use little speakers tuned to a radio channel that broadcasts live birdsound?
Got to go now. We’ve not had an off-day where I can devote 10 straight hours to coding the datalogger analysis or write any of it up. I have two interesting results to report. One being the delay on the GPS, and the second being the clean mathematical relationship between the turning circle and bank angle as measure.
Wednesday, March 23rd, 2016 at 6:16 pm - Flightlogger
Final late blog of the day.
Soldering, laser cutting and 3D printing took up the following week, and it should now small enough to fit onto the glider without getting in the way.
(Tom’s trick of defining a virtual second side of the board which we don’t actually cut, but instead implement with jumper wires worked a treat.)
We’ve got the questionable barometer, GPS, humidity, 2 temperature sensors, wind meter and an absolute orientation sensor (at the top) all logging at high frequency to an SD card and with an OLED screen to show me what’s not working so I can fix it in time. The black slab at the bottom holds 4 AA cells.
First thing that got logged was my fridge over last night using a string of 5 temperature sensors left over from Housahedron days:
It’s the most boring high efficiency fridge in the world with a cooling cycle of four hours and, not surprisingly, different temperatures on each of the glass shelves.
I’m wondering if the new microbit device, of which a million will be distributed to children, has enough tech in it to use as a fridge logger. Everyone has a fridge. This would make an easy project for kids to log and upload the data of their make and model to a common place in order to find where the crappy fridges are. In the future they need to all be found and replaced, because they cost significant energy and CO2, but nobody knows since the electricity bills are aggregated for all appliances in one house and are mostly unknown.
For contrast, here’s an overnight log (interrupted at 4am in the morning for my host to get up and drive to London) of a fridge in Leeds using a different datalogger where the cycle is four times an hour:
I can’t explain the long hiccup at 3am where it skipped 3 cycles. Maybe there is a lot of information in that particular curve, such that the real way to find out about the quality of the fridge is to turn it completely off and measure how warm it gets overnight. Great idea. I can see a lot of kids getting into trouble over that one when the food is all spoiled. To which they can respond: “Hey look, it’s only the fridge. It’s not like I’ve done it to the whole planet.”
Wednesday, March 23rd, 2016 at 5:03 pm - Machining
Carl Bass (CEO): Yeah. I just wanted to say one thing…
The first thing is that I think a number of the 13D filers as well as some of the activist investors have raised legitimate concerns…. I think too much credit is being given to them and not enough credit is being given to our long-term investors, who have asked for a change in a constructive way…
Many of my problems with sort of some of the more activist investors is that their focus is extremely short-term and somewhat simplistic. They just ignore some of the complexities of running a business…
[M]y concern is people who like essentially want to turn Autodesk into Men’s Wearhouse. If you look, I don’t think any of the people who got involved in Men’s Wearhouse intentionally meant to do damage to the company. I don’t think they meant to screw it up, but I think they had some simplistic views and what troubles me is seeing those same views expressed about our business.
Actually I got one little funny story here. I looked at Men’s Wearhouse the other day and they changed the name of the company and the symbol and what I thought was interesting is changing the name makes it actually hard to track the price and how poorly it’s performed. But the symbol is a little bit of a telltale sign because if you just look at it, it’s spelled TURD, it’s actually TLRD, but it’s what it looks like, and it’s probably more like it.
Basically, the investors had declared a truce with the management which involves inserting three of their guys into the chain of corporate command, such as it is.
This is probably the first time in 30-odd years that these folks have had people not of their own choosing within the system. And chances are they’ll find the processes ludicrously informal and ineffective, as they appeared to me lower down.
Wednesday, March 23rd, 2016 at 1:28 pm - Machining
I haven’t got much time for this blogging lark today.
Before this gets too stale, here are some quick notes on the polar drawing robots that we had running from steppers and servos motors using Machinekit and drivers scavenged from the CNC milling machine.
This got shown at Phrased&Confused acoustic festival, where one of them had to perform on stage and almost peeled the corner off the paper it was drawing on.
This was the state of the robot a couple of days before:
And this was at around 5am the night before:
The project management was on github under https://github.com/DoESLiverpool/Tosca/issues.
Problems remained with the Z-axis communication and its operation on the gondola, as well as inadequate pen pressure on a vertical surface from an object hanging down next to the vertical surface. But we did learn a lot more about the CNC servo motor operation, and MachineKit on the BeagleboneGreen performed excellently.
We hope to set it up on the wall some place and continue development.
The less said and remembered about the fighting I’ve had over the past three weeks attempting to get this working the better.
Basically, the problem was eventually traced down to a faulty solder joint on the ground pin of the six channel open collector chip which created too much of a resistance to drain the 5V signal down to ground for the gecko drive to respond in the rare case where four 1-signals were emitted from the Machinekit controller at the same time. This happened only when two of the axes were moving with the direction pins high and two step signals went to the motors simultaneously. This resulted in travel in the Y-positive direction missing 1% of its pulses so that the cutting toolpath drifted ever so slightly in the Y-negative direction as cutting progressed, but there being no effect when you jogged the table or arm axes individually. Drove me nuts, as you can imagine.
It was a learning experience. If we can nail this bug, we can nail anything (we had to check through so many other problems which weren’t there to find it), but it set us back weeks of worry, pain, late nights and missing weekends
Quick edited movie with limited footage as I forgot to film a lot of the exciting bits (like the helix ramping) as was a bit too scared to think of it.
I bricked a BeagleBone Black on Monday by plugging a 5Vs into a 3.3V pin while attempting to get it to run a stepper motor (using the exact same installed software that we have for the milling machine tool).
Oh well. I shall have to financially reward the BeagleBone corporation for their easily broken products by getting a replacement. Time to try out one of these cheaper BeagleNone Greens if I’m going to make a habit out of this.
Here’s what my order from Mouser.co.uk looked like:
Note: I ordered 2 boards so as to qualify for free shipping.
And here’s the report from Fedex of the route:
The seamless efficiency is a little bit scary. I drank a whole cup of coffee staring at it. Then I went downstairs and picked it up from the front desk.
Following a very grumpy Friday and an off-the-cuff comment by someone on Facebook to the Wrynose Pass as a potential easterly site, I headed off from Bull Pot Farm into the Lake District where I have never been before.
I was not in the most ideal mood for this sort of thing, being alone with a hang-glider on an unfamiliar craggy hill at 3degreesC and 27mph wind. Fortunately I stopped myself from doing anything really stupid, and sat in the car stewing and programming until suddenly and unexpectedly the wind dropped to something between too light and perfect.
I didn’t hang around, having already scouted for my hillock of a take-off point.
After months and months of stirring through the compact three-dimensional enclosed arrangement of overheated servo motor drivers and circuit boards, unplugging and plugging them back in again, attempting to tune them, and causing all sorts of interference signal spikes and yanked wire problems, I decided that it would be better just spread everything out on a triangle of scrap plywood.
Now that I have totally lost faith in these Leadshine drivers, it’s going to be easy to replace them with gecko drivers, when they show up. They have Error signal pins, which also need wiring into the system, along with other signals. Everything is now completely accessible. The folded shelter material is to keep out the rain of iron filings from the milling that can’t possibly do this circuitry any good.
Then I performed the same trick on the hang glider logger, which similarly was enclosed in a 3D box of circuits. This has been opened out onto a flat panel of wood — after Adrian warned me that acrylic would likely be too brittle and crack. (He didn’t have any spare Delrin after touting how wonderful this type of plastic is.)
It’s an enormously heavy and large panel, even though it contains exactly what was in the original setup. It’s kind of like unpacking your rucksack into a hotel room and making it knee deep in stuff.
Things have to be in the open to be worked on.
It took forever to measure out all the mounting points and design them, even though I mostly resisted the temptation to over-engineer any of it with convenient clip-together holes.
The hardest thing to design is the battery case. I wanted one where the batteries slid in from the end, instead of the usual side entry from which they tend to easily fall out. This is version 5 where the bolts holding it down go between the two battery cylinder channels.
I must have consumed about a kilo of 3D printing filament (we only had black) building all the mounting points. The old box is the coloured bit.
Originally I was going to have this panel mounted on the upright of the glider and poking out forwards on a aluminium rod, like this:
Then when I tried it yesterday morning I realized there would be too much vibration — something I hadn’t noticed while merely handling the rod in my hands without one end stiffly anchored. This wouldn’t do any good to the accelerometers.
I do get a lot of things wrong, so I am used to changing designs suddenly (hence all that scrap). I wonder how much harder it is to change when working in a team and you have to persuade more than one other person that we need to junk everything right away and not waste more time on the wrong track. It’s the inertia, so to speak.