Freesteel Blog » 2016 » February
Wednesday, February 24th, 2016 at 9:59 am - Hang-glide
Work interrupted by a couple of mid-week trips, first to Long Mynd:
Then to Llangollen, where I didn’t fly so well and spent the entire time getting buzzed by this huge dual hang-glider that seemed always able to keep up with me.
That’s why you’re supposed to learn a lot by flying with really good pilots so you can see exactly why you’re not anything special at any time.
And anyway, the data logger was bust with a loose wire on the I2C connection. I should have enough data from the Long Mynd flight that I ought to be doing stuff with this morning. Instead I’ll probably work on the serial connection to the orientation sensor or do some on-line shopping for other electronic gadgets whose data streams I record and ignore.
Record and ignore
Remember the rule: the further removed in time and place is the data, the lower its value. While some data becomes relevant when it gets old, it’s as rare as antique furniture. You can count on the crap rotting in your garage not being within that category. The conclusion is if you don’t find an application for the data now, you’re not going to find it later on.
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.
Well, at least I sorted out the metal supplies by cycling to Scimitar Steels in Bootle at the furthest public limit of the dock road and persuaded him to cut me the most pitifully small piece of mild steel anyone has ever ordered from him. Couldn’t even be bothered to charge me. I think he said the substance was “080A15 EM32B” steel, which according to kvsteel is:
General purpose steel bars for machining, suitable for lightly stressed components including studs, bolts, gears and shafts. Often specified where weldability is a requirement. Can be case-hardened to improve wear resistance. Available in bright rounds, squares and flats, and hot rolled rounds. Can be supplied in sawn blanks, and bespoke size blocks.
Sounds like the correct stuff to me.
Then, as I was fetching my bike, I spotted a picture of a milling cutter on the side of a Lloyd&Jones Engineering truck parked outside the shop, and went in. I didn’t see any on display, so I had to check their website to find out about their sensibly priced 2 flute solid carbide tian coated end mills among their limited selection. It’s 2 flute so I don’t need to run it so fast according to the feeds and speeds calculations.
Back home on the machine it proved rather good for facing off, being as I could run the spindle at 7000rpm instead of the near-stalling at the minimum of 2400 owing to the fact that the mill cutting speed surface ft/min should be 350 with carbide cutters as opposed to 70 (for “steel 4140″, whatever that is).
I got everything sorted out, probed, position and then gouged.
What happened here is one of the drivers decided to give up and go into an error state, and the other one carried on going back and forth in its arc as though it was still following the rectangle. Luckily it was only a test cut of 0.2mm deep.
This problem means it’s not reliable enough to do the whole job without a proper gouge. We need to put a feedback from the servo driver to the controller to cut everything when one of the axes trips out like this.
I reset it (by power cycling) ran it again far enough to where the linking motions came into play. I’d dialed for a toolpath with the maximum staydown and no retracts — which was a feature I spent a whole year working on.
It’s rubbish. It takes so long to retrace its steps back round the metal instead of nipping over the top. Now I understand why Mr Denmark kept referring to this as a “perception thing” when he urged me to work on this feature, because he knew (even if I didn’t) that it was a waste of time because it made a slower toolpath. But like a know-nothing that I was, I had to try it to believe it. And until you try it, you will want it. But you only need to use it once to be satisfied.
This reminded me of Adrian taking apart a cheap toy car remote control unit the other week and discovering that the aerial poking out the top wasn’t attached to anything. The circuit board didn’t need it, but since most customers believed it should have an aerial, the designers put a pretend one in for them to extend and retract to keep them happy because it was a whole lot easier than attempting to educate them about it.
I was only going for 2D Adaptive clearing here, because I am intending to control the depth with G92 settings to reposition the Z, and so be able to try different depths of cuts. This meant that the retract plane has to be high enough so it works for my lowest cuts, which is not efficient.
I’m pretty sure now that linking motions should totally be calculated by the controller, and not be done in the CAM system. It knows where the material is (and could laser scan it if necessary). That way we wouldn’t have these overly high retract planes, and it could work out its own rounded trajectories, knowing its own kinematics. That should be its job.
Meantime, I found this very detailed video blog of someone systematically testing out four different 3D printer software slicers to see how they performed on the same printer. I watched both episodes last night.
I’ve put this here to tell you that reviewing of CAM software is a thing. In this case it’s just for the extrusion 3D printers by one guy who gets the idea. You can see the core developer teams for the different products being able to use this information to direct their work, as well as for users to be informed about which is the best software to use.
In all my experience, this thing — independent benchmarking and reviewing of CAM software with an admirable degree of curiosity for the benefit of users — has never happened for 3axis machining software. Even though such software costs many thousands of dollars, runs on machines that cost hundreds of thousands of dollars, and has been around in various states of development for decades.
The problem is that customers, who are almost always professional engineering firms, are not curious and don’t go looking for stuff. Instead they’re busy earning money and working all the time. So they don’t do anything until a salesmen comes to them personally to sell them software products for them to consider. This massively inflates the prices (to cover the cost of the salesman) and guarantees that the only information they receive is biased and not even generated. By that I mean that the salesman probably won’t even know what’s the best performing software on the market. It’s difficult to find out, and he doesn’t care, because his commission comes from sales of this product only. This is a business after all. Nobody is paid to care about getting things right.
If a detailed independent review of the 3axis CAM software on the market ever took place, it should to discover which of the different products are actually using the same machining kernels under the hood. That would be a minimum outcome.