Several years ago I picked up a used Dell Chromebook 11 3189 (model code “Kefka”) to play with. At the time it was still receiving ChromeOS updates, had a sticky hinge that required some lubrication and manipulation to get working, and cost around $100 including the separately purchased power adapter. I’ve hacked on it in a wide variety of ways over the years, and the main interesting result is that I’m starting to think a hacked out-of-support x86 Chromebook is, in many ways, now better and cheaper than a Raspberry Pi in that role as a modern accessible extra computer to enable fearless play the Pi was intended to fill. I’ve been taking notes, so way too much detail below.
Every now and then I like to post one of these, just to show process I currently use. The magic of 3D printing is that once you’re set up this kind of quick job comes up all the time.
I have this cheap thread assortment that came on tubes rather than spools. It’s surprisingly decent thread, has good coverage for finding suitable colors for any project… and the 13mm ID tubes wobble badly on standard 4.5x40mm spool pins on sewing machines, especially when filling bobbins.
I was doing a little (ham fisted) machine sewing this weekend and it was irritating me …so I fixed it.
The tube wobbles badly on spool pins, especially when winding a bobbin.A couple quick measurements.A pass through the CAD/CAM processPrinting the part. Silver “Silk” PLA because it was loaded from the previous task. Fits well enough on the first try.
I’m finally getting less-incompetent with FreeCAD. Straight to “Part Design” workbench, sketch only one extruded pads’ features at a time, then decorate in any chamfers etc. at the interfaces. Import into PrusaSlicer with some sane defaults, send to the Anycubic Linear Kossel in the basement via OctoPrint (No, I don’t do it blind, I send and load the file, then go down to keep an eye on the startup sequence and make sure the filament hasn’t cracked and such), receive part.
Fit is intentionally a bit loose on all dimensions, nothing this part interacts with is consistent or close-tolerance, everything should move if it wants to, and the chamfer gets the tube seated well enough to not flop about.
FCStd and 3mf if anyone else happens to have this exact problem, which seems likely because similar thread assortments seem to be pretty ubiquitous on the usual eCommerce sites.
Original RG351 and PowKiddy RGB10 Membranes, installed in a RG351pAngled comparison, to show height.Top down comparision.
I’ve had an Anbernic RG351P for roughly 2 years now, and it’s an absolutely delightful object.
For those unfamiliar: the RG351 is an example of a class of little gaming emulation handhelds that started back in the mid-to-late 2000s with things like the Dingoo A330. They are, essentially, a tiny ARM (+ usually Linux) machine the size and shape of a handheld gaming device, set up with a built-in controller specifically to run games in emulation. The stock firmware on the RG351 is an ancient EmulationStation/RetroArch/Linux stack, but there are better alternatives – IMO, throwing in a decent SD card loaded with AmberElec is the first thing to do when you get one. It will play essentially everything from the dawn of gaming through the PlayStation and some (but not all) of the Nintendo 64 library, and has limited/marginal support for PSP and DS. It is …straightforward but not the sort of thing I’ll link… to obtain the full ROMsets for these platforms, they are frankly not that large. I paid about $90 for mine, I think they’ve gone up a bit, but there are a whole range of similar options at different price points, build qualities, and platform support.
The build quality, however, isn’t perfect. It’s small-brand China-export hardware. You know you have to be a little careful with it just from handling (I keep mine in a fitted case when throwing it in a bag). I’ve been through a screen (I got red lines in my original after about a year), re-gluing the back rubber pads (original glue melted), and now after two years I wore through the membrane behind the “A” button, and that’s actually what this post is about.
I opened it up, found the worn though button, looked around online, couldn’t any in stock, contacted Anbernic through their AliExpress store front (none available), asked the subreddit (no leads), and couldn’t come up with any exact replacement membranes.
HOWEVER on inspection, the membranes from the similar Powkiddy RBG10 appeared extremely similar, and those are readily available (as a $12ish pack of all the membranes and button caps to refit an RGB10, which includes two of the 4x membranes). I ordered this set via Aliexpress, and ~16 days later when it showed up, can confirm the membranes are slightly different, but drop-in compatible.
As you can see from the photos, the Powkiddy membranes have a bit more flat area, and the bottoms of the mounting holes are filled in rather than fully punched through, but the dimensions are exactly right. The height and force of the domes is even almost identical to the originals, and at effectively $6/membrane it’s a very reasonable repair.
Since I recently got my HP Apollo 9000 Series 735 up and running, and it’s March, I decided to have a little Marchintosh fun and load MAE (the Macintosh Application Environment, a real officially-licensed Apple product) on to it this evening. As you can see from the photo (because I don’t have a device that can capture the video this thing outputs, and haven’t figured out screenshots under HP-UX 10.20), it works.
Bad light because that VESA arm mounted monitor is the only one I own that will sync to this thing
Over a year ago I started working on an inert HP Apollo 9000/735 a friend gave me from their collection to avoid moving it cross-country. I’ve recently got it working, and am posting notes about the fun.
At the end of my first post about it, I had recapped the power supply, but had not found a monitor that would talk to the enormousCRX-24z video board with its 1280×1024@72Hz Sync-on-Green via 3x BNC output, or verified the condition of the discs. As you can see from the splash image, all of those things have been remedied.
Last summer I posted about some tiny stepper motors from the internet, thinking about them as an alternative to mechatronic standbys like those terrible SG90 type servos or larger and differently terrible 28BYJ-48 geared steppers driven through a ULN2003.
At the time, I tried one with an A4988 stepstick from the top of my parts bin, and it didn’t work, so I figured there was some limitation and stuck to directly driving with H-bridges. …it turns out the “limitation” was that the cheap current-setting potentiometer on that particular stepstick was broken so it was driving no output current.
Discoveries:
Those little bipolar stepper motors work fine with bipolar stepper drivers.
Generational gains in bipolar stepper driver ICs are substantial (eg. A4988 -> TMC2208).
The venerable 28BYJ-48 unipolar stepper motor is easily modified to run from bipolar drivers.
Giant Escape 3 Disc with SKS B53 fenders, modified to fit
I’ve been biking a fair amount lately after a 20-odd year hiatus; I decided last year that I wanted to start biking, bought a Giant Escape 3 Disc near the end of summer, but didn’t get confident enough riding to use it around campus last year among the students texting their way to their first (next?) vehicular manslaughter charge before they flocked back.
This summer, I’ve been dong my commute into campus on it, plus a significant amount of fun/exercise riding, and the top fixable annoyance has become getting sprayed at the slightest hint of wet. I did some hackin’ that I haven’t seen on the interwebs to fit the fenders I picked to the frame, which is the point of this post.
I have an Onn Surf 8 (One of the surprisingly-not-that-shitty ultra-cheap Walmart tablets) that my research group bought a couple of to use as Android dev testbeds. I’ve been occasionally using it as a normal tablet since I have it around, and have been consistently irritated by the collection of bloatware it comes with…. so I decided to hack it. To tl;dr this whole thing, ignore the collection of typically scammy Android dev forum and blogspam crud, and use the open-source mtkclient for your MediaTek Android device hackin’ needs.
I impulse bought a 5 pack of tiny stepper motors off Amazon for $3 to satisfy my curiosity. A colleague showed them to me and asked if I knew anything about them and …I didn’t, but they were too cheap and interesting not to try.
I couldn’t find any documentation on the internet from the identifying marks, so I burnt an afternoon figuring them out, and I’m posing my notes in case anyone else wants to make use of them.
The labeling on the motor itself is “SRG0808 003PLK5” which doesn’t turn up anything useful in a quick search, and the bag they came in is labeled “Fashion Worlds stepper motor 9496 x5” which is also not something googlable.
The motor comes attached to a flat flex cable with various adhesive pads built in, a boardlet, and a connector at one end. The output shaft is set in a brass gear roughly 2.75mm diameter with 12 involute profile teeth, about 3mm long – I don’t know small gears well enough to infer a ton from this, but it does seem like there is a lot of compatible gearing on the market.
Test setup for one of these steppers
To get around the lack of documentation, I probed one out with a DMM then built a test rig out of a dual L9110S H-Bridge board and a little STM32F103 dev board with the AccelStepper Arduino library to figure out the details.
They appear to be 20 steps per revolution motors, though they seem to work noticeably better with a half-step drive pattern. They work nicely at 3.3V, but get a little hotter than I’m comfortable with if energized for an extended period of time; I also tried 5V and it seems to tolerate that fine as well, gain a noticeable amount of extra torque, and get appreciably louder.
I don’t have the tools around to easily test the effective torque, but was way more than I expected based on my experiences with other small hobby motors. In my little taped-to-the-table test setup (pictured), if I jammed a fingernail into the rotor when it was already at speed at around at about 1000 steps/s on a 5V supply, the motor and/or nail deflected rather than missing steps.
Motor Diagram
If you look at the motor with the output shaft facing away from you and label the four pads A,B,C,D, the phases are A-D and B-C with about 9Ω across each phase.
FPC Connector Pinout
If you look at the attached flat flex cable with the end pointed toward you, it has 7 contacts. For reference, let’s refer to them numbered 1-7 left to right. The ribbon itself is 4mm wide, and the contacts appear to be 0.5mm pitch, so it would probably mate with any of the various “7Pin 0.5mm Pitch FFC FPC” connectors floating around on the market for cheap if you wanted to spin a driver board for it that used the included cable.
The last 4 cable pins correspond to the motor terminals 4-D, 5-C, 6-B, 7-A… but for experimentation it’s easier to just solder leads directly to the motor pads. I used two pairs out of some old stranded CAT5, visible in the top picture.
IR Reflective Object Sensor Breakout
There is a bonus component on a little arc-shaped boardlet built into the flat flex. It appears to be some manner of reflective infrared optical sensor, which I assume was used to establish a home position in whatever these were designed for use in – frankly since it has convenient mounting holes and wiring it would be pretty nice to use the same way in most applications I would want one of these in.
The first three ribbon pins are attached to this part, and none of these pins are shared with the motor itself. For discussion, let’s number the pins 1,2 left to right on the side toward the flex cable, and 3,4 right to left along the other in typical IC fashion. The pins are broken out Part 1 = Flex 1, Part 2 = Flex 2, Part 3 = also Flex 1, Part 4 = Flex 3.
Two of the pins (+ on 2, – on 3) appear to be a diode with a 1V forward voltage, and after I thought about it and checked with a camera with a bad IR filter, it is an infrared LED. The other pair seem to be a phototransistor or similar; it reads about 1.5MΩ from pin 4 to pin 1 in darkness and 1KΩ across the same with an IR LED pointed at it.
I’m not sure what I’m going to do with these, but they seem promising for small motion systems, especially since (if I bought bulk packs of each from China) you could get the motor and pair of H-bridges to drive it for under a dollar. Hopefully I’ll run into something to play with them in and/or my reversing work will enable someone else’s cool project.
I’ve had an Anycubic Linear Kossel for several years now, and have generally been quite pleased with it – if Anycubic were still selling them I’d still be suggesting them as ideal first printers.
It has produced quite a number of useful pieces, a decent assortment of household conveniences, and the usual selection of toys and meme trash for myself and others.
I’ve made a couple recent upgrades that seemed worth documenting.
