Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The Wouxun KG-UV3D radio has two lugs inside the battery compartment:
Wouxun KG-UV3D – battery lugs
The battery packs and DC adapters all have clever spring-steel latches that engage those lugs, with a pair of sliding buttons that depress the ends of the spring to release the pack:
Wouxun KG-UV3D – battery pack latch
That mechanism may be cheap, straightforward, and easy to build in mass production, but I can’t figure out how to duplicate it for a case to house the GPS+Voice interface circuitry. That box had the dual disadvantages of being plug-ugly and not locking to the radio, but it did help establish some key dimensions, which is not to be sniffed at.
A bit of heads-down effort produced this not-so-hideous printable case:
HT-GPS Adapter Case – Overview
The rectangle on the top is a built-in support structure for what will be a window over the four LEDs on the Byonics TinyTrak3+ board. The two holes on the top allow screwdriver access to the TT3 trimpots, although they might not be necessary. The four holes (two visible) along the sides fit 4-40 setscrews that lock the PCBs into slots along the inside of the main case body. The red doodad off to the far side is that plug alignment block for the radio.
The yellow latch plate on the end engages the lugs with a bar sliding in a slot, which looks like this when it’s locked:
HT-GPS Case Latch – locked
A view from the top side shows the notches that release the lugs:
HT-GPS Case Latch – detail
In the unlocked position the notches and lug slots line up:
HT-GPS Case Latch – open
The solid model shows the plastic structure, which is slightly improved from the pictures:
HT-GPS Case – latch and connector plate
The big hole fits around the TinyTrak3+ serial connector to the GPS receiver. The slot across the hole splits the plate so it can fit around the already-soldered connector.
The latch bar consists of a L-shaped brass angle (from the Big Bag o’ Cutoffs) with two snippets of square brass tube soldered to the ends:
HT-GPS Case Latch – bar detail
I cut the angle to length with a Dremel abrasive wheel, soldered two brass tubes, sliced them off with a Dremel cutoff saw, roughed out the slots with the abrasive wheel, and applied some tool-and-die maker’s (aka needle) files to smooth things out. Yup, had to clamp each soldered joint in a toolmaker’s vise to keep from melting it during the nastier parts of that process. A pair of 2-56 screws, with nuts behind the plate, hold the bar in place and provide some friction.
Moving the latch bar requires poking the end with a sharp object (captured by the brass tubing), because I couldn’t figure out how to put finger-friendly buttons on it. This would be completely unusable for an actual battery, but should work OK for a permanently mounted GPS interface.
Conspicuous by their absence:
Holes in the case for the cables (may need more surface area on the ends)
Any way to fasten the latch plate to the main case (I may just drill holes for small pins)
Provision for the TT3 mode switch
A cover for the exposed radio chassis above the latch lugs (may be a separate shell glued to the latch plate)
The whole thing needs a full-up test to verify the serial connector clears the back of the case…
The print failed when the nozzle snagged one of the tines, which instantly jammed up against the bottom of the heater block and stalled the platform motion with a horrible crunch. Surprisingly, the motors didn’t lose all that many steps, but you can see extruded thread drooling off the top layers.
The 0.25 mm layer thickness contributes to the problem: any distortion while the plastic cools produces blobs on the top or poor adhesion, depending on whether the just-printed layer moves up or down.
This was with infill = 60 mm/s, perimeter = 20 mm/s, and moves = 250 mm/s.
That speed difference produces crap quality objects, because the high speed infill produces ragged edges that a single perimeter thread can’t convert into a smooth surface. Two perimeter threads work fine, but the top surface looks ragged from the mechanical wobbles induced at every direction reversal.
The root cause: my heavily modified Thing-O-Matic has too much moving mass and not enough rigidity, of course. Time to back off the speed for better results…
Having suffered flat tires due to the tire liner chafing the tube, I’ve been running the Tour Easy without a rear tire liner since last year. Worked fine, up until the steering went mushy on a recent ride:
Brown glass chip – in tire
Ever notice how a rear flat means you can’t steer and a front flat means you can’t pedal? Works that way on our recumbents, too. Weird.
The chip probably came from a beer bottle tossed out a car window, those being the canonical source of brown glass on the road. That razor edge punched right through the Kevlar belt in the Schwalbe Marathon tire and just barely penetrated the tube:
Brown glass chip – detail
Fortunately, I discovered all that in a nice grassy area, patched the tube, fired a pair of CO2 capsules into the thing, and rode another 20 miles around the block on a lovely day. Unfortunately, I managed to pinch the tube while installing it, producing a very slow leak that flatted the tire by the next morning.
While repairing that flat in the comfort & convenience of the Basement Laboratory Repair Wing, I installed a tire liner with two strips of silicone tape over the ends to see if that reduces the abrasion:
Silicone tape on tire liner
Silicone tape doesn’t adhere to anything other than itself, so I added two duct tape snippets to hold them in position while I buttoned up the tire. And, yes, I left the transparent plastic cover tape in place, in the hope that it can’t do any harm.
Perhaps the inevitable slow leak will produce a flat in the garage, not on the road…
New this year at the Trinity College Firefighting Home Robot Contest will be a Checkout Table, where teams can verify that their robot meets some initial specifications (Section 2.5 of The Rules). The overall size should be the easiest spec to check; I just glued up a pair of suitable Bounding Boxes:
Trinity Robot Contest – bounding boxes
Robowaiter robots must fit in the smaller cube, which is 30 cm on a side. Firefighting robots must fit in the larger box, with wheeled / treaded robots inside the 31 x 31 x 27 cm outline and walkers within the larger 46 x 31 x 27 volume.
Next step: fluorescent orange paint over a white shot coat to kill the lettering.
… look like they ought to fit some sort of tubing and, indeed, a bit of rummaging produced a hank of suitable thick-walled plastic stuff. Heating one end until it went clear and floppy, then jamming it over a syringe’s Luer fitting produced a workable flushing tool:
Syringe with tubing to fit R380
I folded a tissue, laid it over the sponges and wipers at the printhead park position, then pushed the ink tank carrier over the tissue to absorb the spray. Squirting three syringes full of 10% ethanol through the head cleaned out a few of the blocked jets, but didn’t produce a complete fix.
Next up: homebrew window cleaner, diluted about 1:3 to knock back the ammonia concentration.
I dropped that lens cap and the sheet-metal disk popped out; evidently the acrylic caulk doesn’t really count as an adhesive. Cleaned out the residue, ran a thin layer of urethane adhesive around the rim, and applied some clamps:
Re-clamping the cover
Cleaned out the inevitable urethane bubbles that emerge from even the most minute opening and it’s all good.
The Smell of Molten Projects in the Morning 