Check out my tensioning slots on the base plate:
That's a pretty common way to allow a builder to slide the pulleys back and forth until tension on the belt is juuuuust right.
But wait, what's this?
That only works if you calculate your belt length right! Way off the rails and there's still lots of looseness!
Turns out, I had it calculated for ~300mm on an older pulley design. But the old pulleys had to be reduced in size to clear the base plate:
New designs work out to be around 250mm, so I have a couple new belt sizes coming in that bracket that measurement. Bonus: I'm starting to build up a collection of sizes! The rapid prototypers' dream, the space-constrained apartment nightmare.
Here's the initial mechanical design.
It's totally a "throw together" laser cutter design, using mostly components I have on hand and scrap acrylic.
The design is very definitely sub-standard, in both form and function. The critical parts are locations of the DC motor output shaft, and bearings. The surrounding frame is totally unimportant, and will be replaced with something pretty when I've proven the mechanicals.
Yeah, this is entirely made out of scrap-bin materials. Upcycling!
A timing belt from the motor shaft will drive the main shaft, upon which the PCB is mounted. I was planning to finish laser cutting the timing belt pulleys too, but then some friends showed up and we started drinking.
As mentioned in the previous log, I don't have a bespoke solution for batteries yet. This is the area that needs the most improvement at this time.
Currently, the working plan is to stack up 3 LR44 batteries in-line with the PCB, as shown. This has the advantage of being small, axially balanced, and in the right voltage range. That last point is not critical, as I could work with 3V, or throw a boost converter on there if the blue LEDs require.
My initial thought was to throw a wide zap-strap on there to hold the batteries in, and form some copper contacts on either end to make electrical contact.
This is janky and I'd like a better solution! Let me know if there are any. An off-the-shelf axially-mounted battery holder would be boss, but I don't think they exist.
Details are being blocked in, and quick prototypes are being built.
Here's how the PCB is shaping up:
Outer diameter is 70mm. The LEDs are 0805 side-mount LEDs, blue on the right, green on the left. The centre shaft is 3mm, and will not go all the way through the PCB.
Tentatively using 3 LR44 batteries stacked vertically in the centre, but I'm open to suggestions, both in battery and in mounting options.