Our kids are starting to outgrow our double stroller, but will still want to ride from time to time. We've had this wagon for years, but it needed some upgrading. Rather than toss it and buy a new kid wagon, I decided to modify this one. Its biggest deficit was its wheels. They had metal sleeve bushings instead of real bearings and the wheels themselves were basically just an ABS doughnut with a narrow/thin rubber bands for tread. The treads had all cracked and fallen off. All this made the wagon hard to pull and loud.
I decided to make my own wheels to solve both problems. The new wheels consist of two halves and a TPU tread. The halves are keyed to mate with each other and are held together with m3 nuts/threadserts. Each half contains two skate bearings, resulting in four bearings per wheel. It's probably overkill, but I didn't want to leave the two halves unsupported in the center of the wheel at their interface.
Built in bridges for the somewhat weird shape to trick the slicer.
Now my 3 year old can pull me around in the wagon.
I would go with something like an old Meade ETX with autostar and just print some of the eyepieces you'll find that have lens kits you can buy. The eyepieces are nice and the prints are easy. An actual scope is a tricky project to dial in and the longer focal lengths are hard to use in practice. Something like an ETX60 is reasonably cheap and while you'll barely see more than dot with 3-4 tiny specs of Jupiter's moons or the haze of the Orion nebula, they are quite easy to find in practice. Doing initial alignment is also easy and forgiving. That's just my take. I also wouldn't mess with any of the phone camera adaptors. I ended up making my own that had 6 axis alignment, but the bubble lens and software compensation on most phones makes them mostly useless through and additional lens stack of an eyepiece.
Thanks for chiming in on the scope. Are you saying that building one from someone else's plans might be a bit of a slog?
When they're older, if they're still interested in astronomy, we'll probably do as you suggest. Honestly, it's less about the usability scope and more about assembling one with the kid right now. I am trying to get them interested in tinkering and making things while they're young and impressionable. We live in the middle of a large metro with tons and tons of light pollution. We're also on the west side of the timezone, so the sun is down way past bedtime for 2/3 of the year.
Another thing on the list to print for Christmas is a pendulum clock. Our oldest likes "analog looking" watches already, although he's too young and rambunctious to have a mechanical watch. A wall clock will do nicely though.
Optics are very precision oriented. I've messed with designing for optics and found it to be very challenging to make anything effective. It is not the kind of project I would build from scratch on my own without a baseline to compare the scope to. I think a Hadley is more like a second scope built for fun type of side project. I think you'd be better off with something like this: https://www.surplusshed.com/pages/item/L14481.html (no affiliation)
I mean, you can grind your own mirrors, how hard could it be? (Spoiler: very hard)