I'm a big fan of the original geared heart, as is my daughter. I knew she would like the hand cranked version, but since she was just turning 6, I needed something that was a little sturdier and operated a little more reliably. The Beth's Hand Cranked Edition would have been fine for me, but I needed it to take some abuse and be conducive to 6-year old dexterity without skipping gear teeth (which that version did better, thanks to the spacer on the big gear).
All the tolerances are very tight (.1 to .25mm) so that I had to use as little glue as possible. So, you might need to sand them down a little depending on your printer's capabilities.
I made the axle sturdier and incorporated the little gear into it, and rounded it off. It's separated into two pieces and push-fits together. Just put the gear-side axle into the base, slide the other side through the hole and they should fit snug. You may want a drop of superglue here, but i've printed off about 5 of them so far and haven't had any issue with them coming apart when I didn't want them to.
The wheel is slightly different to accomodate the knob i made. The knob push-fits into the wheel and should spin freely, making it easier to turn continuously (again, especially for a 6-year old). The wheel push-fits onto the end of the axle.
The lock ring I made can be used with the base from the Beth version (with a healthy bit of sanding), but I've made a base that has a groove in it. It will be a tight fit to get it on, but once you do and it's in the track, you can turn the lock ring to align the gaps and put the heart in place and then turn the lock ring to hold it in place. The lock ring keeps the top from popping up if the gears give a little resistance.
I also threw a copy of the big gear and a 3.75mm disc. This keeps the same concept as the Beth version, but prints a little cleaner, making the gears mesh a little better.
You can see a video of it in use on my Instagram page here: https://www.instagram.com/p/BuXiaIwH_OG/
That video was before I made the lock ring, so you can see it's not necessary, but I think it's definitely provided a little insurance.