This is an update of thing:1618843.
I've included all the files, not just the updated ones.
The update falls into three categories:
- To provide a larger operating window. The original design worked, but too much less that 100% of the time to be fully satisfactory. The major factors in getting good operation, given that the parts have been made (close to) flat, is that the pawl, and the pendulum assembly can rotate absolutely freely. To that end I've redesigned two support brackets and offer them with a selection of different size bores which are engraved on the side. These make assembly easier. I think that one bracket in each pair should be a neat fit to the shaft however I've found that it's impractical to expect the other bracket in the pair to also be a neat fit. For me the brackets marked 9.6 and 10.4 are the best ones.
The other important change is to the peg stopper. I now offer several variants. The larger the number the more it lags that pawl lifter. The variants 2.5 and 4.5 are 0.5 mm longer than 3 and 4. For me 4.5 is the best one.
As for the pawl.... I'm still of the view that a slightly softer grade of PLA (or ABS) is better that standard PLA as it will bounce less. However as an alternative I've designed pawls with holes in them to accept 3mm screws so that the head end can be made heavier. Not sure it helps - I don't need screws with my Polymaker's PolyMax pawl.
Another change is an adjustable bracket to limit the starting position of the pendulum - this makes it easier, once set, to start the pendulum is a position most likely to work.
- To tune the tick interval to 'exactly' 1 second. To achieve this - without the whole thing become too tall - I've had to add a weight at the end of the pendulum. This has the effect of moving the centre of gravity of the pendulum further from the pivot point, without any increase in the overall length. Nonetheless I've had to make the unit a little taller to get to 1 second.
A drawback of this approach is that the pendulum now requires more input energy so a heavier weight is needed. The weights that work for me are 80g for the pendulum and 702g for the weight (both include the bottle weight but not the bottle cap). I'm using lead fishing weights in a variety of sizes for best packing efficiency.
- To increase the time of operation. To this end the pendulum rod is now significantly offset so the weight can be brought up higher, and extension legs can be added to the (new) frame base. And extensions can be added to the extensions though I haven't done so s I think it would become too unstable. Presently I get around 2 1/4 minutes total time.
Not fitting in the above categories is a redesign of the caps to make them a looser fit on the bottles.
A video of the finished article in action is here:https://youtu.be/1_x9zGTSlHo
Material used - PLA for all parts. I think that the softer ABS would be less satisfactory for most of the rotating parts which need to rotate freely. The exception is the pawl which shouldn't be too 'bouncy'. I made the pawl in PLA, but a softer grade - Polymaker's PolyMax. Note that I changed to this fairly early in the development phase and it's possible the latest design which allow for the fitting of 3mm screws to fine tune the weight of the pawl may mean that regular PLA would be OK. As I've mentioned above it's important to keep the parts flat and I found BuildTak helpful for this - especially as my Ultimaker Original does NOT have a heated build plate. On the wider parts I used a brim.
The design size I use for shafts and the holes in which they rotate is the same. eg 8mm for both. I rely on shrinkage to bring the shaft a little under 8mm and use a straight hand reamer to bring the holes very close to 8mm dead. I't would be a struggle with reamers, I think. (See Summary for info on larger bore brackets).
I also recommend a tapered reamer to open the start of holes intended for screws,
Talking of which, all screws are 3mm Button Head Caps Screws.
Those in the ratchet are 15mm long - 12-off.
The remaining screws are all 10mm long - about 40!
Also, you'll need lead shot (fishing weights) for the bottle weight and the pendulum bob. I used assorted sizes to get as much weight into the bottle as possible. Weight of bottle and lead (excluding the cap) - 80g for the bob and 702g for the weight.
I started with the photos of the metal models (I've uploaded those photos to thing:1618843) and went from there. All the design work was done in Moi (Moment of Inspiration). Once I had an escapement design I ran it as a simulation (unsuccessfully) in SimLab Composer Mechanical and refined the design until it would simulate. I've provided a link to that simulation in thing:1618843.
I cheated a little on the gear spacing. In the interest of making everything as 'free' as possible the gears are 1mm further apart than the intersection of their PCDs.