The biggest problem that I find with any project that I do in my spare time is that it gets dragged out over long periods. The problems that causes is things like forgetting what you were thinking last time you had a 'play' or weather or not you had fully thought out what you had done, then coming back only to continue expanding onto something that may not be correct.
Or maybe thats why they call them prototypes. :)
Well, I had a couple of small problems with this prototype, that could have been disastrous, but all worked out fine, call it luck, or call it something that I did actually work out and forgot that I had worked it out.
The cut of all the parts went well. No mishaps. The first little problem I found was with the internal gear. It just seemed to have a bit of 'grinding' in one place, which I think is a combination of the screw mapping on the cnc machine not being perfect (it will never be) and a bit of sag in the bearings. I use high speed bearings, because they have a bit more 'play' in them for when the bearings heat up and expand.
The next problem came in the form of the 2 gears that you can also see here in the pic above. The clear and the black behind it. The clear gear is 36 teeth and the black one behind it is 33, with the same diameter...impossible you might say, but it just needed a rejig of the tooth shape and width to get it to work.
So I got it running, and quickly found out that it was doing a 1 hour revolution of the minute hand in more than 15 minutes...This was a problem.
Oh, I also found out at the same time that I had made the chassis too short for a 90 BPM pendulum... :(
Thats why you can see it here on aluminium blocks.
This is where I get my comment at the start of this blog from.
A...had I forgotten that I was allowing for a shorter pendulum
B...I had miscalculated the pinion to 24 leaves on the escapement wheel and continued to keep designing the clock. It should have been 6.
Well, after a good sleep I realised, that I could change the pinion on the escapement to be 6 leaves instead of 24...I had never made a 6 leaf pinion, 8 was my smallest. And since it was running a little less than 4 times too fast I could shorten the pendulum to be what I calculated to be about 93 or 94 bpm!!!
BTW, the positioning of the hole for where the new rod with the pinion and esc wheel would have to be PERFECT. Was quite a trick, but it meshes very smoothly.
The next problem came in the form of not having enough fall for the weight for the clock to run 24 hours!!! When I designed this I forgot that the previous clock called Mini, had its barrel and maintaining power above not below. The reason for that was so that there was a rod coming through the clock at the 5 and 7 hour positions, so that the weight could be lifted all the way up to the 10 and 2 hour positions. On this clock, because the rod with the barrel and maintaining power were below, the below supports had to be wider now out at the 4 and 8 hour positions which is directly below the 2 and 10 hour positions...which meant the weights could only be lifted up till they hit that support at the 4 and 8 hour positions.
The only solution was to hope that the weights could be short and drill new holes for a rod out a little wider at the 3 and 9 hour positions. You can see above. This worked fine, but I quickly realised that this gear train really isn't all that more efficient than a traditional gear train (as I was lead to believe) and the proof of that is that here I was really comparing apples with apples. The other clock called Mini would run fine, but this clock would only run for 10 to 20 seconds with the same weight!!! Same parts directly lifted from the design called Mini, using the same materials... It is maybe slightly more efficient. What saved me here was something I have been keeping up my sleeve.
What I did was to shorten the length of the crutch to lessen the arc of the pendulum, which in turn needs less power to run the clock, which meant I could use less weight, which meant that the weights could be shorter and I could get the clock to run for 30 hours (6 hours grace). whew what a mouthful...
Normally shortening the length of the crutch won't shorten the arc of the pendulum, but with this design it does. It is now swinging at less than half its original swing and its running with lots of power!
So for now, Epi is running fantastically! She just needed a little bit of thinking to get her going, instead of rejigging the design to make a beta version, which would have been a lot more work.
I am very happy with the outcome.
Hope you enjoyed the insight.
cheers,
Rosco
No comments:
Post a Comment