Confusions set in!! pendulum length and AutoTrain

[mphil]

Well here I am again with a question that sort of forced me in to confusion.

Please view my project test file attached.

My question is on pendulum length for the project clock. I calculated the who train in Autotrain with the input rotations set at 2 (for a short ish pendulum) Once finalised I calculated the required pendulum for this project and it came out at 388.3mm. Now this is where I get confused. going back to autotrain and the fact I set the input rotation at 2 to work out the train well with the pendulum length at 388mm the rotation comes out at 1.6 (I think)
counting the wheel and pinion teeth the BPM. comes out at 96, 96/60= 1.6...

I'm not seeing the relation between what I've worked out and what I entered in Autotrain.

In reality I'm looking for a clock where escape wheel rotates twice a min, which I thought I'd designed.  ???

please settle my confusion before my brain explodes. 

Regards
Mark

[ArtF]

Mark:

  It looks right to me on a quick check..

  First, lets tell the tree what the rotation time is. On the "Ratchet" right click and select
"Set Time of rotation.". Since you want 2 rotations per minute, enter 30 seconds.

Now, select spur-1, and note the text on the left saying "Time of rotation = 30 seconds.
Sounds good so far. Select Spur-3, note the time of rotation is shown as 1 hour, I assume this
is your minute hand? Finally, select spur-7, it shows 12 hours per rotation, so looks good as a
hour hand. Is this what you expected? I only checked by this method as it takes into account all
of your calculations, trains and toothcounts, if, in the end, you have a 12 hour and a 1 hour gear
time, it should work as a clock..

  Im not sure about the pendulum connection, am I misunderstanding the issue?

Art

[mphil]

Hi Art
Well yeah sort of missing my question but probs because of the way I've asked.

As I see it I have a working clock there this is correct. So now I need to figure out the pendulum length. A quick wheel and tooth count calculates the pendulum for my clock to have a beat per min of 96 and a pendulum length of around 388. This gives my escape wheel a rotation of 1.6 per min.

Now this is where I getting confused-
When I designed the gear train I used AutoTrain as it simplified everything for me. When in AutoTrain to find my possibilities I told it I wanted twice the rotation of the escape wheel (I think) Going back to my pendulum Math and what I've calculated is a escape rotation of 1.6 I'm confusing myself with the two numbers and thinking something is wrong  ???

I suppose easiest is to ask you what should be the length of my pendulum if you were working it out?

Many thanks

[ArtF]

Hi:

Ahh, sorry , I misunderstood. Im not sure where your getting 96 from. We know the clock will run
as designed if the rotation of the ratchet happens every 30 seconds. it has 30 teeth on it, so it needs
a pendulum that moves one tooth every second. A pendulum of approx 250mm will beat a 1 second
period, so wouldn't that make it all work out? The ratchet will then rotate the correct 30 second rotation,
and the display says if that's true the other gears are perfectly on time.

  I guess this is the statement confusing me.. "Once finalized I calculated the required pendulum for this project and it came out at 388.3mm. ", how did you calculate the 388? Is it a design consideration based on the physical size of the
clock rather than the required timing of the gears? (There are ways around that as well if that's the case..)

  Let me know where Ive confused myself.. lol, Ill try to rectify that in my response. It looks to me like
you simply want a 250mm pendulum and your design should be fine. If, for some other design criterion you
NEED a 388mm pendulum, there are ways to make it 388 long, yet work as a 250mm pendulum, its just a matter
of weight distribution in the pendulum itself.

Art

[John T]

Hope this doesn't add to any confusion, but the length of the pendulum is independent of the gear train other than to know how many "ticks" you want per minute or per rotation of the escape, as this table shows.

[mphil]

Thanks for the reply Art.

To explain where I got the 338mm pendulum length from.-
I used the 'clock makers aid' [urlhttp://www.atmosman.com/clockaid.htm][/url]

Using this calculator by entering the required figures.

Enter counts for:-
Centre wheel teeth = 96
Third wheel teeth =  80  pinion= 10
Escape wheel teeth = 30  pinion= 8
These counts (on my clock) once calculated generates a pendulum length of 388.3 with a beats per min of 96.

Well as you can imagine this threw me as I hadn't expected the pendulum to be that long. 388mm isn't important as a design consideration all I'm looking for is the correct length for the wheel train to show the correct time.

Incidentally I'd designed the clock around the 'ratchet' making two full revolutions every minute. This is just a good number for an added ratchet I'm going to add at another point. So In my mind the escape wheel will move two teeth every second?

The 96 beats per min (calculated by the online calc) isn't what I wanted, again in my mind I'd expected it to be 120 bpm, but again I'm trusting the calc to be correct but seeing as I used Auto train and the setting for Input rotation per unit set at 2 as this is what I want my top ratchet (escape wheel) to do.

At this stage I'm trying to get the correct pendulum length sorted so I can design my frame accordingly.

Wehre did you get 250mm from?

I hope bit by bit Art I'm explaining my self enough for you to get my head around my confusion. ;D ;D ;D

Thanks for the patience tho  ;)

Mark
 

[ArtF]

Hi Mark:

>>Incidentally I'd designed the clock around the 'ratchet' making two full revolutions every minute. This is just a good number for an added ratchet I'm going to add at another point. So In my mind the escape wheel will move two teeth every second?

  So the ratchet must make 2 revolutions per minute, or 1 revolution every 30 seconds. It has 30 teeth, so
it means for the proper pendulum it has to make 1 tooth go by every second. On an escapement as your using,
each full period of the pendulum makes 1 tooth go by.
  Theres a button on the indicators tab for calculating pendulum length, its a formula based on gravity
and it basically states that for small angular motions of less than 3 degrees or so each way, a pendulum
will obey the formula of  Time  = 2 * PI * sqrt( length / gravity); so since your clock was designed for
a 1 second pendulum time, ( 2 rotations per minute), a length of about 250mm would work.

2 * 3.1415926 * sqrt( 250 / 9600) = 1.01 seconds..

  Now..the calcs from the clock makers worksheet may depend on definitions used for whats first wheel, second pinion etc.. or on a particular type of escapement... I haven't used it before, but unless your using a train that corresponds
to their definition of the wheels you could get weird results.  It looks good to me at 250mm's or so for
pendulum length.. In gearotic, you design exactly as you did, knowing how many seconds you need for each pendulum
period, and then just look to the formula for pendulum length.. or..better yet, decide on the height you want
your clock to be, figure out how much of that is pendulum, calculate the time from that, and design the mechanics accordingly.. so it looks to be that you've done fine..

Art

[mphil]

Art thank you very much for the effort you've put in for me. It is a leaning curve but one made far easier due to Gearotic so thanks for this also. Along with my 3D printer I will be prototyping my design and I've already tested some wheels with good results.

Mark ;D

[ArtF]

Mark:

No trouble. I find 3d printing gears works real well, Its my preferred method of making something
next to wood. Have fun, show us the clock when its done. :)

Art