Member postings for david bennett 8

John, could that error be "tuned out" with a rating nut?

dave8

John, I think you mean the sketch in the "general" forum? (If this works, it leads to the intrigueing idea that local magnetism can replace gravity in a clock)

Just from playing about with magnets and rollers they accelerate to seek the closest contact at the strongest pole point. This ruins any hope of a high Q and swamps the effect of gravity. I was trying to minimise this by putting the magnet in the centre of the rollers.It just felt wrong.

If this project wasn't already dead, here's another nail in the coffin. In preparing a cirular section to match the required circle ( 125mm radius now), placement of the magnet came up. The only place for the magnetic forces to even out would be in the middle of the bob! Not very practical.

dave8

I don't know how to play! So i've got a real spirograph coming next week.

Nor willI be doing it, even if Iknew how. I agree about the "purity"

dave8

Michael, still just musing. Is it possible to put time-values on those dots and run a comparison within a 10 degee pendulum swing?  --- just for fun!

dave8

Edited By david bennett 8 on 10/09/2023 18:37:07

Now, I wonder how that would look showing only the paths within a 10 degree swing - - - -?

dave8

Thanks everybody for your help in this. I've finally got my head around the change of curve from extending the rod, and even the apparent paradox of a point in a circle being a cycloid one minute and not the next. Sorry for testing your patience so hard.

dave8

I think I now see where the confusion comes from. Much of this discussion has become about Huygens cycloidal cheeks and how they are constructed. The 1/2 pendulum length roller is needed for that.

The method I proposed is based on the rolling wheel principal to produce a cycloidal path. That is a completely different approach to Huygens. The question now is - does the diameter of the roller matter in this context?

dave8

Michael

o.k.

dave8

Michael, guilty. Me, not you. Its because of perceived rissole-like responses from one member. I would be happy to draw a line here.

dave8

If a point on your tread follows a near-enough cycloidal path, you probably need new bearings.

dave8

Edited By david bennett 8 on 09/09/2023 04:45:55

Edited By david bennett 8 on 09/09/2023 04:58:52

On second thoughts, if you find that is a convenient size, please go ahead. Be sure to do a write-up so we can follow your procedures, especially the measuring. It's sure to attract a lot of attention. You'd like that, wouldn't you?

dave8

Then it wouldn't be a convenient size - would it?

dave8

As I tried to show in my post yesterday,at 16:28 the generating circle doesn't matter. A cycloid is a cycloid. Pick any convenient size.

dave8

If you are inside a moving car, observing the wheel will show a circular path (you may need a mirror) If you are outside the car, and stationary, a point on the wheel  of a moving car will be seen to have followed a cycloidal path.

dave8

Edited By david bennett 8 on 08/09/2023 19:41:01

No. A point on the tread follows a circular path.

dave8

Further to this - We had an example on this site where totally unnecessary dimensions can be specified , which could ne misinterpretd. when I enquired on the "general" forum for the best way to produce a 39" curve, I was required to give 3-dimensions for the part. They wheren't needed, but arbitrary sizes where given just so the problem could be visualised. Perhaps that is why Huygens gave his 1/2 pendulum size for producing a cycloid.

dave8

I don't think Huygens suggested that the cylinder had to be half pendulum size in diameter. It was just convenient. He was just using that to present his proof for his particular pendulum. Others since him have mis-interpreted his intentions.He wasn't trying to establish a rule for all cycloids, as we are.

dave8