A simple cam

[path_finder]

Dear riortie,
I put a new post in the Tech Support forum, explaining how to do for the upload of images.
here: http://www.besslerwheel.com/forum/viewt ... 2914#72914
Good luck.

[Tarsier79]

There is another way to make what is trying to be achieved by the egg-shaped cam, both of which I have tested(at least in part). Instead of extending the curve to create the "egg.", you can squash half the circle(see below). In both the designs you have problems with the more extended part of the cam with the angle of inclination causing you issues, at about 1:30 and 4:30. At the 3:00 position, your cam achieves what it is supposed to.

It is easy, considering this, to see why Pathfinder has chosen a cam with straight edges top and bottom. Unfortunately this too has the same problem at the same places. To overcome this you need a greater circumference circle on one side, with the same comparative arc angle, requiring counter-productive ramps top and bottom: giving balance once again. I have also tried to use springs to compensate for the negative parts of rotation with no success.

In saying this, hopefully Pathfinder will find a way to cheat the negatives of this design.

Good luck!

[nicbordeaux]

Limited slip on the cams is what you might be looking for ? Or a system such as the variable distribution engines as per Honda V-Tec .

[path_finder]

Unfortunately the suggested way (the 'vilbrequin') seems to be a bad solution, not because the concept (wich is always valid) but for just some practical reasons as explained in the next animation below. I encountered this problem many times in the past: this is the reason why inside a combustion engine has a so big vilbrequin (the 'crankpins' must be very strong because the torque can twist the junction).
The first image of the animation is the previous one, free of any parts.
The second one shows the two pairs of bearings on the main axis (in green), the two rosettes (in light blue) rotating on the excentered axis (in red), and the cam (in brown).
The third step shows in black the force supported by the cam wich is translated in a counter-torque (black circle arrows) on the main axis.
The two red crosses are the locations were the screws are supporting a big effort.
The assembly has been quickly untied and the cam cannot stay in place
I'm not really surprised. The solution could be to subcontract a one-in-all part, numerically shaped, but it's expensive and the delay for a single part will be eternal.
This disconvenience drove me to another solution for the cam:
May be the famous sentence the car ahead the horse could simply mean this: reverse everything!
The way is an hollow cam in the central plane. More details soon.

[path_finder]

the son of the carpenter could be able to make a copy
A cam made of wires, very close from the solution?
Look at the fluorescent fishing wires and MT137.

[Tarsier79]

Path finder, the quality of your builds continue to amaze me! Are you using a CNC router?

[rlortie]

Path,

I am interested in the source and type of clear sheet plastic used. This material whether Lexan, Tuffak, Zelux, Polycarbonate, acrylic or Vinyl is far from being inexpensive in my area.

You seem to have an insatiable supply at your disposal, maybe you work for such a manufacture and have access to rejected material?

Ralph

[path_finder]

Ralph,
The answer is here: http://www.besslerwheel.com/forum/viewt ... 2256#62256
For each new build, either I recycle some old used parts, either I buy again two new plates (transparent polycarbonate, 5mm thick, 50cm x 50cm size, at 9euros (12US$) each).
The other purchases are standard screws, nuts, spacers, screwed rods 1m.
I got three years ago a bundle of a hundred skate-rollers bearings just for 15 US$.
The use of some cheap parts is not for a question of cost but almost for an easy and quick assembly.

edited: new shot

[rlortie]

Path,

Thank you for the info and reference to the previous related link.

I am impressed as your disk material appears to be much thicker than 5 mm. (0.1968498 or slightly under 13/64")

Ralph

[path_finder]

Ralph,
The thickness of 2,5mm is also available (for the half of the cost), but don't use it at all: it is really too much fragile.
And even the 5mm model can be broken sometime, like earlier explained here: http://www.besslerwheel.com/forum/viewt ... 9564#69564

[Tarsier79]

Path finder.

Have you considered publishing your builds(much like MT), You could call it "Playnerd";?)

[path_finder]

Dear Tarsier79,
The answer is here: http://www.besslerwheel.com/forum/viewt ... 5933#55933
One more thing: I'm not in hurry.

[path_finder]

More than one half day without any post...I'm impressed by the silence in this desert. May be everybody is at work..
Related to my experiments with the wires (very promising), I remembered the clue about the toy of the kids: why not the cat's cradle? see here:
http://en.wikipedia.org/wiki/Cat%27s_cradle
There are two sets of cords. One with a fixed length, forcing the distance during the ascending phase. The second one includes some springs, giving a variable length.
At the rest position all the weights are about close from the center, but when the wheel starts only the weights of the descending side are excentered because the centrifugal force, the weights of the other side remaining close from the center by the first set of cords.
Another clue is the crayfish's tail ('krebs' in german and 'ecrevisse' in french): a particular arrangement of the wires allow a mutual mechanical interaction between the weights, each one supporting the next one (like the crayfish tail).

[path_finder]

This string figure in the video below is similar with the jack in the left side of the MT138:
http://www.youtube.com/watch?v=z-GmljxkGKM
The 'Jacob Ladder' is a particular figure, see here: http://mathworld.wolfram.com/StringFigure.html

Two interesting Web sites on the same subject:
http://en.wikipedia.org/wiki/String_figure
http://www.isfa.org/

Who will find the best figure for the virtual cam?

[path_finder]

Hereafter is the summary of my studies on the hollow cam (physical version, versus 'virtual version' with wires).
The number at the upper right corner of each drawing is the reference of the paragraph below:

1. In yellow is the shape of the physical hollow cam.
Note this shape is open between 1:00 and 3:00 because the weights shall be able to touch the outer rim of the wheel.
The green curves are the path of the axle of each weight

2. This wheel is based on EIGHT weight. Without further explanation, the number of the weights is dependent of the size of each one, and must assume some specific limitations caused by their vicinity in the reversing area (between 4:00 and 6:00). In this drawing are represented the occupated spaces by the eight weights for their mobile path during one rotation of the wheel. As you can see the shape of a physical cam located at the median plane of the wheel, has a very specific shape (in rosa).
If we want to fix some axle on this cam, the authorized space is limited.

3. The same cam (in rosa) where the middle area is obviously empty.

4. Now the cam (in yellow) is surimposed with the outer authorized space of the median plane (in rosa)

5. The previous drawing has been completed with the eight weights (standing on the simple gravity force).
In this drawing we suppose that the cam (in yellow) is fixed in this position, and only the rosa structure is rotating with the wheel.

6. The same drawing but with the springs (in violet)

7. Due to the presence of the springs some corrections must be effective: the weights on the ascending side don't move significantly (just an epsilon), but the weight between 12:00 and 3:00 will support a force increasing their excentricity (this is a good news).

8. The most important point: the rotation of the cam.
If we want that the physical cam be fixed at it's correct position (with the open side oriented at 3:00) we need a specific mechanism to do that.
the cam must rotate counterclockwise at the same rotation speed than the main wheel supposed here to rotate clockwise.
This is the reason why in this drawing the cam don't touch anymore the outer rim of the wheel.

9. The cam is rotating inside the main wheel by the means of some rollers (in red).
The size of these rollers is about small: they must be located in a small space of the rosa area, not disturbing the motion of the weights.
In addition the axles of all these rollers must be linked together and grounded (through an another hollow axle located on the main axis).

Note for the Bessler's fans:
1. The shape of the cam is a 'C'. Any significance related with some clues?
2. The numerous rollers (in red) can be those observed in big amount in a box during the transfer of the wheel.
They are not the acting weights but could feed the confusion (voluntary?).

As you can see, even if a physical hollow cam can be taken in account, the corresponding building seems to be a little bit complex (like touch my links ear with my right hand passing my arm behind my neck). This is the reason why I preferred to investigate further the virtual cam made with the wires.