WM2D

[jim_mich]

Can anyone help please?

I'm trying to simulate a chain and sprocket or vee-belt and pulley linkage but I'm not having any joy.

I'm using the demo software.

Mick

Mick, WM2D will not simulate a vee-belt and pulley. Instead use the gear feature. If both pulleys are a same size then you will need to put an idler between the two vee belt pulleys so that they will turn the same direction. If they are different sizes you can sometimes get away with making one an internal gear.

[Mac]

If both pulleys are a same size then you will need to put an idler between the two vee belt pulleys so that they will turn the same direction.

Actually you always need an idler between two gears in order to make them turn the same direction, no matter if they are the same size or not. But I'm sure ya already knew that. ;)

Mac

[mickegg]

Thanks all

As it's only a simulation I suppose I can use the idler option.

I'm so used to "finished" designs using cad software, I'm forgetting
that I can add elements that would not be in the machine.

As it's only my third idea.......probably won't work anyway <grin>

Regards

Mick

[jim_mich]

Actually you always need an idler between two gears in order to make them turn the same direction, no matter if they are the same size or not. But I'm sure ya already knew that. ;)

Mac

No you don't! If you make one of the gears an "internal" gear then both will turn the same direction. But the program will not let both gears be the same size if one is an internal gear. You can place them anywhere so they can look and act like belt and pulleys.

[Mac]

OOPS sorry, I thought the gears were to be separated.

Mac

[mickegg]

While browsing over past topics and threads I've often come across the situation whereby a member has posted a file with a wm2d extension.

Have those members purchased the software in order to be able to
post said files.....or is this a question I should not be asking?

Nudge,nudge,wink wink.......say no more........etc.

Edit: On second thoughts I think it better I do not receive any replies to this.

Mick

[jim_mich]

This is for Ralph...

HOW TO MAKE A WHEEL in WM2D

When in WM2D look at the bottom left corner of the window and you will see little help phrases telling about whatever the mouse is pointing at. When pointing at the yellow circle icon it says 'circle'. Click the yellow circle icon and the curser becomes a little 'x' and is ready to draw a circle. Position the mouse 'x' pointer at a location that you want the center of the circle to be. Press down and hold the left mouse button while you drag the mouse diagonally across the screen a little ways then let up the button. You should now have a yellow circle on the screen. When you let up on the mouse button the 'arrow' icon in the menu at the top will look like it is depressed. That is because you are done drawing the circle so the selection arrow is now active. Position the arrow cursor on the circle that you just made and hold down the left mouse button then drag the mouse. It will drag the yellow circle along to anywhere on the screen.

When you click on an object such as the yellow circle (which you just made) then it becomes selected and you can see and change its values at the bottom of the screen. Set X and Y both to 0.000 and set the 'r' to the radius you want your wheel to be. There are a lot more properties available for your circle. Click the 'window' menu and click 'Properties' if you want to change the weight or other properties of your yellow wheel. Open the 'Appearance' window if you want to change the looks such as color. Use the 'Geometry' window to change polygons corner points or circle radius. Note that these windows (and others) change according to what objects are selected.

If you hit 'Run' your yellow wheel will fall off the bottom of the screen so it needs to have an axle pin. Reset the program by clicking the 'Reset' menu button. Click the green 'pin joint' icon to select it. Remember that when the mouse if over the 'pin joint' icon the help message at the bottom will say 'Pin joint: Joins 2 bodies with a hinge". I think 'pivot point' would be a better word than 'hinge' but I didn't write the program. After selecting 'pin joint' you will notice that the curser now looks like a tiny little circle which represents the pin joint. Move the curser to the center of your wheel and click the left mouse button. This will pin the top two objects together. In this case they are your wheel and the background. You now have a wheel on an axle.

Make a square or rectangle the same way you made the circle. Pin it to the wheel. Click the 'Run' button and the out of balance weight will rotate the wheel.

Most everything else is made the same way. If you want a rod connecting two points first click the 'rod' icon then click the first location then click the second location or you can click and drag like when you make circles.

Ralph, if you have can't figure something out then just ask!

Enjoy!

[rlortie]

Jim_Mich,

Thank you for taking you valuable time to print this out for me.

I will print it out where I can have right beside me to follow step by step.

It is now 1:39 AM my time, going to say good night and I will give this a go in the morning with a fresh mind.

Thanks again!

Ralph

[ken_behrendt]

Ralph...

Being able to make a simple circular wheel is about 70% of what you need to know to start making working models with WM2D! The rest will quickly take care of itself. I tried another highly touted CAD program for beginners before I tried WM2D and, after spending about two weeks with it, gave up in disgust never having made anything with it. With WM2D, I had a very crude, but working construction Running in about 5 minutes!

You should read the 7 page tutorial that comes with the free download. It guides you step by step through the various things you can do with the program. It uses next to zero math and is meant to get you used to clicking on the various "tools" available to make parts with.

It took me, however, about 6 hours of part time practice with WM2D until I could use it to make about 90% of what I wanted to make and it all worked (not, unfortunately, as a PM device!). It's now over a year since I started with WM2D and I still do not know all of its intricacies. But, that's okay, I have enough of a basic understanding of the program to pick things up along the way IF I have need to. Now, whenever I see someone post a sketch of a design for a wheel, I'm automatically thinking of how I would build it with WM2D!

One's first impression of any CAD program, WM2D included, can be a little intimidating. That is really just an illusion that will quickly evaporate as you begin to see your designs "come alive"...


ken

[Gregory]

I'm trying to simulate a single pulley in Wm2d, and have a problem. I think somebody can help to solve it.

I have a circle, a weight, and a rope.
I attach the rope to the perimeter of the circle at 3 o'clock.

The problem is, that I always want the rope to be attached to the wheel at 3 o'clock while the wheel is turning, so always at different points on the wheel perimeter but always at 3 o'clock.

I guess it can be done with sin or cos functions, but I wasn't too good with these functions. 8] And didn't have too much joy in trying so far...

Any ideas? What is the correct math for this problem?

I think in this way and with one or more additions an approximately realistic pulley can be simulated, right?

[jim_mich]

Gregory, what I've done in the past is construct 'bead chain' around the pulley. It's made from a number of very small circles wraped around the pulley. Each small circle is connected to the next circle with a rod or rope. The small circles contact and collide with the pulley. You can locate each bead circle by calculating its X & Y coordinate. Or just eyeball them. Or write a WM basic script program to create the bead chain.

[Gregory]

Hhmm... Not a bad idea. I haven't have it, Thanks!

But, Is there any other way for pulleys? It cannot be done as I described?

I mostly need a smoothly and easily running pulley with ropes. (as good as the gears in wm2d)
A trick to simulate it properly in Wm2d.
There must be a way...

[jim_mich]

It can be done using formulas that define the current length of the rope based upon the rotation of the pulley. You need to know what you're doing becasue if your formula is wrong then your results will be wrong.

[Gregory]

It can be done using formulas that define the current length of the rope based upon the rotation of the pulley.

Yes, I know that one and have figured out an approximate formula for that.
My problem is that while the lenght of the rope is changing, I want to attach the rope to the pulley at a position (3 o'clock), and I want this attach position to be changing dynamically on the perimeter of the pulley, but stay at the same position inside the global coordinate system. Just like in the case of a real pulley....

But I don't know the math formula for that... :(

Perhaps... Rainer can you help me??

[Tinhead]

Sorry for the late response, my internet is going crazy and they can't sort it out. Hardly able to read the board, responding is just tempting fate. Let's see if this goes through :)

Ok, Pulleys, there is an example under
C:\Program Files\WorkingModel\Simulations\Mechanisms
It's called PulleysWithMassAndFriction.wm2d, I'll try to attach it.

The formula for a 3 o'clock attachment point would be:

Custom point properties:
X: body[?].radius*cos(body[?].p.r)
Y: -body[?].radius*sin(body[?].p.r)

? = the number of the circle it is attached too.

Hope this comes through :)

Cheers,
Rainer