Constraining reference geometry

[siggy]

Constraining reference geometry

I'm trying to constrain a pair of gears so that their motion is properly simulated in AD. In order to do this I need to determine what the angle of a reference plane on the part is in relation to a reference plane on the assembly. That way, I can generate angle constraints with an equation that relates that angle to the second gear's angle and produce accurate motion for any gear ratio. Problem is that I can't find any way to determine this angle. I also don't see any functionality that would allow me to define an angle dimension myself in the assembly that I could use for this purpose. I know in AutoCAD there are a number of system variable that keep track of things like this. Are there similar system variable in AD that I can use to determine these relationships? I know in the sheet metal modules there appear to be a number of system variables for bend thickness, etc.

Am I making this harder than it should be?

 

[MikeHenry]

One approach that might work is to create a reference plane or axis in the gear(s). These would then be visible in the assembly when "Show reference geometry" is enabled.

You should also check out the "Make flexible" option for the part in the assembly. Wish I could explain the ins and outs of that but it still confuses me a bit.

Mike

 

[MikeHenry]

One approach that might work is to create a reference plane or axis in the gear(s). These would then be visible in the assembly when "Show reference geometry" is enabled.

You should also check out the "Make flexible" option for the part in the assembly. Wish I could explain the ins and outs of that but it still confuses me a bit.

Mike

 

[Gaspar]

Mike is right in saying that you can generate any plane on the part and then make it visible within the assembly and use it for constraining purposes.

There is one consraint option called "angle". This will set the angle to a certain value (fixed or from an equation).

I have sometimes found that I have to play with the angle value adding or substracting 90º, it seems to be a bug, but once you find the right value to get the parts the way you want them, everything works fine.

 

[siggy]

Right, I think the reference planes will be required to make this happen.

But, in order to make the gear ratios work, I need to determine the included angle between the first gear's reference plane and the assembly reference plane so that I can then calculate the corresponding angle I need to move the 2nd gear. I can do this easily by adding an angle constraint to the second gear that is defined by an equation that relates to the first angle. The problem is that I can't find a way to get the angle between the referene planes of the 1st gear. That is why I think I need to find a system variable or something that may expose this angle.

Thanks,

Robert

 

[Gaspar]

Hey Siggy,

If I'm getting it right, your problem is to find the actual value of the first angle used in the angle constraint in order to be able to use it for the second constraint.

If it is so, when you create the first constraint, the value of the angle will be linked to an equation number (which is a system variable) such as A1. When creating the second constraint, you can hit the box with three dots "..." and it will open the equation editor. There you will find the angle value for the first gear and you will be able to create a new equation for the second gear using the first one as a variable.

If I didn't get you right, please mention it so you keep getting input from the group

 

[siggy]

What I need to end up with is actually two angles. Let me see if I can explain myself a bit more clearly:

Lets assume I have Gear1 and Gear2 and their centers of rotation are about an axis pointing along Z. Lets also assume that I have reference planes defined on both gears that I can use for the constraints.

As Gear1 rotates about it's Z axis, the angle between the reference plane of Gear1 and the *Assembly* reference plane (which won't be rotating) will change *dynamically* as the Gear1 rotates. (This angle is what I can't seem to figure out.) Lets call this angle AG1.

If I can find a way to get AG1 described above I can than easily constrain Gear2 with an angle constraint (Let's call it AG2) and use a formula to get the right gear ratio. For example, for a 1:1 gear ratio the angle constraint would be AG2=-AG1. For a 1:2 gear ratio it would be AG2=-2*AG1, etc.

Every possible scanario I have come up with that would make gear ratios possible all start with getting that first AG1 angle. This is why I was hoping there might be some way to get this angle to use in my calculations. Unfortunately, I can't find it anywhere.

I'd love to entertain thoughts from others who may have a different methodology to try.

Robert

 

[Gaspar]

I get you now,

As far as I know, there is no way to declare and then use a system variable for the angle as you describe. I guess you already thought of this, but you can get it to work for a 1:1 ratio by constraining the reference plane of gear2 directly to the reference plane of gear one (do not use the assembly's ref plane). I would try to make them parallel (with a 0º constraint or an orient constraint).

For any other ratio, you would have to constrain the first gear to an assembly plane (as you propose) and vary the angle in the constraint to make them "rotate" (no real time though, unless you do it from the constraint window with the up/down arrows for the value :cry: ).

I just went through a situation in which I also wanted to "read" a dimension value, but in assembly or part you can only apply "driving" dimensions. It would be nice if one could define "driven" dimensions and be able to use that value.