Hello Everyone,
I'd like to be able to use the length of an arc in a Parametric formula but I'm not seeing a means to add a parametric dimensional constraint to an arc's length.
In the attached pic, I'd like to create a parameter formula that adds the two 8'6" lengths to the 8'7' arc length to give a length of my choice...for example...I'd like them to total to 30'
Does anyone know how to get the parameter constraint for the arc length?
Any help will be greatly appreciated.
Kind Regards,
David
Hello
Welcome to the Autodesk / AutoCAD Forums !
1) I am not a specialist of Blocks with Constraints !
2) But I don't remember any option which is "Arc Length" !?
You have only an Angular Dim Constraint !
3) Maybe by combining Angular Dim Constraint + Aligned/Horizontal/Vertical Dim Constraints,
you can get what you wish !?
Sorry, Regards Patrice
Patrice BRAUD
I'm not sure about the core question, but however that may be solvable, other questions arise....
How much of that needs to remain as shown? If the 31 degrees and 149 degrees and the tangency of the Arc with the Lines are what matter, the simplest way to get a total length of 30' would be to connect the Arc and 2 Lines into a Polyline, and SCALE it with Reference scaling, using the current total length as the Reference and 30' as the new length, but that will increase the 8'-7" dimension. The peak could be STRETCHed upward until the total length is 30', but then the Lines won't be tangent to the Arc, if that's a criterion. If the 31 / 149 degree angles are what's flexible, but the tangency is required, sliding the Lines around for increased length will change the tangency points, so to maintain a specific Arc length will require changing the radius. That looks like the kind of thing that could only be done by brute-force trial and calculation of a new length, and repeated fine-tuning to get to within some tolerance. Any of those approaches will also change the peak-to-top-of-Circle dimension.
So what are the critical elements?
Arc length can be figured using a formula.
http://www.mathopenref.com/arclength.html
There may be better forumlas out there for your situation but ill leave the task of determining that for you.
so if you take length=2(PI)R(C/360) and solve for r and put this into your forumula for your radius this can be achieved.
I crudely threw something together to show this. I used a user defined parameter to house the desired arc length. the results is a little off but this was a proof of principle and would need to be tweaked per the situation. I set the ar length to 10 and the forumla using the radius forced the arc length to 10.. and some change.
CADnoob
Hi,
First point... The 8'7" arc length you show is rounded. If the two lines have an included angle of 31 degrees and line lengths of 8'6", then the arc length will be 8'8-1/4" when tangentially terminated to the lines.
Second point... Something must be a rule. That is, the included angle, the vertical relationship of intersection & center point of arc, and/or line lengths. Once a rule or two are in place you can aim at a formula for the arc length but I'm trying to figure out how to create a constrain for it. Looks like making the arc a block will lose tangent constrains so that's not good.
Inventor allows vertical relationships for points (intersect to center in this case). ACAD doesn't seem to allow the same.
Look for rounding issues and make determinations on what constraints need to be fixed in this. It's a very interesting problem to me so I'll persist.
Blaine Young
Senior Engineering Technician, US Army
@Anonymous wrote:
...
- the circle diameter...which must stay at 56 inches...
Ah, left out the critical dimension.
Graphical solution (more or less, actually slightly more....).
Got it a little closer. All dimensions shown in decimal feet.
@Anonymous wrote:
....
- the circle diameter...which must stay at 56 inches.
- the total length of the orange lines...which must be a total of 30 feet, and
- the straight orange lines must remain tangent to the circle no matter how long they get.
....
So, not the 8'-7" Arc length, after all....
Again, apart from the question of whether constraints can help, if by the "total length of the orange lines" you include the Arc, then the geometry of it, given the angle A [in radians] as shown here:
boils down to this, if my quickie reduction is correct [or something very similar if it isn't]:
A = pi - 180/14 + tan A
which means the required angle is defined in terms of its own tangent. That's the kind of situation I feared earlier, where trial and re-calculation and refinement to get to within some acceptable degree of tolerance is the only way to do it -- there can't be an "exact" solution.
[The problem is similar if you really only mean the Lines.]
Initially i misunderstood your goal and starting conditions.
Im not sure what acceptable tolerance are for what you are doing but I was able to get a very close answer using the techniques i alluded to earlier.
If you treat the problem as though you are finding the distance between two pulleys given a belt size you can solve using the following formula. (assuming one pull has a radius of 0)
Where b is the following formula
A ME friend said this may be a good site to pull that formula from. But make sure you run this by some one qualified to determine if its correct.
http://sudenga.com/practical-applications/figuring-belt-lengths-and-distance-between-pulleys
CADnoob
@Anonymous wrote:
.....
I'd like to be able to use the length of an arc in a Parametric formula but I'm not seeing a means to add a parametric dimensional constraint to an arc's length.
...........
Not sure how to do that with a parametric formula in AutoCAD. If a static solution is needed, try below application. It uses Microsoft Excel and will not work if excel isn't installed on the system. The solution is placed at co-ordinates 0,0,0. Minimal testing.
@Anonymous wrote:
Great!...that solution worked CADnoob...
Big thanks to everyone who contributed and helped to find the solution for me thus far. Honestly, this is the first time I've used this forum and I have to say that the help I received here was EXTREMELY GOOD! and I've learned much more than I was looking to learn. I especially like the videos that were attached to the responses.
I'm just a newbie and I hope that one day I'll be able to help someone the way you guys helped me.
Warmest Regards,
David
Following the forums is like a magical education on AutoCAD (or what ever forum you are working in). The depth and breadth of knowledge of the volunteers here is amazing!! There are some truly fabulous people in these forums.
The videos were created using screencast ( https://knowledge.autodesk.com/community/screencast ) its a pretty handy way of showing how to do things and or explain the problems you are having. Its FREE.
Aint nothing wrong with being a noob here 
and even noobs can help on occasion.
CADnoob
