Is it possible to sweep an object along a path that is determined by the freedom of an under-constrained sketch?

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eggyal
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Joined: Sun Oct 21, 2018 2:42 am

Is it possible to sweep an object along a path that is determined by the freedom of an under-constrained sketch?

Post by eggyal »

I'd like to draw the object that would be formed if a (planar) face of some other object was bound to an (under-constrained) sketch and then fully swept through that sketch's (limited) degrees of freedom... Is this approach known by some particular name, and is it something that can be done in FreeCAD?
chrisb
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Re: Is it possible to sweep an object along a path that is determined by the freedom of an under-constrained sketch?

Post by chrisb »

eggyal wrote: Sun Oct 21, 2018 3:31 am... and then fully swept through that sketch's (limited) degrees of freedom...
Hi eggyal, welcome to the forum.
In FreeCAD you sweep through sketches but not through their degrees of freedom. And I have no idea how that should look like. Can you give an example? You can provide a file, a link to an explanation in the web, a doodle ...
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eggyal
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Joined: Sun Oct 21, 2018 2:42 am

Re: Is it possible to sweep an object along a path that is determined by the freedom of an under-constrained sketch?

Post by eggyal »

Hi Chris—thanks for your reply.

I'm trying to draw a Moineau-type progressive-cavity/eccentric-screw pump. I've drawn the rotor, but am not sure how best to draw the stator. My instinct was to try sweeping the rotor through its full motion, subtracting from a body as it goes. I've drawn a sketch that has freedom to move through the rotor's hypocycloid, but I don't think this is the right approach?
Last edited by eggyal on Sun Oct 21, 2018 3:56 pm, edited 1 time in total.
ulrich1a
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Re: Is it possible to sweep an object along a path that is determined by the freedom of an under-constrained sketch?

Post by ulrich1a »

eggyal wrote: Sun Oct 21, 2018 10:27 am but I don't think this is the right approach?
From the referenced wiki page, you can look up the patent: https://patents.google.com/patent/US1892217
It has images of the profiles and explains the construction:
Each gear member is obtained by winding the corresponding profile in a helix fulfilling the condition concerning the pitches of the helices (that is said pitches will be in the same ratio as the numbers of threads or teeth of the two profiles).
My understanding of this is, you just have to sweep the profile of the rotor along a helix and sweep the inner profile of the stator with another helix with different pitch. The stator helix should than have double (or half?) the pitch in case of the following profiles:
mono_pump_profile.png
mono_pump_profile.png (72.93 KiB) Viewed 798 times
At least it gives some hints and a few tests should give you the right answer.
Ulrich
eggyal
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Joined: Sun Oct 21, 2018 2:42 am

Re: Is it possible to sweep an object along a path that is determined by the freedom of an under-constrained sketch?

Post by eggyal »

Hi Ulrich,

Thanks for the reply. The problem is that, because the stator's cross-section effectively rotates along its axial path, it's really defined (swept?) by a double- rather than a single-helix. This drawing may help to show the situation better.

I've been playing a little more with the sweep tool and wonder whether its "auxiliary" orientation provides the answer? I just can't find any documentation on how the orientation profile should be defined...
ulrich1a
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Re: Is it possible to sweep an object along a path that is determined by the freedom of an under-constrained sketch?

Post by ulrich1a »

Hi eggyal,

I made a design of an eccentric-screw pump after a few trials. I made a rotor with two turns and a stator with one turn.
I found out how the Stator should look like, by placing three clones of the rotor at their positions at angles of 90°, 180° and -90°.

Here is my design for a simple version.

Ulrich
Attachments
Mono_pump.FCStd
(207.94 KiB) Downloaded 27 times
Mono_Pump.png
Mono_Pump.png (90.5 KiB) Viewed 733 times
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