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README.md

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+# FreeCAD 2026 Design Contest
+This is my entry to the (2026 FreeCAD design contest)[https://forum.freecad.org/viewtopic.php?t=105082].
+For assembly instructions see the assembly guide.
+
+## Initial Design Choices
+As the contest specifies a 5V operating voltage, and custom PCBs or more complex electronics would significantly increase development time, replication effort, and cost, I decided to limit myself to components that already ran on 5V and could immediately be used, so could be connected to a microcontroller without any special intermediate board.
+That cuts the list of mechanical actuators down quite a bit. I could use a small DC motor maybe, though that is difficult(-ish) to drive bidirectionally, or maybe maybe maybe a low voltage solenoid, or, as I decided to do, a small, cheap RC servo. I think this is a pretty obvious choice, and I'd be surprised if I was the only contestant to choose this option.
+To use that actuator to pinch the tube I decided on a linkage system, since I wanted to maximize the force I could apply to the tube, to then maximize the pressure I could switch.
+I also decided that, for convenience of switching out the tube, the mechanism would need to be open on one side, so that no end of the tube ever needs to be fed through the mechanism (which I imagine could lead to cross contamination of the previous and current setup). 
+So I wanted to convert the 180° rotation to about 1.5mm of linear actuation. I also figured the amount of force required would vary based on how far along those 1.5mm we are. Specifically I believe the last little bit will require far more force. So I decided to design a linkage system, that would reach top dead centre at full squish, to basically fully relieve the motor of force at the end of travel. This is done both in the bell crank that interfaces with the tube, and on the crankshaft that mounts to the servo. This way the valve fails further back in the stroke if the pressure is to high, wich should make failure more obvious, and since it matches the force curve better it should also work up to higher pressures. (I wasn't able to test any of this, these are really just my assumptions I built this first version on.)
+
+## Implementation
+I chose to use fairly common tools. I think 3D printers and simple hand tools (which could also be reasonably aquired if missing), are a good set for this design.
+
+I also wanted to avoid using many different mass purchasable components. This is why all the pivots are 2x12mm pins, rather than pins of the "correct" length. There's enough space for them, and if you need to buy 100 of them regardless, and only want to build a couple of valves it's more convenient. (that, and I had them on hand myself. More convenient.)
+
+The custom parts are all 3D printed, and most of the closer toleranced holes (the pivots mostly) should be drilled out after printing.
+
+## Build requirements and cost
+The tools I used to assemble the parts are:
+* A (FDM) 3D printer (I used a modded Ender5+, it doesn't need to be very fancy)
+* A vise, to press in and hold parts
+* A 2mm drill to drill out the holes (I just held the drill in the vise and spun the parts)
+* A screwdriver (PH1 and HEX2.5, for the plastic screws for the servo, and the M3 socket head cap screws)
+
+The Materials per valve are
+* 1 SG90 Micro-Servo (Including the screws they usually come with, one to screw in the servo horn, two to screw the servo into the frame) 10,79€/5
+* 8 2x12mm Dowel pins (m6 tolerance) 9,67€/100
+* 4 M3x10 socket head cap screws (DIN 912) 3,11€/20
+* ~25g of PETG 3D-Printer Filamet 32,99€/1000g (I used the filament I had, which was Prusament PETG, it probably works fine with cheaper filament, but it's what I was working with)
+
+So if you're building a lot of them the price per unit comes out to
+| Count | Price per order/count of ordered parts | price per unit |
+| 1x | 10,79€/5 | 2.16€ |
+| 8x | 9,67€/100 | 0.78€ |
+| 4x | 3,11€/20 | 0.63€ |
+| 25x | 32,99€/1000 | 0.83€ |
+= 4,38€/unit
+
+If you build 5 of them (Which I think is pretty realistic) the price per unit comes out to
+Price per order/number of units|price per unit|
+| 10,79€/5 | 2.16€ |
+| 9,67€/5 | 1.94€ |
+| 3,11€/5 | 0.63€ |
+| 32,99€/5 | 6.60€ |
+=11.32€/unit = 13.12USD < 14USD (as of writing this)
+and youd be left with with 60 dowel pins ("worth" 5.80€) and 875g of PETG (worth 28.86€). This is PPU particularly high because of the expensive filament used in the calculation.
+
+I think a fair cost assesment is somewhere inbetween the two, since most people will have some filament, and so the 6.60€ per valve of filament are a bit over the top. I think the average maker would probably spend around 5-6€ per valve.
+
+## Performance Assesment/Concerns/Room for improvement
+I have not had the opportunity to test maximum holding and closing pressure, nor how many close/open cycles it can handle. I hope to get around to running those tests in the final week before the submission deadline. (The only test I've managed so far)[https://chaos.social/@la/116727325081926518] was me blowing into the tube with the other end in a glass of water, to see if it closes and seals agains my lung pressure. 
+
+I am particularly concerened with the requirement in the contest brief, requireing gas sealing at 0.5bar, and wear resistance.
+
+I belive my valve is likely to hold a seal at those pressures given that the servo sees none of that force, it's directly pushed into the housing. I am however woried that it might not manage to close against that kind of pressure.
+
+And, wear wise, the entire valve has no roller bearings. It runs entirely on dowel pins in drilled out holes. This works pretty well, but I could imagine some of those holes deforming or wearing over time, especially when running unter pressure and thereby bigger forces. I am particularly worried about the pivots of the bell crank, which take the forces of the sqished tube directly.
+The second worry point for wear is the tube itself. Because of the top-dead-centre design aproach the pin rubs along the tube quite a lot. This, I imagine, could wear the tube itself down over time. Some lube would certainly go a long way there, but adding a roller bearing to the contact side of the bell crank would eliminate the problem entirely. Same would be the case for the pivot holes. This would increase the BOM by about 3-4€, which arguably would be worth it. I will have to test if the wear gets to be a problem in the first place, and then, if it turns out to be worthwhile I might add a variant of the design which solves this problem using 682 bearings (which I have, just in case, ordered already)

assembly_guide.md

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+# Assembly guide
+## Required Tools
+* A vise
+* A 2mm drill bit
+* A screwdriver (PH1, 2.5mm hex key)
+* A FDM 3D-printer
+## Required Materials (BOM)
+* 1 SG90 Micro-Servo (Including the screws they usually come with, one to screw in the servo horn, two to screw the servo into the frame)
+* 8 2x12mm Dowel pins (m6 tolerance)
+* 4 M3x10 socket head cap screws (DIN 912)
+* ~25g of PETG 3D-Printer Filamet
+## Prepearation
+All parts in the step-export need to be printed.
+The lower and upper linkage halves, as well as the bell crank need support, which will need to be removed before proceeding.
+All 2mm holes need to be drilled to actually be 2mm (Most printers will print them significantly undersize). This is easily done without an actual drill, just by clamping the drill bit in the Vise, and turning the parts on it with some light downwards pressure. Carefully to roughly maintain alignment with the existing hole initially, though once started the drill will follow it. Once through give the part a few turns on the bit to ensure that the hole is fullly formed and round.
+On the upper half of the Crankshaft, run the drill through the holes a few more times to ensure it will slip onto the pins of the lower half easily.
+## Assembly
+Connect the servo to a way to give it an input (for example a microcontroller), and set it to 0°.
+Insert the Servo into the cutout on the lower casing. Ensure that the output is on the correct side, in relation to the rest of the linkage. Check the 3D model if unsure. //todo add pictures .-.
+Screw it into place using the two longer screws included with the servo.
+
+Insert the three pins into the lower half of the crankshaft. Ensure that the chamfered end is facing the upper half, and that the other side is flush with the bottom of it.
+Push the lower half of the crankshaft onto the servo, aligned so that the crank pin is facing the outside (top) of the housing. This should take a little bit of force, though it shouldn't be enough to worry you of damaging the servo.
+Screw in the final screw that came with the servo through the lower half of the crankshaft and into the servo output shaft.
+
+Insert the centre pin of the bell crank, so that it pokes out 2mm either side, as well as the pin that will make contact with the tube, it should poke out a little further on the bottom than the top (by about a millimeter more).
+Take the bell crank, and the two halves of the linkage arm and push the pin through them. Ensure that the linkage arms halves are correctly oriented to give the clearance for full range of motion. This pin should poke out either side equaly.
+
+Push the other half of the linkage arm over the crank pin of the crankshaft, and position the bell crank in it's final spot. Then push the upper half of the crankshaft onto the lower, trapping the linkage arm between them.
+
+Insert the opposing contact pin, as well as the bearing pin for the crankshaft into the upper half of the casing,
+Push the upper half of the casing onto the lower, ensuring everything is seating where it needs to be as you do.
+Screw in the 4 M3x10 screws to connect the two.
+
+Slide the tube into the slot in the front and connect the servo to power. Test the range of motion to ensure it can fully open and close the valve.

license.txt

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+CERN Open Hardware Licence Version 2 - Weakly Reciprocal
+
+
+Preamble
+
+CERN has developed this licence to promote collaboration among
+hardware designers and to provide a legal tool which supports the
+freedom to use, study, modify, share and distribute hardware designs
+and products based on those designs. Version 2 of the CERN Open
+Hardware Licence comes in three variants: CERN-OHL-P (permissive); and
+two reciprocal licences: this licence, CERN-OHL-W (weakly reciprocal)
+and CERN-OHL-S (strongly reciprocal).
+
+The CERN-OHL-W is copyright CERN 2020. Anyone is welcome to use it, in
+unmodified form only.
+
+Use of this Licence does not imply any endorsement by CERN of any
+Licensor or their designs nor does it imply any involvement by CERN in
+their development.
+
+
+1 Definitions
+
+  1.1 'Licence' means this CERN-OHL-W.
+
+  1.2 'Compatible Licence' means
+
+       a) any earlier version of the CERN Open Hardware licence, or
+
+       b) any version of the CERN-OHL-S or the CERN-OHL-W, or
+
+       c) any licence which permits You to treat the Source to which
+          it applies as licensed under CERN-OHL-S or CERN-OHL-W
+          provided that on Conveyance of any such Source, or any
+          associated Product You treat the Source in question as being
+          licensed under CERN-OHL-S or CERN-OHL-W as appropriate.
+
+  1.3 'Source' means information such as design materials or digital
+      code which can be applied to Make or test a Product or to
+      prepare a Product for use, Conveyance or sale, regardless of its
+      medium or how it is expressed. It may include Notices.
+
+  1.4 'Covered Source' means Source that is explicitly made available
+      under this Licence.
+
+  1.5 'Product' means any device, component, work or physical object,
+      whether in finished or intermediate form, arising from the use,
+      application or processing of Covered Source.
+
+  1.6 'Make' means to create or configure something, whether by
+      manufacture, assembly, compiling, loading or applying Covered
+      Source or another Product or otherwise.
+
+  1.7 'Available Component' means any part, sub-assembly, library or
+      code which:
+
+       a) is licensed to You as Complete Source under a Compatible
+          Licence; or
+
+       b) is available, at the time a Product or the Source containing
+          it is first Conveyed, to You and any other prospective
+          licensees
+
+           i) with sufficient rights and information (including any
+              configuration and programming files and information
+              about its characteristics and interfaces) to enable it
+              either to be Made itself, or to be sourced and used to
+              Make the Product; or
+          ii) as part of the normal distribution of a tool used to
+              design or Make the Product.
+
+  1.8 'External Material' means anything (including Source) which:
+
+       a) is only combined with Covered Source in such a way that it
+          interfaces with the Covered Source using a documented
+          interface which is described in the Covered Source; and
+
+       b) is not a derivative of or contains Covered Source, or, if it
+          is, it is solely to the extent necessary to facilitate such
+          interfacing.
+
+  1.9 'Complete Source' means the set of all Source necessary to Make
+      a Product, in the preferred form for making modifications,
+      including necessary installation and interfacing information
+      both for the Product, and for any included Available Components.
+      If the format is proprietary, it must also be made available in
+      a format (if the proprietary tool can create it) which is
+      viewable with a tool available to potential licensees and
+      licensed under a licence approved by the Free Software
+      Foundation or the Open Source Initiative. Complete Source need
+      not include the Source of any Available Component, provided that
+      You include in the Complete Source sufficient information to
+      enable a recipient to Make or source and use the Available
+      Component to Make the Product.
+
+ 1.10 'Source Location' means a location where a Licensor has placed
+      Covered Source, and which that Licensor reasonably believes will
+      remain easily accessible for at least three years for anyone to
+      obtain a digital copy.
+
+ 1.11 'Notice' means copyright, acknowledgement and trademark notices,
+      Source Location references, modification notices (subsection
+      3.3(b)) and all notices that refer to this Licence and to the
+      disclaimer of warranties that are included in the Covered
+      Source.
+
+ 1.12 'Licensee' or 'You' means any person exercising rights under
+      this Licence.
+
+ 1.13 'Licensor' means a natural or legal person who creates or
+      modifies Covered Source. A person may be a Licensee and a
+      Licensor at the same time.
+
+ 1.14 'Convey' means to communicate to the public or distribute.
+
+
+2 Applicability
+
+  2.1 This Licence governs the use, copying, modification, Conveying
+      of Covered Source and Products, and the Making of Products. By
+      exercising any right granted under this Licence, You irrevocably
+      accept these terms and conditions.
+
+  2.2 This Licence is granted by the Licensor directly to You, and
+      shall apply worldwide and without limitation in time.
+
+  2.3 You shall not attempt to restrict by contract or otherwise the
+      rights granted under this Licence to other Licensees.
+
+  2.4 This Licence is not intended to restrict fair use, fair dealing,
+      or any other similar right.
+
+
+3 Copying, Modifying and Conveying Covered Source
+
+  3.1 You may copy and Convey verbatim copies of Covered Source, in
+      any medium, provided You retain all Notices.
+
+  3.2 You may modify Covered Source, other than Notices, provided that
+      You irrevocably undertake to make that modified Covered Source
+      available from a Source Location should You Convey a Product in
+      circumstances where the recipient does not otherwise receive a
+      copy of the modified Covered Source. In each case subsection 3.3
+      shall apply.
+
+      You may only delete Notices if they are no longer applicable to
+      the corresponding Covered Source as modified by You and You may
+      add additional Notices applicable to Your modifications.
+
+  3.3 You may Convey modified Covered Source (with the effect that You
+      shall also become a Licensor) provided that You:
+
+       a) retain Notices as required in subsection 3.2;
+
+       b) add a Notice to the modified Covered Source stating that You
+          have modified it, with the date and brief description of how
+          You have modified it;
+
+       c) add a Source Location Notice for the modified Covered Source
+          if You Convey in circumstances where the recipient does not
+          otherwise receive a copy of the modified Covered Source; and
+
+       d) license the modified Covered Source under the terms and
+          conditions of this Licence (or, as set out in subsection
+          8.3, a later version, if permitted by the licence of the
+          original Covered Source). Such modified Covered Source must
+          be licensed as a whole, but excluding Available Components
+          contained in it or External Material to which it is
+          interfaced, which remain licensed under their own applicable
+          licences.
+
+
+4 Making and Conveying Products
+
+  4.1 You may Make Products, and/or Convey them, provided that You
+      either provide each recipient with a copy of the Complete Source
+      or ensure that each recipient is notified of the Source Location
+      of the Complete Source. That Complete Source includes Covered
+      Source and You must accordingly satisfy Your obligations set out
+      in subsection 3.3. If specified in a Notice, the Product must
+      visibly and securely display the Source Location on it or its
+      packaging or documentation in the manner specified in that
+      Notice.
+
+  4.2 Where You Convey a Product which incorporates External Material,
+      the Complete Source for that Product which You are required to
+      provide under subsection 4.1 need not include any Source for the
+      External Material.
+
+  4.3 You may license Products under terms of Your choice, provided
+      that such terms do not restrict or attempt to restrict any
+      recipients' rights under this Licence to the Covered Source.
+
+
+5 Research and Development
+
+You may Convey Covered Source, modified Covered Source or Products to
+a legal entity carrying out development, testing or quality assurance
+work on Your behalf provided that the work is performed on terms which
+prevent the entity from both using the Source or Products for its own
+internal purposes and Conveying the Source or Products or any
+modifications to them to any person other than You. Any modifications
+made by the entity shall be deemed to be made by You pursuant to
+subsection 3.2.
+
+
+6 DISCLAIMER AND LIABILITY
+
+  6.1 DISCLAIMER OF WARRANTY -- The Covered Source and any Products
+      are provided 'as is' and any express or implied warranties,
+      including, but not limited to, implied warranties of
+      merchantability, of satisfactory quality, non-infringement of
+      third party rights, and fitness for a particular purpose or use
+      are disclaimed in respect of any Source or Product to the
+      maximum extent permitted by law. The Licensor makes no
+      representation that any Source or Product does not or will not
+      infringe any patent, copyright, trade secret or other
+      proprietary right. The entire risk as to the use, quality, and
+      performance of any Source or Product shall be with You and not
+      the Licensor. This disclaimer of warranty is an essential part
+      of this Licence and a condition for the grant of any rights
+      granted under this Licence.
+
+  6.2 EXCLUSION AND LIMITATION OF LIABILITY -- The Licensor shall, to
+      the maximum extent permitted by law, have no liability for
+      direct, indirect, special, incidental, consequential, exemplary,
+      punitive or other damages of any character including, without
+      limitation, procurement of substitute goods or services, loss of
+      use, data or profits, or business interruption, however caused
+      and on any theory of contract, warranty, tort (including
+      negligence), product liability or otherwise, arising in any way
+      in relation to the Covered Source, modified Covered Source
+      and/or the Making or Conveyance of a Product, even if advised of
+      the possibility of such damages, and You shall hold the
+      Licensor(s) free and harmless from any liability, costs,
+      damages, fees and expenses, including claims by third parties,
+      in relation to such use.
+
+
+7 Patents
+
+  7.1 Subject to the terms and conditions of this Licence, each
+      Licensor hereby grants to You a perpetual, worldwide,
+      non-exclusive, no-charge, royalty-free, irrevocable (except as
+      stated in subsections 7.2 and 8.4) patent licence to Make, have
+      Made, use, offer to sell, sell, import, and otherwise transfer
+      the Covered Source and Products, where such licence applies only
+      to those patent claims licensable by such Licensor that are
+      necessarily infringed by exercising rights under the Covered
+      Source as Conveyed by that Licensor.
+
+  7.2 If You institute patent litigation against any entity (including
+      a cross-claim or counterclaim in a lawsuit) alleging that the
+      Covered Source or a Product constitutes direct or contributory
+      patent infringement, or You seek any declaration that a patent
+      licensed to You under this Licence is invalid or unenforceable
+      then any rights granted to You under this Licence shall
+      terminate as of the date such process is initiated.
+
+
+8 General
+
+  8.1 If any provisions of this Licence are or subsequently become
+      invalid or unenforceable for any reason, the remaining
+      provisions shall remain effective.
+
+  8.2 You shall not use any of the name (including acronyms and
+      abbreviations), image, or logo by which the Licensor or CERN is
+      known, except where needed to comply with section 3, or where
+      the use is otherwise allowed by law. Any such permitted use
+      shall be factual and shall not be made so as to suggest any kind
+      of endorsement or implication of involvement by the Licensor or
+      its personnel.
+
+  8.3 CERN may publish updated versions and variants of this Licence
+      which it considers to be in the spirit of this version, but may
+      differ in detail to address new problems or concerns. New
+      versions will be published with a unique version number and a
+      variant identifier specifying the variant. If the Licensor has
+      specified that a given variant applies to the Covered Source
+      without specifying a version, You may treat that Covered Source
+      as being released under any version of the CERN-OHL with that
+      variant. If no variant is specified, the Covered Source shall be
+      treated as being released under CERN-OHL-S. The Licensor may
+      also specify that the Covered Source is subject to a specific
+      version of the CERN-OHL or any later version in which case You
+      may apply this or any later version of CERN-OHL with the same
+      variant identifier published by CERN.
+
+      You may treat Covered Source licensed under CERN-OHL-W as
+      licensed under CERN-OHL-S if and only if all Available
+      Components referenced in the Covered Source comply with the
+      corresponding definition of Available Component for CERN-OHL-S.
+
+  8.4 This Licence shall terminate with immediate effect if You fail
+      to comply with any of its terms and conditions.
+
+  8.5 However, if You cease all breaches of this Licence, then Your
+      Licence from any Licensor is reinstated unless such Licensor has
+      terminated this Licence by giving You, while You remain in
+      breach, a notice specifying the breach and requiring You to cure
+      it within 30 days, and You have failed to come into compliance
+      in all material respects by the end of the 30 day period. Should
+      You repeat the breach after receipt of a cure notice and
+      subsequent reinstatement, this Licence will terminate
+      immediately and permanently. Section 6 shall continue to apply
+      after any termination.
+
+  8.6 This Licence shall not be enforceable except by a Licensor
+      acting as such, and third party beneficiary rights are
+      specifically excluded.