V0.21/Assembly4--Ultralight Helicopter--Update #4

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freedman
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Re: V0.20/Assembly4--Ultralight Helicopter--Update #2

Post by freedman »

Wow! As always, one of the most impressive displays of FreeCAD and technique.

Could you show what setups you use in Sketcher visibility automation (pic)?

Thank you
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ppemawm
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Re: V0.20/Assembly4--Ultralight Helicopter--Update #2

Post by ppemawm »

freedman wrote: Sat Jul 09, 2022 5:31 pm Could you show what setups you use in Sketcher visibility automation (pic)?
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"It is a poor workman who blames his tools..." ;)
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ppemawm
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Re: V0.21/Assembly4--Ultralight Helicopter--Update #3

Post by ppemawm »

The tail rotor gearbox and associated pitch control are now complete which finishes up all the drawings with the exception of the main rotor blades which I will tackle next. My friend has since lost interest and confidence in this particular ultralight helicopter design because of all the errors we uncovered in the drawings during modeling. Neither of us are component helicopter designers. However, I've decided to keep on the project and finish up the remaining details of the assembly which I should be able to glean from the build videos mentioned in a previous post.

What follows are a few images and comments about the control mechanism that changes the blade pitch of the tail rotor:

This is the complete tail rotor sub-assembly including the gearbox, blades, and control mechanism.  The gear and pinion are the same as the transmission with the exception that the pinion shaft is hollow allowing for the tail rotor control actuator to pass through to the blade controls.<br /><br />The pitch control mechanism receives input from the cables attached to the pilot foot controls and converts this motion to axial displacement required by the blade pitch controls.
This is the complete tail rotor sub-assembly including the gearbox, blades, and control mechanism. The gear and pinion are the same as the transmission with the exception that the pinion shaft is hollow allowing for the tail rotor control actuator to pass through to the blade controls.

The pitch control mechanism receives input from the cables attached to the pilot foot controls and converts this motion to axial displacement required by the blade pitch controls.
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This image is a detail showing the pitch controls isolated from the gearbox.  The mechanism is fairly complex and in order to assemble the model you have a real challenge to adjust all of the attachment offset for any given cable input or you have to constrain each component according to its intended function by using a master sketch solver.  I chose the latter.
This image is a detail showing the pitch controls isolated from the gearbox. The mechanism is fairly complex and in order to assemble the model you have a real challenge to adjust all of the attachment offset for any given cable input or you have to constrain each component according to its intended function by using a master sketch solver. I chose the latter.
Capture26.JPG (251.9 KiB) Viewed 2077 times
This is the master sketch generated from the component's detail drawing showing all the assembly attachment points in the mechanism.  The sketch is generated at an arbitrary position and dimensioned with expression variables that represent the linear input from the foot pedal cables.<br /><br />The orange horizontal dimension on the left of the sketch is the linear input variable which is converted to the rotary motion of the pulley of radius R by a simple calculation:  degrees of rotation=input*pi*2*R/360.<br /><br />The remaining dimensions are from the drawings.  All the attachment points are free to rotate (coincident contraint) except for the attachment to the control shaft which is a point on object constraint. The latter constraint simulates a sliding joint with no rotation allowed.<br /><br />The blue construction line is the axis through the pinion shaft that the reciprocating control shaft has to pass.<br /><br />The sketch is anchored at the main pivot point on the gearbox housing and at the pulley rotation axis fixed to the tail rotor boom.
This is the master sketch generated from the component's detail drawing showing all the assembly attachment points in the mechanism. The sketch is generated at an arbitrary position and dimensioned with expression variables that represent the linear input from the foot pedal cables.

The orange horizontal dimension on the left of the sketch is the linear input variable which is converted to the rotary motion of the pulley of radius R by a simple calculation: degrees of rotation=input*pi*2*R/360.

The remaining dimensions are from the drawings. All the attachment points are free to rotate (coincident contraint) except for the attachment to the control shaft which is a point on object constraint. The latter constraint simulates a sliding joint with no rotation allowed.

The blue construction line is the axis through the pinion shaft that the reciprocating control shaft has to pass.

The sketch is anchored at the main pivot point on the gearbox housing and at the pulley rotation axis fixed to the tail rotor boom.
Capture27.JPG (206.2 KiB) Viewed 2077 times
Assembly4 LCS's or &quot;connectors&quot; are attached to each pivot point as shown in this sketch with a tangent to edge mode even though the property panel displays normal to edge, a bug no one seems to care about.<br /><br />The tangent mode aligns the LCS properly with the lines in the sketch.<br /><br />The LCS's and master sketch fully constrain the assembly for any arbitrary cable linear input.  The LCS's can now be used to assemble all of the control components.
Assembly4 LCS's or "connectors" are attached to each pivot point as shown in this sketch with a tangent to edge mode even though the property panel displays normal to edge, a bug no one seems to care about.

The tangent mode aligns the LCS properly with the lines in the sketch.

The LCS's and master sketch fully constrain the assembly for any arbitrary cable linear input. The LCS's can now be used to assemble all of the control components.
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The master sketch is treated as the parent of the sub-assembly.  Each body is attached to the master sketch LCS as shown in this example and the attachment offsets adjusted as necessary.<br /><br />When the assembly is complete the sketch variables can be changed and the sketch solver will properly reposition all of the body links for any cable linear input dimension within the design control range.
The master sketch is treated as the parent of the sub-assembly. Each body is attached to the master sketch LCS as shown in this example and the attachment offsets adjusted as necessary.

When the assembly is complete the sketch variables can be changed and the sketch solver will properly reposition all of the body links for any cable linear input dimension within the design control range.
Capture29.JPG (210.94 KiB) Viewed 2077 times
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This is a video of the control mechanism over a range of cable linear input:
phpBB [video]

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Code: Select all

OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.21.29450 (Git)
Build type: Release
Branch: master
Hash: 8b52db90c5a775fd976276186e11bac34a79eaed
Python 3.8.13, Qt 5.12.9, Coin 4.0.0, Vtk 9.1.0, OCC 7.5.3
Locale: English/United States (en_US)
Installed mods: 
  * Assembly4 0.12.2
  * fasteners 0.3.46
  * fcgear 1.0.0
"It is a poor workman who blames his tools..." ;)
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ppemawm
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Re: V0.21/Assembly4--Ultralight Helicopter--Update #4

Post by ppemawm »

This project is nearing completion now that all of the drawings have been checked but found wanting. That was the original objective so I have little incentive to add any further detail except at my leisure.

The following images show the last of the progress so far:

The main rotor blades, motor mounting infrastructure, exhaust pipe transition to the muffler, and the pilot seat have been added since the last post.<br /><br />The main rotor blades are a simple loft from two airfoils one of which (root) is twisted 6 deg.<br /><br />The pilot seat is a stock CAD model from GrabCAD scaled to fit this model.
The main rotor blades, motor mounting infrastructure, exhaust pipe transition to the muffler, and the pilot seat have been added since the last post.

The main rotor blades are a simple loft from two airfoils one of which (root) is twisted 6 deg.

The pilot seat is a stock CAD model from GrabCAD scaled to fit this model.
Capture30.JPG (208.54 KiB) Viewed 1937 times
If you have not noticed, there are many adjustable couplings and rod ends in this model used primarily to connect the controls components as highlighted in this image.  The threaded length allows some minor adjustment at assembly but there is also a requirement for several lengths of couplings between the two spherical-joint rod ends.<br /><br />Assembly4 has a nice feature that allows you to create a variant link to a part which can greatly add to productivity.  An example is shown in the next image.
If you have not noticed, there are many adjustable couplings and rod ends in this model used primarily to connect the controls components as highlighted in this image. The threaded length allows some minor adjustment at assembly but there is also a requirement for several lengths of couplings between the two spherical-joint rod ends.

Assembly4 has a nice feature that allows you to create a variant link to a part which can greatly add to productivity. An example is shown in the next image.
Capture31.JPG (256.44 KiB) Viewed 1937 times
This is a sub-assembly file with a variable length coupling.  To create the variant coupling, simply add an Assembly4 Part, Model, and a Variables place holder and a Body for the coupling as shown in the above image.  I drag the Model Variable into the Part container in the Parts folder to be used by the variable body.  The variables object must be in the Part container to be visible to the top-assembly links.<br /><br />You can then assemble multiple links of the sub-assembly using the Assembly4 &quot;Create a Variant Part&quot; tool and adjust the required length in the top assembly for each variant.  How cool is that?<br /><br />The sketch also shows an easy way to create a hex shape with a chamfer.  The 60 deg triangle in the XZ plane has an inside radius of the distance across flats/2 and the width of the nut.  After this is revolved, pocket with the proper size hex sketch (from the YZ plane in this example).  Voila, a perfectly chamfered nut shape.
This is a sub-assembly file with a variable length coupling. To create the variant coupling, simply add an Assembly4 Part, Model, and a Variables place holder and a Body for the coupling as shown in the above image. I drag the Model Variable into the Part container in the Parts folder to be used by the variable body. The variables object must be in the Part container to be visible to the top-assembly links.

You can then assemble multiple links of the sub-assembly using the Assembly4 "Create a Variant Part" tool and adjust the required length in the top assembly for each variant. How cool is that?

The sketch also shows an easy way to create a hex shape with a chamfer. The 60 deg triangle in the XZ plane has an inside radius of the distance across flats/2 and the width of the nut. After this is revolved, pocket with the proper size hex sketch (from the YZ plane in this example). Voila, a perfectly chamfered nut shape.
Capture22.JPG (224.52 KiB) Viewed 1937 times
The engine is a .step file of a model from GrabCAD.  In order to create a mounting plate highlighted in this image you can use a PartDesign Binder to exactly capture all of the dimensions.  Add the binder of the mounting face of the engine to a body.  The binder can be then be padded and modified as required.
The engine is a .step file of a model from GrabCAD. In order to create a mounting plate highlighted in this image you can use a PartDesign Binder to exactly capture all of the dimensions. Add the binder of the mounting face of the engine to a body. The binder can be then be padded and modified as required.
Capture32.JPG (338.83 KiB) Viewed 1937 times
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The only major components to be added are an air cleaner, radiator, and the fuel tank so I am tempted to call the project complete for now.

Hopefully, this project provides some encouragement if you are a new user and adequately demonstrates the basic capabilities of the PartDesign and Assembly4 workbenches. IMHO they have proven to be more than satisfactory for the mechanical design of complex engineered assemblies.

Code: Select all

OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.21.29450 (Git)
Build type: Release
Branch: master
Hash: 8b52db90c5a775fd976276186e11bac34a79eaed
Python 3.8.13, Qt 5.12.9, Coin 4.0.0, Vtk 9.1.0, OCC 7.5.3
Locale: English/United States (en_US)
Installed mods: 
  * Assembly4 0.12.2
  * fasteners 0.3.46
  * fcgear 1.0.0
"It is a poor workman who blames his tools..." ;)
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