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Space X Falcon 9 Crew Dragon BT-60

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I've started working on a new build at 1/88th scale of the Space X Crew Dragon that flew Bob Behnken and Doug Hurley to the International Space Station (ISS) on May 30, 2020. You can view the launch here.

The goals of this build are ambitious:

1: 1/88th Scale so BT-60 tubes can be used for the body
2: A working two stage rocket with the Crew Dragon as the second stage
3: Hidden fins for the second sage based on Tim's design at Apogee Rockets
4: Working landing fins based on Antsinafrica's design on Thiniverse.
5: No glue, so parts can be replace as needed.

I will also leverage Apogee Rockets' Falcon 9 Crew Dragon since it was scaled for BT-60 tubes.

The two stage ignition will work like my previous Falcon Heavy where a BT-50 tube carries the ejection charge to ignite the second stage motor in the Crew Dragon.

I plan to use the same rear ejection technique as I have used before. But I am planning to move the upper motor centering ring down to the level of the top of the landing legs where small magnets will hold them in place until the ejection charge ejects the motor tube assembly. Then the landing legs will be deployed into landing position using the tension of those tiny rubber bands used for dental braces.

Lastly, I plan to attach the recovery parachute line of the first stage to the top of the body (rather than out of the bottom) so the F9 lands "legs first" (before it tips over and explodes).

If this new design works out, I'll carry this forward to a Falcon Heavy II that integrates the new landing legs and hidden fins for the second stage.

The 3D printing will be done on a Prusa i3 MK3s 3D printer and all of the designs will be created using FreeCAD software.

Here is the first print of the landing legs section. I forgot to change the filament to white...
 

Switch

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I've started working on a new build at 1/88th scale of the Space X Crew Dragon that flew Bob Behnken and Doug Hurley to the International Space Station (ISS) on May 30, 2020. You can view the launch here.

The goals of this build are ambitious:

1: 1/88th Scale so BT-60 tubes can be used for the body
2: A working two stage rocket with the Crew Dragon as the second stage
3: Hidden fins for the second sage based on Tim's design at Apogee Rockets
4: Working landing fins based on Antsinafrica's design on Thiniverse.
5: No glue, so parts can be replace as needed.

I will also leverage Apogee Rockets' Falcon 9 Crew Dragon since it was scaled for BT-60 tubes.

The two stage ignition will work like my previous Falcon Heavy where a BT-50 tube carries the ejection charge to ignite the second stage motor in the Crew Dragon.

I plan to use the same rear ejection technique as I have used before. But I am planning to move the upper motor centering ring down to the level of the top of the landing legs where small magnets will hold them in place until the ejection charge ejects the motor tube assembly. Then the landing legs will be deployed into landing position using the tension of those tiny rubber bands used for dental braces.

Lastly, I plan to attach the recovery parachute line of the first stage to the top of the body (rather than out of the bottom) so the F9 lands "legs first" (before it tips over and explodes).

If this new design works out, I'll carry this forward to a Falcon Heavy II that integrates the new landing legs and hidden fins for the second stage.

The 3D printing will be done on a Prusa i3 MK3s 3D printer and all of the designs will be created using FreeCAD software.

Here is the first print of the landing legs section. I forgot to change the filament to white...
Here's the prototype of the landing leg:
LandingLeg.JPG


I suspect that I'm not going to need the rubber band in flight. I think once the landing leg is released, air resistance will pull it out. There are two landing leg struts. Limits of 3D printing at this scale prevent doing four sections like in the actual landing legs. The upper strut has an internal collar and the lower strut has an external collar so they lock when fully extended:
LandingLegStruts.PNG

Here's a test of the landing leg deployment. I'm moving a magnet on the inside of the tube with my finger.

 

Switch

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Here's the prototype of the landing leg:
View attachment 432918

I suspect that I'm not going to need the rubber band in flight. I think once the landing leg is released, air resistance will pull it out. There are two landing leg struts. Limits of 3D printing at this scale prevent doing four sections like in the actual landing legs. The upper strut has an internal collar and the lower strut has an external collar so they lock when fully extended:
View attachment 432931
Here's a test of the landing leg deployment. I'm moving a magnet on the inside of the tube with my finger.

Here is the FreeCAD rendering of the second stage flip out fins. The Prusa 3D printer failed with a "Bed preheat" error. I've tested as much as I can from their excellent support web resources, but I'm stuck until I get that fixed. In the pic below, the interstage tube is made transparent so you can see what is inside. The peg on the lower arms and slot in the fin are for small rubber bands. Once I get this printed I'll verify geometry and no doubt have to do the whole thing over again.

Capture.PNG
 

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The transparent inter stage extends longer than the fins in the first drawing I posted.

The fin pivots are just inside the BT-60 tube. Here's a view from the bottom:
Capture1.PNG
 
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Switch

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I've started working on a new build at 1/88th scale of the Space X Crew Dragon that flew Bob Behnken and Doug Hurley to the International Space Station (ISS) on May 30, 2020. You can view the launch here.

The goals of this build are ambitious:

1: 1/88th Scale so BT-60 tubes can be used for the body
2: A working two stage rocket with the Crew Dragon as the second stage
3: Hidden fins for the second sage based on Tim's design at Apogee Rockets
4: Working landing fins based on Antsinafrica's design on Thiniverse.
5: No glue, so parts can be replace as needed.

I will also leverage Apogee Rockets' Falcon 9 Crew Dragon since it was scaled for BT-60 tubes.

The two stage ignition will work like my previous Falcon Heavy where a BT-50 tube carries the ejection charge to ignite the second stage motor in the Crew Dragon.

I plan to use the same rear ejection technique as I have used before. But I am planning to move the upper motor centering ring down to the level of the top of the landing legs where small magnets will hold them in place until the ejection charge ejects the motor tube assembly. Then the landing legs will be deployed into landing position using the tension of those tiny rubber bands used for dental braces.

Lastly, I plan to attach the recovery parachute line of the first stage to the top of the body (rather than out of the bottom) so the F9 lands "legs first" (before it tips over and explodes).

If this new design works out, I'll carry this forward to a Falcon Heavy II that integrates the new landing legs and hidden fins for the second stage.

The 3D printing will be done on a Prusa i3 MK3s 3D printer and all of the designs will be created using FreeCAD software.

Here is the first print of the landing legs section. I forgot to change the filament to white...
Here's the motor mount for reverse recovery. The magnet mounts to secure the landing legs are in green. The magnet mounts for attaching to a Falcon Heavy core are in blue and red at the bottom left.

Motor mount for rear ejection with transparant rocket and landing leg.PNG
 

Switch

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I've started working on a new build at 1/88th scale of the Space X Crew Dragon that flew Bob Behnken and Doug Hurley to the International Space Station (ISS) on May 30, 2020. You can view the launch here.

The goals of this build are ambitious:

1: 1/88th Scale so BT-60 tubes can be used for the body
2: A working two stage rocket with the Crew Dragon as the second stage
3: Hidden fins for the second sage based on Tim's design at Apogee Rockets
4: Working landing fins based on Antsinafrica's design on Thiniverse.
5: No glue, so parts can be replace as needed.

I will also leverage Apogee Rockets' Falcon 9 Crew Dragon since it was scaled for BT-60 tubes.

The two stage ignition will work like my previous Falcon Heavy where a BT-50 tube carries the ejection charge to ignite the second stage motor in the Crew Dragon.

I plan to use the same rear ejection technique as I have used before. But I am planning to move the upper motor centering ring down to the level of the top of the landing legs where small magnets will hold them in place until the ejection charge ejects the motor tube assembly. Then the landing legs will be deployed into landing position using the tension of those tiny rubber bands used for dental braces.

Lastly, I plan to attach the recovery parachute line of the first stage to the top of the body (rather than out of the bottom) so the F9 lands "legs first" (before it tips over and explodes).

If this new design works out, I'll carry this forward to a Falcon Heavy II that integrates the new landing legs and hidden fins for the second stage.

The 3D printing will be done on a Prusa i3 MK3s 3D printer and all of the designs will be created using FreeCAD software.

Here is the first print of the landing legs section. I forgot to change the filament to white...
With the Prusa 3D printer awaiting parts, I have not been able test fit the design of anything. So I've moved forward with other design work that needed to be done.

Outstanding were the fins for the F9. I thought about mounting the fins at 45° to the landing legs as others have done. But that won't work for the Falcon Heavy core because the fins would project into the boosters. This is one of the many reasons my previous Falcon Heavy doesn't have landing legs. So I have been looking at integrating the fins into the landing legs themselves.

It looks like there is a lot of room to work with:

Fins on landing legs.PNG


The figure above shows how much surface area the landing leg mounted fin can have in both the retracted and extended position. I'm going to need some time with RockSim to figure out the minimum fin size. And that will differ with the F9 for the Crew Dragon and the Falcon Heavy core, which are completely different core rocket payloads.

Here is what it would look like with all four fins in the retracted and extend landing leg configuration:
4 Fins on landing legs.PNG


Here's what a minimal landing leg fin would look like:
4 smal Fins on landing legs.PNG


4 smal Fins on landing legs full size PNG.PNG


promising...
 
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Switch

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Here is the FreeCAD rendering of the second stage flip out fins. The Prusa 3D printer failed with a "Bed preheat" error. I've tested as much as I can from their excellent support web resources, but I'm stuck until I get that fixed. In the pic below, the interstage tube is made transparent so you can see what is inside. The peg on the lower arms and slot in the fin are for small rubber bands. Once I get this printed I'll verify geometry and no doubt have to do the whole thing over again.

View attachment 433046
The Prusa 3D printer is fixed! Here's the first prototype of the flip out fin. I'm going to move the rubber band mount to the middle of the motor tube.

Flip Fin test video

flip fin.jpg


The motor mount is printed in two parts. The upper section has a hole to receive the motor tube with fin arms. Here is an older version with the parts separated. I'm adding a notch on the next version so the two parts align perfectly.

motor mount two parts.jpg
upper motor mount.jpg


This is based on this Apogee Rockets design:
 
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Switch

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The Prusa 3D printer is fixed! Here's the first prototype of the flip out fin. I'm going to move the rubber band mount to the middle of the motor tube.

Flip Fin test video

View attachment 433695

The motor mount is printed in two parts. The upper section has a hole to receive the motor tube with fin arms. Here is an older version with the parts separated. I'm adding a notch on the next version so the two parts align perfectly.

View attachment 433696View attachment 433697

This is based on this Apogee Rockets design:
Fortunately Tim created a RockSim file for his Apogee Rockets' Falcon 9 Crew Dragon. So it was easy work to modify that for a 2 stage version.
rocksimF9.PNG

RockSim can't do flip out fins but I just wanted to see that the second stage was stable.
rocksimF9 second stage.PNG
rocksimF9_plot.PNG
rocksimF9_flight_profile.png


Here is a video of the completed prototype of the Crew Dragon second stage flip out fins.

Here's the FreeCAD rendering of the completed flip out fins motor mount. The fins work as the coupler to the bottom BT60 tube. So the top ring can be completely inserted into the 2nd stage tube.
1601769422774.png

I've also attached the Rocksim files to this post.
 
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Switch

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So here is my update on this build.


I'll start with a summary of the past two weeks:
MiscParts.jpg



Basically, a lot of trial and error (mostly error). I figured out that it is easier and faster to print smaller sections to focus on specific issues. The weakest part of the landing legs are the holes at the ends where they attach to the rocket. I had a lot of trouble with the position of the upper landing leg strut mount. Too low and the leg cannot fold completely in the upright position. Too high and there isn't enough room for the landing leg struts (that's a pile of failed attempts at landing leg struts on the lower right in the photo above).

From this work, I concluded that the landing leg struts could not be printed and would have to be made from telescoping aluminum tubing. Then two options were developed. The first one uses a dental rubber band to extend the landing leg:

IMG_1687.JPG


The second option uses a small spring made from guitar string:
IMG_1700.JPG



Here you can see the coil of the spring around the screw that holds the smaller landing leg strut in place and a small magnet used to secure the landing leg in place during launch:
IMG_1692.JPG


The spring extends out of the smaller tube and is bent so as to protrude through a hole in the larger tube to lock the extended landing leg tubes into place:
IMG_1694.JPG


The force of this spring and the friction of the end against the larger tube is a delicate balancing that is not completely debugged. I may end up using the rubber band for the "pull" and the smaller strut spring just to lock the extended landing leg into place. Note that it is not clear that any force is needed to extend the landing legs. The actual Falcon 9 uses gravity for this purpose. But as Galileo Galilei observed in his Dialogues Concerning Two Sciences: the effects of falling differ greatly between larger and smaller animals...

But this guitar string spring mechanism does look much better than the rubber band, so I'm going to keep working on it:
IMG_1688.JPG


I also finished the lower motor centering ring (shown here with the magnets that would be used to secure a a booster F9 to the core of a Falcon Heavy).
IMG_1698.JPG



I'm currently working on the mechanism to hold the landing leg securely during launch. The small magnet you see at the end of the landing leg is not enough to withstand the tension of the spring (although the magnet works fine for the rubber band version because the rubber band isn't applying much lateral force when fully extended).

Once that is done, I can work on the 1st stage recovery and finish the work started on the second stage.
 
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So here's my update. I want to land the Crew Dragon like it landed on March 8, 2020. This means recovering the Crew Dragon separately from the second stage (and "Trunk" service module). So I need an attachment/detachment mechanism so that the Crew Dragon can separate from the 2nd stage (and trunk) so that recovery of the Crew Dragon and second stage are separate. I don't know how many parachutes can realistically be done at this scale but the Crew Dragon used 4 parachutes. So that is the goal. For the Crew Dragon Capsule attachment mechanism, my solution was to embed a ring of magnets in the Trunk and Crew Dragon Heat Shield like this:
thumbnail_IMG_1712.jpg
thumbnail_IMG_1713.jpg


You will noticed 16 holes but I determined that only 8 magnets were needed. You'd be surprised how strong the magnetic attachment is.

Then for fun, I setup the Capsule so that it had its own magnetic connection to the heat shield. So that I can put people inside (LOL). Basically I needed mass in the nose cone anyway.

This is the bottom of the Crew Dragon Capsule and heat shield showing the attachment magnets.
thumbnail_IMG_1724.jpg


And the complete Crew Dragon
thumbnail_IMG_1727 (1).jpg


In the meantime I have a draft of the 4 landing legs ready for testing. Testing is going to be throwing the rocket off a local parking structure...

thumbnail_IMG_1721.jpg


This whole damned thing is so fragile.
 

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Switch

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Getting closer to completion. I got the grid fins and interstage working and cut the clear polycarbonate fins. I hid the vent holes needed for the second stage ignition behind the grid fins. The idea is that the grid fins will pop out when the first stage ejection charge ignites.

I still need to debug the landing legs, attach launch lugs, complete exterior details, and complete all three recovery systems.

IMG_1761.JPG
IMG_1763.JPG
IMG_1762.JPG
 

hermanjc

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This is a great build! Will you be willing to share your 3D Print files when completed?

Keep it up!
 

Switch

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This is a great build! Will you be willing to share your 3D Print files when completed?

Keep it up!
I'll post the stl files when I have a working version.

I have a lunch window this weekend! The build is not as far along as I had hoped. Lots or details missing but all of the functional parts are ready to do a test flight...

IMG_1779.JPG
 

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