ISO a 75mm hardpoint like Giant Leap sells for 38 and 54.

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Hey I haven’t been on here in awhile due to amount of conveyor engineering work I’ve had lately. Recently just got over the flu last week. Anyways, I have access to autodesk inventor at work and any excess time permitting I could try to come up with a freeware solution for you guys and gals to try out. I’ve gained about 6 months professional proficiency at modeling using that software. I’m thinking either weekend or lunch time this week might work.

Now I don’t own any 75mm+ diameter rockets so if you all have preferred motor tube sizes ID and OD to build one of these units around that would be sweet. (Loc tubes/Wildman/Madcow insert favorite tube here). If you want certain bolt diameters and threads let me know. I’m figuring I could release the part files and drawings for free and y’all could take them to a local shop or online contract it out or whatnot for machining.

Just off the top of my head I’d like a grove or two that could hold epoxy better internally against the inside of MMT and help with alignment. If anyone else has other ideas just post below. Saw this post and sorta took a interest in it as with feedback we can make improvements to design as we see fit. Was thinking user could supply own bolt/nut hardware.
 
Hey I haven’t been on here in awhile due to amount of conveyor engineering work I’ve had lately. Recently just got over the flu last week. Anyways, I have access to autodesk inventor at work and any excess time permitting I could try to come up with a freeware solution for you guys and gals to try out. I’ve gained about 6 months professional proficiency at modeling using that software. I’m thinking either weekend or lunch time this week might work.

Now I don’t own any 75mm+ diameter rockets so if you all have preferred motor tube sizes ID and OD to build one of these units around that would be sweet. (Loc tubes/Wildman/Madcow insert favorite tube here). If you want certain bolt diameters and threads let me know. I’m figuring I could release the part files and drawings for free and y’all could take them to a local shop or online contract it out or whatnot for machining.

Just off the top of my head I’d like a grove or two that could hold epoxy better internally against the inside of MMT and help with alignment. If anyone else has other ideas just post below. Saw this post and sorta took a interest in it as with feedback we can make improvements to design as we see fit. Was thinking user could supply own bolt/nut hardware.

Mighty gracious of you Andrew. For me the 54mm design scaled up to 75mm would be adequate. I bolt mine in no glue.
 

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The bolting idea is neat. We can dump glue idea. Just curious of any idea why you are enamored with the giant leap style of design? I realize while possible to make a component similar to their design with cross bolts radially like you show, it begs to ask why a coupler tube can’t be inserted into the motor mount tube then simply drilling a hole through both tubes and using a single larger cross bolt through the walls of the tube which would eliminate all machining needs by say a shop and turn it into something you could do with a electric drill. Granted the bolt head and nut would stick out further.

One thing I can’t find is theoretical hand equations for shearing a bolt in the position that giant leap put it in. I suspect in that position would shear threads before the shaft itself snaps but to be honest mechanics materials isn’t my strongest set of skills so far. That’s a lot of loading on the threads but maybe I’m over looking something else in the giant leap design. At least with bolts perpendicular to material is easier to know theoretical when they fail under shear from basic mechanics.

This is kinda the difference between designing the part and just chunking it into cad. I’d like to understand further with some math when the component would fail. We rarely do FEA at work from my novice mech engineering perspective but maybe a project like this would be a good excuse to play with the FEA capability of software. Honestly now I’m kinda creeped out I can’t find a shearing mode for the giant leap design style. Most bolt shearing examples load the bolt perpendicular to the axis of the bolt?

Not trying to bash giant leap but now just skeptical of its strength lol. Honestly don’t know if the threads or head would shear first in that position. Assuming threads would go first for that design.
 
The bolting idea is neat. We can dump glue idea. Just curious of any idea why you are enamored with the giant leap style of design? I realize while possible to make a component similar to their design with cross bolts radially like you show, it begs to ask why a coupler tube can’t be inserted into the motor mount tube then simply drilling a hole through both tubes and using a single larger cross bolt through the walls of the tube which would eliminate all machining needs by say a shop and turn it into something you could do with a electric drill. Granted the bolt head and nut would stick out further.

One thing I can’t find is theoretical hand equations for shearing a bolt in the position that giant leap put it in. I suspect in that position would shear threads before the shaft itself snaps but to be honest mechanics materials isn’t my strongest set of skills so far. That’s a lot of loading on the threads but maybe I’m over looking something else in the giant leap design. At least with bolts perpendicular to material is easier to know theoretical when they fail under shear from basic mechanics.

This is kinda the difference between designing the part and just chunking it into cad. I’d like to understand further with some math when the component would fail. We rarely do FEA at work from my novice mech engineering perspective but maybe a project like this would be a good excuse to play with the FEA capability of software. Honestly now I’m kinda creeped out I can’t find a shearing mode for the giant leap design style. Most bolt shearing examples load the bolt perpendicular to the axis of the bolt?

Not trying to bash giant leap but now just skeptical of its strength lol. Honestly don’t know if the threads or head would shear first in that position. Assuming threads would go first for that design.

You mean something like this?

Beyond that I think you are assuming lots. First, I'm not ever "enamored" with a design. Second, what you're describing does not sound like the Giant Leap hardpoints.
 

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Looking at the GL hardpoint it appears to use a standard 1/4 inch eyebolt.
shockcord-hardpoint.jpg

With bolt in attachment compare the three failure scenarios, possibly four. 1/4 inch bolt shear, body tube tearout at the attachment bolts, attachment bolt shear or device web failure. I think in most "reasonable" cases all would hold.
 
Of course if you don't like the math and are designing from scratch, all components can be reinforced. :)
 
Of course if you don't like the math and are designing from scratch, all components can be reinforced. :)
True. Very true. I just got rambling about the math because I couldn’t find a mathematical model for that scenario yet: I need to dig up info on threads shearing just for enlightening myself. I think the threads shearing in that case is more probably what could happen if it encounters a high enough load.
 
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You mean something like this?

Beyond that I think you are assuming lots. First, I'm not ever "enamored" with a design. Second, what you're describing does not sound like the Giant Leap hardpoints.

Okay sorry. Yeah that photo was an idea of what could be done without machining and it is not like GL product at all but from a Math perspective it’s easier to know when the bolt in that scenario fails with knowledge that I have so far.
 
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Looking at the GL hardpoint it appears to use a standard 1/4 inch eyebolt.
shockcord-hardpoint.jpg

With bolt in attachment compare the three failure scenarios, possibly four. 1/4 inch bolt shear, body tube tearout at the attachment bolts, attachment bolt shear or device web failure. I think in most "reasonable" cases all would hold.
Thread failure from impact loading has me more concerned than bolt shear, body tube tearout, or device web failure to be honest with you. In a practical sense it’s probably easier to break a hardware store quick link over this.
 
https://www.greensladeandcompany.com/wp-content/themes/greenslade-theme/pdf/articles/engineering/Engineering - Bulletin - Calculating Thread Strength.pdf

Yeah I found this one too and ran some math on how much thread engagement I need so it doesn’t strip on internal or external threading and it appears at least 0.235” of threading length is very safe for quarter twenty to avoid stripping.

Other specs were
Tensile strength grade five 3816 pounds.
Bolt thread shear strength 22080 pounds per inch.
Bolt engagement to avoid stripping 0.172”.
Bolt engagement to avoid internal stripping 0.235”.
 
Sorry I’d never done anything with thread stripping and math before and felt a bit queasy.
 
Now with some data to avoid stripping I feel way more confident in GL’s design and upscaling it.
 
Apogee markets a 75mm internal motor retainer for MD birds that is very similar in design to the hard point you seek. It could be used as-is or modified to meet your particular needs. You can drill it and epoxy tee-nuts inside the unit for screw installation.
 
Apogee markets a 75mm internal motor retainer for MD birds that is very similar in design to the hard point you seek. It could be used as-is or modified to meet your particular needs. You can drill it and epoxy tee-nuts inside the unit for screw installation.

I'm not seeing it. Do you have a link?
 
Hey I haven’t been on here in awhile due to amount of conveyor engineering work I’ve had lately. Recently just got over the flu last week. Anyways, I have access to autodesk inventor at work and any excess time permitting I could try to come up with a freeware solution for you guys and gals to try out. I’ve gained about 6 months professional proficiency at modeling using that software. I’m thinking either weekend or lunch time this week might work.

Now I don’t own any 75mm+ diameter rockets so if you all have preferred motor tube sizes ID and OD to build one of these units around that would be sweet. (Loc tubes/Wildman/Madcow insert favorite tube here). If you want certain bolt diameters and threads let me know. I’m figuring I could release the part files and drawings for free and y’all could take them to a local shop or online contract it out or whatnot for machining.

Just off the top of my head I’d like a grove or two that could hold epoxy better internally against the inside of MMT and help with alignment. If anyone else has other ideas just post below. Saw this post and sorta took a interest in it as with feedback we can make improvements to design as we see fit. Was thinking user could supply own bolt/nut hardware.

Andrew,

Why not design something anyways, and post it in the 3D-Printer forum. We can start a discussion on the design; yo might get some traction & feed back..


Jahall, have you looked at other extruders? I've seen some similar type shapes in my searches for extruders, both structural & for heatsinks. But nothing comes to mind for what you're after.
 
Jahall, have you looked at other extruders? I've seen some similar type shapes in my searches for extruders, both structural & for heatsinks. But nothing comes to mind for what you're after.

Only cursory, issue seems to be the webbing, suggests the 38 and 54mm are custom extrusions.
 
Only cursory, issue seems to be the webbing, suggests the 38 and 54mm are custom extrusions.

Yeah, the giant leap is definitely an extrusion (with has it's own limits, but that's another thread! :D ) I've done a few extrusions, and some extrudes do have a series of specific / custom profiles. Finding one that's "close" is tough. But, sometimes, there' some that close enough, but with a bit of modding to fully fit..

The other thought I had for you, is a 3D printed part. My initial thought was for you to search a local Markforged dealer, and have them make you one. The Markforged printer can inlay Kevlar or fiberglass strands for some added strength. Their filament is a proprietary blend, mainly ABS.. They also do metal printers, and can make the part you want in metal.. cost though..

https://markforged.com/
 
Yeah, the giant leap is definitely an extrusion (with has it's own limits, but that's another thread! :D ) I've done a few extrusions, and some extrudes do have a series of specific / custom profiles. Finding one that's "close" is tough. But, sometimes, there' some that close enough, but with a bit of modding to fully fit..

The other thought I had for you, is a 3D printed part. My initial thought was for you to search a local Markforged dealer, and have them make you one. The Markforged printer can inlay Kevlar or fiberglass strands for some added strength. Their filament is a proprietary blend, mainly ABS.. They also do metal printers, and can make the part you want in metal.. cost though..

https://markforged.com/

To make just one I suspect would be very cost prohibitive. I could fabricate myself, but the time involved to do so.
 
Drill press.

Sure, but then you are back to some fabrication that will weaken the mount. The GL is designed to be vented and support the load of the whole rocket. The aeropack is designed to support the motor via the bolt, big difference! The Aeropack is a motor retainer the GL is not.
 
Someone posted looking for a 75mm hard point.

That motor retainer is machined aluminum. Drill a symmetrical pattern of half inch holes around the top for your venting, jam-nut the eyebolt in place, and install it.

If you can break that aluminum, or pull out the eyebolt, something was VERY wrong.

Rest assured, the phenolic paper or even fiberglass motor mount tube will give up long before that aluminum.
 
If you can (or want to) do a bit of fabrication:

a piece of sheet steel, 16ga, with a few bends.. (add more bends to get more of a curve..)

HARDPOINT2.jpg HARDPOINT.jpg

(Sorry Andrew, not trying to steal your thunder..)

put an eye bolt thru the tabs.. or just a quick ling thru the hole..
 
No it’s cool Dr. Wogz. Sheet metal fab is a valid tactic there are many ways to do this.
 
Make your own for 10 bucks. 2in. section coupler+ bulkplate+ E-bolt.
I do same thing...held in place with # 8 screws. Want it vented, drill some holes in BP.

100_9365.jpg
 
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