HPR Exchangeable Motor Mount

[jqavins]

I had an idea for an exchangeable motor mount system for HPR. Since there's nothing new under the sun, I googled "exchangeable motor mount" and "exchangeable motor mount hpr" and came up empty. A few for LPR/MPR, but nothing for HPR. So, I wonder if, just maybe, this is something new after all. Here's the idea.

In a large airframe tube, add a smaller tube, one "standard" size down or roll your own to a different size. Call that the MMT socket. TTW fins can be attached to the socket. Then the operational MMT goes into the socket. The MMT's forward CR would fit the socket, and the aft CR would fit the airframe tube. Either large T-nuts or threaded studs are installed in aft CR of the socket, and bolts or nuts hold the MMT in. The MMT could have a thrust plate if desired.

Has this been done? Is there a reason it should not be done, such as some much simpler way that I'm overlooking?

 

[Bowman]

I had an idea for an exchangeable motor mount system for HPR. Since there's nothing new under the sun, I googled "exchangeable motor mount" and "exchangeable motor mount hpr" and came up empty. A few for LPR/MPR, but nothing for HPR. So, I wonder if, just maybe, this is something new after all. Here's the idea.

In a large airframe tube, add a smaller tube, one "standard" size down or roll your own to a different size. Call that the MMT socket. TTW fins can be attached to the socket. Then the operational MMT goes into the socket. The MMT's forward CR would fit the socket, and the aft CR would fit the airframe tube. Either large T-nuts or threaded studs are installed in aft CR of the socket, and bolts or nuts hold the MMT in. The MMT could have a thrust plate if desired.

Has this been done? Is there a reason it should not be done, such as some much simpler way that I'm overlooking?

PML sells a mount called the "Quik Switch" for 29 - 54mm.

 

[heada]

LOC has the "LNR" as well. 54mm main tube with step down adapters for 38mm and 29mm. Comes standard in some of their 4" kits.

 

[bobbyg23]

Loc precision mms.
https://locprecision.com/product/modular-motor-can-mmc/

 

[jqavins]

The adapter options don't offer cluster mounts, which (I failed to mention) is part of what I'm thinking of. The LOC MMC seems very similar to what I'm describing. Does it come for other airframe sizes than 2.6"? Obviously, one could make one's own inserts for other cluster configurations.

The link for one of the thumbnails seems to be broken, as it brings up a different full size picture. It looks like the coupler that the motor can is built into would preclude TTW fins; am I missing something?

I'm thinking of a system for rockets that really need TTW fins. Like a six inch airframe with a five inch socket. Swap over from a 98 mm MMT to a 7× 38 mm. That sort of thing.

 

[heada]

LOC MMC excludes TTW fins. I have several of the kits that use it and the fins use slots in the BT but the fin tabs are only as deep as the BT thickness.

It is a good setup but...

The rivets are sometimes hard to remove
The rivet holes were ever so slightly different between 2 of the kits I have so I had to make one of the MMC module rivet holes wider
getting the top CR in place that acts as a thrust ring is difficult. To get around that, I installed a baffle and use that as the thrust ring
There is no active motor retention so plan for that
They're more designed for LPR/MPR and not so much HPR. I wouldn't use it for a high thrust H or I 29mm motor. I don't see a 38mm option any more but they used to have that as well. I wouldn't trust 38mm in this except for single grain, low thrust motors.

 

[jqavins]

So maybe I have got a new design approach? Now if only I had the time and money to build something worth using it.

 

[Dugway]

US Rockets has kits like the Stiletto (https://www.rocketreviews.com/us-rockets-usr-stiletto-by-lance-alligood.html) that come with a heavy-duty 66mm core and adapters for everything from 1x54mm to 4x24mm, and everything in between. I bought a Warp 1.5 kit from Jerry recently just to get more of the 66mm tubing for my own scratch builds, I haven't found anything quite the same dimensions anywhere else.

 

[tsmith1315]

You'll need a name for it. Would it be a JAMM?

 

[jqavins]

US Rockets has kits like the Stiletto (https://www.rocketreviews.com/us-rockets-usr-stiletto-by-lance-alligood.html) that come with a heavy-duty 66mm core and adapters for everything from 1x54mm to 4x24mm, and everything in between. I bought a Warp 1.5 kit from Jerry recently just to get more of the 66mm tubing for my own scratch builds, I haven't found anything quite the same dimensions anywhere else.

Yeah, that looks like what I'm talking about. That's a relief; I wouldn't want the responsibility if I'd been first.

 

[afadeev]

The adapter options don't offer cluster mounts, which (I failed to mention) is part of what I'm thinking of. The LOC MMC seems very similar to what I'm describing. Does it come for other airframe sizes than 2.6"?

Yes, 2.6" or greater (with a little planning).
First of all, LOC's MMC fits into 2.6" tube "sleeve", and supports upto 38mm motor mount (1x38mm, or 1x29mm, or 1x24mm, or 3x24mm, or 4x18mm inner motor tubes).
There is no requirement restricting you from going with larger airframes. All you would need to do is to mount an internal 2.6" motor-mount "sleeve" inside a wider airframe, drill rivets access holes, and continue swapping out MMC motor mount modules. There will be a practical limit with total rocket weight, as the largest 38mm motor will be a J (unless you have a spare Loki's 38mm Ks), and there is only so much weight that a J can accelerate, safely.

It looks like the coupler that the motor can is built into would preclude TTW fins; am I missing something?

No TTW only on the 2.6" airframes.
If you insert a 2.6" "sleeve" into a larger airframe, you can TTW mount fins to the "sleeve".

I'm thinking of a system for rockets that really need TTW fins. Like a six inch airframe with a five inch socket. Swap over from a 98 mm MMT to a 7× 38 mm. That sort of thing.

LOC's TTW system was on my "to build" list for a while, but I got side seduced by other projects. I would only fly it for mid-/low-HP rockets, for the reasons stated above.
A rocket big and heavy enough to warrant a 98mm MMT, must be build to withstand very serious thrust levels and ejection charge deployments. You could upscale LOC's MMC idea to something bigger, but it would take careful consideration to not end up with a MMT system that shoots though the airframe as soon as 98mm motor comes to full thrust!

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