My darkstar4 dd

[gagreen]

Picked up a darkstar 4 dd from a fellow trf'er at mwp and have been sitting on it for a while now so i decided to get building.


Started off with the motor mount tonight. Overbuild? quite possibly but i wanted something that would last.

I drilled a few holes for the u-bolt in the top cr, i was afraid that it may be too much pressure on the top cr. to reinforce i ran three runs of all thread down through the other cr's to spread the force down through all the centering rings and the rear will double as motor retention. More on the retention later after i get to the shop to fab the retainer. anyway here it is mocked up just gotta sand and add fillets from the crs to the mmt.

[UPscaler]

awesome! Who doesn't love a good darkstar? I'll be watching!




Braden

[G2Rockets]

Picked up a darkstar 4 dd from a fellow trf'er at mwp and have been sitting on it for a while now so i decided to get building.


Started off with the motor mount tonight. Overbuild? quite possibly but i wanted something that would last.

I drilled a few holes for the u-bolt in the top cr, i was afraid that it may be too much pressure on the top cr. to reinforce i ran three runs of all thread down through the other cr's to spread the force down through all the centering rings and the rear will double as motor retention. More on the retention later after i get to the shop to fab the retainer. anyway here it is mocked up just gotta sand and add fillets from the crs to the mmt.

Geoff,
Overbuilt? yeah probably, but it makes it look really technical, and that can be cool. It looks like the standard 54mm Motor mount, which mean you probably don't need that much strength. What it comes down to is if you like what you are doing and if it flies well.

Just a heads up that you MAY or may not be aware of. Make sure you don't forget to line your all-thread up properly. you don't want it in the way of your fin slots. Also, chances are you will change the CG, so make sure you retest when its complete and ad weight in the forward if it needs it. I am sure you are aware of these things, but a reminder can be helpful.

Keep us updated. "NO PICS? IT DIDN'T HAPPEN"

John

[gagreen]

Geoff,
Overbuilt? yeah probably, but it makes it look really technical, and that can be cool. It looks like the standard 54mm Motor mount, which mean you probably don't need that much strength. What it comes down to is if you like what you are doing and if it flies well.

Just a heads up that you MAY or may not be aware of. Make sure you don't forget to line your all-thread up properly. you don't want it in the way of your fin slots. Also, chances are you will change the CG, so make sure you retest when its complete and ad weight in the forward if it needs it. I am sure you are aware of these things, but a reminder can be helpful.

Keep us updated. "NO PICS? IT DIDN'T HAPPEN"

John

The technical look is really really cool lol looks like i planned to build it this way "cough cough". the real story is i cant find my aeropack for this one and wanted to build it anyway so i wondered into the hardware store. I got forged eye bolts for the avbay, some all thread for the avbay then it hit me that i could run three lines of all thread through the mmt cr's and make a retaining plate that will simply be tightened down with a nut so all problems solved kinda lol.


I didnt take pics of me drilling or pre drill of the cr's but it was really simple.

1. Insert a cr evenly and mark the fin slot on the side of the cr through the slot in the bt. then remove

2. Use a straight edge and draw the line across the top of the cr to the center hole, repeat for all 3 fin slots.

3. transcribe that mark to the other 3 cr's. these marks show where the fin wll be so the holes for the allthread can be marked centered between them.

4. On the fwd cr i measured and marked the location for 2 other drill holes, these will allow me to install my recovery harness U-bolt.

5. Double check accuracy of marks by prefitting the cr's into the bt and verify lines are good, technically this was a wasted step in my case...

Then to the drill press. I stacked and clamped all the cr's together with the one on top clearly marked to show me where to drill. Drilling them all at the same time and marking the holes in some way ensure that the allthread will not bind or bend when they are installed on the mmt. i drilled the three holes out then unclamped them. I took the cr i marked for my fwd cr and drilled the U-bolt holes.


The hard part of this method is getting the spacing right on the cr's up and down the allthread. Measure measure and more measuring. Each cr is held in place by a nut on both sides. to get the spacing right between the rings i used a digital caliper and a makeshift square (the edge of a machinists scale). This part took a while but making sure each one was equally spaced but in the end it was worth it.

It is important to note that everything should be sanded before doing this step, you wont want to have to take it apart and start over because you forgot to sand adhesive areas.... look at the pics attached and you will see how i know this


The pics show the fwd cr epoxied into place. pic is from cell phone so you cant hardly see tell they are sanded but they are gritty gritty to the touch... now lol first time not so much

second pic shows a little more detail in the assembly of the cr's on the all thread. nut on each side, kind of like k&s's avbay set up.


I am in the process of weighing everything and adjusting the rocksim as i go, right now i havent added enough weight to change stability much so as long as i stay conservative on the rest i should be ok.

[JDcluster]

There is no need for the threaded rod .
It just added another 3lbs to your rocket's tail end.

Which probably means you'll be adding another pound of nose weight to counter balance it, when you put a motor in it.

A heavier rocket isn't always a stronger rocket.
It's your rocket, have fun with it.

JD

Picked up a darkstar 4 dd from a fellow trf'er at mwp and have been sitting on it for a while now so i decided to get building.


Started off with the motor mount tonight. Overbuild? quite possibly but i wanted something that would last.

I drilled a few holes for the u-bolt in the top cr, i was afraid that it may be too much pressure on the top cr. to reinforce i ran three runs of all thread down through the other cr's to spread the force down through all the centering rings and the rear will double as motor retention. More on the retention later after i get to the shop to fab the retainer. anyway here it is mocked up just gotta sand and add fillets from the crs to the mmt.

[G2Rockets]

There is no need for the threaded rod .
It just added another 3lbs to your rocket's tail end.

Which probably means you'll be adding another pound of nose weight to counter balance it, when you put a motor in it.

A heavier rocket isn't always a stronger rocket.
It's your rocket, have fun with it.

JD

JD,
It kind of reminds me of one of my first MPR's. I put a 29mm motor mount into a Big Daddy. I know it isn't a big deal, but I completely overbuilt. I changed to Basswood fins and a cool motor retentions system. When all was said and done. One of the guys at a launch put his standard Big D up on a f and totally blew me away. I learned sometimes its better not to over think. On the other hand it was one of my favorite builds.

John

[Tronman]

Subscribed. Mine is in the basement and I've been waiting for a build thread to appear before starting it.

Why not span the motor tube with a U-Bolt so the stress is centered?

[Eric1]

I'll be watching this!!

Goeff, Man that's some serious rear end!

[dixontj93060]

Building on top of Christmas wrapping paper--that's a new one!

[Eric1]

Building on top of Christmas wrapping paper--that's a new one!

New meaning to, "I Can't Wait!"

[gagreen]

Subscribed. Mine is in the basement and I've been waiting for a build thread to appear before starting it.

Why not span the motor tube with a U-Bolt so the stress is centered?

if i am comprehending you correct, i dont want anything blocking the top of the mmt in case i decided to put something longer than the mmt in there.

Building on top of Christmas wrapping paper--that's a new one!

Its an actual table cloth you never know when the day after christmas sale will produce a .45 cent rocket part drop cloth lol

I'll be watching this!!

Goeff, Man that's some serious rear end!

Its almost a shame for me to have to hide it all away lol.

[Tronman]

if i am comprehending you correct, i dont want anything blocking the top of the mmt in case i decided to put something longer than the mmt in there.

I think you got my drift, based on your answer. A u-bolt over the top of the motor tube would limit the length of the motor.

[gagreen]

I think you got my drift, based on your answer. A u-bolt over the top of the motor tube would limit the length of the motor.

exactly

Well i thought i had a few food injectors at the house but i was wrong so till i get those this project is on hold. THe mmt is test fit and will sit there till i get my injector and some rail buttons.

Here is a pic of the business end to give you an idea of where im going with the retention system. Pretty standard i believe. Just need to fabricate a plate that will tighten down onto the allthread studs

[MasonH]

I know I'm late, but why use threaded rods for support? You are just adding unnecessary weight. If the purpose is strength with high thrust motors, why not just use a thrust plate such as those found at Apogee? They are made of aluminum so they can take the stress off the rings, as they butt up against the main airframe and have the same OD as the main airframe. Light, cheap, effective, and you dont have to worry about the CG.

[eggplant]

I know I'm late, but why use threaded rods for support? You are just adding unnecessary weight. If the purpose is strength with high thrust motors, why not just use a thrust plate such as those found at Apogee? They are made of aluminum so they can take the stress off the rings, as they butt up against the main airframe and have the same OD as the main airframe. Light, cheap, effective, and you dont have to worry about the CG.

I don't know his reasons, but for me,
1. Money
2. The thrust plate actually adds about a quarter of a pound of weight, directly on the back of the rocket. I bet the threaded rod weighs less. They are also not right at the end, so they don't pull the CG back as much

[MasonH]

I don't know his reasons, but for me,
1. Money
2. The thrust plate actually adds about a quarter of a pound of weight, directly on the back of the rocket. I bet the threaded rod weighs less. They are also not right at the end, so they don't pull the CG back as much

While it may weigh a considerable amount, on a rocket this length, I don't think it will matter that much. Additionally, it is removable for low thrust flights, and the flanged areopac adapter mounts to the thrust plate. As for money, whats a few dollars for a removable peice of hardware that will last and last?

[eggplant]

$42.00 isn't really a few dollars.

[MasonH]

$42.00 isn't really a few dollars.

True, but a single piece of aluminum hardware is much cheaper than the cost of replacing a whole rocket because precaution wasn't taken into consideration.

[eggplant]

He probably doesn't even need reinforcement. He said himself. He said that it is mainly going to be used as an attachment point for his engine retainer plate. He most likely couldn't attach the ring he is making to a thrust plate.

[gagreen]

it serves as an attachment point for motor retention (a thin plate that works like madcow's retainer with a hole in the center for the nozzle. as well as serving for retainment it also distributes the load from the ejection charge through 4 centering rings rather than just the top one that the ubolt is attached too. no need for a thrust plate. the thrustplates serve a different purpose than the all thread does.