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hmm, aren't the wheels in the blast zone? or am I missing something?
Rex

Well, you would have to zoom in reeeaaaallllyy close to see it, and I entirely failed to mention it. I originally toyed with the idea of fenders in the line of fire (literally), but went with NASCAR pit-change friendly wheels. Once the pad is up on its feet, the tires are quickly removed from the axle and moved somewhere safe as well. Just an "R" pin holding them on. Doesn't take much to start a tire fire ...

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I expect that stacking them near the step ladder would work, though putting the pins in your 'pocket' might be a good idea. thanks for the info, I did wonder a bit :).
Rex
 
I soooo want to see something fly off of the small scale version!

And so you shall.... although YouTube conversions lose a lot of the resolution from the original slow motion iPhone video. The screen shots show it in better detail.


[video=youtube;pzGDopujWFU]https://www.youtube.com/watch?v=pzGDopujWFU[/video]

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looking good, though some 'minwax spar urethane' would look nice on those wood bits :).
Rex
 
Winter break is over, time to get back to work...

Threw on a quick coat of primer last fall to protect the bare metal from seasonal garage humidity. Results of latest weld session.

Attached the tray to the frame on 1"x1" square tubes, to set the height where the footlocker top will open without hitting the upper side rails. (photo 1)

Attached 2"x2" angle iron under the frame for the tongue. 2"x2" tongue fits between and locks in with two 5/8" clevis pins (one shown in underneath views). Since the distance between the holes is fixed, the tongue can be inserted in the opposite direction (out the "back") and function as the third leg. (photos 2, 3, and 4)

Forward edge of angle iron to be drilled for clevis pins used to uplock the truss in launch position. Bracket on truss fits between the 2"x2" square crossbar and the 2"x2" angle iron. (photos 5 and 6)​

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Starting work on the legs.

The angled top of the leg has a 20° and a 70° cut, but my abrasive-wheeled chop saw only has generic 15°/30°/45° markings on a rudimentary mitre. So, to ensure I make accurate cuts, I made a 20°/70° triangle out of scraps of particle board. Since the 2" x 2" square tubing has a radius edge, I made the triangle a full 2.25" thick (3 x .75") to ensure it aligned the face of the steel and not just the rounded edge. The angles were double checked by linear measurements (and some math), as well as angular measurements with the protractor on my trusty PLU-6/C. (photos 1 & 2)

Making a jig for the legs. This is to ensure alignment of the pieces for welding AND to allow me to make multiples exactly the same. Steel supports bolted temporarily along the bottom edges to keep the jig flat. Interior bracing next to be cut. Some weird angles in there, too. (photos 3 & 4)

Big shout out "Thank You's" to my good friend sodmeister (Paul) for all the jig and tool suggestions I have stolen over the years, and good friend Feckless Counsel (Geoffrey) for engineering ideas and those great DeWalt tools!

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Finishing up a few other projects, which frees up some time to continue progress on this one. The legs will each swing 120° forward from the stowed position (along the side of the trailer), so the hinges needed to be made deep enough to allow for that without binding or catching. Therefore, the spindles on the legs (5/8" I.D. tubing) were shimmed out with a C-channel and a 1/8" steel strip. (Back in Post #42. Yeah, I know, over a year ago.) The nice thing with a slow build is time to catch and fix mistakes. I had planned on 3 spindles per leg, using a 5/8" bolt as a kingpin in each. When I laid everything out, I realized a bolt long enough to reach through each spindle bracket was too long to fit between them for installation. My options are then to either install the bolts prior to welding everything together (forever dooming the legs to never being disassembled), or just to use one long 5/8" rod as a continuous kingpin. The latter option won out, with the added benefit of being able to up the total number of spindles per side to 4.

Photo 1 shows the 4 spindles on one 2" x 2" leg vertical, with the 4 spindle brackets (to be welded to the vertical supports on the pad frame), utilizing one long kingpin. The remaining photos show the kingpin and spindle brackets removed, and a jig I made to hold the spindles in position for welding. (and repeatable spacing)

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Very nice work!

Thank you. Long, slow project, but happy so far with where we are with it.

The wooden jig in Post #67 sets the vertical spacing of the spindle brackets, but needed something to ensure the vertical alignment remains, in fact, vertical. So, added scrap pieces of wood to the ends of the base, in which the kingpin fits, which will hopefully keep everything within tolerance during welding, so the leg swings remain in plane.

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A little time with my welder today... spindles attached to the outrigger (leg) verticals. A little more 2" x 2" cutting before I can finish the legs themselves.


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Thanks. Wish when I said "spending time with my welder" I was talking about having the equipment and knowing how to use it. Neither of which is a reality. The next best thing is having someone with both equipment and ability, so thats where I go. And he does do really nice work.

Now comes the part where I am going to start getting hate mail.... Had some placards printed up on metal plates to attach to the sides of the frame after final paint. Personal preferences (my choice), not criticizing anyone whose preferences don't align with my own. I.e., we plan to fly this on my school club's field, which we fiercely protect, so don't want to ever start a corn stalk rubble fire.

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OK, so what is wrong with metal rail guides??? At our launches the rails get so crudded up an occasional metal guide will possibly clean off some of the black crud. You would have to launch 10's of thousands of rockets for wear to be an issue...the rail will be useless due to normal use long before that...
 
Thanks. Wish when I said "spending time with my welder" I was talking about having the equipment and knowing how to use it. Neither of which is a reality. The next best thing is having someone with both equipment and ability, so thats where I go. And he does do really nice work.

Now comes the part where I am going to start getting hate mail.... Had some placards printed up on metal plates to attach to the sides of the frame after final paint. Personal preferences (my choice), not criticizing anyone whose preferences don't align with my own. I.e., we plan to fly this on my school club's field, which we fiercely protect, so don't want to ever start a corn stalk rubble fire.

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Sather, your pad; your rules. Makes perfect sense to me. ;)
Beats having to extract repair funds form someone who damages your pad and refused to reimburse you.
 
I also wondered why no Vmax motors? Although my question may be irrelevant at this point as it seems CTI has quit selling them....

You ARE going to put some kind of blast deflector plate on the launch rail, right? Help protect the field you fly from, as well as following rocket safety codes.
 
I also wondered why no Vmax motors? Although my question may be irrelevant at this point as it seems CTI has quit selling them....

You ARE going to put some kind of blast deflector plate on the launch rail, right? Help protect the field you fly from, as well as following rocket safety codes.

Hi thrust motors like VMax put a lot of force onto a pad for a short time. My Quad Pod needed replacement legs after a few heavy hitting motors. All the legs bent.
 
Sure, it’s that equal and opposite reaction. High thrust exhaust that is decelerated by striking the blast plate puts force directly onto the launch pad.

I agree. But the thrust from a Vmax j is not greater than the thrust from a big k or L motor. For example, a K1440 has initial thrust on the pad of just less than 2250 newtons, but a Vmax J1520 only has a little over 1500 newtons on the pad. Both of these are 54 mm motors and both will fly in my 4 inch Dark Star.
So which motor puts more stress on the pad? I think the answer is fairly obvious. So again, why no Vmax motors?
I could understand restricting the size, or thrust of the motors.
 
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I agree. But the thrust from a Vmax j is not greater than the thrust from a big k or L motor. For example, a K1440 has initial thrust on the pad of just less than 2250 newtons, but a Vmax J1520 only has a little over 1500 newtons on the pad. Both of these are 54 mm motors and both will fly in my 4 inch Dark Star.
So which motor puts more stress on the pad? I think the answer is fairly obvious. So again, why no Vmax motors?
I could understand restricting the size, or thrust of the motors.

Your point is correct, it’s possible to select a higher impulse motor that has a higher thrust. Higher thrust will do more damage, especially if delivered for a longer time as a higher impulse motor might. I should have said, typically VMax has more thrust than other motors. That particular K motor, the K1440 with its initial spike would be harder on the pad, but all other things being equal VMax motors have higher thrust and are more likely to do damage. I suspect he called out VMax only as a matter of convenience.
 
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Pardon an obvious question . . . How much will the completed pad weigh ?

Really good question... wish I had the answer. Way more than I initially thought. The plan has evolved during the build, and with it being on wheels and jacks, it hasn't really been a problem yet. Rolling it over and tipping it upside down for welding access has been challenging at times, but moving it around on its wheels has been pretty easy. Will be easier once the tow bar / hitch is complete, as I have a tongue dolly for my actual trailer. I'll weigh it when it gets closer to being finished. The legs / outriggers will add a lot of weight, as will the 3 jacks.

Higher pad weight, IMHO, is a good thing. Provides a more stable platform, less likely to move or shift during launch. Seeing how much Steve's pad (pretty substantial in itself) got moved laterally in his Saturn V launch gives emphasis to pad weight (and stakes)!

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OK, so what is wrong with metal rail guides??? At our launches the rails get so crudded up an occasional metal guide will possibly clean off some of the black crud. You would have to launch 10's of thousands of rockets for wear to be an issue...the rail will be useless due to normal use long before that...

The simple reason is metal on metal causes wear. We don't clean our motor casings with steel wool or anything abrasive. Hot soapy water and a good stiff nylon brush are your friends.

"As indicated by accuracy testing, the steel cased/bimetal jacketed ammunition caused accelerated wear to the inside of their respective bores. While the barrel of the Federal carbine had plenty of life left, even after 10,000 rounds at extremely high rates of fire, the Wolf and Brown Bear barrels were subjected to the same rates of fire and were completely “shot out” by 6,000 rounds. At the end of the test, the chrome lining of the Wolf and Brown Bear barrels was almost gone from the throat forward, and the barrels had effectively become smoothbores, with the rifling near the muzzles acting only as a mild suggestion on the projectiles. A throat erosion gauge could be dropped into the bore from the muzzle end with absolutely no resistance." (https://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/)​
 
I also wondered why no Vmax motors? Although my question may be irrelevant at this point as it seems CTI has quit selling them....

You ARE going to put some kind of blast deflector plate on the launch rail, right? Help protect the field you fly from, as well as following rocket safety codes.

Yup, planning a substantial blast deflector. (Future post in this thread.) And I found it easier to arbitrarily limit rocket weight (100 pounds) and Vmax motors (none) than the other possible ways to minimize pad damage, some requiring case-by-case thrust curve analysis and hair-splitting math. Vmax motors are still allowed on the smaller pads, but if you need the away cell at our launch, you're probably not launching a 4" rocket on a J.

Vmax, SS, sparkies, and research motors were eliminated from personal experience. I also had to replace my Quad Pod's original legs, (which were admittedly not the sturdiest to begin with. The originals were round tubing, the new are square.) Smoky Sam leaves a lot of black residue and difficult to clean. Tired of getting burn scars in aluminum rails from sparkies, and really want to avoid that with the (expensive) aluminum truss. And finally, once watched a research motor sit on the pad and blowtorch for almost 2 minutes, providing ZERO thrust, but completely destroying the pad.

Yeah, I know I'm being picky. And I use 3 out of the 4 banned motors myself, so am also shooting myself in the foot. But having invested over a grand (so far) and going on 3 years of my life in this project, I want it to outlast me.
 
The simple reason is metal on metal causes wear. We don't clean our motor casings with steel wool or anything abrasive. Hot soapy water and a good stiff nylon brush are your friends.

"As indicated by accuracy testing, the steel cased/bimetal jacketed ammunition caused accelerated wear to the inside of their respective bores. While the barrel of the Federal carbine had plenty of life left, even after 10,000 rounds at extremely high rates of fire, the Wolf and Brown Bear barrels were subjected to the same rates of fire and were completely “shot out” by 6,000 rounds. At the end of the test, the chrome lining of the Wolf and Brown Bear barrels was almost gone from the throat forward, and the barrels had effectively become smoothbores, with the rifling near the muzzles acting only as a mild suggestion on the projectiles. A throat erosion gauge could be dropped into the bore from the muzzle end with absolutely no resistance." (https://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/)​
OK, so how are you equating a launch guide with a gun barrel, that is comparing apples to oranges, the launch guides are not a friction fit into the rail and are not abrasive. I have one or two rockets where I used tiny brass washers and screws for 1010 rail guides. they work fine. even high power rockets with warp 9 propellant are not travelling at supersonic speed at the end of the launch rail... I see no point in spending $4 for rail buttons for a model rocket built with $10 worth of parts. and the typical rail buttons I have seen don't fit a BT60 size or smaller anyway, the weld nut is too big.
 
That pad will never be used for BT-60 tubes.
We're talking 6in and above [with occasional 4in. M-N's] Metal on metal can cause 'galling:Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together.

This will & does cause permanent damage to rails/strut on something this size, when weight combined with high thrust comes into play.
This pad is designed just for such large, heavy, high thrusting motors= lots of friction between guides and rail/struts.
Fiction = heat=wear on suffices like these.
Why delrin/nylon or ball bearing guides are used on large amateur projects.

In gun barrel heat is your enemy. Using copper jacket bullets[being softer than steel] will not nearly cause the wear steel jacket on steel barrel will.

Translate that to a rail [aluminum] with aluminum guides it's a perfect storm for galling where high friction heat is caused by heavy rockets sliding their way up the rails.

If you have ever seen large guides after being flown just once, there is a large amount of wear on them, with none on rail
If you used metal guides there would be wear on both rail & guide
 
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That pad will never be used for BT-60 tubes.
We're talking 6in and above [with occasional 4in. M-N's] Metal on metal can cause 'galling:Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together.

This will & does cause permanent damage to rails/strut on something this size, when weight combined with high thrust comes into play.
This pad is designed just for such large, heavy, high thrusting motors= lots of friction between guides and rail/struts.
Fiction = heat=wear on suffices like these.
Why delrin/nylon or ball bearing guides are used on large amateur projects.

In gun barrel heat is your enemy. Using copper jacket bullets[being softer than steel] will not nearly cause the wear steel jacket on steel barrel will.

Translate that to a rail [aluminum] with aluminum guides it's a perfect storm for galling where high friction heat is caused by heavy rockets sliding their way up the rails.

If you have ever seen large guides after being flown just once, there is a large amount of wear on them, with none on rail
If you used metal guides there would be wear on both rail & guide


I was mainly referring to smaller stuff, i have not had any wear problems on a 1010 rail with a rocket less than 3 lbs with h motors. everything is a bit different when the rocket is 200# with an M motor, I agree... Take a look a a real Nike Tomahawk... metal guides on a metal rail...greased
 
Now comes the part where I am going to start getting hate mail....

how are you equating a launch guide with a gun barrel, that is comparing apples to oranges, the launch guides are not a friction fit into the rail and are not abrasive. I have one or two rockets where I used tiny brass washers and screws for 1010 rail guides. they work fine. even high power rockets with warp 9 propellant are not travelling at supersonic speed at the end of the launch rail... I see no point in spending $4 for rail buttons for a model rocket built with $10 worth of parts. and the typical rail buttons I have seen don't fit a BT60 size or smaller anyway, the weld nut is too big.

The Brass vs Steel-cased ammo experiment remains a perfectly valid comparison. Brass is a softer metal and in a controlled lab experiment, caused much less wear than steel in the same exact application. On Mohs hardness scale, Aluminum comes in at 2.5 to 3.0, Copper and Brass tie at 3.0, and steel 4.0 to 4.5. Couldn't quickly find a number for nylon, but I can scratch it with my fingernail (2.0-2.5), so pretty sure it is softer than aluminum. The scale uses a simple principle for each material: Which materials can scratch it, and which materials it can scratch. "Scratching" is literally a definition of abrasive.

This, being a privately funded project, with the sole patron also standing in as the RSO and post-launch clean-up crew, gets to make the rules. Having had my fair share of equipment (rails, trackers, motor hardware, ...) damaged or destroyed by well-intentioned people with bad luck that day, I have some incentive to add simple rules not subject to committee. This is an "away cell" pad, which is probably not going to see many $10 rockets. And definitely won't see anything that doesn't have $4 in rail buttons.

Personal preferences (my choice), not criticizing anyone whose preferences don't align with my own.
 
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Continued slow progress. Those who know me will attest I do most of my work in brief bursts of energy, which get fewer and farther apart as I get older. The long lulls between give me a chance to reflect on past mistakes and plan ahead a little. I spent a bit of time over the winter precision grinding the spindles previously welded to the leg verticals. The weld bead on top and bottom prevented the spindle brackets (which will be in turn welded to the frame body) from fully turning through their 180° of motion without binding, so they needed to be (very carefully) ground down. Now, with the kingpin installed, they move freely.

Another disadvantage of long builds, especially ones that start without a real plan, is design specs change and sometimes one has to backtrack and fix something. Early on, I had planned three spindles per leg with 5" bolts as kingpins. Later, I decided to use four spindles per leg, and found the 5" bolts would not longer fit between the spindles for installation. This forced me to change (fix #1) to one long, continuous kingpin, installed from the top. Alignment of individual spindles is critical, as the kingpin cannot "bend" if it has to make a course correction going down multiple holes in sequence. Also, I had made a jig for the legs (since I have to make 2 and I want them to be the same). The jig uses small scraps of wood blocks to keep the metal in position for welding. I had used 2 blocks on the spindle side of the leg upright, which was fine as they would have fit between the three spindles. When I changed to four spindles, the blocks are now in the wrong spots. A couple taps with a chisel (fix #2) and the wood pops off, taking chunks of MDF with them. A little sanding and wood filler and ready to add new blocks.

My "Problem Shock" reference* applies here as well. The interior space of each leg gets some cross bracing to distribute forces (like a truss bridge). Angles are gonna be tricky to cut, as the sway brace sits at 70°, so the bottoms of the internal bracing is 45° and the tops are either 25° or 65°, depending on which way the bracing faces, and length (interior to the leg) is critical. Anybody out there with a ninth-grader in High School Geometry that can check my math?

* - I took credit for this observation in August 2011 in my recycling container odd-roc build thread. In his 1970 book, Alvin Toffler defined "future shock" as a personal perception of "too much change in too short a period of time". The accelerated rate of technological and social change leaves people disconnected and suffering from stress and disorientation. Here is the connection to rocketry. When you build a kit, the directions are laid out in a logical order, basically engineered for ease of assembly. In scratch-building, however, as you run into problems, they get deferred. Eventually, when all the fun, easy to do stuff is finished, all you have left are the problems and they pile up in front of you like a giant wall.
 

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