Lengthening my rod.

[Richard Dierking]

Like they way you are thinking it through.

Hopefully, someone will recall the paper and know where to find it. A lot of my files were discarded when our section discontinued activities. Perhaps there's even more recent data.
I did clean all the rods before every monthly launch and use furniture wax on them. I think the largest aluminum rod we had was 1/4" and 6' long. btw, 6061 aluminum.

 

[Blast it Tom!]

Like they way you are thinking it through.

Can't help it... I'm an engineer. But thanks! Cleaning and waxing is very important - with bare aluminum a passivating oxide coat forms almost immediately. You do recognize what aluminum oxide is, right? And yes, it's very thin, but surprisingly effective. I just investigated a case where an aluminum sleeve welded around a section of a shaft led to cracking of a tough, ductile 4340 shaft with about 120,000 psi yield strength. I did the fracture mechanics workup, and by all the data I could find, it shouldn't crack via the usual stress/strain fatigue. But it turns out the aluminum oxide was fretting off and new oxide reformed immediately and that led to almost imperceptible cracks that eventually joined and then stress/strain cracking took over. So yes, keep them clean and waxed!

 

[Richard Dierking]

I just investigated a case where an aluminum sleeve welded around a section of a shaft led to cracking of a tough, ductile 4340 shaft with about 120,000 psi yield strength.

Wow!
I use Bonderite cleaner and conversion coating for epoxying aluminum fins and other times when I'm using aluminum. Good surface bonding. I've tried other techniques like wet sanding aluminum with the epoxy on the material. Kind of messy, but does work a bit better than just applying epoxy to untreated aluminum.

When I took care of a lot of launch equipment, keeping the launch rods clean was a chore. The rods were kept in ABS tubes and you can imagine if there was any moisture in the tube. Also, keeping aluminum rods with steel ones is not good.
I would like to find that paper on rod whip and still looking.
I don't suggest aluminum rods for club launch equipment. They bend too easily and very difficult to get them straight after being bent.

 

[Greg Furtman]

You have a Delorean?

You mean a Snow Mobile?

 

[Blast it Tom!]

@Richard Dierking , you are right, keeping aluminum with steel will lead to corrosion just due to atmospheric moisture, much less condensation. etc, I think the term is "electrogalvanic corroision" & can occur when two dissimilar metals are in contact. I hope you find that paper, it sounds interesting. & yeah, it pretty much is impossible to straighten a rod after it's been bent. "Straight enough", perhaps, but just ask any auto body repairman if you can ever get it really straight...

 

[Nytrunner]

Its been awhile since galvanic coupling popped up on this forum

Interestingly enough, aluminum bike frames are considered to feel "stiffer" than steel tube frames.

 

[Blast it Tom!]

I would expect that, due to their light weight, we don't expect them to be a stiff as they are.

 

[Senior Space Cadet]

https://www.mcmaster.com/metals/diameter~0-25inches/shape~rod-and-disc/stainless-steel/
Not threaded but you can get longer lengths and of stiffer material

It's costing me a pretty penny, but I ordered three rods from McMaster-Carr. A 3'x3/16, a 6'x3/16, and a 6'x1/4.
I'm not too impressed with the Estes rods. The rod it's self isn't too bad, but the connections aren't much to brag about. If you plan on staying in rocketry for any length of time, I think quality rods are a good investment. Hope they arrive OK.

 

[rharshberger]

It's costing me a pretty penny, but I ordered three rods from McMaster-Carr. A 3'x3/16, a 6'x3/16, and a 6'x1/4.
I'm not too impressed with the Estes rods. The rod it's self isn't too bad, but the connections aren't much to brag about. If you plan on staying in rocketry for any length of time, I think quality rods are a good investment. Hope they arrive OK.

Make sure and make a storage tube to protect those rods, a piece of PVC pipe works great with one end cap glued and one left friction fit.

 

[Senior Space Cadet]

Its been awhile since galvanic coupling popped up on this forum

Interestingly enough, aluminum bike frames are considered to feel "stiffer" than steel tube frames.

I'm a bike guy. Aluminum isn't nearly as stiff or strong as steel, but to compensate, the tubes are thicker and bigger in diameter. Aluminum doesn't absorb shock as well, so the bikes are harsh riding. One of the earliest aluminum bikes, the Alan, had steel sized tubes, so it had a soft ride, but was too flexible. Flexing equals power loss. I almost bought a Scandium frame. Titanium was big, for a while, but carbon fiber has pretty much sidelines everything else, in high end bikes. I have several custom steel bikes. It's hard to make a true custom carbon fiber frame.

 

[mbeels]

Interestingly enough, aluminum bike frames are considered to feel "stiffer" than steel tube frames.

I think that there are a couple of aspects to this. One is that aluminum seems to transmit vibration better, so you feel the road bumps more. Also, for the same strength, the aluminum tubes have a larger diameter, making them stiffer. The steel tends to return any flex as a spring that makes the bike feel different.

Edit: posted simultaneously with Senior Space Cadet.

 

[bobbyg23]

This is what I bought. $6 and I am ready to go. Did the same for my 3/8" rod but only went 4' instead of 6'.

https://www.lowes.com/pd/Hillman-1-...Rolled-Steel-Weldable-Solid-Round-Rod/3059271

 

[bobbyg23]

This is my home made launch pad that has my 1/4" x 6' rod on it. Works great.

 

[bobbyg23]

Here is my 3/8" launch pad in action.

 

[Richard Dierking]

This is my home made launch pad that has my 1/4" x 6' rod on it. Works great.

I suggest if you add a blast deflector you just install it on the ground and not attached to the pad. That is, if you use a blast deflector.

 

[bobbyg23]

I suggest if you add a blast deflector you just install it on the ground and not attached to the pad. That is, if you use a blast deflector.

Sorry, forgot that was not finished in that pic.

 

[Richard Dierking]

No worries. It's just that PVC is relatively light and you don't want the pad to move from the blast. I would still consider a blast deflector placed on the ground. Maybe with a stake if it's light. Anyway, the deflector isn't angled so that's good.
I've made several pads constructed of PVC. ROC has been using three for the front row for years now. They have been improved several times since I made them. Kind of amazed they have held up so well.
Have you considered using a mini rail?

 

[bobbyg23]

No worries. It's just that PVC is relatively light and you don't want the pad to move from the blast. I would still consider a blast deflector placed on the ground. Maybe with a stake if it's light. Anyway, the deflector isn't angled so that's good.
I've made several pads constructed of PVC. ROC has been using three for the front row for years now. They have been improved several times since I made them. Kind of amazed they have held up so well.
Have you considered using a mini rail?

That is next on my list. Can't justify the $$ right now. If I get anything larger, I will have to make that happen though.

 

[Ronz Rocketz]

The local hobby store (LHS?) sells piano wire for $15 but only in 36" lengths so I bought a 1/8" at 36" and 3/16" at 48" at Home Depot at $3/$4. When I watch the slomos on my videos, I don't see significant whipping of the rods, so decided to stick with the cheaper rods. HD also has a 1/8" at 48" but when I held it up, I could see it wobbling a lot.

 

[Blast it Tom!]

Kinda off topic, @rklapp, but how do you trigger the camera to go into slow motion for the first instant of ignition like that? Switched in with your launch button or something? It's a very interesting technique.

And you are correct. Piano/music wire has better dimensional/straightness control and hardening, so that it is harder to permanently bend it. But stiffness-wise there is no difference between the mild steel at HD and the $15 stuff at the LHS. As I said, though, I believe the dimesional tolerances and the straightness of the music wire is better (surface finish too, I just remembered), so "ya pays your money and ya takes your choices!"

 

[Ronz Rocketz]

Kinda off topic, @rklapp, but how do you trigger the camera to go into slow motion for the first instant of ignition like that? Switched in with your launch button or something? It's a very interesting technique.

I import the GoPro video to MS Video Editor (free). Then I trim the video to 15 seconds, then split the video to the point where I start to see smoke coming out of the motor, then split again about .5 seconds, then change the speed to 0.12x which seems to work for my camera (YMMV). It's an old GoPro3 and the most it can do is 120fps at 720p. I know newer cameras can do 240fps at 1080p+ which I've been thinking about upgrading.

I made a lot of snorkeling videos you can see in my channel that I made with the GoPro so glad it's being used again. I've been thinking about taking it to the range to film up close video of the targets but would need to put it in a bullet proof box because people are assholes.

Since we're going off topic, here's one of my best snorkeling videos.

 

[Senior Space Cadet]

I think that there are a couple of aspects to this. One is that aluminum seems to transmit vibration better, so you feel the road bumps more. Also, for the same strength, the aluminum tubes have a larger diameter, making them stiffer. The steel tends to return any flex as a spring that makes the bike feel different.

Edit: posted simultaneously with Senior Space Cadet.

Just like I said. We are in total agreement.

 

[dr wogz]

$15 for piano wire?!! Holley smokes! I think I paid about $3 or $4 for my rods.. (And that's in Canadian dollars, so , like about $0.29 in US dollars!!) Mind you, this was about 10 or 15 years ago..

 

[gna]

Its been awhile since galvanic coupling popped up on this forum

Interestingly enough, aluminum bike frames are considered to feel "stiffer" than steel tube frames.

Yes, aluminum doesn't bend much, it breaks. In addition, aluminum is not as strong as steel, so aluminum tubing needs to be larger and thicker to be as strong as steel. They tended to be made stronger, then. Some people believe the rides are different; others say it's a myth: the Gospel According to St. Sheldon

 

[Blast it Tom!]

Thanks for the link @gna, that explains it well. I've done a lot of analysis that way (structural and natural frequency) and can vouch for what they are saying. With aluminum, the strength and ductility depends a lot on the alloy and the temper, but you are right - to be worth buying, the temper is generally hard enough that it doesn't bend much. But below the bending (yield) point, the stiffness of aluminum is the same across the board.

 

[lakeroadster]

Probably me, and they are slightly more flexible, however they also do not require near the care of a carbon steel rod to maintain functionality, forget to clean a carbon rod once and its going to be difficult to clean later.

As an alternative, our local *True Value stocks zinc coated steel... I just picked up a 5/16" dia. x 72" long launch rod... it was $6. Fits great with a T3 body tube, which has an i.d. of 0.349".

*(which is by no means a "value" up here in the mountains)

 

[Ronz Rocketz]

This is what I bought. I left the 1/8” version in the field overnight. It was corroded from the park sprinklers. Sanded and oiled afterwards.

https://www.homedepot.com/p/3-16-in-x-48-in-Plain-Steel-Round-Rod-801577/204273971

 

[mikewrt]

The local hobby store (LHS?) sells piano wire for $15 but only in 36" lengths so I bought a 1/8" at 36" and 3/16" at 48" at Home Depot at $3/$4. When I watch the slomos on my videos, I don't see significant whipping of the rods, so decided to stick with the cheaper rods. HD also has a 1/8" at 48" but when I held it up, I could see it wobbling a lot.

This is what I bought. I left the 1/8” version in the field overnight. It was corroded from the park sprinklers. Sanded and oiled afterwards.

https://www.homedepot.com/p/3-16-in-x-48-in-Plain-Steel-Round-Rod-801577/204273971

I purchased 4' lengths of both 1/8" and 3/16" yesterday from HD. Figured I could cut down the 1/8" if needed.
@rklapp Are these the rods you have been using in your recent videos? Why type of oil do you use to maintenance? Light machine oil like 3 in 1 or silicon spray or???

 

[Ronz Rocketz]

I purchased 4' lengths of both 1/8" and 3/16" yesterday from HD. Figured I could cut down the 1/8" if needed.
@rklapp Are these the rods you have been using in your recent videos? Why type of oil do you use to maintenance? Light machine oil like 3 in 1 or silicon spray or???

I use them in my videos.

I use Ballistol in my firearms. It does an amazing job on getting rid of rust. The rods typically get soot on them from the exhaust so I wipe with talc powder occasionally.

 

[Joshua F Thomas]

This is my home made launch pad that has my 1/4" x 6' rod on it. Works great.


View attachment 426138

This is neat. Do you have a simple how-to set of instructions? I'd like to build one.