3-Rail 6' Launch Tower

[Adrian A]

First, an introduction with what I'm starting with, which is motivating my goals for the new tower. I made a launch tower in about 2012 and have been using it ever since for lots of record attempts, some of which were successful. It still works, but it's getting kind of ragged and it's a pain to set up and take down. Here it is at BALLS this year:




It has 1.5" diameter, 6' poles that are held in place on the bottom by some wooden 2x3's that are clamped around some sliding 1.5" square aluminum tubes. The base is 3/4" plywood with galvanized steel sheet metal screwed on the top side. On the top end of the tower, there is a wooden triangular frame and the poles are "held in place" by some balls on the end of 3/8" bolts. I put the scare quotes on that because the top frame balls are just resting on the top of the poles, and the guy ropes hold it down. It needs 2 people to set up so that you don't get the wooden frame falling on your head before the guy ropes are installed. It does break down into a pretty compact transportable package, but all the plywood, etc. is heavy (about 40 lbs) and has weathered a lot, as you would expect from painted wood.

I got inspired to make a new tower, and rather than putting it off, I decided to just go for it. All the materials arrived from McMaster today.

The goals for the new tower are:

• Quick and easy to set up and use, so I'm not tempted to put rail buttons on my small rockets
• Able to piggy-back on standard rail towers
• Light enough to take to the pads in one hand while carrying my rocket in the other hand.
• Adjustable from 24mm to 54mm, expandable to 3" diameter rockets
• Easy to clean
• Easy to transport
• Weather-resistant so I don't worry about it getting rained on
• No welding or machine shop needed to build it

Here are the parts, about $300 + tax so far.



The most expensive parts are the 3x 6' aluminum rails, 1" x 2" with 1/16" walls. They were $35 each, but reasonably light and impressively stiff in the 2" direction. The aluminum plate is 8" x 8", 1/4" thick. Lots of knobs for tool-free assembly were about $2.30 each. The T-slots rails and attachment are designed for 1/4 bolts, and that's what everything here uses.

I'll try to keep updating this as I start to put it together.

 

[Adrian A]

I assembled the brackets that will clamp the tower to standard rails:


The little hex shoulder bolts are just there as guides to keep the nut plate aligned so that it will slide straight onto the rail without any fuss. They are tightened against the nut plate ahead of time but they are free to slide in the slot. They are left alone when the tower is installed on the rail, and the knob does the job of locking the tower down to the rail by clamping the nut plate to the inside of the rail. When the knob is tightened, the nut plate clamps to the inside of the slot with an impressive amount of holding force.

A better view of the nut plate that goes into the slot:



I had to shorten the bolts and the knob to keep them from hitting the back of the slot on the rail, and the slot in the aluminum bracket was also a smidge short, which I fixed with a file. The little shoulder bolts work, but it's kind of a waste of a fancy expensive bolt. A regular bolt and spacer would work as well.

 

[Buckeye]

I am not envisioning how this all goes together. Got a sketch?

 

[Adrian A]

I am not envisioning how this all goes together. Got a sketch?

No, but I have some pictures today. I drilled the baseplate for the rails, but I still need to drill a thrust exhaust hole and the rail mounting bracket. I think I will also cut off the unused corners.


Here's the whole thing standing up:


The rails are currently only attached to the feet with the corner brackets. I have a plan for another connection to the rails on the other short side that will be easier to show than to describe.

38mm rocket example:


The whole tower looks like it would weigh a ton, but it's at 10 lbs, so definitely still in the category of easy to carry in one hand. I still need to add the top plate, but that should only a pound or two.

I'm now thinking about adding some removable legs, so I have ordered more stuff from McMaster.

 

[markg]

This looks like a pretty neat setup. Would you mind posting the final materials list from McMaster when you are done?

 

[Adrian A]

Sure.

 

[waltr]

Looking good. I've never use a tower but seen many pictures. best way to go for lowest drag rocket.

Always have wondered about friction to the guides as the rocket slides up through the tower.
Would lining the insides of the guides with a low friction material be beneficial?
Was thinking of a Teflon tape like this:
https://www.mcmaster.com/ptfe/extreme-environment-low-friction-fiberglass-tape/

 

[robopup]

Probably not worth changing things at this point, but one "feature" to keep in mind for the future. All my group's towers have slots at the base, and the rails are held in by friction fit with a couple fasteners in the sides. An entirely unintentional but appreciated feature is that if a motor catos, the rail bases just slide out the slots. Several bigger motors - m's, n's (including one of Mike Fisher's coaxial motors) have cato'd on ignition over the years and I can't remember any of us ever having to replace a bent rail.

Looking good. I've never use a tower but seen many pictures. best way to go for lowest drag rocket.

Always have wondered about friction to the guides as the rocket slides up through the tower.
Would lining the insides of the guides with a low friction material be beneficial?
Was thinking of a Teflon tape like this:
https://www.mcmaster.com/ptfe/extreme-environment-low-friction-fiberglass-tape/

I've never personally played with Teflon tape, but a good friend has gone through the gamut of Teflon products - tape, screw on rails etc. and never found a solution. It tends to work great for one flight, maybe two, and then just gets gross.

 

[Adrian A]

Probably not worth changing things at this point, but one "feature" to keep in mind for the future. All my group's towers have slots at the base, and the rails are held in by friction fit with a couple fasteners in the sides. An entirely unintentional but appreciated feature is that if a motor catos, the rail bases just slide out the slots. Several bigger motors - m's, n's (including one of Mike Fisher's coaxial motors) have cato'd on ignition over the years and I can't remember any of us ever having to replace a bent rail.

I see what you mean. Yeah, there's not really a breakaway capability with this design. Looking at how corroded and dirty the base of that tower is reminds me to put a good-sized hole down the middle so that the exhaust blows on by when the rocket is close to the bottom. Not sure if a closed bottom could add a few Ns of impulse but I'd like to keep this tower as clean as I can.

 

[mikec]

Would lining the insides of the guides with a low friction material be beneficial?
Was thinking of a Teflon tape ...

I use Teflon tape on an old Giant Leap tower that's made out of 1/2" steel (?) rods. It's a pain to apply and lasts for one flight or maybe two. Just keeping the guides in good clean condition is probably an easier option.

 

[waltr]

Ok, thank all for posting experience of Teflon. I did wonder if it would last multiply flights or not. Apparently not.

 

[schworer]

Ok, thank all for posting experience of Teflon. I did wonder if it would last multiply flights or not. Apparently not.

How about a shot of WD-40 on the rails before loading/launching?

 

[WFWalby]

How about a shot of WD-40 on the rails before loading/launching?

We use Blaster Dry Lube with Teflon. No gunky residue easy to clean. YMMV
William

 

[waltr]

We use Blaster Dry Lube with Teflon. No gunky residue easy to clean. YMMV
William

That sounds like a better method to lubricate the guides.
Maybe even make cleaning the exhaust residue off easier.

 

[Adrian A]

I'm nearly done with the tower, and I'm planning to use it tomorrow. I put it on a scale with everything that will be hung onto a rail. 11.3 lbs. It easily passes the 1-hand test, and it feels stiff and stable once the top plate is on.

Here is the base, without the tower rails attached. The black things are t-slot nuts. The attachment to pre-existing rails is on the upper left.


This one shows how the tower rail slides out of the way to install the rocket.


I'm happy with how the top plate attaches without tools to the tops of the rails to hold them straight:



The rectangular aluminum pieces are sized to fit inside the tower rails. They are tapped so that knobs thread into them. I picked out some rubber bumpers with the same OD as the ID of the rails, so when the knob is tightened down, the bumpers are squeezed vertically and they expand outward to lock the top plate in place.



The top plate is the least expensive 0.093" thick 12" fiberglass plate offered by McMaster, and it seems about right in terms of stiffness and weight.

The knobs are also accessible enough from the bottom for fine-tuning the width while the tower is upright. This also shows more detail on the attachment to existing launch rails


A 29mm rocket pretty surrounded by the tower rails. The fact that the rails are rectangular rather than round seems to provide a gentler and more stable contact area than round tubes. I'm not sure yet how much the GPS reception is affected though. Larger diameter rockets would of course be more open.

 

[Adrian A]

One hiccup today during the build. If you look closely at the base of the tower rails, you can see that their t-slot bases are a little short on the inside to accommodate some 1/4" thick aluminum bar that is bolted onto the end of the t-slot rail and inserted into the tower rails. My intention was to then drill and tap some #6 flat head fasteners to connect the inside wall of the rails with the 1/4" thick bar that is bolted onto the t-slot rail, so that the rail would be held down on both of its short sides for extra rigidity. The bar also prevents exhaust crud from getting into the t-slot rail bases where it would be too hard to clean. The first problem was that I immediately broke off my tap on the first #6 fastener I tried to install (I tried using a combo drill/tap with a cordless drill; bad idea.) That's the one shown in the photo below. The second problem is that I realized I really wanted the slot on the bottom to be clear so that I could slide the rail onto the base from the outside like I showed in my second photo from today. So for 2 of the three rails, I cut the bar back to expose the bottom slot. The one with the broken tap is semi-permanently installed, but it's not a big deal to have to install one of the three rails from the center rather than the outside. And as it turns out, with the top plate installed, the rails are plenty stiff against bending outward even though they are just held on at the bottom by the triangle brackets.

 

[Adrian A]

I also made some progress toward legs for when a tower with a rail isn't available. My plan for the feet is 1" square thick wall Al tubing cut into 4" lengths, but I haven't done any work to attach them and I'm not sure that's the solution I want. The way the legs attach to the base isn't quite the right answer I want, either. It's not ready for prime time, but it could do in a pinch if it's on a hard surface and I'm not hitting it with a huge motor.




The legs fold down nicely for travel, though, and are held together by a triangular plate I cut out from scrap from my original 8" x 8" baseplate:


That part goes on the bottom to help keep the 3 legs in a plane. I'm not really liking the knobs for attachment in this case though. I think I might need to break down and use a regular socket cap screw to get the strength I want.

 

[Adrian A]

The launch tower worked great over the weekend. The tower rails pack nice and flat against each other, easier than round tubes, and it takes less than 2 minutes, and no tools, to assemble it to be ready to put on the rails. I had a nice flight on a G118 that went higher than expected, just under (cough cough) the 8000 ft waiver.




About the only room for improvement is that the brackets for the rail attachments are kinda wimpy. They are fine once the tower is attached to the rail, but getting the tower onto a dirty rail is the challenging part, and the flexibility of the brackets contributes to the rail attachments jamming. I may replace them with some steel ones if I can get them in the same form factor. Greasing the rail clamps may help too.

 

[Adrian A]

As promised, here's the McMaster-Carr information. First a screen grab that shows pictures of the items:


And attached is a pdf that includes part numbers.

The knobs with the longer studs go on top of the tower and the shorter ones go on the base. The plate at the top of the tower is not included here but I think this has everything else needed for the leg-less version of this. The 7/8" bar is cut into 1 7/8 long pieces to get inserted into the top of the tower rails, and then the rest of it I split into thirds to make the cover pieces at the bottom (which are optional). The triple nuts go on the base for attaching the rails with the knobs and the double nuts go inside the bottom of the tower rails to permanently attach the triangular brackets to the rails. On the list is a 1/4-20 tap with a hex head that makes tapping this aluminum relatively easy and fun with a cordless screwdriver.

 

[manixFan]

Very interesting take on a tower – I like the light weight and tool-less adjustment design. In my experience the Teflon tape is not worth the effort - as others have said it only lasts a flight or two, and then removing it is a PITA.

I know you've flown out of towers a bunch, so this may already be obvious, but I'd protect those top handles. The top of my tower got quite a roasting at Balls this year and the residue really gunked everything up. The motor that really seemed to cook it was the 38mm Aerotech J510 (which one observer said didn't exist!) in a Shadow Aero Raven 3. It's a White Lightning propellant. I also flew a Loki K627 which has a much narrower flame, which is what I was used to.

Great write up and thanks for taking the time to post the build sheet.


Tony

You can clearly see the exhaust flame of the AT J510 directly impinging on the top of the tower:


vs. the Loki K627, which has a much narrower flame:


EDITED: I added the picture of the K627

 

[Adrian A]

Very interesting take on a tower – I like the light weight and tool-less adjustment design. In my experience the Teflon tape is not worth the effort - as others have said it only lasts a flight or two, and then removing it is a PITA.

I know you've flown out of towers a bunch, so this may already be obvious, but I'd protect those top handles. The top of my tower got quite a roasting at Balls this year and the residue really gunked everything up. The motor that really seemed to cook it was the 38mm Aerotech J510 (which one observer said didn't exist!) in a Shadow Aero Raven 3. It's a White Lightning propellant. I also flew a Loki K627 which has a much narrower flame, which is what I was used to.

Good points and great photos. A K627 is bonded in my garage and waiting for the right opportunity. The knobs on top happen to be phenolic so they may do o.k. Al foil wrapped over them could help if I fly a J510. Or if they get toasted it's easy to replace them and it's less than $10 for the set. The fiberglass top plate may be more vulnerable, and would be more of a pain to replace. If it gets trashed I'll look into waterjet-cut aluminum.

I have been thinking about what changes I would recommend for people who might want to build their own.

To make the attachment to existing rails easier and stronger, replace the wimpy angle brackets with a vertical 2" section of t-rail that is tapped at one end to bolt to the top plate or bottom plate, and cross-drilled through to hold the t-slot nut that clamps to the existing rail. Maybe add a second attachment from the 2" t-slot section to the plates in the form of a small bracket or hidden bracket like this one: https://www.mcmaster.com/5537T315/ The result will be a lot stiffer when installing onto a sticky rail and it should be easier to use because it will be obvious how to align the 2" section parallel to the existing rail. I'm probably going to do this mod myself.

If you would like to trade some extra fabrication to save money:
Skip the triangular brackets at the bottom and attach the bottom of the tower rails to the T-slots bases by making some inserts for the rails out of 7/8" wide bar that's 1/2" thick. I would tap the insert on the sides to accept two flat head screws on each of the long sides of the tower (4 per rail base) and tap it for 2 screws that come up from the bottom to attach the t-slot rail with this kind of fastener: https://www.mcmaster.com/47065T155/ This would also be stiffer and stronger, though IMO it's strong and stiff enough already.

To make the stand more durable but more expensive, make the top plate out of water-jet aluminum. To make it independent of existing rails, add a base of 3 legs like I started to do, but maybe make them out of triple-height 1" rail or 1.5" double-height rail.

 

[crossfire]

Very interesting take on a tower – I like the light weight and tool-less adjustment design. In my experience the Teflon tape is not worth the effort - as others have said it only lasts a flight or two, and then removing it is a PITA.

I know you've flown out of towers a bunch, so this may already be obvious, but I'd protect those top handles. The top of my tower got quite a roasting at Balls this year and the residue really gunked everything up. The motor that really seemed to cook it was the 38mm Aerotech J510 (which one observer said didn't exist!) in a Shadow Aero Raven 3. It's a White Lightning propellant. I also flew a Loki K627 which has a much narrower flame, which is what I was used to.

Great write up and thanks for taking the time to post the build sheet.


Tony

You can clearly see the exhaust flame of the AT J510 directly impinging on the top of the tower:
View attachment 545418

vs. the Loki K627, which has a much narrower flame:
View attachment 545420

EDITED: I added the picture of the K627

Do you still have the Raven?

 

[Adrian A]

I have been pretty happy with my 6' tower, so not content to leave well enough alone, I'm working on extending it to 12 feet tall.

After buying three new 6' x 1" x 2" thin-wall aluminum tubes, the next order of business is to figure out how to couple them together. The ID is 7/8" x 1 7/8", and I couldn't find any readily available aluminum tubes with those outside dimensions. There are a lot of multiple-piece combinations I could do that would fit inside there, but what I settled on was two 7/8" x 7/8" x 6" aluminum bars per rail. 7/8" + 7/8" leaves 1/8" left over, and I was going to fill that with some 1/8" tall rubber strip. But then I had a better idea. I'm loosely bolting the two inserts together with two counter-bored bolts, and then I have a threaded rod with a knob at one end that threads into one insert and pushes against the other.



After quite a bit of time on my belt sander, the pieces slide easily into the ends of the tubes, and then when I turn the knob, they push apart against the inside walls of the tubes and join them together stronger than the original tube.



I have made one of the three sets so far and screwed up the second set by drilling a clearance hole in the wrong spot, but I'll come back to this over the next few days to finish up.

In the meantime, my original top plate got cracked last year when I was using the tower on a rail on a tripod, and the launch blew the whole thing over. I thought it was a little under sized, thickness-wise. I repaired it with some JB Weld, which surprisingly has worked so far, but since I want another circular frame at the joint between the two sets of rails to control the spacing in the middle, I'm going to repurpose the original red top plate for that job, and I made a new top plate out of thicker 1/4" black fiberglass that's also better quality. I have added holes so that I can hook in tie-down straps at the top to crank down the tower. The new plate is upside down in this view, and I have attached the inserts that grab the top of the rails with rubber stoppers that expand outward when the knobs are cranked down.



I will cut off the inner lobes of the red plate, and then attach one 2" long piece of 1010 t-slot for each rail, on the perimeter, pointed inward. Each threaded rod will have a slip fit through the 1010 piece and the radial distance will be controlled by a wing nut on either side of the 1010 piece.

I did a quick check of how tall a 12" combination of two rails is, and yes, it is in fact tall. Quite tall. I'll need to work out how to assemble the whole thing horizontally and adjust the rail spacing at the top plate, and then lever it up before securing the tie-down straps.

 

[manixFan]

What I do to adjust my launch tower (which can go from 29mm to 98mm) is to have a section of body tube that matches the diameter of my rocket. If it’s oversized, I take a regular body tube and wrap heavy paper (called builders paper at Home Depot) to get it to the right diameter. I then use that to set the tower rail spacing. Maybe that’s how most folks do it but it was a revelation to me not to have to use my actual rocket.

I don’t know if that’s what you’re wondering about, but just in case.


Tony

 

[Adrian A]

Thanks to your suggestion I brought along a couple pieces of 38mm BlueTube that helped with this.

Unlike other aspects of my rocketry this weekend, the tower did great:


I was able to carry the whole thing in one trip from the car, and it assembled together in just a few minutes.
The tube couplers worked went together easily and clamped down tight, the new base option kept the adjustment knobs off the ground, and the 20' tie down straps were the appropriate length. The straps were causing some oscillation when it got windy, but at Vic's suggestion I twisted them, and that took care of the problem. I was able to load the rocket in from the bottom by loosening one rail and pulling it out to the side. The tracker lost GPS lock while it was in the tower, but I had powered it up outside the tower and kept it on during the rest of the prep, so it still had good satellite information it was able to use to track as soon as the rocket started its flight.

 

[manixFan]

Wow – that is quite the photo – very dramatic background! Glad to hear my suggestion helped – I also now know about twisting straps to reduce oscillation.

Your message is a bit of a cliff-hanger – I hope we get a full report later. Bummer that it does not sound like it was a successful flight though.


Tony

 

[Rocketjunkie]

Similar to my dedicated tower. 1992 at LDRS XI. Minimum diameter O power.

 

[Adrian A]

Similar to my dedicated tower. 1992 at LDRS XI. Minimum diameter O power.

Convergent evolution on the top plate shapes. How did that flight turn out?

 

[Rocketjunkie]

Convergent evolution on the top plate shapes. How did that flight turn out?

Flew to just under 25,000'. No electronics at the time O3000-40 motor ejection. Way late. Propellant was Smoky Sam instead of the low smoke I was expecting. Motor was made by Vulcan. We didn't know about the problems with BP charges at high altitude. It carried 7 lb. of chalk dust for tracking. The only video I've seen is Earl Cagle's LDRS XI video (Point 39 Productions). I didn't have a camera at the time, got one the next year.

 

[Buckeye]

I have been following. Interesting build, @Adrian A.

Looks like you cut the top plate freehand. Did you use a saber saw/jig saw? What type of blade?