"Flying MooMoo" Scratch Build Thread

So, the fins are beveled, so it's go time. For fin installation I have TRF member Wizard to thank for this little gem. When I mark my tubes for slotting, I mark both sides:



Because I went to Harbor Freight and got their finest $45 laser. If you sight the laser on the bottom mark of the tube, on the top mark on the tube, all the way up the fin and center it all the way down the airframe, odds are damn good your fin is true:



Blurry, but shows what it needs to:



Now I'm certain there is a way to mess this up, but using this method I'm pretty sure there is only so far wrong you can go. Fingers crossed.

Looks good Chris, I have not sen a laser level used yet but it does look promising. I am thinking making sure that the tube is centered correctly would be the biggest point. How did you line up the tube?

mpitfield said:

Looks good Chris, I have not sen a laser level used yet but it does look promising. I am thinking making sure that the tube is centered correctly would be the biggest point. How did you line up the tube?

Click to expand...

The laser is plumb, and you've marked the aft end of the tube at 180 degrees, so as long as the laser hits both your marks and runs up the full trailing edge and top edge of the fin you know the fin is plumb to the tube. To my thinking, you can only be off if you're off when initially marking the tube. When the laser runs down the middle of the rest of airframe, that's confirmation that you're both square and plumb - but that's more dependent on your slotting than anything else.

3 pics before getting the kids off to school. Like I said, the day the fins go on it officially becomes a rocket. Happy days:



This technically isn't part of the MooMoo build, but I thought I'd share this pic too. My 5 year old son designed this rocket, which will have a motor mount ejection and 4 boosters. Quackstonaut will ride in this rocket too. The boosters aren't on yet, but as per above, the day the fins are on and secure is the day it officially becomes a rocket:

Barkley said:

One of the tips Jim Jarvis gave me is that the difference between MPR and HPR is how you deal with shock loads, and that wherever possible try not to have just one piece of material responsible for the whole load. In this situation, instead of the lid taking all the load, the pull on the all thread bypasses the lid entirely and pulls the whole nose cone from the tip. However, I've yet to figure out how to do this with the parachute cord attachment point in the rocket body. If anyone has any ideas, please speak up.

Click to expand...

Ok, if you build in a Binder Design type baffle (look at the Velociraptor.rkt file on rocket reviews), you could put a T nut in the bottom baffle plate, and a T nut in the top baffle plate. Then run your all thread inside, linking both plates together so both would have to fail before the mount could be ripped out.

K'Tesh said:

Ok, if you build in a Binder Design type baffle (look at the Velociraptor.rkt file on rocket reviews), you could put a T nut in the bottom baffle plate, and a T nut in the top baffle plate. Then run your all thread inside, linking both plates together so both would have to fail before the mount could be ripped out.

Click to expand...

Gold - I'm not sure whether I'll use T nuts, but I'm going to incorporate that concept into the build for sure. Thank you!

Update time. The aft centering ring is on and the NC just needs a touch more fill and fair, so the goal is for a maiden flight at NASA this Saturday.



One of the design specs was for it to be able to be launched with a mid powered motor, and weight is now my enemy. The only MP motor that has a chance of keeping this above 12 m/s off the rail is the Aerotech G76-G, and if I could just slap a bulkhead in and be done I'd be fine, but the passenger compartment and GoPro bay add about 180 grams - and that puts it over the top of what's safe. As a result I'm having to save every gram of weight I can. I've determined that the rocket will need 2 configurations, specifically a MP setup and a HP setup. MP will be single deploy (which is fine), and if I remove most of the allthread and the end cap from the NC I can save the weight I need. I'm going to make the bulkhead and weigh everything before I cut the airframe just to be sure. For the GoPro/Quackstronaut bulkhead/compartment the plan is now to do away with the heavy outer cylinder and have a 29mm tube to let the ejection gases through.

Does anyone know where I could find the maximum recommended takeoff weight for a given motor? I'd like to confirm that G76G is up to the task.

Barkley said:

Does anyone know where I could find the maximum recommended takeoff weight for a given motor? I'd like to confirm that G76G is up to the task.

Click to expand...

76N/4.4= 17.27lbs avg. thrust, to convert Newtons to lbs thrust, and 17.27lbs avg thrust /5=3.45lbs (55ozs) rocket weight (if I have done the math correctly, this is the way I figure it without a simulation but it doesn't tell me my required delay). If you are looking for the recommended 5:1 thrust to weight ratio, the math is just based on the average thrust in this case. Have you tried downloading OpenRocket it is free and will allow you to design and sim your rocket along with whatever motors you wish to try and its reasonably accurate in my experience. Also check out www.thrustcurve.org its free as well. If you push a G76G to the edge you will need a very short delay 4 seconds may be too long, the reason I know this is my kids Crayon rockets weigh about 64 ozs and one ejected the nosecone about 40' above the ground allowing the parachute just enough time to save the nosecone and altimeter the fincan slammed into the ground just before the shockcord pulled taught under the chute, second flight with a G64W only went moderately better, this time the chute opened about 60' AGL and the rocket was okay, both boosted fine off a 6' rail to about 480' according to the alt.

rharshberger said:

76N/4.4= 17.27lbs avg. thrust, to convert Newtons to lbs thrust, and 17.27lbs avg thrust /5=3.45lbs (55ozs) rocket weight (if I have done the math correctly, this is the way I figure it without a simulation but it doesn't tell me my required delay). If you are looking for the recommended 5:1 thrust to weight ratio, the math is just based on the average thrust in this case. Have you tried downloading OpenRocket it is free and will allow you to design and sim your rocket along with whatever motors you wish to try and its reasonably accurate in my experience. Also check out www.thrustcurve.org its free as well. If you push a G76G to the edge you will need a very short delay 4 seconds may be too long, the reason I know this is my kids Crayon rockets weigh about 64 ozs and one ejected the nosecone about 40' above the ground allowing the parachute just enough time to save the nosecone and altimeter the fincan slammed into the ground just before the shockcord pulled taught under the chute, second flight with a G64W only went moderately better, this time the chute opened about 60' AGL and the rocket was okay, both boosted fine off a 6' rail to about 480' according to the alt.

Click to expand...

I use OR religiously, I was looking for a backup to make sure I wasn't cutting the margin too fine. In light of our sport's recent first fatality, safety is at the forefront. OR is saying 12.1 m/s off the rail, and I've been told not less than 12 (40 fps). OR says optimum delay is 4.7 seconds.

Barkley said:

I use OR religiously, I was looking for a backup to make sure I wasn't cutting the margin too fine. In light of our sport's recent first fatality, safety is at the forefront. OR is saying 12.1 m/s off the rail, and I've been told not less than 12 (40 fps). OR says optimum delay is 4.7 seconds.

Click to expand...

I always use OpenRocket and even Rocksim on occasion, and my experience with OR has been very good, as the sims have bee pretty close to what the actual performance of the rocket turns out to be so far.

The G76G motor starts out at 150 Ns initial thrust and drops off at a pretty even rate.



Using a 5:1 ratio you should be able to lift a 6.75 lb rocket off the pad.

With that said, I would still sim it in WRasp32, OpenRocket, or RocSim. A quick WRasp32 sim at 55 oz, 3" diameter and 0.6 Cd with the G76G says about 570 ft with 43 ft/sec at the end of a 4' rod.

Interesting. I just weighed it (with the full NC but without motor, parachute and parachute cord) and it was 2 pounds 15 oz. The total weight won't be anywhere near 6 pounds. I'm wondering whether 5:1 is a valid ratio given that at 4 pounds it wouldn't be going fast enough at the end of the rail.

Building the parachute attachment/GoPro and Quackstronaut bay tonight, and will weigh it. The clear tubing is .25" thick and 77mm OD, so just shy of the OD of the rocket. After building it we'll see how it looks... and yes, that pun was intended.

This is awesome! thanks for the Epoxy pointer. Best of luck Saturday if you guys are able to launch. It's great seeing kids so involved and excited about the rockets!

Quackstronaut/GoPro bay not quite done yet, but getting close. Launch is scheduled for T minus 38 hours and epoxy needs time to cure, so ... tick tock.

Barkley said:

Quackstronaut/GoPro bay not quite done yet, but getting close. Launch is scheduled for T minus 38 hours and epoxy needs time to cure, so ... tick tock.

Click to expand...

lol, Chris that looks fantastic...love it!

I just realized that I'm a moron. I've been worried about the speed of the rocket at the end of the launch rail (which was in the neighbourhood of 12 m/s), but I'd forgotten to lengthen the launch rod to what they use at NASA. I think it's an 8 foot rod, but if I assume it's 6 feet at a minimum the G76-G gives it plenty of speed off the rail (15.8 m/s or 51.8 fps). I've been worried all this time for nothing.

So that's good news... but we'll just be ready to fly. She'll have to earn her paint.

Measure twice, cut once... I put the 77mm OD clear tubing over where I marked out the tube and realized that it wouldn't work as intended. At best I need to keep the window as small as possible, so the actual cut was smaller than the top pic.





I'd tacked everything down with the Bob Smith 5 minute epoxy, so everything needed West System reinforcement (with added filleting compound). Lots of extra epoxy on stuff on stuff that will be inaccessible and that needs to stay buttoned down.





Now to cut the plexiglass to fit, massage the middle shelf so that the thicker plexi has clearance, add some foam to the bulkhead and mount it in the airframe. The plan is to attach the plexi with screws that fit into t nuts, but I'll make the mounting points when I know everything fits.

Thought I'd dry fit everything first, and am now glad I did. First, in order to drop it down the airframe I needed to pull it back out, so I put tried to assemble the quick disconnect and swivel, only to see that the opening in the disconnect wasn't big enough:



So with this temporary solution I can't have a swivel at the bulkhead. I'm wondering whether to make this permanent. In theory I may be able to replace it in the future if I feel it's needed. We'll see.

And for the dry fit:



IMHO the look is a winner, and the slip fit is very tight so with epoxy it'll be nice and solid. The bad news is that it was a major PITA to fit everything in the little opening, so I need to expand it a bit.

Edit to add: 90% chance of 1/4" of rain tomorrow morning. Odds are good the NASA launch will be scrubbed. Disappointing...

Barkley said:

Thought I'd dry fit everything first, and am now glad I did. First, in order to drop it down the airframe I needed to pull it back out, so I put tried to assemble the quick disconnect and swivel, only to see that the opening in the disconnect wasn't big enough:

So with this temporary solution I can't have a swivel at the bulkhead. I'm wondering whether to make this permanent. In theory I may be able to replace it in the future if I feel it's needed. We'll see.

And for the dry fit:

IMHO the look is a winner, and the slip fit is very tight so with epoxy it'll be nice and solid. The bad news is that it was a major PITA to fit everything in the little opening, so I need to expand it a bit.

Edit to add: 90% chance of 1/4" of rain tomorrow morning. Odds are good the NASA launch will be scrubbed. Disappointing...

Click to expand...

I have to show my kids this. Have you tested the video? My concern is that the lens being recessed as far as it is on the side closest to the center-line that you will have a good portion of the video framed by the inside of the rocket. Also is auto focus and issue?

Re the eye-bolt and quick link, if you grind the raised lettering off the eye-bolt do you think it would fit? You could possibly saw it off in the middle by grinding off some of the raised lettering as well as a bit of the quick-link, or should I call it a quack-link

mpitfield said:

I have to show my kids this. Have you tested the video? My concern is that the lens being recessed as far as it is on the side closest to the center-line that you will have a good portion of the video framed by the inside of the rocket. Also is auto focus and issue?

Re the eye-bolt and quick link, if you grind the raised lettering off the eye-bolt do you think it would fit? You could possibly saw it off in the middle by grinding off some of the raised lettering as well as a bit of the quick-link, or should I call it a quack-link

Click to expand...

I haven't tested it yet. Given that the GoPro has a bit of a wide angle lens, I expect it to catch a bit of the inside, but at the moment I'm not concerned because we'd be losing what has the biggest fisheye distortion. I will say I'm not happy with the plexi, as it distorts the view by more than a little. Tomorrow's launch has been scrubbed, so I now have time to get this right.

Barkley said:

I haven't tested it yet. Given that the GoPro has a bit of a wide angle lens, I expect it to catch a bit of the inside, but at the moment I'm not concerned because we'd be losing what has the biggest fisheye distortion. I will say I'm not happy with the plexi, as it distorts the view by more than a little. Tomorrow's launch has been scrubbed, so I now have time to get this right.

Click to expand...

One thing I heard of using was a clear 2 liter soda bottle to cut a window from to close the opening in the side of the rocket for the camera.

K'Tesh said:

One thing I heard of using was a clear sided 2 liter soda bottle to close the opening in the side of the rocket for the camera.

Click to expand...

Yes, I saw that in the instructibles link upthread. I certainly like that price point, but I'd like this rocket to exceed M1 and I'm not sure that would happen with a flimsy piece of plastic. I'd bet it would flap. Still... it could be worth a try.

Widened the viewport by 1.5 cm:



So the view isn't restricted by the airframe anymore. Unfortunately my ugly mug was in the frame for the test shot:



Just a tiny bit of frame restriction in the lower right, which I can live with - and my daughter gave it her blessing. Time to mix the epoxy.

Edit to add: it's 41F (5C) outside, and not much warmer in the garage. Definitely using 205 hardener instead of 206, as at that temperature it may be too cold for the 206 to kick. Or, lay it up in the garage then bring it inside when I'm done.

So I've taken a couple of days away from the build - I know, shame on me. The kids were off school yesterday, so I asked them what they wanted to do... and the answer was go to NASA. Go figure.

Back to the build. Here's the clear polycarbonate tubing that I bought:
https://www.amazon.com/gp/product/B000OMFMMK/?tag=skimlinks_replacement-20

The issue with it is that at 77mm in OD isn't quite the same as the 79mm OD of the rocket, but I'm pretty sure it's close enough that I can get it to work. The downside is that when I cut the tubing it compressed and the diameter reduced. Add to that the thickness of the material (1/4"/4mm) and it's now not quite as easy as I thought it would be. I bought a 1L bottle of coke and cut the flat section out, then did two test shots:

Coke Bottle Plastic:



Polycarbonate:



They're both clear enough to work, although there were sections of the poly with obvious distortions (that I just wouldn't use) and I'm still not sure the coke plastic won't flap as the speed increases. So... the obvious solution is to build both options and see what works best.

In other news, my daughter leaned up the rocket against a wall, only to have it fall on the uneven tile floor. You guess it - the point load cracked it. It's an easy fix, and I'm glad it happened before paint, but it also taught me that the nose cone method still needs some work. I see 3 possible solutions: (1) just add more peanut butter than I did. Weight wise not ideal, but the weight is exactly where you'd want it. (2) Glass the inside of the nose, reinforce the inside with peanutbutter, and put a bit of fill in the outer gaps. Or, (3) have more crowning tips. I had 6, and I'm wondering whether 10 or 12 would have been better. That would reduce the size of the gaps between the glass, which should improve the overall strength. I suspect the solution is a combination of 2 and 3. And of course, the real solution is to make the NC the "right" way.

GoPro/Quackstronaut bulkhead is epoxied in:



Nose cone and fin fillet touch up. Both should sand down to true. Rail guides and MMT masked for paint. A tip from John Coker's website, I haven't put on the motor retainer yet, and won't until after I finish painting.

Haha I love the see through mess of the epoxy lol. You have been making such great work on these, good job man.

Update. Real life has happened over the past few weeks, so I haven't been on TRF as much. Flying MooMoo had a revised launch date of December 12th at the Tripoli Houston launch, so given the aforementioned real life, I got the rocket in a flyable state without that many bells and whistles. There were several more versions of fill and fair with the fairing compound, then several with primer, then 2 coats of actual paint. The "cow" paint job will come soon. The windows in the pic below are taped in place so if the plastic gets scratched it's easy enough to replace. The original curvature of the plastic is slightly less than that of the rocket, and it's sandwiched between the rocket and the door, so the thin plastic is surprisingly rigid. So we were all set to launch...



But we didn't. Another flier put one up and had to retrieve it half a mile downrange, 12 feet up in a tree. The av sled wasn't in the nose, and even if it were there there was no tracking method mounted. (An Eggfinder has been purchased, but is yet to be soldered.) Discretion was the better part of valor, and next launch we'll be really ready to go.

In the pic you can see the Quackstronaut in his command position, but the GoPro hadn't been fitted yet. That's as close as we got.

Barkley said:

And now we have an idea of what the bottom will look like. There will be a lock nut on the all thread holding the ring in place, a cup for the ejection charge, and I still have to figure out how the cable cutter will be positioned. One of the tips Jim Jarvis gave me is that the difference between MPR and HPR is how you deal with shock loads, and that wherever possible try not to have just one piece of material responsible for the whole load. In this situation, instead of the lid taking all the load, the pull on the all thread bypasses the lid entirely and pulls the whole nose cone from the tip. However, I've yet to figure out how to do this with the parachute cord attachment point in the rocket body. If anyone has any ideas, please speak up.

Click to expand...

This is exactly how I do my e-bays. I always try to find a way to attach the recovery gear to an all thread running through the e-bay. I've never had a failure. I have one ebay that's seen 2 flights with a single 6/32 rod on a 9 pound rocket. That might be pushing the limit but it's worked just fine. The biggest issue with this set up is preventing the eye nut from spinning off during descent. A buddy of mine had a failed L3 because and eye nut spun off. Usually what I do is glue the charge holder just close enough that it doesn't get in the way for the eye nut to get put on and then zip-tie the eye nut to the charge holder so if the chute wants to spin it will spin everything at once. Another option to eye nuts (which can be rather pricey) is install a small L bracket to the rod. Use a nut to hold the bracket on the rod and then quick link the recovery gear to the vertical part of the bracket.

Anyways, where in the world did you find that eye nut and what size thread is that rod? The smallest I've been able to find is for 1/4 20 rod which is ridiculously big for smaller rockets.

DAllen said:

This is exactly how I do my e-bays. I always try to find a way to attach the recovery gear to an all thread running through the e-bay. I've never had a failure. I have one ebay that's seen 2 flights with a single 6/32 rod on a 9 pound rocket. That might be pushing the limit but it's worked just fine. The biggest issue with this set up is preventing the eye nut from spinning off during descent. A buddy of mine had a failed L3 because and eye nut spun off. Usually what I do is glue the charge holder just close enough that it doesn't get in the way for the eye nut to get put on and then zip-tie the eye nut to the charge holder so if the chute wants to spin it will spin everything at once. Another option to eye nuts (which can be rather pricey) is install a small L bracket to the rod. Use a nut to hold the bracket on the rod and then quick link the recovery gear to the vertical part of the bracket.

Anyways, where in the world did you find that eye nut and what size thread is that rod? The smallest I've been able to find is for 1/4 20 rod which is ridiculously big for smaller rockets.

Click to expand...

I've cut the allthread just long enough so that I can put another nut on, then I torque it down. It locks the eyenut in place. That rod is 1/4 20, and yes the eyenut is ridiculously big. It's also so thick that I needed a 5/16 shackle just for the size of the gap. I'll load a pic of the finished product when I can.