Pershing 1A Maxi-Brute Clone 3D Printed

In the 70s I remember being at Service Merchandise and they had all the Maxi-Brutes, but I had only enough money to buy one. At the time it felt like the hardest decision of my life. I finally settled on the Honest John, but I always wanted the Pershing 1A too. I do have a TLP Pershing on the workbench, but it's just not the same. Then back at the end of March I decided to get a small 3D printer to give it a try, rocketry parts was one of the reasons. After a few weeks, I realized how useful 3D printing was and decided to buy a bigger better 3D printer, which opened up all kinds of possibilities. Then early last week I stumbled onto this thread by Leo Nutz here on TRF https://www.rocketryforum.com/threa...a-clone.150742/.

Holy smokes!

Leo has done a really good job putting together the 3D files and making them available for the rest of us to use.

This is my first large 3D project I've attempted, plus I decided to use PETG since it can be way tougher and tolerate heat (aka Sun) than PLA. But PETG can be a challenge, especially with stringing. I had several fails at first printing the nose cone, but finally it came together. Leo recommended spiral/vase mode, which is single wall, but I couldn't get 0.8mm wall thickness Leo's parts are designed for, it was always too thin. Switching from a 0.4mm to 0.8mm nozzle would likely solve it, but I don't have one. So I printed mine double wall in Standard mode, combined with slower printing speed for PETG, my print time was a little over 30 hours combined for the 3 nose cone sections! So yeah, like Leo I can't offer to print these for anyone either, sorry. The results turned out great!

 

Here are the 3 sections that comprise the nose cone.

 

Here are the sections dry fitted. My caliper measures my wall thickness as 0.80mm, and the combined weight of the nose cone parts dry fitted is 113 grams in total. Wow, it's huge!

 

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Last night I printed one of the lower fins. Took about 2 and a half hours. Leo provided 2 versions of the upper and lower fins, one version is larger for flight like the Estes fins, and the other is scale. I'm printing the larger for the lower fins, although I might print the smaller scale fins for the the upper to help stability. The weight of the fin is 10 grams. 5 more fins to go!

 

Excellent print quality!!

 

May I ask what 3D printer you purchased? How was the learning curve?

 

I have a Creality CR-10S Pro, it's what I used to print these parts. The cost was $650. I got my feet wet with 3D printing with a Monoprice MP Select Mini 3D Printer V2, $190. The learning curve isn't too bad, but it does take some patience and time, 3D printers are slow. And the sub $1000 printers are not always out of the box ready to go. For the CR-10S the components seem to be good quality, you do have to do some minor assembly, but while not a big deal I had to tighten a few loose screws and adjust some rollers, but my pre-purchase research prepared me to look for things like this. So do your research before you buy, there are lots of video reviews on youtube for most printers that help you know what to expect and how to resolve issues and improve the printer quality. Your printer choice sort of depends on the quality you want coupled with how much time you are willing to invest in tuning the printer, versus having an out of the box experience. If you are willing to put the time into tuning the printer and sometimes printing parts to enhance it, you can get great results from the lower end printers versus a multi thousand dollar unit. I can't stress enough that if you buy one take the time at the beginning to learn how to properly level the print bed and how to make sure your prints stay adhered to the print bed during the printing process, it will save you a lot of frustration. The CR10S has been a much better experience than my MonoPrice in this respect. And there is the learning curve of how to setup your print settings and work with different kinds of plastics, but that you are going to encounter despite the printer. It was said on another thread that 3D printing for rocketry is sort of a hobby within a hobby. I'd liken it to changing your own oil versus taking it to a shop. I think it really comes down to how much of your time you are willing to put into it, how many uses you might have for 3D printing, and the personal satisfaction you can get from the I made that feeling. I've made a lot of bad prints trying to figure it out, but I stuck with it.

 

Thank you Tim for the recommendation and the heads up on doing my homework on set up. Do you find that detail pieces are out there already for you to download or are you having to recreate the wheel with designs? Mostly, I'd like to make pieces like the SpaceX Dragon capsule and module scaled to a 56mm tube. Ariane 6 P120 boosters. Tops of the GEM's for the Atlas V, etc.
Another statement for you and I should probably PM for this, but here I go, I do not have room in my home for the 3D printer. I'd have to put it in my shop which is not heated or cooled. I live in Charleston SC where the humidity is extreme. I have to keep my rocket parts in plastic tubs in a closet in my home so tubes don't deform or suck up too much moisture. With that said, do you think a 3D printer would be able to work in such an environment? It would not get wet but temperature fluctuations could be as much as 25 degrees per day and humidity going up and down. I'd hate to spend the energy with setup and fine tuning (and money) for a printer that would not work well for me. What are your thoughts on my two questions?

 

I'm still a newbie at this 3D stuff myself, so keep that in mind, I could be totally wrong. So far my results searching for designs that have been already done versus me having to create has been mixed and depends on whether the design is available for free download or you have to pay for it, such as Shapeways. Try searching this site https://www.thingiverse.com. Keep in mind there are rocket designs that aren't meant for flying model rockets, but you might be able to adapt them. And sometimes a design is available, but not in the scale I might want, although it can be rescaled with the Slicer program for example. I've only just started to look into creating my own, I think I'm still a ways away from that.
You may want to check out a 3D Printer board or facebook group with experienced 3D printer users and pose the question on ambient temperature and humidity. My understanding is that filaments can draw moisture and it can cause flaws in prints. I keep mine sealed in a bag was a desiccant pack when not in use. As far as the impact ambient temperature has, I'd think your temperature fluctuations could have an impact. How fast the filament cools can impact strength and finish. But you may be able to compensate by adjusting print speed, nozzle temperature and cooling fan speeds. You may want to look at 3D printers that have enclosures to stabilize the printing environment, but that's in the context of temperature from what I've seen. I've also seen people create their own enclosures for printer that don't have them. Really have no idea about humidity levels during the actual printing process. Good luck with your research!

 

I did print the smaller scale version of the fin Leo provided. But, for better or worse, I decided to go with the larger, it visually looks more appealing with the larger lower fins. The larger version weighs 13 grams and the smaller 11 grams.

 

Fins printed. Printing cable covers and charge retainer next.

 

I mentioned at the start of this thread I'm also building a TLP Pershing 1A. I started this before I got into 3D printing. I'm not building it stock, I'm making changes to make it look a little more like the Estes kit, I even decided to have the nose ejection break at the bottom like the Estes kit versus the small balsa nose at the tip. Trying to get the paper cones assembled for the nose was a bit of a pain to get to look right, it's not perfect, but it works. I wanted fins that had the dimensional profile of the real Pershing 1A, so I used aileron stock to achieve the lower and upper fin profiles, saves a lot of sanding. And I made the fin pads from balsa, that did take a lot of sanding, especially to get the tube contour right. I'm not quite done with the nose and I know I added some weight with the coupler to achieve the change to the nose ejection break point and there will be a little more to go to finished the cone. It doesn't have any nose weight added and it comes in at 111 grams, compared to 113 grams for the 3D printed cone. I have the inner core tube installed in the airframe, but not the engine mount yet. In total I'm at 235 grams so far for the TLP. Here are some pictures and a comparison of the nose cones between the TLP and the 3D printed.

 

The larger lower fins will also improve stability. You will also be able to use a little less weight in the nose cone.

 

Nicely Done!

 

Okay, I'm subscribed. Thx for sharing.

 

I've printed the last pieces from Leo's files. The cable covers, the charge retainers, and the shock cord plate. The combined weight of these last parts is about 26 grams.

long cable cover 9 grams
short cable cover 6 grams
charge retainer 2 grams each
shock cord plate 7 grams

 

I put all the printed parts on the scale at once to see what the combined weight was, figuring it to be a little more accurate since my scale is only accurate to 1 gram. 206 grams.

 

To help with adhesion of the fins to the body tube with epoxy, I am drilling small holes in the back. To ensure I don't accidentally drill through the front of the fin I am using my drill press so I can control the depth

 

Put the motor mount together. 24mm, I figure if I conclude the E12 won’t lift it, there are 24mm composite options, like the E30. And if I crash it, I might be unhappy, but I can always build another. Since it might fly with an E30, I used a heavy wall BT-50 and added a third centering ring for a little extra strength, which is glued inside the body tube, used a long skewer to get the epoxy in the right place as I installed the mount. Also used the Estes Pro Series 24mm motor retention and a kevlar leader.

 

Making real progress now, it’s starting to come together. I’m basically following the Estes plans. I epoxied all 6 fins on. I took my time I did them one at a time to make sure they went on straight, which was easy, as Leo did an excellent job on getting the curvature to match the body tube. I made sure to work the epoxy into the holes I drilled and I roughed up the back of the fin pads with sandpaper to further help with adhesion. I also tried to keep the amount of epoxy I used low making sure to get a nice even thin coat that wouldn’t ooze out.

 

Use tape to hold the cable covers in place while the glue dries.

 

Looking good!

 

Nice build. I think you'd have been safe with regular BT-50 and avoid the weight penalty. The 3 rings is a good idea for extra bond area.

 

Very nice so far. I built the Boyce BT80 Pershing and attempted it on an E12 with like 6 oz of weight in the nose. It started coning so I'll try an E18W reload or something next in it to see if that fixes it. OpenRocket said 6 oz would bring it to like 1.1/1.2 stability.