New to Mid Power Rocketry

[CrazyModelGuy]

So ive been into rockets since I was 10 or so. But always launched Estes and Quest rockets. I am getting a MadCow Rocketry "lil Goblin hopefully soon. First I read that It can use Reloadable motors but when I search those motors all that comes up is just the repacking stuff. Dont I need a "cannister" for it all to fit inside of? What am I missing. And lastly, the 'lil goblin ive been reading online and a few other sources the body tube is fiberglass but others say its cardboard. Im just looking for clarification.

 

[ThirstyBarbarian]

Are you talking about this rocket? https://www.madcowrocketry.com/2-6-lil-goblin/

I’m pretty sure that’s cardboard, not fiberglass, so it’s not going to be very different to build than some of the rockets you are already used to. It will be similar to a larger, sturdier Estes kit.

There are reloadable motors that can work with that rockets, and you would need the appropriate motor cases, closures, hardware, etc. to use the reloads. I’d suggest starting off with some single-use motors to make it easier. You could use something like these F20 motors http://www.buyrocketmotors.com/aerotech-f20-white-lightning-econojet-29-mm-single-use-2-pack/ There are also F23, F27, F42, and F67 single-use motors sold this same way in 2-packs that will fit that rocket. You can search that vendor website for those. You would want to do a flight simulation of some kind to see how those would perform with your rocket. Some might be pretty high, and maybe you should keep it lower to start.

 

[CrazyModelGuy]

Ok yes thats the rocket im speaking of.

 

[CrazyModelGuy]

Are you talking about this rocket? https://www.madcowrocketry.com/2-6-lil-goblin/

I’m pretty sure that’s cardboard, not fiberglass, so it’s not going to be very different to build than some of the rockets you are already used to. It will be similar to a larger, sturdier Estes kit.

There are reloadable motors that can work with that rockets, and you would need the appropriate motor cases, closures, hardware, etc. to use the reloads. I’d suggest starting off with some single-use motors to make it easier. You could use something like these F20 motors http://www.buyrocketmotors.com/aerotech-f20-white-lightning-econojet-29-mm-single-use-2-pack/ There are also F23, F27, F42, and F67 single-use motors sold this same way in 2-packs that will fit that rocket. You can search that vendor website for those. You would want to do a flight simulation of some kind to see how those would perform with your rocket. Some might be pretty high, and maybe you should keep it lower to start.

And what launch controller do you recommender for igniting higher power motors. I used to just use a motorcycle battery. Back in the day!

 

[teepot]

I use a 12 volt car battery.

 

[ThirstyBarbarian]

I think typically the igniters for composite motors like 12-volts. They will probably light with 9 volts or more, but 12 should be very reliable. So a car battery, motorcycle battery, jump pack, or combination of dry cell batteries that add up to 12 volts should work fine.

 

[Scott_650]

And what launch controller do you recommender for igniting higher power motors. I used to just use a motorcycle battery. Back in the day!

The Estes #2240 Pro Series II Launch Controller is a good choice for the money if you don’t want to gin up your own - available discounted from online vendors for less than $30. There are others but they can get a bit pricey.

Nice thing about the #2240 Controller is you can power it with regular alkaline C cells or rechargeable Cs (I use NiMH rechargeables in mine) and it has a JST connector for a LiPo battery pack too.

 

[mtnmanak]

The Go Box from Pratt is a classic and has been around for a long time. It is only a little more expensive than the Estes and, in my opinion, much better built. It can connect to any 12V power source you want:

https://pratt-hobbies.com/products.asp?cat=9
Car batteries, motorcycle batteries, etc all work great, but I don't like lugging them around. LiPos are also great, but expensive. One of these cheap 12V lantern batteries lasts me a long time (last one I bought was in 2019 and it is still cranking LPR/MPRs into the air at our local park) and is pretty lightweight compared to other options:

https://www.amazon.com/gp/product/B000ROFZFE/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[samb]

So ive been into rockets since I was 10 or so. But always launched Estes and Quest rockets. I am getting a MadCow Rocketry "lil Goblin hopefully soon. First I read that It can use Reloadable motors but when I search those motors all that comes up is just the repacking stuff. Dont I need a "cannister" for it all to fit inside of? What am I missing. And lastly, the 'lil goblin ive been reading online and a few other sources the body tube is fiberglass but others say its cardboard. Im just looking for clarification.

The "cannister" is usually called a case or reload case, and yes, you will need one if you go with the reloads. Since Madcow lists both single use and reloadable motors in the recommended list for this model, you could go with the single use and defer the cost of the reload case. Like Thirsty mentioned, the single use motors are a good way to start with composite propellent.
That said, reloads are another step in the journey. The Madcow lil' Goblin lists 3 : E16W-4, E23T-5, F40W-7. Aerotech makes alot of different cases for alot of different motors so you need to get the right case for the right motor. There are several places on the web to get this info and my favorite is the Aerotech Master Motor Matrix:

Aerotech motor matrix

At first glance, it's alot. On second glance, it's alot ! It has everything you need to know about an Aerotech motor in one convenient place. The motors that you're looking for are under the 29mm Model Rocket RMS Reloadable subcategory. Reading across tells you that these need the RMS-29/40-120 case.

There are two ways to learn how to use the reload system. Youtube video:

Apogee video - How to assemble a reload using the RMS 29/40-120 case

Or, my favorite, find a local club and get a hands-on demo.

Hope this helps.

 

[CrazyModelGuy]

thank you for all the great input. I definitely have my reading and research to do. And when I finally get the 'lil goblin built I will likely use single use at first just to get accustomed to flying it. But right now I have an Estes Hiflier and Epic 2 (2 stage) to build.

 

[gldknght]

If you don't want to hassle with the fiddly bits of Aerotech reloads and iffy availability of Aerotech hardware, check out
https://wildmanrocketry.com/collections/cesaroni-tech-29mm/products/p29-1g-case
and
https://wildmanrocketry.com/collections/motors-cesaroni-technology-29mm-1-grain

The CTI reloads cost a bit more than Aerotech but are way easier to use. The CTI cases are way cheaper!

 

[CrazyModelGuy]

Thank you again for all the input. I feel a tad idiotic not knowing what some of these "impulse" things mean. Im used to estes rockets. LOL

 

[mtnmanak]

Thank you again for all the input. I feel a tad idiotic not knowing what some of these "impulse" things mean. Im used to estes rockets. LOL

Impulse is the letter rating of the motor. It is a classification of the amount of power, with the higher letters being more powerful. Each letter on the chart is twice as powerful as the letter before it, so they scale up quickly. With Estes motors, you are most familiar with the A-E classes.

Impulse is measured in Newton Seconds:



Here are a couple links explaining the motor basics:

https://themodelrocket.com/model-rocket-engine-sizes-and-classifications/
https://www.apogeerockets.com/Rocket-Motor-Basics-Quick-Start-Guide?m=quickside
Also, Apogee has a whole slew of videos to teach you about motors:







And many more.

Best thing to do is pick up a copy of Harry Stine's Handbook of Model Rocketry. It goes into detail about a lot of questions you will have.

https://www.amazon.com/Handbook-Mod...=1&keywords=harry+stine&qid=1622499582&sr=8-4
Also take a look at Mark Canepa's and Mike Westerfield's books on high power rocketry. They also discuss different motor types.

 

[CrazyModelGuy]

Impulse is the letter rating of the motor. It is a classification of the amount of power, with the higher letters being more powerful. Each letter on the chart is twice as powerful as the letter before it, so they scale up quickly. With Estes motors, you are most familiar with the A-E classes.

Impulse is measured in Newton Seconds:

View attachment 466741

Here are a couple links explaining the motor basics:

https://themodelrocket.com/model-rocket-engine-sizes-and-classifications/
https://www.apogeerockets.com/Rocket-Motor-Basics-Quick-Start-Guide?m=quickside
Also, Apogee has a whole slew of videos to teach you about motors:







And many more.

Best thing to do is pick up a copy of Harry Stine's Handbook of Model Rocketry. It goes into detail about a lot of questions you will have.

https://www.amazon.com/Handbook-Mod...=1&keywords=harry+stine&qid=1622499582&sr=8-4
Also take a look at Mark Canepa's and Mike Westerfield's books on high power rocketry. They also discuss different motor types.

Thank you. Yeah I knew some of this. But you know being new to something I just wanted to make sure.

 

[dpower]

Best bang for the buck in mid-power reloadables are the Aerotech RMS 24/40 and 29/40-120 "Hobby-Line" cases. The Lil Goblin will fly quite high on a reloadable E18. The Estes 24/29 adapter works perfectly with the 24/40 case for 29mm birds like the Lil Goblin.

 

[CrazyModelGuy]

Ok so I mocked up my lil goblin build on Sunday. I noticed the centering rings were a little loose. But Mad Cow told me its not uncommon and to use larger fillets and it will be fine. However. I ordered and Aeropack Aluminum Motor retainer what Madcow recommended with the 29 L3 and it is really loose. About .040" of play. Is there a way I can tighten that up even though its just a motor retainer id like it to me some what concentric.

 

[teepot]

I would recommend Balsa Machining Service as a motor vendor and just about everything else place. Very competitive pricing and a large inventory. Bill is very helpful.

 

[CrazyModelGuy]

I would recommend Balsa Machining Service as a motor vendor and just about everything else place. Very competitive pricing and a large inventory. Bill is very helpful.

I mean im a machinist but dont do too much wood. I could make something out of delrin?

 

[Sooner Boomer]

Ok so I mocked up my lil goblin build on Sunday. I noticed the centering rings were a little loose. But Mad Cow told me its not uncommon and to use larger fillets and it will be fine. However. I ordered and Aeropack Aluminum Motor retainer what Madcow recommended with the 29 L3 and it is really loose. About .040" of play. Is there a way I can tighten that up even though its just a motor retainer id like it to me some what concentric.

Centering rings - do you mean the rings are loose in the body tube, or that the motor mount tube is loose in the centering rings? You can often build up tubes with a wrap of typing paper, glued down with yellow glue (sometimes you need to thin it a bit).

 

[neil_w]

I would recommend Balsa Machining Service as a motor vendor and just about everything else place. Very competitive pricing and a large inventory. Bill is very helpful.

Must be nice to be able to just pop in and get stuff there.

 

[Jay Rairigh]

I've had play around the retainer before. I believe it was because I did not have a heavy walled motor mount tube.

Tighten the retainer around an actual motor, (an AT motor casing for me), and put the motor casing with the retainer screwed on into the motor mount tube while gluing the retainer. This keeps the retainer centered really well around your motor mount.

Oh, careful you don't glue the casing into your rocket!

 

[afadeev]

Ok so I mocked up my lil goblin build on Sunday. I noticed the centering rings were a little loose. But Mad Cow told me its not uncommon and to use larger fillets and it will be fine.

Looking good.
Centering rings can move freely inside the airframe without any negative consequences (within reason). When you glue them, just make sure that you get a good bead of glue (TiteBond II or Epoxy - better for filling gaps as it doesn't shrink while curing) around the entire circumference of the contact area.

If the centering rings are loose around the motor mount (MMT), that is also not a big deal. That does make it slightly trickier to glue them on perfectly perpendicular to the length of the MMT. As an aid, consider building a masking tape "barrier" on one side of the MMT, place the centering ring with glue on top of it, and let it dry. Then remove the tape, and apply the glue fillet on the side where the tape prevented fillet formation.

Before the glue fully dries, roll the motor mount with the centering rings on the work table, and see if the "wheels" of your "axle" are wobbling too much. If they do, adjust the angle to remove the wobble (use masking tape to keep them in position), and the rings will be perfectly aligned afterwards.

However. I ordered and Aeropack Aluminum Motor retainer what Madcow recommended with the 29 L3 and it is really loose. About .040" of play. Is there a way I can tighten that up even though its just a motor retainer id like it to me some what concentric.

It sounds like your MMT tube is a bit on the thin side of things, thus likely causing a bit of play with the motor retainer and the centering rings.
Another possibility is that you had ordered Aeropack retainer (good choice, BTW) sized for fiberglass tubes, and not the thinner paper ones (they come in two varieties, with slightly different inner diameters).
Again, not a big deal. Use a highly viscous epoxy, like JB Weld (available everywhere, including Walmart). Mix it, apply liberally to the MMT, and for extra brownie points, see to it that it abuts the aft centering ring. Leave it to cure overnight. Done.

https://www.amazon.com/J-B-Weld-826...ocphy=9003763&hvtargid=pla-320192516391&psc=1
HTH,
a

 

[MidOH]

Float the tube.

Heavy epoxy application on the tube and inside the mount. Epoxy will fill the gap. Let it cure with the rocket vertical so that it lines up evenly.

 

[teepot]

Must be nice to be able to just pop in and get stuff there.

Yes it is. No hazmat fee's. Orders filled by the next day.

 

[boomtube-mk2]

3

 

[CrazyModelGuy]

So I have a plan. Since I am a machinist and apparently also a part time engineer now. LOL. Im going to use a bit of G10 and make a shim ring for the aeropack motor retainer. Just to take up some of the space. I dont have any actual motors for this rocket just yet. I considered making a "plug" 29mm in diameter and using that to ensure no motor mount tube shrinkage.
And if you need to know what G10 is, its Glass Reinforced Phenolic. Older stuff but takes to Epoxy and JB weld well. And its very very strong.

 

[Dane Ronnow]

I had the same problem with a motor mount kit from Apogee, which, by the way, has a thick-walled tube. Regardless of which method you use to take up the slack—heavy application of epoxy, blue tape dam, or just gluing it up and crossing your fingers—the problem is getting the motor tube aligned with the long axis of the rocket. If it's off—and it can be with very loose centering rings—the rocket will arc over in flight.

My solution was to wrap the motor tube with narrow strips of 24# copy paper (20 will do), .375" wide (assuming a .125" centering ring). That leaves a bit sticking out on both sides of the CRs.

First, figure out how many wraps of paper you need to get a slightly loose fit. You want a thin film of glue between the motor tube and the CR, so don't make it a tight fit. Then mark the position of the CRs on the tube. Lay a thin bead of Elmer's Carpenter's Glue on the first mark, then wrap the strip of paper and press it tight. If a second layer is needed, apply another thin glaze of Elmer's, then the paper.

Do the same for the second CR. And for the Aeropack retainer. (You can test fit the CR and retainer before the glue is dry.)

I did this on my motor mount, with an Aeropack, and it worked great.

[Edit] I don't mean to disparage the Apogee motor mount kit. It's an excellent, heavy duty motor mount. Knowing what I know now, I'd still order it.

 

[CrazyModelGuy]

Looking good.
Centering rings can move freely inside the airframe without any negative consequences (within reason). When you glue them, just make sure that you get a good bead of glue (TiteBond II or Epoxy - better for filling gaps as it doesn't shrink while curing) around the entire circumference of the contact area.

If the centering rings are loose around the motor mount (MMT), that is also not a big deal. That does make it slightly trickier to glue them on perfectly perpendicular to the length of the MMT. As an aid, consider building a masking tape "barrier" on one side of the MMT, place the centering ring with glue on top of it, and let it dry. Then remove the tape, and apply the glue fillet on the side where the tape prevented fillet formation.

Before the glue fully dries, roll the motor mount with the centering rings on the work table, and see if the "wheels" of your "axle" are wobbling too much. If they do, adjust the angle to remove the wobble (use masking tape to keep them in position), and the rings will be perfectly aligned afterwards.



It sounds like your MMT tube is a bit on the thin side of things, thus likely causing a bit of play with the motor retainer and the centering rings.
Another possibility is that you had ordered Aeropack retainer (good choice, BTW) sized for fiberglass tubes, and not the thinner paper ones (they come in two varieties, with slightly different inner diameters).
Again, not a big deal. Use a highly viscous epoxy, like JB Weld (available everywhere, including Walmart). Mix it, apply liberally to the MMT, and for extra brownie points, see to it that it abuts the aft centering ring. Leave it to cure overnight. Done.

https://www.amazon.com/J-B-Weld-826...ocphy=9003763&hvtargid=pla-320192516391&psc=1
HTH,
a

This worked like a charm. JB Welded the motor retainer to the Engine Mount Tube. I applied a decent amount to the "grooved" section and a small thin layer on the tube. And when I "threaded" the grooved section on engine tube it seemed to self center and I just sanded the excess off tonight.

 

[CrazyModelGuy]

So the motor mount is done. And im going to use wood glue for the centering rings. Large fillets. Only thing im questioning now is how to ensure the fin roots adhere to the motor mount tube. I have an idea. Just not 100% sure.

 

[dr wogz]

The retainer is usually the last thing you glue on.

This way, the rear-most centering ring can be placed / positioned to help get things aligned. Then it is removed to apply internal fillets. Then finally glued in place. Then glue on the retainer.

But this is how we all learn!

Another helpful hint:
If you are using buttons, add a piece to the centering rings, another piece of 1/4" ply or... Sand to match the CRs! Align them when you glue the two CRs onto the MMT tube. Then mark off on the BT where these will be located in the BT. Once it is all together, you now have two 'thick' points to mount your buttons. Drill your holes, then use wood screws to mount them buttons! No need to futz with blind nuts or ..