RMS or single use?

[bcook7135]

So perhaps this has been discussed before. If so, I apologize. But I am curious as to the opinions on reloadable engines vs single use. In particular I am curious about the Aerotech versions. I have read differing reviews- some say the Aerotech RMS motors are not precisely made or that they are difficult assemble.
So is it worth the reduced cost per launch to go with RMS (after the initial cost)? Are there tips to use?

 

[kuririn]

I have not had any difficulty assembling RMS motors. Sometimes the liner is too tight, in which case I peeled off a thin layer of paper to fit.
Whether or not it's more economical depends on how often you lose rockets. With an RMS motor you not only lose the rocket but the casing and closures as well.

 

[Kane]

I don't find the Aerotech RMS motors difficult to assemble at all. Not sure how one would find them "not precisely made" either. There is, of course, the possibility of user (assembler) error. They do require a little time to assemble, but most motors are pretty straight forward until you get into grain bonding or motors that require inhibiting (even then, not too complicated). If you can follow directions, you can assemble an RMS motor.

 

[Jmhepworth]

I don't find the Aerotech RMS motors difficult to assemble at all. Not sure how one would find them "not precisely made" either. There is, of course, the possibility of user (assembler) error. They do require a little time to assemble, but most motors are pretty straight forward until you get into grain bonding or motors that require inhibiting (even then, not too complicated). If you can follow directions, you can assemble an RMS motor.

I agree. They aren’t difficult, but there is a bit of a learning curve. I found it really helpful to have someone watch me while I assembled the first couple, and then again as I went up in size. YouTube is helpful, especially with learning how to bond the grains to the liner.

 

[Rocket86]

In my 12 year experience with RMS I've found them to be very well made and easy to assemble, from 18mm through 75mm. In hundreds of flights I've had one failure that was totally my fault, and that had nothing to do with complexity. I've had far more failures with single-use motors.

 

[rharshberger]

Watch Gary' video...
https://www.rocketryforum.com/threa...w-up-your-rms-reloadable-rocket-motor.176610/

 

[JRL303]

I don't find the Aerotech RMS motors difficult to assemble at all. Not sure how one would find them "not precisely made" either. There is, of course, the possibility of user (assembler) error. They do require a little time to assemble, but most motors are pretty straight forward until you get into grain bonding or motors that require inhibiting (even then, not too complicated). If you can follow directions, you can assemble an RMS motor.

Totally agree

 

[sriegel]

One of the nice things about the RMS is the ability to adjust the delay. E.g., if you buy a load with an 11-sec delay, you can drill it down shorter. Nice to have that flexibility.

 

[ThirstyBarbarian]

I think even if you get into RMS, you will still be using some single-use too. When I go to a launch, I like to have about 5 flights, give or take. You can’t do that if you are cleaning and building motors at the launch. And buying that many cases is kind of cost prohibitive out the gate, so it might take years to build up the hardware.

If you are currently flying single-use, you can probably plan to keep doing that and then get into RMS and mix that into your flights a bit at a time.

Reloads offer a variety of propellants and thrust curves that might be interesting to you. It takes awhile to break even on cost, but some people think it pays off. And some people like the process of building motors (I don’t). So there might be reasons to give it a try, but it’s not an all-or-nothing decision.

Personally, I fly a mix of single-use and CTI. For midpower, it’s almost all single-use, except for a few specialty loads, like the CTI G54. For high-power, it’s pretty evenly split between Aerotech DMS and CTI reloads, with an edge for CTI as the motors get bigger. DMS are single-use, but with an adjustable delay, CTI is about as simple as DMS, with the added step of sliding the reload into a case (you don’t “build” a CTI motor). I’ve got some Aerotech DMS standby favorites I really like and almost always have on hand, and I use CTI for the variety.

 

[bcook7135]

Thanks for the responses so far. I am breaking in with a 24 RMS. But I do plan to still use single use too. Just want to make sure they are dependable.

 

[Neutronium95]

If you're looking at 29mm motors and you don't have a local vendor, hazmat shipping is a major consideration.

The 29/40-120 case has non hazmat G and E motors, but the F reloads do require hazmat shipping. The Econojet single use 29mm F motors do manage to slip under the limits for hazmat fees, so they might be a better option than the reloads.

 

[kuririn]

Another consideration is if you want to advance to larger motors than 29 mm, they are all reloads.
So having experience with the smaller reloads is good practice for stepping up.

 

[g.pitts]

Another consideration is if you want to advance to larger motors than 29 mm, they are all reloads.
So having experience with the smaller reloads is good practice for stepping up.

There are quite a few AT DMS in 54 mm, and a couple in 75 and 98 mm as well.

@bcook7135 if you are thinking about a certification flight, a DMS motor takes some element of risk out of the flight since it is assembled by the manufacturer. One less "worry factor" if you're uncomfortable assembling a motor on your own. But as others have said, assembling an RMS is not difficult, and the online resources help show you what well-intentioned instructions may not.

 

[teepot]

I'm all DMS. I don't fly enough to warrant the cost of a RMS system. I looked at the initial cost and savings. Just not enough difference in cost to go RMS. But that's me.

 

[Hobie1dog]

my hands are really weak, so my first choice is single use.

 

[lawndartman]

Put a sign on your table at the launches. Wanted: 18 & 24 & 29 cases. In a few launches you will have several of each. 25.00 for 18mm -30.00 for 24mm and 35.00 -40.00 for 29/40-120. I load the night before, most reloads come 3 to a pack, so I load all 3 at once.Just start doing this and in a few years you will have a pile of cases. Used is as good as new. Just my 2 cents.

 

[tsmith1315]

Just want to make sure they are dependable.

Absolutely. They've been around for decades for that very reason.

 

[T-Rex]

Years ago I started with a 29/40-120 case, next was a 24/40, and it grew from there. The only single use composite motors I have flown are Estes labeled 29mm that I picked up on clearance..

I enjoy the variety of motors available for MPR using the 24 & 29mm hobby cases. I have no problem finding a motor that will fly what ever rocket in what ever conditions.

 

[Antares JS]

Remember that you can absolutely assemble RMS ahead of time and not worry about assembling at the field. However, I do very much recommend disassembling and cleaning the case at the field, as soon as it's cool enough to handle. You'll have a much easier time cleaning if you do that.

Also, I find RMS fun to assemble. Handling propellant grains and sealing them up in the case is exciting to me. Another thing you might want to consider.

 

[mbeels]

Remember that you can absolutely assemble RMS ahead of time and not worry about assembling at the field. However, I do very much recommend disassembling and cleaning the case at the field, as soon as it's cool enough to handle. You'll have a much easier time cleaning if you do that.

Also, I find RMS fun to assemble. Handling propellant grains and sealing them up in the case is exciting to me. Another thing you might want to consider.

Ditto, and be sure to check the prices on a case by case basis. It's not an either-or situation, you can fly both. Even though I have a 38/360 case, I bought the DMS version of the H550 (instead of the RMS) because it was actually cheaper than the reload (during Wildman's sale).

 

[mh9162013]

I don't have personal experience with AT RMS products, but here's my general impression from online research:

18mm: There's no cost savings and reload options are limited.
24mm on up: The primary reason to use RMS is for the ability to "customize" your motor. A secondary reason is to enjoy the process of assembling your own motor.

Saving money for most people will take some time and there's a risk of losing your casing and never making back your initial investment.

TL;DR: Don't get into RMS to save money.

 

[MikeT]

I find that part of the fun is assembling motors for the next launch.

 

[JRL303]

I find that part of the fun is assembling motors for the next launch.

This. I primarily only use RMS 18, 24, 29 and 38. Gives you a little bit more immersion into the hobby.

 

[mh9162013]

This. I primarily only use RMS 18, 24, 29 and 38. Gives you a little bit more immersion into the hobby.

What kind of rockets do you use with the 18mm RMS?

 

[mikec]

Don't get into RMS to save money.

24 and 29mm and a few 38mm AT reloads ship without hazmat, so that can be a significant cost savings. All DMS requires hazmat.*

Over the years DMS has had some reliability issues, hopefully all resolved now. With RMS that's more in your hands, at the cost of greater complexity and more things to do wrong.

* Note that "DMS" technically refers to high-power motors. There are single-use AT motors not usually called DMS that don't require hazmat.

 

[JRL303]

What kind of rockets do you use with the 18mm RMS?

Minimum diameter up to BT-50. D13 in a Mini Bertha, or fat boy or such is fun.

 

[tsmith1315]

24 and 29mm and a few 38mm AT reloads ship without hazmat, so that can be a significant cost savings. All DMS requires hazmat.

This is a real savings if you don't buy in larger quantities.

 

[mh9162013]

24 and 29mm and a few 38mm AT reloads ship without hazmat, so that can be a significant cost savings.

I didn't know that; good to know.

 

[Black Bart]

i fly lots of 29 mm motors single use and AT RMS 180 and RMS 240 here's some 180 motors not hazmat. Great price for Sirius Rocketry

 

[DeltaVee]

Remember that you can absolutely assemble RMS ahead of time and not worry about assembling at the field. However, I do very much recommend disassembling and cleaning the case at the field, as soon as it's cool enough to handle. You'll have a much easier time cleaning if you do that.

Also, I find RMS fun to assemble. Handling propellant grains and sealing them up in the case is exciting to me. Another thing you might want to consider.

I totally second what Antares says! Tip: unscented baby wipes (pretty much any brand...) are excellent for hardware cleanup in the field.