Can you change delay on a single use motor?

[BABAR]

Bought some of these on sale a while back (years!)
Got a big draggy rocket I want to fly, but I think the 7 second delay is gonna be too long. Can I drill down the delay on this single use motor?

 

[58pan]

Well, Number 2 of the N.A.R. Safety Code says
"Motors. I will use only certified, commercially-made model rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer.
So no.
Save them for a lighter rocket.

 

[58pan]

Just looked and my 3 in. tube fin rocket weighing 2 lbs. sims at 6.22 sec. delay and there isn't a draggier rocket than a tube fin. So depending on what you have you might be ok.

 

[ChicagoDave]

Aerotech does make single use motors with an adjustable delay, called Disposable Motor System (DMS). Unfortunately I don't think your G80 is a DMS motor.

FWIW, there is the "Aerotech G80-14A New Blue Thunder 29 mm - DMS" which does have the adjustable delay.

 

[jimzcatz]

Well, Number 2 of the N.A.R. Safety Code says
"Motors. I will use only certified, commercially-made model rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer.
So no.
Save them for a lighter rocket.

That's wrong. Per manufacturer in person conversation. It's perfectly fine to trim the delay of a single use motor. I do it very often.

 

[UhClem]

That's wrong. Per manufacturer in person conversation. It's perfectly fine to trim the delay of a single use motor. I do it very often.

NFPA 1125 has provisions for user adjustable delays but the user codes do not allow that for single use motors.

NFPA 1127 (4.5) and 1122 (4.19) allow for adjusting delays for reloadable motors only. Both prohibit altering single use motors.

 

[Maxwelljets]

NFPA 1125 has provisions for user adjustable delays but the user codes do not allow that for single use motors.

NFPA 1127 (4.5) and 1122 (4.19) allow for adjusting delays for reloadable motors only. Both prohibit altering single use motors.

Every single Aerotech DMS motor is designed to have adjustable delays. Aerotech sells a DMS delay cutting tool. Those are all single use motors.

 

[jimzcatz]

Gary said it was OK..... 20 years ago to be truthful. In the end, don't ask don't tell.

 

[kuririn]

DMS, LMS, and RMS motors are assembled by the user, so the delay grain is accessible and can be adjusted with the proper drilling tool.
Babar's G80-7 is a single use motor with the hex cap sealed with epoxy from the factory.
So the delay grain is not accessible.
Don't see how the delay can be drilled without cutting open the case.
I think that's a no-no.
My 2 cents.
Back to building.

 

[Maxwelljets]

DMS, LMS, and RMS motors are assembled by the user, so the delay grain is accessible and can be adjusted with the proper drilling tool.

DMS motors are not assembled by the user until 75 and 98mm motors, unless you're talking about the user needing to put the ejection charge and cap in (which really shouldn't count as "assembly" in my opinion).

Babar's G80-7 is a single use motor with the hex cap sealed with epoxy from the factory.
So the delay grain is not accessible.
Don't see how the delay can be drilled without cutting open the case.

It's trivial to take the red cap out of the top, pour the BP charge into a suitable temporary storage container, and then drill the delay in the same manner that it's done for regular DMS motors. You then put the powder and cap back. The regular DMS delay cutting tool doesn't work since the bit is too wide, but it's very easy to measure the cutting depth needed on a smaller drill bit and then mark the end of the cut with tape.

 

[kuririn]

The regular DMS delay cutting tool doesn't work since the bit is too wide, but it's very easy to measure the cutting depth needed on a smaller drill bit and then marking the end of the cut with tape.

Would the smaller diameter bit change the delay amount the same as the wider bit?

 

[Maxwelljets]

Would the smaller diameter bit change the delay amount the same as the wider bit?

Yes. All that matters is depth (as long as the hole is large enough for black powder to reach the bottom, so don't use something silly like a 1/128" bit). Pick a drill bit that's roughly the same diameter as the hole in the bottom of the charge well.

 

[jimzcatz]

Been doing it that way since 92. It works.

 

[shreadvector]

The new 137 N-s G80 is not sold with a delay shorter than 7 seconds BECAUSE the largest legal Model Rocket will coast for about 7 seconds with this motor.

https://www.rocketryforum.com/threads/aerotech-open-thread.125657/page-109

Read post number 3241 and 3248.

 

[blackjack2564]

what rocket Babar, that would be a more realistic approach too the issue.

 

[BABAR]

I will try to post a pic tomorrow. It’s a version of @neil_w ‘s Stop Sign rocket, crosses with my Air Brake recovery rocket. Square profile, about 3 3/8” diameter, pyramid nose cone. Gonna have a lot of base drag. When I skimmed it on thrustcurve for G80 it is giving me a 4 second delay. I am already at 280 grams mass, that’s before I add motor mount, motor, some internal structure. Nose pyramid is cardboard, weighs about nothing, unless I add weight.

 

[afadeev]

Bought some of these on sale a while back (years!)
Got a big draggy rocket I want to fly, but I think the 7 second delay is gonna be too long. Can I drill down the delay on this single use motor?

If you can disassemble the motor casing and access the delay element, then you can drill it.
I don't have any G80 motors in my stash, so not certain on how it has been put together, and whether the delay grain is accessible.
Some DMS's are glued together solid, others require assembly and provide access to the delay element.

Whether or when one should engage in such an activity, is another subject altogether.

 

[ebruce1361]

This is a bit of a tangent on this topic, but if I have a DMS motor that has the rubber cap holding in the ejection charge (Say, a E15-4W or equivalent), can I simply remove the ejection charge altogether if I have something like a cluster or alternate deployment method so the motor never ejects? Would that count as motor tampering?

 

[afadeev]

This is a bit of a tangent on this topic, but if I have a DMS motor that has the rubber cap holding in the ejection charge (Say, a E15-4W or equivalent), can I simply remove the ejection charge altogether if I have something like a cluster or alternate deployment method so the motor never ejects?

You would also want to fill the ejection well with epoxy, to avoid unintended airframe pressurization when the delay element burns through.

Would that count as motor tampering?

I will defer to our volunteer Legal department on that one...

 

[Nytrunner]

Folks remove ejection charges when doing electronic deployment all the time.

Clustering sounds like another application for this method

 

[58pan]

Folks remove ejection charges when doing electronic deployment all the time.

??? I never do. If the electronics fail motor ejection will at least separate it.

 

[Nytrunner]

??? I never do.

I didn't say all folks. In some cases you'll be flying longer than the delay and removing it is necessary. Or of flying redundant, you can take out the motor charge and use it as one of the others

 

[Steve Shannon]

??? I never do. If the electronics fail motor ejection will at least separate it.

If you use “zipperless” construction you have to leave out the charge or perforate the coupler bulkplate.

 

[cerving]

Folks remove ejection charges when doing electronic deployment all the time.

If I use a one-time use motor with electronics, I'll remove the powder IF the delay is going to be shorter than the expected apogee. If you don't, it will pop on the way up, and things will not go well. If the motor has a nice long delay, I'll drill it to the apogee + about 2-3 seconds for redundancy. However, that doesn't happen very often...

 

[Tyler P]

I've got a single use Aerotech H135 for my L1 certification attempt. It has a drillable delay and you have to add the deployment charge depending on body tube diameter. I also have a G80 with a drillable delay. I also have the tool do it.

 

[tOD]

Maybe I'm missing something, and my experience with adjusting delays is limited to reloadable motors, but isn't the drilled end of the delay grain supposed to face the propellant rather than the ejection charge?

 

[dhbarr]

In reloadables that can matter a lot if you have a spacer in the delay train, allowing the powder to fall past the touch hole.

Then too, you don't want remaining delay grain slivers burning freely post-ejection with a path for hot gas to exit the top end, as that will cook the forward like a nozzle.

I don't think either of these are a significant concern with single-use.

 

[Steve Shannon]

Maybe I'm missing something, and my experience with adjusting delays is limited to reloadable motors, but isn't the drilled end of the delay grain supposed to face the propellant rather than the ejection charge?

It doesn’t seem to matter. All DMS motors have the drilling done on the charge end.

Now leaving out the washer afterwards can ruin your day. [emoji851]

 

[cerving]

Steve, I think the OP was referring to an EconoMax or similar retail-packed motor, not DMS. You could remove the cap and dump the powder, drill it down with an appropriately-sized drill from the TOP, then replace the powder and cap. I don't think that the motor was DESIGNED for that, so my guess is that the non-DMS OTU motors cannot be "legally" (TRA/NAR) drilled.

 

[AstroMFPII]

What if you want zero delay in the case of using the SUM as a Booster stage. In my case I use Avionics to do dual deployment and I want to stack 2 F52-5C motors on a 2inch Homemade 2.4 lb rocket. Can I eliminate or minimize the delay for two stage vehicle?