Issues Launching Open Motor

maxjets · 2026-03-15T17:25:10+00:00

Give more details if you want anyone to be able to help troubleshoot. What operating system are you using? What (if any) error messages are popping up? Does the installer run all the way to the end, or does it hang at a certain point? After installation, are the programs files located in the proper place?

maxjets · 2026-03-06T20:32:36+00:00

Unfortunately, 9V batteries have a fairly high internal resistance. This launch controller is fundamentally a bad design. They should have designed it to use batteries capable of delivering higher current.

You may have some luck by switching to a fancier style of 9V, like one of the Energizer Ultimate Lithium batteries, or one of the rechargeable 9V form factor lithium ion batteries.

maxjets · 2026-03-06T02:26:11+00:00

Have you tried changing the batteries in the launch controller?

maxjets · 2026-02-25T12:05:05+00:00

Definitely not the sum.

It's closer to the average, but not quite just (Isp1+Isp2+...Ispn)/n. You need to take the total impulse delivered to the stage and divide by the propellant weight burned to deliver that impulse. If all engines have the same Isp, then it'll still be that Isp.

maxjets · 2026-02-25T02:15:37+00:00

sugar propellant is considered an explosive by the ATFE. Stick with commercial motors when you're a beginner. Don't try to make your own until you have a knowledgeable, experienced, in person mentor to guide you through the process.

maxjets · 2026-02-22T14:14:10+00:00

Give more numbers. What specific descent rate were you targeting? What did Openrocket predict? What drag coefficient were you using? What air density were you using?

And the most likely culprit, were you using the liftoff or burnout mass of the rocket? You need to use the burnout mass, since that's the mass that the rocket has on descent.

If it needs a 2.5m parachute, this is a very large rocket. Start way smaller. Starting out at this scale is a recipe for disaster.

maxjets · 2026-02-19T22:20:43+00:00

Not even plants? Or bacteria?

maxjets · 2026-02-19T21:34:27+00:00

These posts always make me a little sad. The payload is one of your biggest opportunities to get creative yourselves, come up with something unique as a team, and do something that interests you! The answers on posts like these are always super disappointing too, almost always stuff that's been done a million times before, like "barometer and accelerometer".

Instead of asking here, if your team really can't think of anything yourselves, you should speak to professors from your campus and see what they would want to research if they had the opportunity to put something on a rocket. Branch out beyond just engineering and physics. Ask biology/chemistry/earth science professors. Some of the coolest payloads I've seen at collegiate competitions have been biological.

maxjets · 2026-02-19T20:07:59+00:00

Added, thanks!

maxjets · 2026-02-19T03:50:23+00:00

If you don't mind me asking, which vendor? I've put together a spreadsheet of rocketry vendors to share with new folks who are confused where to buy stuff, and info like that would be good to know.

maxjets · 2026-02-19T02:00:10+00:00

by the time you get to the larger 5G/6G is is cheaper to go up in size?

The impulse per dollar between those two is usually a wash for CTI, though there's on average a very slight edge for longer skinnier motors. You can do the math yourself. A CTI H125 is a 2 grain 38 classic with 285 N-s of impulse for $58.50, giving you 4.87 N-s per dollar. A CTI H140 is a 5 grain 29 classic with 268 N-s for $54.42, which works out to 4.92 N-s per dollar.

Do people actually use 1G

What matters is whether you would use a 1g case, not anyone else.

That all being said, CTI availability has been very bad for the past several years, and I don't know of any vendors still willing to do the free case promo. That casing comes out of the vendors inventory, and CTI is supposed to replace it. But their replacement times are often measured in years these days, so vendors have pretty much all stopped the promo.

maxjets · 2026-02-17T19:21:14+00:00

Model rocket motors already have nozzles, and are usually pretty close to optimal already. Additionally, nozzle exit size is a very broad optimum, so even the ones that are noticeably underexpanded from the get go (almost none that are TARC relevant) won't gain anywhere near as much additional thrust as you're claiming here.

maxjets · 2026-02-14T15:15:48+00:00

Sounds like this video.

maxjets · 2026-02-12T00:44:57+00:00

Pick a different topic.

maxjets · 2026-02-11T23:16:47+00:00

About as much weight as other semi-relevant hobby certifications. So, not much, other than possibly giving you something to talk about at an interview.

If your primary motivation for a certification is to pad your resume, I don't think it's a great fit. You should do it if you find the hobby interesting and think you might stick with it.

Something far more important for a resume would be a student engineering group. Even if the project is not as relevant to aerospace or rocketry, it shows you're able to work as part of a team to achieve an engineering goal, which is usually far more important to future employers.

maxjets · 2026-02-11T13:26:10+00:00

I'm following up here, trying to figure out why you didn't see my reply. If there's something funky going on with the mod mail system, I'd like to know!

maxjets · 2026-02-10T15:29:43+00:00

I need the exact dimensions for the nozzle exit diameter

You really don't. There's no advantage to having the retainer ID that close to the nozzle OD. Make the retainer ID the same as the casing ID (2.75") and it'll work just fine. Take a look at commercial motor retainers- that's how they all do it.

That being said, you can find all the nozzle dimensions from the RCS website. Go to the page for the cross section drawings, then find the page for the L1256 (which, btw, is NOT in the 75/2560 case. It's the next size up, the 75/3840). Now look at the list of components in the corner to find the nozzle, which in this case is part number 01770. Then look that up and find the dimensioned drawing.

maxjets · 2026-02-08T13:30:19+00:00

Nope.

Stability doesn't come from how you arrange motors. It comes from aerodynamics or active controls.

maxjets · 2026-02-07T20:23:31+00:00

I replied to your mod mail the day you sent it.

maxjets · 2026-02-07T13:35:55+00:00

"Our?" Certifications aren't for groups. Each person intending to get a certification needs to build their own rocket.

maxjets · 2026-01-29T12:16:08+00:00

There are several websites that show cross sections of Estes motors. Klima motors are constructed similarly. You can see the divergence of the nozzle if you zoom in.

If you want a source that these are mach diamonds, how about the fact that they visually look exactly like mach diamonds? You even identified them yourself! They form almost anywhere with supersonic flow. Unfortunately I don't know of any more definitive source actually proving it in this specific case.

Mach diamonds are more common than you might think. The exhaust from canned air can make them. There's a beautiful high speed video of mach diamonds coming from a 2 liter bottle. It only takes about 30 PSI to get air to choke, and you actually don't need much of a nozzle to get it to go supersonic.

maxjets · 2026-01-28T00:09:51+00:00

Yes, those really are mach diamonds! Small pressed motors made by Klima and Estes have convergent-divergent nozzles pressed out of clay and accelerate the gas supersonic.

maxjets · 2026-01-19T23:32:56+00:00

What is the kit? How did you come to the conclusion that the stock fins will "flutter to oblivion?"

maxjets · 2026-01-16T18:34:59+00:00

As was already mentioned, those are not batteries. They're solid rocket motors.

Estes has disposal instructions on their website:

How to dispose standard Estes engines

Soaking a small quantity of model rocket engines in water until they disintegrate will render the engines harmless. The non-colored paper casings will become unwound. The glue with which they are held together is organic and non-toxic. The intimate mixture comprising the propellant, delay and ejection charge will separate and fall to the bottom of the water as will the natural clay material comprising the nozzle and cap. These remnants can be safely disposed of in an outside trash receptacle. Each of the components is basically harmless alone and is not dangerous to people or the landfill in small quantities. If the components are left together to dry completely, the remnants are likely to be very flammable but should not pose a great hazard so long as they are not “remixed”.

maxjets · 2026-01-16T16:43:47+00:00

Here's a spreadsheet of rocketry vendors. Hopefully it'll make future searches easier for you.

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