ThrustCurve.org future directions

JohnCoker · Dec 21, 2015

dpower said:
Wish there was a simple way to update rocksim with the latest engine data, but maybe that's more of a rocksim issue.

Mark Koelsch maintains master lists on his rocketryfiles.com site, which is an alternative to copying files one-by-one. I agree that the simulators should pick up new files automatically, but have yet to convince Tim or Kevin.

SpaceManMat said:
My thought is that the following information may be handy...

The case info is already there for reloadable motors. The others are good ideas, but don't show up on the certification docs, so I'm not sure where we'd get the values.

FYI, I've already started thinking about the re-implementation. The code will be public.

SpaceManMat · Dec 22, 2015

JohnCoker said:
The case info is already there for reloadable motors. The others are good ideas, but don't show up on the certification docs, so I'm not sure where we'd get the values.

My thought is that the case should be a listed individually for each motor. IE this requires a 5G case or a 6G with a spacer and along with that the separate weights and CG for each. Defaulting to the standard case of course.

markkoelsch · Dec 23, 2015

SpaceManMat said:
My thought is that the case should be a listed individually for each motor. IE this requires a 5G case or a 6G with a spacer and along with that the separate weights and CG for each. Defaulting to the standard case of course.

Interesting idea, but it would be very difficult to implement. The motor Cg info is not part of any testing by any of the testing orgs. Then throwing in the spacers makes a situation with no data become even worse. Also, that data will fit an Rse file but not an eng.

Where I really wish we had expanded Cg data and additional data (tank volume comes to mind) is for hybrid motors. Also, the way they are certified usually does not count the oxidizer as fuel, which does not make a lot of sense. Heck, many hybrids fundamentally are mono propellants with the fuel grain really not supplying much impulse but instead supplying heat to break down the nitrous. This has been and continues to be something on my mind. That is less about Thrustcurve than about motor certa in general.

Len B · Dec 24, 2015

SpaceManMat said:
My thought is that the case should be a listed individually for each motor. IE this requires a 5G case or a 6G with a spacer and along with that the separate weights and CG for each. Defaulting to the standard case of course.

I've thought about doing this myself. I would be guessing on the CG but the weights are more important anyway. I plan to do so for the few motors where I may actually use a spacer. Anyone can do this fairly easily themselves. Maybe we could agree on a nomenclature for this info so it can be added to Thrustcurve.org. Just a different name for the motor that designates it as including a spacer. Like-SP1, -SP2.

markkoelsch · Dec 24, 2015

Then we are throwing anything that uses a Eng/rasp file out the window as that data is unsupported/ i.e. Cg data.

Len B · Dec 25, 2015

To me, the weight is a far bigger issue. The weight of a heavy case and spacer with a smaller motor seems to me to be important. Throw out the CG data. Anyway, I will try one in eng/rasp and see if it is worth it to bother. It might not be worth it for a 1 grain reduction but I wonder about 2 spacers in a 75mm or 98mm motor. It certainly is something I want to simulate before I fly a motor in that configuration. There are other ways to deal with those differences but this is one of them.

wighty44 · Dec 25, 2015

The case & spacer weight issue was something I wondered about when I first began using Thrustcurve (TC). As I was unable to find information on that subject from TC, I assumed TC used the manufacturer's initial mass values. After I weighed a few CTI motors, I found those values to be close to the engine file initial mass values, but also realized they did not account for configurations using longer cases with spacers. So when I use longer cases with spacers, I adapt my RockSim model to account for those additional weights.

Given the various manufacturer's casing configuration possibilities, I'm not sure how TC could easily create such motor tables without becoming overly complex. Assuming TC does not attempt to do that, I think the website should state that as a default condition.

JohnCoker · Dec 25, 2015

wighty44 said:
The case & spacer weight issue was something I wondered about when I first began using Thrustcurve (TC).

Our primary source of data is the certification documents from the testing organizations. All cert docs include initial weight (mass) so it should be valid for each motor as it will be flown.

For example, here is the C.A.R. data for the AMW K700: www.canadianrocketry.org/mcc_motor.php?motor=1660%20K700-P.
This can be accessed through the "data sheet" link on the ThrustCurve.org motor page (when known): www.thrustcurve.org/motorsearch.jsp?id=623

UhClem · Dec 25, 2015

Missing from the list of choices in the poll is the XML API.

I updated an old Chuck Gibke launch stats program a while back. It used a local motor list for some information but of course was a missing a lot of recent motors. Rather than add those by hand, I added the ability to query thrustcurve.org using XML

wighty44 · Dec 25, 2015

JohnCoker said:
Our primary source of data is the certification documents from the testing organizations... For example, here is the C.A.R. data for the AMW K700...

Understood. However in the case of a 54mm CTI 4 grain K740, the motor could be used in 3 different 54mm casing configurations: 4-grain; 5-grain with 1 spacer, & a 6-grain with 2 spacers.

Would I be correct in thinking the weight used by TC would be representative of using the 4-grain case?

mikec · Dec 25, 2015

wighty44 said:
Would I be correct in thinking the weight used by TC would be representative of using the 4-grain case?

The certification document gives the weight without spacers. If you want to model the effect of the spacer(s), add that weight to the rocket dry weight. Per
https://www.pro38.com/pdfs/Pro54_Case_Spacer.pdf it's 120 grams per spacer.

Expecting TC to handle this in general is unrealistic IMHO, as the number of permutations in the report would get really large really fast. It's also a small effect for many rockets.

I guess TC could allow you to define which hardware you actually had access to and generate reports using only that hardware -- that would be a neat capability.

BTW, let me take this opportunity to thank John for this incredible resource, it's been an invaluable help to me.

wighty44 · Dec 25, 2015

mikec said:
The certification document gives the weight without spacers. If you want to model the effect of the spacer(s), add that weight to the rocket dry weight.... Expecting TC to handle this in general is unrealistic IMHO.

Yes, I understand and agree - I believe I made a similar comment in my post above (#37)...

mikec · Dec 25, 2015

wighty44 said:
Yes, I understand and agree - I believe I made a similar comment in my post above (#37)...

Then I guess I was confused about what you were asking in post #40.

wighty44 · Dec 25, 2015

I was trying to get a confirmation from Mr. Coker of my assumption that TC uses standard casing/hardware/motor weights for any given motor. Hence my specific example using the CTI K740 motor, and my final question, "Would I be correct in thinking..."

markkoelsch · Dec 25, 2015

wighty44 said:
Understood. However in the case of a 54mm CTI 4 grain K740, the motor could be used in 3 different 54mm casing configurations: 4-grain; 5-grain with 1 spacer, & a 6-grain with 2 spacers.

Would I be correct in thinking the weight used by TC would be representative of using the 4-grain case?

We use the weight listed in the cert data, which would be the mass of the motor as designed I.e. A four grain reload in a four grain case.

markkoelsch · Dec 25, 2015

mikec said:
The certification document gives the weight without spacers. If you want to model the effect of the spacer(s), add that weight to the rocket dry weight. Per
https://www.pro38.com/pdfs/Pro54_Case_Spacer.pdf it's 120 grams per spacer.

Expecting TC to handle this in general is unrealistic IMHO, as the number of permutations in the report would get really large really fast. It's also a small effect for many rockets.

I guess TC could allow you to define which hardware you actually had access to and generate reports using only that hardware -- that would be a neat capability.

BTW, let me take this opportunity to thank John for this incredible resource, it's been an invaluable help to me.

I think difficult is an understatement. You would need a motor file for each permutation of case/spacer. So, say there is a k700 in a four grain, but you could use it in a five and six grain case with spacers- that is three motor files. Actually six files as you need it in both Rse and eng formats.

wighty44 · Dec 25, 2015

markkoelsch said:
We use the weight listed in the cert data, which would be the mass of the motor as designed I.e. A four grain reload in a four grain case.

Thank you for confirming my assumption.

mikec · Dec 25, 2015

markkoelsch said:
I think difficult is an understatement. You would need a motor file for each permutation of case/spacer.

From the single motor file, the software could calculate the additional mass for each permutation and simulate accordingly for each, but that would only make a lot of sense if it had some idea of what you actually had access to. For example, if in your profile you told it you had a CTI 54mm 3G case and 1 spacer, it could produce a list of sim results with all the 3G reloads and 2G reloads plus spacer. But whether this is really worth doing or not is debatable. Spacers don't really weigh that much compared to the overall rocket in most cases.

woferry · Dec 25, 2015

markkoelsch said:
I think difficult is an understatement. You would need a motor file for each permutation of case/spacer. So, say there is a k700 in a four grain, but you could use it in a five and six grain case with spacers- that is three motor files. Actually six files as you need it in both Rse and eng formats.

I don't understand. Why would a different casing require a new motor file? It wouldn't affect the thrust curve at all, it's just extra mass and a different Cg. These are parameters specific to the rocket, not the motor. I can adjust the mass & CG of my rocket in ThrustCurve and it doesn't need new motor files, it just needs to re-run the simulations using the motor files it already has, right? The standard weight of the spacers should be easy and their position known, and the extra weight of the lengthened case and it's affect on the CG for the overall case also shouldn't be that hard I'd think, now sure somebody would have to actually take those measurements. I only have a few cases myself since I use the spacers rather than having every possible case size, so I could collect measurements on the few cases I have but there's no overlap with what I have.

Len B · Dec 25, 2015

woferry said:
I don't understand. Why would a different casing require a new motor file? It wouldn't affect the thrust curve at all, it's just extra mass and a different Cg. These are parameters specific to the rocket, not the motor. I can adjust the mass & CG of my rocket in ThrustCurve and it doesn't need new motor files, it just needs to re-run the simulations using the motor files it already has, right? The standard weight of the spacers should be easy and their position known, and the extra weight of the lengthened case and it's affect on the CG for the overall case also shouldn't be that hard I'd think, now sure somebody would have to actually take those measurements. I only have a few cases myself since I use the spacers rather than having every possible case size, so I could collect measurements on the few cases I have but there's no overlap with what I have.

Really, this is the best way to handle the spacer use. A user (could) make a motor file for each permutation but this is simpler and doesn't require anything new on TC.

JohnCoker · Dec 26, 2015

wighty44 said:
Understood. However in the case of a 54mm CTI 4 grain K740, the motor could be used in 3 different 54mm casing configurations: 4-grain; 5-grain with 1 spacer, & a 6-grain with 2 spacers.

Ah, OK I didn't realize that. That would potentially make the rocket more stable than one would expect by using the shorter case, but also with higher lift-off mass. I don't think the ThrustCurve.org Motor Guide simulations are precise enough for it to matter, but it might matter with more sophisticated simulations.

wighty44 said:
Would I be correct in thinking the weight used by TC would be representative of using the 4-grain case?

I'm guessing that's true, but it depends on what CTI delivers to CAR for testing. They do list the case length, so that could be used to double-check. I didn't see the K740 on the CAR site, but here's the data sheet for the K750: www.canadianrocketry.org/mcc_motor.php?c=1&motor=2352%20K750-18A

JohnCoker · Dec 26, 2015

UhClem said:
Missing from the list of choices in the poll is the XML API.

I'll preserve that in the new site since RockSim and OpenRocket also use it, not to mention the smart phone app. I will also introduce a more modern JSON/REST API for future projects and easier web mash-ups.

JohnCoker · Jan 3, 2016

Thanks to those who responded to the poll. It looks like all the major features have significant usage, so I won't obsolete anything in the new site. I will however try to make it more obvious that there are multiple ways of finding motors.

Just a quick note that if you registered with an invalid email address, your account will be deleted soon. You can fix your email address on the My Stuff page: www.thrustcurve.org/login.jsp.
For those who don't want to share their email address, note that you can hide it by un-checking "Allow others to see your email".
(I've already started working on the database migration and was surprised by how many people entered garbage.)

JohnCoker · Feb 2, 2016

Now that the implementation of the new site is well underway, I put together a list of re-implemented and new features:
TODO page on GitHub

I tried to include the feature requests made in this thread. If you suggested features here, please double-check that they made to the to-do list. (They may not all get done, but I at least want to not forget any.)

wighty44 · Feb 2, 2016

I would like to see the units for the parameters in the downloaded motor list (Excel CSV) align with those chosen by the user in the Display Settings. Presently when I select inches & feet, the downloaded velocities & altitudes that are in those files are shown in meters & meter/sec.

wighty44 · Feb 7, 2016

Using Thrustcurve today I received this error message related to the download files:
Unable to generate download file from guide run!
Client: 73.29.242.230
Protocol: HTTP/1.1
URI: /motorguide.jsp
Method: GET
Query: rocket=4687
java.io.FileNotFoundException:

ThrustCurve.org future directions

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