OpenRocket 22.02: A very quick introduction to pods

[neil_w]

Surely you've already downloaded and installed the new OpenRocket beta? If not -> https://www.rocketryforum.com/threa...blic-beta-is-underway-download-it-now.171295/

One of the big new features in this version of OR is pods. @H. Craig Miller wrote up a quick overview over on the OpenRocket wiki (https://wiki.openrocket.info/Assembly_Components_Basics); here I want to walk you through the three most common uses for them.

Part 1: Basics, and Pods on the body

Let's start with the simple case of something that looks like boosters attached directly to the main airframe.

The Pods component is in the new "Assembly Components" section up at the top:

The first important thing to note is that a pod set can only be attached to a body tube. This will hopefully change in future releases, but that's the way it is for now. In the screenshot above, the body tube is selected in the tree view at left, so the Pods button is enabled. Clicking that button adds a pod set and brings up the config window:

The Radius Positioning Method determines how OR will calculate the distance of the pod components from the center of the rocket. The most commonly useful option, shown selected, is "Position Relative to the Component's Surface". This method means that the Radial Distance value will define the distance from the surface of the airframe to the surface of the pod body. If we want our pods to be mounted to the surface of the body, we leave Radial Distance set to zero and we're good to go.

• We've already discussed setting "Radial Distance" to zero.
• "Angle" determines the position of the first pod, just like a fin set. We'll set it to 60 so the pods will be positioned between the fins.
• "Number of Copies" is how many pods are in the set. We'll use three, one between each pair of fins.
• The last two positioning settings are just like any other component that gets mounted to a body. We'll keep our pods flush with the tail of the rocket.

Now, we add components to the pod set just like we were building a new rocket. We'll start with a nose cone...

Then add a body...


And voila! Note that we could add anything we want to the pods, including more pods!

 

[neil_w]

Part 2: Pods on Fins

Sometimes you might want the pods to go on the ends of fins. Lets take the pods from the previous post and move them there.

Edit the pod set:

• Because our fins are 1.25" high, we set Radial Distance to that value, which means that the surface of the pod body tube will be exactly at the end of the fins.
• We change the Angle back to 0, so it matches the fins.
• And finally, we set the offset to 1/2 inch, which will move the pods back and look a bit better.

And the result is...

 

[neil_w]

Part 3: Fins on Fins

So far so good. What about fins on fins?

First let's delete the nose cones, and edit the body tube on the pods:

We're setting body tube length and diameter to "0". This is the infamous "phantom body tube", which will be invisible but will give us something to which to attach some fins.

NOTE: when you use a phantom body tube you'll get a warning in the corner of the screen, because OR isn't quite sure how to simulate it. In practice, the error is likely to be very small, but be aware.

Back to the matter at hand: let's add a trapezoidal fin set to the phantom tube:


Two fins, set at 90 degrees. For each pod, Zero degrees represents the direction pointing directly away (perpendicular) from the body tube. So if we set fin rotation to zero, our pod fins would be coplanar with the main fins, which is not what we want. By setting them to 90 degrees, they'll be perpendicular. And here they are:



So now you're ready to go build an OR model of a T-LOC, or an Interceptor, or darn near anything. Like, say, this (sorry for the shameless self-promotion):

Let's see what you can do!

 

[K'Tesh]

Let's see what you can do!

Nice Tutorial!

Ok... Here's an example:

 

[neil_w]

On the announcement thread, @DeltaVee asked about the fin fairings on the Saturn V.

If you use conical nose cones for the fairings, and set the pod's radial distance to 1/2 the diameter of the nose cone, you can come close. Then you can attach freeform fins directly to the cones, and voila:

This a very quick and dirty hack job, but you get the gist. It will not simulate completely accurately (OR doesn't know that the nose cones are partially inside the airframe) but I can't say how far off it would be.

 

[DeltaVee]

On the announcement thread, @DeltaVee asked about the fin fairings on the Saturn V.

If you use conical nose cones for the fairings, and set the pod's radial distance to 1/2 the diameter of the nose cone, you can come close. Then you can attach freeform fins directly to the cones, and voila:
View attachment 506552
This a very quick and dirty hack job, but you get the gist. It will not simulate completely accurately (OR doesn't know that the nose cones are partially inside the airframe) but I can't say how far off it would be.

Nice! I'm also glad I don't have to rely on an installer... I like that you guys kept the options open. I keep multiple VMs on my system and use version appropriate ones to run Java programs via hand crafted shortcuts.

 

[Bat-mite]

Very slick, Neil.

 

[BigMacDaddy]

I finally installed the new version... Thank you for sharing this clear overview of pods.

Can we import pods via Rocksim file format? Seems no (at least for a rocket I wanted to load just now), any work arounds? Does anyone know if there are future goals to make OR pods compatible with RKT pod format / imports?

 

[neil_w]

I finally installed the new version... Thank you for sharing this clear overview of pods.

Can we import pods via Rocksim file format? Seems no (at least for a rocket I wanted to load just now), any work arounds? Does anyone know if there are future goals to make OR pods compatible with RKT pod format / imports?

I wouldn't rule it out, but it's not straightforward. OR pods behave somewhat differently from Rocksim pods. There are some future plans to extend OR pod functionality to be closer to Rocksim; at that point it might be easier to do this.

 

[BigMacDaddy]

I wouldn't rule it out, but it's not straightforward. OR pods behave somewhat differently from Rocksim pods. There are some future plans to extend OR pod functionality to be closer to Rocksim; at that point it might be easier to do this.

Any work around to modify the RKT file to make it import Pod data?

Wow I see what you mean -- I am going to try to dig into the RKT files to figure out what is the critical inforamtion to at least let us quickly re-create the pods that exist in an RKT file.

 

[Tobor]

I wouldn't rule it out, but it's not straightforward. OR pods behave somewhat differently from Rocksim pods. There are some future plans to extend OR pod functionality to be closer to Rocksim; at that point it might be easier to do this.

This begs the question, Will Tim be cross with OR devs for creating such functionality?

 

[neil_w]

This begs the question, Will Tim be cross with OR devs for creating such functionality?

Software is commonly inspired by other software. This is generally not something to be concerned about, as long as we don't cross a line into copyright infringement. Also, remember that OpenRocket functionality already overlaps Rocksim. I'm sure Tim would prefer that he had the market all to himself (who wouldn't?), but that isn't life.

Specifically regarding pods, our interest would not be in cloning Rocksim pods, just extending the functionality of OR pods to be more useful. At some point they may acquire sufficient functionality to support more reliable mapping from Rocksim to OR. There are almost certainly a subset of pods in Rocksim designs that could translate. The work on our side just hasn't been done yet to figure out what we can and can't do, and how.

 

[BigMacDaddy]

Software is commonly inspired by other software. This is generally not something to be concerned about, as long as we don't cross a line into copyright infringement. Also, remember that OpenRocket functionality already overlaps Rocksim. I'm sure Tim would prefer that he had the market all to himself (who wouldn't?), but that isn't life.

Specifically regarding pods, our interest would not be in cloning Rocksim pods, just extending the functionality of OR pods to be more useful. At some point they may acquire sufficient functionality to support more reliable mapping from Rocksim to OR. There are almost certainly a subset of pods in Rocksim designs that could translate. The work on our side just hasn't been done yet to figure out what we can and can't do, and how.

Thank you - and having pods is better than not having pods but I always try to start with an existing design file where I can. I wondered why everyone was building pod designs from scratch instead of showing an RKT file import. Now I know.

 

[neil_w]

I added this as a feature request: https://github.com/openrocket/openrocket/issues/1350

[edit: BigMacDaddy beat me to it.... https://github.com/openrocket/openrocket/issues/1348]

 

[Starfire73]

I'm curious. Does OR calculate the CP and Cd effects on the pods or are they just cosmetic?

 

[neil_w]

Pod aerodynamics are fully incorporated., to the best of the app’s ability.

 

[Buckeye]

This begs the question, Will Tim be cross with OR devs for creating such functionality?

When TVM opened the rkt file format with XML 20+ years ago, he actively lobbied programmers to write add-ons, utilities, and companion software. He probably didn't expect a complete duplication of RockSim, but it happened, and he can't really complain.

 

[thzero]

When TVM opened the rkt file format with XML 20+ years ago, he actively lobbied programmers to write add-ons, utilities, and companion software. He probably didn't expect a complete duplication of RockSim, but it happened, and he can't really complain.

It's not a duplicate. There have been plenty of "simulation" in this space over the years. Thrustcurve has a nice list of them.

It's good that the file specs have been published to allow some form of interoperability.

 

[bibbster]

How would one go about attaching a pod at the same angle to the top most angled part of the fin, the longest side, on the design below? I've fiddled with it long enough. I give up. lol

 

[neil_w]

Sorry, you can't angle pods like that. They must be parallel to the main airframe.

 

[bibbster]

Doh! Any way to so something similar instead of a pod? I'm modeling something with dowels that go from the fin and angle forward and attach to the body tube.

 

[neil_w]

Doh! Any way to so something similar instead of a pod? I'm modeling something with dowels that go from the fin and angle forward and attach to the body tube.

Just do them as regular fins. You'll probably get a jagged fin warning, just ignore.

 

[neil_w]

Found it... here is a design I was messing with way back when, similar concept.

 

[bibbster]

Thanks, Neil! I think this will do for my Dynamic Carrier 2x upscale...

 

[bibbster]

I'm getting a "Too many parallel fins" error. I add a motor and apogee is less than a foot.

 

[neil_w]

Too many fins can be ignored… 1ft apogee is usually a motor problem… post the file if you want help

 

[bibbster]

Thanks, Neil. I'm obviously overlooking something. See attached.

 

[CalebJ]

Thanks, Neil. I'm obviously overlooking something. See attached.

You're trying to launch a 1.24kg rocket on an E9?

 

[neil_w]

Just spitballing but this might be part of the problem


Your nose cone is 27 oz on its own (pretty sure you don't want 1" thick walls on a plastic nose cone).

Rear fins are currently cardboard, making them quite heavy.

Basically you need to go through all the components and check things like wall thickness and material.

Even after you finish cleaning it all up, you're probably still not going to get a 2.6" rocket into the air on an E9.

 

[bibbster]

What a mess on the weights! I clearly didn't check those. The entire rocket only weighs 11oz w/o the motor. Thanks for the extra eyes guys!