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Wrong Size fo M2020

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The Carbon

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Hello, me and my team are preparing for a rocket competition. We were given 2 engine options for us to use in our rocket. First choice is M2150 and second choice is M2020.

We have to draw rockets in for 2 options. No problem for M2150. But the dimensions of the M2020 are incorrectly given in OpenRocket. The motor length should be 893 mm, but it is given 757 mm in the OpenRocket.

How can I fix this problem?

Thanks for your help.
 

HVArcas

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What is an "M2020"? Helps to list the brand.

Lots of openrocket motor files have bogus dimensions. I think some people want to measure the liner length, some the casing length, and still others want the entire length including the narrow portion of the forward closure. maybe the aft closure, maybe not!

So, why do you need dimensions? If it is to make the hardware fit in your design, the best bet is to use the hardware dimensions, and all the major brands put (precise) blueprints online as PDF or similar.

If it is for super precise CG calculations and simulation, well I would caution against shaving down to minimal margins of stability or using overly naive rules of thumb.. but hey
 

DAllen

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Hello, me and my team are preparing for a rocket competition. We were given 2 engine options for us to use in our rocket. First choice is M2150 and second choice is M2020.

We have to draw rockets in for 2 options. No problem for M2150. But the dimensions of the M2020 are incorrectly given in OpenRocket. The motor length should be 893 mm, but it is given 757 mm in the OpenRocket.

How can I fix this problem?

Thanks for your help.
All the major motor manufacturers have schematic drawings of all their motors - CTI, Aerotech and Loki.

I am assuming you are referring to the M2020 made by CTI which is the only motor of that designation I can find on Thrustcurve. This is a Pro75 6 grain case. Those drawings can be found here:

http://www.pro38.com/pdfs/Pro75_dimensions.pdf

I would put little stock in the OR files and go off manufacturer drawings instead. Also, don't fret about getting the dimensions perfect in the sim. If they are close you'll be fine - should have little to no impact on your overall CG for the purposes of flight sims...Besides CG is not something you're going to get precise until the entire rocket is built anyways. Hope that helps.

-Dave
 

HVArcas

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I think(?) there is a new aerotech M2020 which is why I mentioned, list the mfg (that and being specific is a good idea anyway)
 

The Carbon

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What is an "M2020"? Helps to list the brand.

Lots of openrocket motor files have bogus dimensions. I think some people want to measure the liner length, some the casing length, and still others want the entire length including the narrow portion of the forward closure. maybe the aft closure, maybe not!

So, why do you need dimensions? If it is to make the hardware fit in your design, the best bet is to use the hardware dimensions, and all the major brands put (precise) blueprints online as PDF or similar.

If it is for super precise CG calculations and simulation, well I would caution against shaving down to minimal margins of stability or using overly naive rules of thumb.. but hey
Sorry for not specifying the brand. The brand is "Cesaroni".

I need dimensions because I have to prepared a detailed report for the competition and I am using OpenRocket for this report.

I checked for real motor dimensions from Pro38 site to use in CAD drawing.
 

The Carbon

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All the major motor manufacturers have schematic drawings of all their motors - CTI, Aerotech and Loki.

I am assuming you are referring to the M2020 made by CTI which is the only motor of that designation I can find on Thrustcurve. This is a Pro75 6 grain case. Those drawings can be found here:

http://www.pro38.com/pdfs/Pro75_dimensions.pdf

I would put little stock in the OR files and go off manufacturer drawings instead. Also, don't fret about getting the dimensions perfect in the sim. If they are close you'll be fine - should have little to no impact on your overall CG for the purposes of flight sims...Besides CG is not something you're going to get precise until the entire rocket is built anyways. Hope that helps.

-Dave
Thank you, I checked Pro38 site.

I need for real dimensions, because my calculations are based on the OpenRocket. The competition board wants us to use OpenRocket for the report.
 
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DAllen

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Thank you, I checked Pro38 site.

I need for real dimensions, because my calculations are based on the OpenRocket. The competition board wants us to use OpenRocket for the report.
Ok well then you'll have to get the rse file from Thrustcurve.org. I just downloaded it and it appears that has the wrong length in it too so I think its just a matter of opening it in a text editor and changing the length and then uploading it into OR. However, this is a process I am not very familiar with. Doesn't really make a lot of sense to me why that has to be so precise for them but if that's what they require...that's that.

Looks to me like OR has the M2020 dimensioned for the Pro75 5g case rather than the 6g case fyi.
 

The Carbon

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Ok well then you'll have to get the rse file from Thrustcurve.org. I just downloaded it and it appears that has the wrong length in it too so I think its just a matter of opening it in a text editor and changing the length and then uploading it into OR. However, this is a process I am not very familiar with. Doesn't really make a lot of sense to me why that has to be so precise for them but if that's what they require...that's that.

Looks to me like OR has the M2020 dimensioned for the Pro75 5g case rather than the 6g case fyi.
I solved the problem. OR > Edit > Preferences > Add New Motor.

Thanks for your help.
 
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