Assistance needed for MDRM altitude/apogee simulation

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redleder

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I downloaded the RocketSim software and found out that is does not currently support macOS Sierra. I am ready to launch my MDRM and would like to learn a bit more about what the projected altitude and apogee is going to be so I can properly setup my Jolly Logic Chute release. Can someone help me generate a SimOutput report for this? I plan on using the following motors; AeroTech G80-7T and the Estes G40-7W. Any guidance or advice would be really appreciated.

Thank you,

Jarod
 

MikeyDSlagle

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What is the weight of your rocket ready to go minus the motor? I can run some sims in a bit if someone doesn't beat me to it.
 

smugglervt

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What is the weight of your MDRM and CG location?
 

redleder

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Thank you for offering to help out. I will get that information as soon as I get home. Not at home at the moment. Thx!


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redleder

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Without a motor, retention ring and wadding but all of my other stuff it weighs approximately 945gms, 2.0814lbs or 2lbs 1.35oz. CG is approximately 26.35in. from the tip of nose cone. This might change a little bit as the decals are not on yet and I might spray another coat of clear on it.

Thanks for the help.
 

MikeyDSlagle

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A quick down and dirty with what a file I found on TRF: 30.9 oz rocket

Openrocket had two files for the G80-7, both are similar

View attachment 313565

View attachment 313567

View attachment 313570

View attachment 313569

Set your JLCR to 500 and you should be fine. These were ran with 6 mph winds.

I flew my 4" Cowabunga with a JLCR set to 500. It fell at 51 fps before chute opened. It's not letting me upload anymore pics ATM. Anyway. Using the 51 fps as a base your rocket should land within 200 feet. I flew my Cowabunga on a super windy day to 1500 and it still landed fairly close. Well it landed on a power line is what it did, but it wasn't far away.

*edit* I ran more sims with your weights and added 2 oz for wadding, it lowered the altitudes some and your deployment speed on the G40 is around 49 FPS, should be okay. You're pushing it with that motor, but it should clear the rod with enough speed. It just may arc quite a bit. When it lets me, I will upload the new files.

Good luck.

Mikey D
 
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redleder

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Thanks Mikey, that is close enough for what I needed today. When the paper specs says 500 ft and you are thinking of setting the altitude auto chute open to 300ft it probably would not slow down enough to not damage the rocket. At least that is what is going though my head anyway. I hope you got your rocket off the power lines, that would be the worst thing after stuffing $200+ worth of JollyLogic stuff in it!
 

MikeyDSlagle

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Yeah I got it back. Hung there all night. Adept22 beeping out altitude the next afternoon when I made it back to the launch site.
Adept22 in the nose. I use it to pop the nose cone at apogee. Every HP flight so far has had electronics to pop at apogee, I don't trust the delays or me drilling them.
JLCR
Jolly Logic Altimeter 3
Loki hardware.
Yeah it would have been an expensive loss. Especially with it being right there in sight.
 

redleder

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Glad to hear you got it back. The electronic stuff is new to me, I am used to just stuffing motors in them and letting them rip-off. As my new, more advanced rockets get bigger and nicer I figure I better get it a bit under more control. Still have a lot to learn, but this forum has been awesome so far. Now if I can get the RocketSim software to work on macOS Sierra soon, that would be cool.

J
 

MikeyDSlagle

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Yeah its a bit of a bummer you bought the software and it doesn't work for you. I use Open Rocket, it's free. Don't know if it works with Apple though.
The MDRM has lots of room in the NC for electronics. I have one tried and true setup and working on another more refined setup. You may be interested in both so you can get you some electronic goodness in your nose. My new one SHOULD allow for a tracker in the nose as well.
If you like short stubbies, check out Madcow's 4" offering. Cowabunga, Tembo, and Squat. I have the first two. I love my Cowabunga. The Squat has a 54mm hole, the other two have 38mm. Upgraded my Tembo for a 54mm motor.
 

redleder

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I hear you. Good news is that it was an evaluation copy, so I haven't lost any money yet. I will have to check out Open Rocket software next. Ironically, I just bought a Cow Rockerty 4" Squat from a fellow forum member this past week. When I opened it up I immediately noticed that it needed a huge motor. A quick search said I need to be L1 or L2 certified to buy more than 1 motor and I could get 1 for certification purposes. Would be interested in feedback on motor setup for this rocket. I don't mind building or packing my own motors, I have just never done it yet.

J
 

MikeyDSlagle

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Madcow makes good kits. Though I had a few issues with the Tembo I am working on, the other two I have had no issues.

The Squat may need some nose weight, especially on the 54mm motors. My Cowabunga (Wastelander) flew just fine on an H148R with no nose weight...but I do have a bay in the nose, so it actually had about 4 oz in the shoulder.

The Squat will probably fly on high thrust G's and maybe even F's, you would have to adapt down to fly those though. Look into getting an Aeropack adapter for this purpose. They are a bit pricey but they are simple and they work. Because it will cost you a Grant to fly the smallest 54mm, 50 bucks. You can do a 38mm for half that, some 29mm are a bit less. And only the loads for the "Soda Can Motors", AT 54/426 and CTI Pro54 1G can you fly on level 1, after that you will need level 2. I wouldn't worry with trying to build it to fly the G's and F's, save your MDRM for that and build the Squat for level 1 and 2 motors. You will find a sweet spot with nose weight to where it will fly on the Soda Cans and can also handle some J's.

Nearly all of my experience is with Aerotech motors, and a bit with Loki, so that is what I will be talking about. You can usually catch good deals here on TRF for cheap motor hardware. I have over a dozen motors and have only flown 4 of them. I've never paid full price for any of my hardware save for one closure.

The Squat will fly nicely on 38/240 motors with the adapter, Loki and Aerotech. Wastelander loves em.

You'll have folks tell you to grab an Aerotech 29/40-120 to start out with. And that is sound advice. Less money gone if you have a blowout. My only failure has been with that case though. But don't shy away from the bigger ones. There is really nothing to it. My first reload was the G53 in that case. My second reload was an H123 in the AT 38/240 for my level 1 cert flight. Just follow the instructions. Having a mentor helps. Someone to give you pointers. It wouldn't hurt to assemble a few in the 29/40-120 case just to get the feel.

I would say grab an Aerotech 38/240 or 38/360 motor for the Squat. The 38/240 will give you nice flights to 1500 feet or so. The 38/360 will probably take it to 2000. Still within sight. And that case offers all their propellants. Then you can build up your 38mm hardware collection with more cases. 54mm can get pricey in a hurry. Hardware and reload.

Now that I have a JLCR, Wastelander will probably ride a 38/600 motor soon.

Mikey D
 

noffie79

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Here's a great video from Apogee on building an AT motor. The example is for the 29mm 40-120 case, but even the 38mm and 54mm stuff goes together the same way. Even when you watch the video, always read your assembly instructions. Have fun and good luck!
https://youtu.be/g0GsbQS7GKI
 

Swissyhawk

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I don't think anyone mentioned it, but https://www.thrustcurve.org/ is a great way to do a quick simulation. You input the diameter of the rocket and the weight, and it will give launch velocity, altitude, and delay time. It may not be as accurate as using Rocksim or OpenRocket, but it's easy and for most rockets, it gets you close enough to what you need.

My MDRM is 35 oz. Thrustcurve has a projected altitude of 875 ft with the G80. It recommends against the G40 because the speed at the end of the launch rail (6 ft) is too slow (45 ft/s). If I increase the rail to 7 ft - the launch velocity increases to 48 ft/s and the projected altitude is 639 ft. However, the delay time is only 4 secs. I probably wouldn't use a G40-7. A 7 second delay is probably way too long.
 

redleder

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Guys, all of this information has been very helpful. Thank you, I will be mentally processing all of this and researching all of the different motor information. Somewhat overwhelming it is so varied but have already learned a lot.


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ThirstyBarbarian

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I've got a couple of comments.

First, congratulations! The Mega Der Red Max is a fun rocket! It has hi-drag design that makes for great low-and-slow flights. On G motors, you'll be able to easily watch the entire flight from launch to apogee and back down. You will never lose sight of it.

I think the packaging says the maximum altitude on recommended motors is 500 feet. That's not true. Usually Estes over-estimates max altitude, in my opinion, but this time they underestimated. I've seen the rocket push 1,000 feet on G motors, which is still not incredibly high, but it's certainly more than 500! Simulations will tell you what to expect for each motor, and I expect they will range from around 500 to 900 on G motors.

Because of the low altitude, you probably don't need the Chute Release. If you want to use it just for fun, then go for it. Just be sure you set the deployment altitude below the max altitude! In other words, don't set it for 500 feet if there is any chance the rocket won't reach 500 feet. An example would be if the G40 were siimmed to just around 500 feet, but it takes off in a low arc instead of straight up, then you might not reach the max altitude, and if you don't at least reach the deployment altitude, the Chute Release won't open. Honestly, if you think you will easily recover the rocket without using the Chute Release, then you might want to fly your first couple of flights without it. As you learn how the rocket flies, then you might want to give it a try.

There are a lot of Aerotech single-use G motors that will work great in the rocket. The G80 is fast and loud, and there is not much visible flame or smoke (it's great for fast, reliable launches, but I personally prefer more effects). G79 has white smoke and flame. G78 has green flame, plenty of smoke. G77 has a bright red flame. G74 is also white smoke and flame, but it's a small G, so it burns fast and won't go nearly as high as a G79. That's also a more affordable motor. All of those should have a good speed off the launch guide and result in a reliable flight.

There are two other Aerotech single-use motors that would be marginal. G40 has white smoke and flame like the G79 and G74, but it burns much slower, so it has lower thrust, but a longer burn time. That kind of flight really compliments the slow characteristics of the MDRM, so it can be great fun. But it also means the rocket takes off slowly and has the potential to arc over for a cruise missile type flight and crash! You have to be careful with that! I'd recommend you don't start with that motor, and if you do try it, use a long rail (not a rod), calm winds, and a large field with nothing to be damaged be an errant flight. The G38 is also in that class of low-thrust G motors, and would be risky. That motor makes thick black smoke.

So you have a lot of single-use motors to choose from. You would not go wrong with one each of the G77, G78, G79, G80 motors, and that would give you a taste of the different propellant types. And and if you get into reloadables, there are even more choices!

I'm thinking that for most of these motors, you might want a 4-second delay, not 7 seconds. You will need to run the sims with your finished built weight after decals and paint to be sure. Open Rocket will tell you the ideal delay for an ideal flight to apogee. Then you need to decide what fixed delay to pick, and it's never exactly right. You need to get close and consider whether to go long or short. So if the sim says the ideal is 6 seconds, then picking 7 is probably better than picking 4. But if it is closer to being right in the middle (5.5 seconds or less), I'd err on the side of going short and pick the 4-second delay. Rockets don't alway fly straight up, so sometimes they don't go as high as predicted, and they reach apogeee sooner than the simulation says. When that happens, shorter is better. Do your sims and use your best judgement.

Have a great time with your rocket!
 

John Beans

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Thanks Mikey, that is close enough for what I needed today. When the paper specs says 500 ft and you are thinking of setting the altitude auto chute open to 300ft it probably would not slow down enough to not damage the rocket.
It's an understandable and commonly-held misconception that it takes rockets much time at all to slow down after the chute opens.
Once your chute opens, the rocket will slow to landing speed in less than 50 feet of descent. Practically speaking when your chute is fully inflated, your rocket has slowed to landing speed. I say this based on data from recording altimeters that show that the descent curve is almost immediately straight after chute deployment (not a curve, like you'd see if the rocket was decelerating on the way down).

Here are some reasons to set your release point at 500 feet or more:

1. You want your chute to open high where you can see it well (in case you lose site of it on the way up)
2. Your rocket is weathervaning upwind, and you need more time for it to blow back toward the pad
3. There are hills nearby that you might land on
4. You are nervous about how long it will take your chute to open after release (answer: practice and measure)

But NOT because you think your rocket needs time to slow down.
 

redleder

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The main reason I bought the chute release was to keep the drift on small fields to a minimum since I don't have a super large area. I figured regardless of high the rocket reaches, I could always control the release of the parachute to around 500ft.

Also, I thought I read in the manual for the chute release that it would open once it sensed that it was falling regardless if the set altitude was reached. Basically a failsafe. so if I set it at 500ft and it only reaches 490 once it sensed a decrease in altitude it would release.

Jarod
 

John Beans

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Jarod,
Yep, that's what it would do.
 

ThirstyBarbarian

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Also, I thought I read in the manual for the chute release that it would open once it sensed that it was falling regardless if the set altitude was reached. Basically a failsafe. so if I set it at 500ft and it only reaches 490 once it sensed a decrease in altitude it would release.

Jarod
Jarod,
Yep, that's what it would do.
That's great to know. I didn't know it worked like that!
 

LithosphereRocketry

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OpenRocket is a .jar.... It should work on anything that has Java (i.e. not Chrome OS). Mac is fine, I've see it work on a fairly new Macbook Pro, and everything else relatively new should work fine.
 

redleder

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OpenRocket is a .jar.... It should work on anything that has Java (i.e. not Chrome OS). Mac is fine, I've see it work on a fairly new Macbook Pro, and everything else relatively new should work fine.
Thanks for insight. I will check it out tomorrow for sure.


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TangoJuliet

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I've launched my MDRM on a AT SU G40-7 and a G80-7 off 1/4"x6' SS Rod. Both flights were perfect and I did not use a chute release. I would note though, that if you fly it on the G40 with a rod, be sure to launch it as vertically as possible to minimize any rod whip, and thus a less than desired trajectory. :wink:
 

redleder

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I've launched my MDRM on a AT SU G40-7 and a G80-7 off 1/4"x6' SS Rod. Both flights were perfect and I did not use a chute release. I would note though, that if you fly it on the G40 with a rod, be sure to launch it as vertically as possible to minimize any rod whip, and thus a less than desired trajectory. :wink:
So let's talk about "Rod Whip". So I have an InterLock launch pad and controller but I know the 1/4" rod that came with it is not that tall. Maybe 36-48" would have to double check, but know for sure it is not 6'. It sounds like that is not stout enough for it. I have 1010 rail buttons that I can install, but no rail for the launch pad. So I have a few questions; Where can get a rail? How can I easily attach it to the interlock? Or where can I get a 6' 1/4 rod that will my needs for this MDRM?

Thanks!
 

swatkat

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I've flown on the G64 W and G76 G reloads. Sims said 6 second delay. I'd say 5 seconds is about right. For the G80, which has a bit more total impulse, I'd think 6 seconds is a pretty good estimate. Mine is 32.4 Oz w/o motor. Heights are around 600-650'.
 
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