Madcow FG 4" Frenzy XL build thread

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That's an oddly high amount of force that you predict being required to get your drogue out. I don't use shear pins for my drogue compartment, and I use a 2.0g charge for the my main apogee charge and 2.5g for my backup. Same with my main parachute using 3x 2-56 nylon shear pins from McMaster Carr
 
That's an oddly high amount of force that you predict being required to get your drogue out. I don't use shear pins for my drogue compartment, and I use a 2.0g charge for the my main apogee charge and 2.5g for my backup. Same with my main parachute using 3x 2-56 nylon shear pins from McMaster Carr

It's just based on how much force it took to break the shear pins when I tested it myself... 2x 2-56 took 65lbs one time I tried it, so probably want 80-100lbs of force from the BP to be safe. The main should probably have 150lbs+ to be safe. I'm using 2g for both primary and secondary on the mean. Currently planning on 1.5g primary 2g backup for apogee (1.5g worked great when I was friction fitting) but I need to ground test again with the 2x shear pins.
 
Looks like I'll be flying the maiden flight this coming weekend on a J600! It won't be painted in time, but that's OK since I'll be ground testing before flight anyway and it'd be a shame to mess the paint. I may fly a second time on a K2000. The big goals this weekend are (1) shake down (2) get a better sense of the drag situation and see if it's possible I can fly this under 10k on an M. The camera shrouds are nice and draggy and I won't sand too well :) I can get openrocket to sim around 9k, and I canalso get it to sim to 11.5k depending on settings.

Let's talk AV bay. I have two eggtimer quantums with two batteries each, so I'm using two DPDT switches, one for each altimeter. The switches are mounted to the inside wall of the switch band with holes cut to make the toggle accessible. To make the avbay fully removable, I'm using powerpole connectors to connect the switches to the main board. Here are the switches with wires soldered on and connectors crimped.
IMG_20170429_143447.jpgIMG_20170429_152908.jpgIMG_20170429_143133.jpg

Here's a diagram showing my wiring for each altimeter. It isn't all that interesting:
image


I designed a laser cut wood assembly to hold the quantums, connector jacks and batteries. This is the top. As you can see, one bulkhead is semi-permanently attached (wires are soldered on), while the other is removable using more powerpole connectors. The two sets of jacks in the bottom are where the switches plug in.
IMG_20170429_152133.jpg

This is the bottom of the board. You can see the 4 wells for batteries and the JST connectors run to each well.
IMG_20170429_152207.jpg

This is what it looks like with the batteries put in. A thin piece of plywood slides in over them, locking them in the wells. I use a pin then (middle right side) to keep the plywood in place.

IMG_20170429_152835.jpg

I'm pretty pleased overall. Everything is very very secure. It's certainly on the heavy side, but I'm not concerned at all about that for this rocket and it was fun to design and build.
 
Av-bay looks nice. Also looks hefty. Should aid in trying to keep large motors low.

I think I'll try and make the trip up next weekend. I've got a K740 that I can't keep below 10k unless it's in my Frenzy. But if I can get my hands on an L910 I'll fly that instead.
 
Av-bay looks nice. Also looks hefty. Should aid in trying to keep large motors low.

I think I'll try and make the trip up next weekend. I've got a K740 that I can't keep below 10k unless it's in my Frenzy. But if I can get my hands on an L910 I'll fly that instead.

It is hefty indeed :) Though the rocket seems to be at a weight where a pound up or down doesn't have a big effect.

No joke, I'm seriously considering mixing a small amount of glitter into my future+simplegreen clearcoat when I paint the rocket (not before this weekend). Should aid with visibility and definitely add some drag :) I won't use a lot, but I was inspired after seeing a sculpture a month ago that had been finished with a small amount of glitter mixed in to the final coat and it looked pretty cool.

Let me know if you'll be able to come this weekend, it'd be great to meet and person and I'd love to see your Frenzy.
 
The glitter would probably aid in visibility quite a bit. That being said, in early April I had visibility on it all the way up and down from 12,400'. Granted at altitude all I could see was the smoke trail and then the drogue chute. But visual tracking was nice to have.

But yes I'm trying to see if my weekend is open and if it is I'll be on my way up to Maine. The drive is only about an hour and a half for me. Will be worth it even if I only get one motor off.
 
The glitter would probably aid in visibility quite a bit. That being said, in early April I had visibility on it all the way up and down from 12,400'. Granted at altitude all I could see was the smoke trail and then the drogue chute. But visual tracking was nice to have.

Wow would've loved to see that flight. How much does your Frenzy weigh fully loaded except for the motor case/reload? L395 looks pretty slow off the rod with my build though it'd be tempting! And where did you go to fly it to 12400? It looks like the L395 would take it nearly as high as an M1101.
 
Looks like the launch this weekend may be canceled :-( so I won't be able to fly until June 3 most likely.

I'm looking at motors. The first flight will be on a J600 that I've already bought to 2k or so feet. I'm eyeing the K2045 for the second flight to 3.5k or so to serve as kind of a stress test (acceleration and deceleration) before sending it up really high. I don't own 75mm hardware yet, and I was going to put that off until I'm ready to do the cert flight in case the rocket gets lost before then. I'm also considering just doing DMS for the cert.
 
Ive got a k2045. Still trying to figure out what I want it to go in. But I flew my frenzy in Maryland at LDRS this past April for that flight. The L395 is indeed very slow. Fully loaded it was 31 pounds. The RSO was very reluctant to let it go but MDRA staff (who had seen my fly the same motor in the same rocket the previous year) let it go.
 
Ive got a k2045. Still trying to figure out what I want it to go in. But I flew my frenzy in Maryland at LDRS this past April for that flight. The L395 is indeed very slow. Fully loaded it was 31 pounds. The RSO was very reluctant to let it go but MDRA staff (who had seen my fly the same motor in the same rocket the previous year) let it go.
Woah 31lbs? Isn't the l395 load plus case around 12.5lbs? So your frenzy without motor is 18-19lbs? Btw I think I found your flight on youtube when searching for l395, looked awesome :)
 
Ground tested again now that I'm using 2x 2-56 pins for the drogue separation. 1.5g (which is what I used when I was planning to friction fit) was enough to shear the pins but the rocket didn't separate as much as I'd have liked, so I'm going with 2g as shown in the video below. I'm also using 2g for my main charges so on the plus side I don't need to worry about messing up on launch day and mixing up where each size charge goes - they are all the same size now!

[video=youtube;pQtiKHUq_ZQ]https://www.youtube.com/watch?v=pQtiKHUq_ZQ[/video]
 
Flew the maiden flight on a CTI J600 to 1651 feet. Everything worked perfectly, including the pair of video cameras I mounted to opposite sides of the rocket. I'm going to try and turn that into a 3d video, but for now here is a composite video of those two cameras and the ground camera synced up:

[video=youtube;CP_baSY0c6g]https://www.youtube.com/watch?v=CP_baSY0c6g[/video]

The video is pretty high resolution because of the combined cameras, so feel free to go to full screen and enjoy!

It looks the rocket falls around 60-65fps under the 15" drogue, and (as expected) around 18fps under main.

I've also purchased my 75mm hardware, hoping to try for my L3 late this fall down at MDRA. Between now and then I'd like to fly on one of the K2000ish Vmaxes to try and test it out under a harsher flight without risking losing it, and maybe another K or two.
 
Congrats on your maiden flight! I was impressed with the lack of rotation. Your fins must be lined up well with the body tube. (I'm slowly working to correct my fin slots)
Do you have and pictures of your camera mounts?
 
Congrats on your maiden flight! I was impressed with the lack of rotation. Your fins must be lined up well with the body tube. (I'm slowly working to correct my fin slots)
Do you have and pictures of your camera mounts?
Thanks! Yeah the two things I was happiest with about the video were:
1) Very very little rotation during the boost (the lens distortion makes it hard to tell exactly, but I'm guessing 30 degrees total from liftoff to apogee)
2) My paint job is shiny enough to see all sorts of awesome reflections off the body and fins :)

Regarding rotation, I was pretty sure that my fin slots weren't all that perfect (pretty certain they were worse than yours based on the measurements you gave in your thread), but unlike you I didn't try and correct them since I didn't trust I had the tools/skill to do a better job. I also thought the bevels weren't perfect either, and I had to sand the fins some to make them all the same size. I used a jig to mount them as perpendicular to the rocket and self-aligned as possible, but the slots are the biggest determinant of rotation. As such, I was pretty shocked at how little rotation there was, though to be fair this was a pretty low-key flight. I'm pretty sure there will be a lot more than 30 degrees total rotation when I let her rip :)

I don't have a closeup of the camera mounts and I'm traveling so I can't take any pictures until next weekend. However, here's a full-length shot of the rocket, and you can one of the two gray camera shrouds about 3 feet up:
IMG_20170531_222259.jpg

The cameras are 808 type keychain cameras with a #16 lens. I have one mounted in-line with a fin and the other between the other two fins. This seemed to be the least likely placement to cause any effects on the rocket flight. I used these shrouds from additive aerospace, and attached them with 4-40 screws into standard 4-40 nuts that I epoxied to inside of the airframe. The shrouds work great, with the only annoying thing for my purposes being that the 808 camera has an offset lens, so I'm going to need to do some funny cropping to line the videos up to try and make a 3d video (you can see in the video above that the rocket body isn't perfectly lined up between the two cameras).

All in all though, I couldn't have had a much better first flight! Though the shrouds aren't draggy enough to keep me under 10k on an M, so I won't be doing that in Maine....
 
I think the long boards you clamped to your fins with the bevel cut edges that sat on the booster tube helped with fin alignment. The slots that Madcow put in my booster tube were a sloppy fit to the fins, and then after sanding the fins, there will be even more slop in the fin slot. I think your jig then forced the fins to align with the body nicely, using any available slop in the slot-2-fin joint.

Regarding your camera mounts, I am familiar with those same units.. in fact I have both the 808 and Mobius versions for 4" airframes. Would you believe that I simply drilled and tapped my 4" FG booster tube for 3mm metric and used four 3mm nylon screws threaded into the thin body tube to secure the camera? After tightening the screws, I simply used a razor to cut them off flush on the inside of the body tube. It's worked perfectly for over 10 flights up to 1000 ft/sec so far... and even survived being dragged through a bumpy plowed hard dirt farm field for about 15 minutes without breaking. If I wanted to spend more money, and I don't, I would put one of the new camera enclosures and shrouds that Madcow is carrying... I forget the name of the manufacturer, but they are nice with a carbon fiber fairing that covers just the camera lens which has been removed from the camera body to minimize how much the camera protrudes into the airflow.

That really was a nice first flight. I just ran a quick sim on my OpenRocket FG Frenzy 4" XL and the CTI J600RL sims to 2,500 ft! I don't have the camera shrouds modeled, but they can't explain the difference between 1,600 and 2,500 ft. The model shows 249 oz with this motor. I did not add any adapter mass to convert from 75mm motor mount to the 38mm case either. What does your simulation predict for the J600? That's a 998 N-sec impulse, correct?

I'm glad you posted this.. I will motivate me to work on my rocket and stop fixing things around the house!
 
I think the long boards you clamped to your fins with the bevel cut edges that sat on the booster tube helped with fin alignment. The slots that Madcow put in my booster tube were a sloppy fit to the fins, and then after sanding the fins, there will be even more slop in the fin slot. I think your jig then forced the fins to align with the body nicely, using any available slop in the slot-2-fin joint.

Regarding your camera mounts, I am familiar with those same units.. in fact I have both the 808 and Mobius versions for 4" airframes. Would you believe that I simply drilled and tapped my 4" FG booster tube for 3mm metric and used four 3mm nylon screws threaded into the thin body tube to secure the camera? After tightening the screws, I simply used a razor to cut them off flush on the inside of the body tube. It's worked perfectly for over 10 flights up to 1000 ft/sec so far... and even survived being dragged through a bumpy plowed hard dirt farm field for about 15 minutes without breaking. If I wanted to spend more money, and I don't, I would put one of the new camera enclosures and shrouds that Madcow is carrying... I forget the name of the manufacturer, but they are nice with a carbon fiber fairing that covers just the camera lens which has been removed from the camera body to minimize how much the camera protrudes into the airflow.

That really was a nice first flight. I just ran a quick sim on my OpenRocket FG Frenzy 4" XL and the CTI 600RL sims to 2,500 ft! I don't have the camera shrouds modeled, but they can't explain the difference between 1,600 and 2,500 ft. The model shows 249 oz with this motor. I did not add any adapter mass to convert from 75mm motor mount to the 38mm case either. What does your simulation predict for the J600? That's a 998 N-sec impulse, correct?

I'm glad you posted this.. I will motivate me to work on my rocket and stop fixing things around the house!
My rocket ended up heavy - 16lbs or so with no motor (though including all batteries, cameras, tracker, etc), and then another 0.5lbs for a pair of aeropack adapters to get me from 75mm to 38mm. That left it at 18.5lbs on the pad for the J600 which yeah is about 1kNsec.

My openrocket file for this is at home (I'm traveling) so I can't check the specifics, but I did add the camera shrouds to the model as a pair of thick fins with dimensions chosen to match the shrouds. I think I may have left them and the main fins as "rounded", and left the finish as smooth paint, and the sim was just about the same as the actual flight after you account for taking off 8 degrees from vertical in fairly substantial winds (12mph at surface if I remember correctly)
 
Very nice on it's first flight. Wish I was there to see. I'm going to re build the av-bay on mine before I fly it again. Got a lot of things I want to correct from the first one I did on it.
 
Very nice on it's first flight. Wish I was there to see. I'm going to re build the av-bay on mine before I fly it again. Got a lot of things I want to correct from the first one I did on it.
Thanks! The next MMMSC launch I might be at is July 15. I'd like to fly on the 75mm K2000 next, but that's contingent on them getting back in stock and the wind playing nice :) Barring that, perhaps a 54mm K445

I'd be curious to hear about what you are changing about your av bay - going to be on a build thread?
 
Not going to be on a build thread. But I've been using key switches to arm/disarm my electronics. While they look cool and are pretty robust, but since they are mounted to the vent band, it requires me to use some pretty lengthy wires so I can actually take the av-bay lids off, so I'm going to replace them with screw switches mounted to the sled. Also I need to accommodate for my MissileWorks RTx unit. Going to add charge cups, replace the terminal blocks, and tidy up the wiring.
 
Welp.... sad news. The rocket lawn darted into the woods (and I couldn't find it) this past weekend on a 75mm K510. This was quite a shock to be honest - I felt quite good about the redundancy of my altimeters, switches, charges, batteries and circuits (completely independent systems). I know for a fact that I had full continuity on all charges and that both the altimeters were armed, and both the drogue and main sections were attached with shear pins that had been well ground tested.

The quantum altimeters that I used (two of them) have a failsafe mode where if they detect free fall they deploy the main. This mode was enabled. The fact that I don't believe there was any separation event at all suggests that both altimeters were non-functional OR somehow both the main and drogue sections of the rocket were jammed.

My working theory is the following: I was annoyed by the noise in the altitude graphs from the previous flight and I thought it came from the vent hole being too close to the altimeter pressure sensor, so I constructed a plastic shield that I placed over the altimeters (with some space) to block direct gusts from the vent holes. I thought there was plenty of space for air to move around the shield, but perhaps not? That's the only change I made from previous successful flight, and it's the only thing I can think of that would cause not a single event to occur off of the two fully redundant altimeter and charge circuits. My theory is it would have prevented lift-off detection perhaps?

After I got home, I realized that I could probably guess with some accuracy where the rocket landed because I had used a compass and my phone to direct the angle and bearing of the launch rod, and used a multi level wind extension in open rocket to input the winds at different altitudes. I don't know when I'll be able to get back up to Maine though to look, so knowing this doesn't do me much good.

So... yeah. I'm pretty bummed. And I had just put together plans to go down to MDRA in Jan for the L3 attempt. Oh well. Time to go build a new rocket though! I'm currently working on a Blackhawk 38, but I'm eying the madcow terminator 5 as my next model to use for L3.
 
I'm sorry to read this. I know you put a lot of time and thought into this rocket. I doubt that the "gust shields" you placed around your altimeters prevented them from sensing pressure. Did you have your EggFinder on? Did you get any usable position data from the flight? If you use the LCD receiver, I'm pretty sure it stores the last received position in memory. That last position can be looked at even after you shut off the LCD and turn it back on. Let me ask a bunch of obvious questions.. perhaps it will jog something useful here...
What common mode failure could have prevented both of them from deploying?... Bad igniters.. unlikely. Bad powder.. What type of powder do you use for deployment, 4F Black Powder? Low battery voltage? What type, voltage/mAh batteries did you use for your Quantums? How many volts were packs at after your armed the Quantums over WiFi? (I'm assuming you verified both drogue and main continuity for each quantum on the arming page.) Could something have broken off and disconnected both the altimeters during the boost?
I was reviewing your excellent flight video.. and though I may have noticed something just before the drogue deployment... Listen for the noise at 28 seconds in the video.. could that be a primary drogue charge going off, but not separating?.. or is that a quick link clanking on the side of the rocket at nose over just before deployment? I hope you are able to get back there and find this rocket. I can't imagine how it must feel to loose it.
 
I'm sorry to read this. I know you put a lot of time and thought into this rocket. I doubt that the "gust shields" you placed around your altimeters prevented them from sensing pressure.

I agree with your skepticism whole heartedly. I wasn't worried in the slightest about this problem when I made the change. My only thought though is that perhaps the sides of the plastic were touching the edges of the body tube. Here is what the bay looked like before the shield was added:
IMG_20170413_214415.jpg
The plastic shield I added sat on top of the wooden posts and was the same lateral width as the board. It ran from post 1 to post 4 counting left to right, so it sat right over both altimeters. I've drawn it in red:
ex0nZBOpY77.jpg

I'm wondering if perhaps it was touching the sides of the body tube (I don't think it was but maybe...), then the only way for air to get to the altimeters would be through the end, and maybe that obstruction was enough to prevent launch detection from happening?

Did you have your EggFinder on? Did you get any usable position data from the flight? If you use the LCD receiver, I'm pretty sure it stores the last received position in memory. That last position can be looked at even after you shut off the LCD and turn it back on.
Eggfinder was on and I had a track in the Rocket Locator app. Track wasn't useful - the rocket never was slow enough for long enough to have a reasonable GPS lock. The rocket definitely ended up in the woods and the track never left the field. The predicted impact point from open rocket with all the winds dialed in was 43°18'26.6"N 70°53'36.5"W: https://goo.gl/maps/oseXMj2fND12


Let me ask a bunch of obvious questions.. perhaps it will jog something useful here...
What common mode failure could have prevented both of them from deploying?... Bad igniters.. unlikely. Bad powder.. What type of powder do you use for deployment, 4F Black Powder? Low battery voltage? What type, voltage/mAh batteries did you use for your Quantums? How many volts were packs at after your armed the Quantums over WiFi? (I'm assuming you verified both drogue and main continuity for each quantum on the arming page.) Could something have broken off and disconnected both the altimeters during the boost?

Good questions to ask.
I used 4 charge cannisters (large size) from pratt hobbies. They are extremely reliable and have an integrated igniter. All 4 measured the correct resistance before I loaded them, and all 4 showed connectivity on the launch pad (the quantum let's me see that visually).

Black powder is the stuff supplied by AMW, I think it may be 3F. I've always used it. The same powder worked successfully that same day in my previous flight, which also used the pratt charge cannisters loaded in the exact same way.

Batteries were 2s 460maH Lipos. Same as I've used with all quantum flights. Each altimeter had two batteries, a deploymenet battery and a main battery. All batteries were charged (checkd with voltmeter) and the quantums confirmed charge (and I have a screenshot of the secondary altimeter showing battery voltage of 8.1V from right before the flight).

Your theory about something flying around in the AV bay is a good one... except (a) there isn't much that could. The batteries are on the opposite side of the board from the altimeters, each sitting in a separate little wooden well with a wooden board holding them in. (b) the plastic shield would have made it harder for anything loose to bang into the altimeters. This wasn't it's intended purpose, but it is a side effect.



I was reviewing your excellent flight video.. and though I may have noticed something just before the drogue deployment... Listen for the noise at 28 seconds in the video.. could that be a primary drogue charge going off, but not separating?.. or is that a quick link clanking on the side of the rocket at nose over just before deployment? I hope you are able to get back there and find this rocket. I can't imagine how it must feel to loose it.

WOW great observation. I will go home tonight and see if that sound is coming from the ground video or the on-rocket video. It certainly does seem like it could be a charge going off. I do remember being a bit concerned that I couldn't hear the backup charge fire after the drogue charge fired in the video, but chalked it up to being hard to hear over the wind noise.

That doesn't explain why the failsafe mode on the quantums didn't then fire the main once freefall was detected. BUT those are based on velocity measurements. I wonder if the shield was enough to mess with the velocity measurements as the rocket fell and cause the failsafes to not trigger? The theory I guess would be that the drogue charges weren't enough to separate the drogue, and then the failsafe didn't fire. I don't actually know for sure that the main's didn't fire at 600' (400' backup) since I'd lost visual sight of the rocket by then. My assumption had been that the failsafe not firing the mains meant the mains didn't fire. We also heard the rocket whistle as it came in hot, but AFAIK no one saw the impact or heard an impact, it is possible that the main did deploy right before impact and we just didn't see it happen.
 
Any chance that those DPDT switches may have come loose or glitched? Which way were they oriented (up-down or sideways)?
 
Any chance that those DPDT switches may have come loose or glitched? Which way were they oriented (up-down or sideways)?

Great question. The switches are rated (and tested) by the manufacturer to 50Gs on all axes. They were mounted up-down such that "down" was on. As such, the only time in the flight that any acceleration would have tried to turn them off would be deceleration after motor burn. Acceleration during motor burn would just push them "on". OpenRocket claims that the deceleration immediately after motor burn was around 2Gs, so far far less than the rated limit.

Each switch was attached to the airframe by a pair of buttonhead #4 metal screws mounted through the fiberglass body tube. The button head was on the outside of the body tube and then a metal nut with some glue was on the inside that held the switch metal tab against the airframe:

|Screw Head| |body tube| |metal tab on switch| |nut glued to switch|

The glue was not particularly strong - it was just to hold the nut in place during assembly. I believe (but don't remember for sure) that I used blue loctite on the screws as well. Either way, the screws were perhaps 0.375" longer than needed and would have had to turn against meaningful friction (I believe I tapped the holes through the body tube) many times before coming out of the nut. I also confirmed that the switches were firmly in place before flight.

The wires were soldered to the screw terminals and covered with hot glue. The switches were mounted 120 degrees apart on the rocket body tube.

As such, I think it is very unlikely that the switches were affected by G forces. It is conceivable (though unlikely, the switches had never loosened on their own before from flight or transport) that a switch could have unscrewed itself. They would both have had to unscrew though or one would have had to unscrew and then bounced around badly enough to both turn itself off (or break a connection) and damage the redundant other circuit.

Regarding the theory of the drogue charges not being enough, I just confirmed (yay L3 design doc...) that I had configured the quantum failsafes to fire at 125fps sustained for 1 second. I wonder whether my plastic shield could have interfered enough with airflow to break that calculation. Alternatively, what if it created weird air currents that made the sustained 1 second component of that threshold not satisfied?
 
Kevin - I found the original unedited videos of the first flight, and the sound you heard is coming from the ground video rather than the videos from the rocket. I also can see the backup charge go off in that flight (it is easier to see frame by frame on a computer). Here are screen shots of the frame before and frame after I can see the backup apogee charge fire:
frenzyframe1.jpgfrenzyframe2.jpg

So, we are back to square one. In the first flight, both primary and backup drogue charges fired and the primary was sufficient to separate the rocket, which isn't surprising given the extensive ground testing. As such, there is no evidence of the charges ever being insufficient, and so I think it is highly likely that the problem came from something disabling both altimeters (or preventing launch detection) during flight.

I am still befuddled as to how the plastic shield that I added could have caused such trouble, but I can't think of anything else and it is the only thing that was changed since the previous flight.
 
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Unless you completely sealed up the little hole in the pressure sensor (which would be very hard to do) it's unlikely that your plastic shield had anything to do with it. I'm assuming that the battery/switch/ematches were the same as your previous flight and your ground test, so they should have been adequate. Since your wires were soldered to the board that leaves either the battery or switch disconnecting in flight as the likely culprit. What did you do to keep the battery wires and connectors from flopping around and becoming disconnected in flight?
 
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