Ejection Charges

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+1 on securing the battery with zip ties if practical. I have seen dual deploy rockets destroyed because people thought duct tape was good enough to hold the battery in place. It isn't. Also, I recommend Duracell if you are using 9 volt batteries. Cheap batteries may not survive a high G event. Seen that failure too; ain't pretty.

+20 on having someone at the launch look everything over and even helping you assemble the motor if you are new to that.
 
So then... I thought to my self, what if I used the drogue AND a jolly set at 500 to double ensure a decent landing, then I reminded myself...im probably way to deep to even go there.. uggh...
 
CPUTommy said:
So then... I thought to my self, what if I used the drogue AND a jolly set at 500 to double ensure a decent landing, then I reminded myself...im probably way to deep to even go there.. uggh...
Click to expand...

Jolly logic set on the main? I'm confused as to what you're trying to do here.
 
Zeus-cat said:
having someone at the launch look everything over
Click to expand...

You may feel dumb asking what seems like basic questions at a launch, but you'll feel even more dumb when your rocket fails in a spectacular and public way because you didn't do something right. Not that I'd ever know how that feels :)
 
almost there...I have an idea for the battery. battery is bottom down but im sure it will still move around some.. which is a major problem.

20170726_224722.jpg20170726_224803.jpg20170726_224812.jpg20170726_224831.jpg
 
You need something more to hold the battery in position IMHO, unless there is something that I am not seeing in the images.

Boost accelerations and impulses from ejection charges can have surprising effects on masses within the rocket. You may want to consider how you will withstand the forces in your assembly. As a rule of thumb I would consider an impulse from an ejection charge to generate 50-70G of acceleration, and consider the forces generated by the relevant masses in the avionics bay. I like using Velcro between the battery and the mount, to take the shear stresses axially in the rocket. I then use cable ties to hold the battery down onto the Velcro.
 
I was thinking along the lines of a battery shroud mounted to the sled. Or I could use more bolts to really secure it. Definitely has to be addressed. The connections are also a concern, I'll sleep on it.
 
CPUTommy said:
I was thinking along the lines of a battery shroud mounted to the sled. Or I could use more bolts to really secure it. Definitely has to be addressed. The connections are also a concern, I'll sleep on it.
Click to expand...

The sled looks good. Your coming along. For the battery, a zip tie in each direction will work well. Or a shroud. I would not recommend bolts as I've crushed the end of a lipo before because the acceleration pushed the lipo against a small bolt.

Regarding the connections, the JST connectors are fine. I clip them an install minifit Jr. plugs but it's not necessary.

Where's your switch?
 
NateLowrie said:
The sled looks good. Your coming along. For the battery, a zip tie in each direction will work well. Or a shroud. I would not recommend bolts as I've crushed the end of a lipo before because the acceleration pushed the lipo against a small bolt.

Regarding the connections, the JST connectors are fine. I clip them an install minifit Jr. plugs but it's not necessary.

Where's your switch?
Click to expand...

I was thinking of 2 vertical bolts, with insulated stand offs to keep it from moving "south" , yet be removable. I also am going to zip tie it in a few directions.

I have the switch on my desk on my desk so I can solder the terminal connections. Its just a standard push button, as I couldn't find a decent one locally. Next AV bay will have a key switch. I plan on putting the switch on the bottom of my AV bay so that I can secure the top of the AV bay and easily slide the unit up from the base, activate the sled and just slide it back into the tube. Being able to activate the switch through the Band is also a possibility but would take some designing and securing. I realize the ejection charge will degrade the life of the switch and im ok with that.

The connections seem a bit on the weak side to me. They will work for the time being.
 
CPUTommy said:
I was thinking of 2 vertical bolts, with insulated stand offs to keep it from moving "south" , yet be removable. I also am going to zip tie it in a few directions.

I have the switch on my desk on my desk so I can solder the terminal connections. Its just a standard push button, as I couldn't find a decent one locally. Next AV bay will have a key switch. I plan on putting the switch on the bottom of my AV bay so that I can secure the top of the AV bay and easily slide the unit up from the base, activate the sled and just slide it back into the tube. Being able to activate the switch through the Band is also a possibility but would take some designing and securing. I realize the ejection charge will degrade the life of the switch and im ok with that.

The connections seem a bit on the weak side to me. They will work for the time being.
Click to expand...

Your switch arrangement is going to be a safety issue with the RSO... When the RRC3 is powered up it goes through self-checks and then arms for flight. You do NOT want the arming for flight to happen until the rocket is vertical on the pad, because your jostling or moving could change the baro pressure inside, which could trigger a lift off event and fire the charge. It's not as much of a danger with baro altimeters like the RRC3 as it is with accelerometer based altimeters, but it's still a danger and can injure anyone that's in the way of the separating components. Rocket vertical, then arm without taking apart the stages.

You should be able to mount the push button so you can trigger it through a vent hole. That way you can arm on the pad without taking it apart.
 
You also need to be able to disarm it safely without taking it apart.
MissileWorks sells screw switches. PML sells slide switches. Eggfinder sells wifi switches. There are many, many, posts regarding switches on TRF and they are a very important part of safely working with rockets.


Steve Shannon
 
Steve Shannon said:
You also need to be able to disarm it safely without taking it apart.
MissileWorks sells screw switches. PML sells slide switches. Eggfinder sells wifi switches. There are many, many, posts regarding switches on TRF and they are a very important part of safely working with rockets.
Click to expand...

Screw switches are ok but they can & will back out at the most inopportune moment. WiFi switches are ok but they are battery hogs! I find the most effective & simplest these days is just a twist & tape!
 
timbucktoo said:
Screw switches are ok but they can & will back out at the most inopportune moment. WiFi switches are ok but they are battery hogs! I find the most effective & simplest these days is just a twist & tape!
Click to expand...

Its esay to fix screw switches from the screw coming out. Put the screw all the way in tight then flip the switch over and using a sharp cold chisel "stake" the corner of the end of the screw, it buggers the very end of the threaded section enough that you can't accidentally unscrew the screw all the way.
 
I got a Micro switch that will be easily assesable from the vent band, now I just need to mount it.. hmmmmm
 
timbucktoo said:
Screw switches are ok but they can & will back out at the most inopportune moment. WiFi switches are ok but they are battery hogs! I find the most effective & simplest these days is just a twist & tape!
Click to expand...

I'm a big fan of Featherweight magnetic switches, but at $25 a pop, that gets pricy fast. I have over a dozen redundant dual deploy rockets that use the twist and tape method, and as long as you have a switch band, it's the easiest, cheapest method. No fiddling around trying to find a button in a hole, no doubt about if the switch is gonna open under thrust, it just works.
Problem with micro switches is the little tiny parts can move around inside and remove power to your altimeter at the worst time.
I use 24 gauge stranded pair copper wire, stick it through the static port on your switch band and twist the ends together. Tape it down on the payload (upside) of the switchband, so it won't come loose when the fincan separates at apogee, and tie it off inside to the altimeter stand-off. Connect it to the terminal block marked "switch" on your RRC-3 and it's a bullet-proof switch that you can access right there on your avbay.
I have done literally hundreds of flights with this method and only had one failure when I was too lazy to replace and old piece of electrical tape. Fortunately, it was a redundant system.
 
Proper safety code launch sequence:
  1. Load and secure all chutes and harnesses.
  2. Wire up altimeter with no powder and check continuity.
  3. Turn off altimeter.
  4. Add charges and assemble AV bay/rocket.
  5. Add shear pins, if using.
  6. Install motor in rocket and retain, but do not insert igniter.
  7. Fill out flight card
  8. Take rocket to RSO for check and weight.
  9. Wait for "Range is clear" signal.
  10. Take rocket to pad and install on pad.
  11. Raise pad to vertical so that rocket is pointing up, and lock pad.
  12. Turn on altimeter and listen for continuity.
  13. Insert and secure igniter.
  14. Attach launcher clips to igniter and walk away.
 
Bat-mite said:
Proper safety code launch sequence:
  1. Load and secure all chutes and harnesses.
  2. Wire up altimeter with no powder and check continuity.
  3. Turn off altimeter.
  4. Add charges and assemble AV bay/rocket.
  5. Add shear pins, if using.
  6. Install motor in rocket and retain, but do not insert igniter.
  7. Fill out flight card
  8. Take rocket to RSO for check and weight.
  9. Wait for "Range is clear" signal.
  10. Take rocket to pad and install on pad.
  11. Raise pad to vertical so that rocket is pointing up, and lock pad.
  12. Turn on altimeter and listen for continuity.
  13. Insert and secure igniter.
  14. Attach launcher clips to igniter and walk away.
Click to expand...


This I just printed out to keep my head straight. Huge Thank YOU !!!!
im useless at work today...

My list goes like this..
1-remind myself to inhale oxygen
2-gulp some coffee
3-think of the things I still need to do on my dual deploy rocket
4-think of the things I still need to do to my other 38mm rocket
5-re take the level 2 practice tests
6-pack car
7-re take the practice tests
8-worry about what could go wrong
9-fiddle with rockets to verify my baseless suspicions
10-check that car is loaded
11-stare at loaded car from living room.
12-check that everything is in car
13-roll around in bed until 4:30 am so that I can start the worrying, coffee drinking process until 6am
14-drive 2 hours to field all while worrying
15-take test and fail, then drive home in disappointment.

im doing nothing at work and im way stressed. go figure...
 
Bat-mite said:
Proper safety code launch sequence:
  1. Load and secure all chutes and harnesses.
  2. Wire up altimeter with no powder and check continuity.
  3. Turn off altimeter.
  4. Add charges and assemble AV bay/rocket.
  5. Add shear pins, if using.
  6. Install motor in rocket and retain, but do not insert igniter.
  7. Fill out flight card
  8. Take rocket to RSO for check and weight.
  9. Wait for "Range is clear" signal.
  10. Take rocket to pad and install on pad.
  11. Raise pad to vertical so that rocket is pointing up, and lock pad.
  12. Turn on altimeter and listen for continuity.
  13. Insert and secure igniter.
  14. Attach launcher clips to igniter and walk away.
Click to expand...

You nailed it John, great post!

CPUTommy said:
This I just printed out to keep my head straight. Huge Thank YOU !!!!
im useless at work today...

My list goes like this..
1-remind myself to inhale oxygen
2-gulp some coffee
3-think of the things I still need to do on my dual deploy rocket
4-think of the things I still need to do to my other 38mm rocket
5-re take the level 2 practice tests
6-pack car
7-re take the practice tests
8-worry about what could go wrong
9-fiddle with rockets to verify my baseless suspicions
10-check that car is loaded
11-stare at loaded car from living room.
12-check that everything is in car
13-roll around in bed until 4:30 am so that I can start the worrying, coffee drinking process until 6am
14-drive 2 hours to field all while worrying
15-take test and fail, then drive home in disappointment.

im doing nothing at work and im way stressed. go figure...
Click to expand...

I'm marking things in yellow that you should take off your list. I would add line 13, but that's what we all do, it's inevitable. When you take the test, you're gonna wonder why you stressed so much about it.
 
Seriously, though, here is my best advice.

If you can, prep the rocket entirely at home, where you are relaxed and have plenty of time. Test your e-matches with a meter, and if you are the least bit suspicious of one, don't use it.

I arrive at the range with the rocket ready to fly, motor in. At the range, I simply need to fill out the flight card and go to the RSO table. No stress, no wind blowing my black powder, no forgetting my shear pins, no being too hot/sweaty/cold, etc.
 
its the little stuff I need to finish up.. Like zip tie the av Bay, screw on the rail guides to the t-nuts, powder the chutes, etc..

and its not raining so im going to do some more ground testing to "pass the time"

Stress.. its whats for dinner...
 
CPUTommy said:
its the little stuff I need to finish up.. Like zip tie the av Bay, screw on the rail guides to the t-nuts, powder the chutes, etc..

and its not raining so im going to do some more ground testing to "pass the time"

Stress.. its whats for dinner...
Click to expand...

What kind of chutes (material) are you using? I've only ever heard of powdering plastic chutes. Ripstop nylon doesn't need it. Neither does silk.
 
there nylon and ive always powered my chutes, probably out of habit, the para cord and nylon seem to slip apart when it comes time to deploy.

I have a few different chutes that I interchange between rockets with swivels.

and here I sit...thinking about powder...to powder or not to powder.. what will be the impact.. what if.. what if..

wow.. ive reached new levels of insanity...
 
Plastic chutes have lots of inherent problems, which is why you don't see them used in larger rockets. They crumple and retain shape, they melt, and they often don't open because the weight of the rocket doesn't provide enough wind resistance to force the chute open. Ripstop nylon, however, can be left in a ball pretty much forever, and then spring to life as soon as they encounter an upward air current. I wouldn't worry about it.

I have at times loaded a rocket ready to fly, and then had to miss the launch. I just take it out to the next launch a month later and let her rip. I would never do that with a plastic chute.

My 15' silk chute lives crumpled in its deployment bag in a box in my basement. When it's time to fly, I attach the pilot chute and shove it in the payload bay.
 
I know quite a few people who powder nylon chutes. The main benefit is the puff of powder on deployment, but the talcum does lessen friction slightly also. There's nothing wrong with it, especially if it helps you feel less stressed.
 
I second the advise from John about prep-prepping your rocket in the comfort of your shop. Nothing is more nerveracking and frustrating than taking a half finished rocket into the field and prepping it onsite.
 
NateLowrie said:
I second the advise from John about prep-prepping your rocket in the comfort of your shop. Nothing is more nerveracking and frustrating than taking a half finished rocket into the field and prepping it onsite.
Click to expand...

Yeah, like dumping 100 2-56 nylon screws on the ground, or spilling your BP, or realizing you forgot your jeweler's screwdriver for tightening down your terminal blocks, or ....
 
Bat-mite said:
Yeah, like dumping 100 2-56 nylon screws on the ground, or spilling your BP, or realizing you forgot your jeweler's screwdriver for tightening down your terminal blocks, or ....
Click to expand...

Measuring BP in the wind, or dragging your tools along with you, or setting up and tearing down a workbench, or finding out the mounting holes for the altimeters don't mate with the holes in the sled, or finding your lipos are charged, or no remembering the manual to configure the altimeter, or any number of a hundred things that are easy to remedy in the shop but are major detriments or showstoppers in the field.
 

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