Options for ebay arming mechanism?

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tibbe

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I'm building my rocket with an ebay and was looking through options for turning the electronics on and off. All options seem a bit annoying to build or use. Options I've seen are:


  • Cables twisted on the outside of the rockets. I guess this works but I'd like something more solid.
  • Switch on the sled and tiny whole in the airframe to poke at it through. This seems really annoying to use. You need to install the switch so it lines up with the hole and when you use it you need to poke at it with a small screwdriver.

Are there easier options? Switches that attach to the ebay body itself? In this day of technology where are the mobile phone controlled dual deploy boards? :)
 
If you can solder, Eggtimer Rocketry sells a WiFi enabled altimeter which is nice. The easiest in my opinion is the twist and tape. Use it all the time and is likely the most reliable in my opinion. Just pull the wire through one of the ebay vent holes, twist it securely together and then tape it to the body tube. I use electrical tape and it does not come off in flight.
 
Many options. I personally like twist & tape because it's simple. Eggtimer products make a wifi switch. Just need to have the extra space or you could build an Eggtimer Quark which has the wifi switch incorporated on the altimeter.
Also there is a magnetic switch that is sold by Featherweight. there are also Shruter switches. Sold by Binder design amongst others I am sure.

https://www.eggtimerrocketry.com/page43.php

https://www.featherweightaltimeters.com/store/p4/Magnetic_Switch.html

https://binderdesign.com/store/page25.html
 
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The Eggtimer Quantum is a nice option, but I've started adding screw switches to my e-bays anyway. I really like the ability to arm the rocket from stand-off distance, but the Wi-Fi switch on the Quantum is a bit of a power hog (relative to a non-Wi-Fi alt) and adding an externally accessible switch lets me fully load the rocket hours beforehand (even the night before) and not power up until I'm actually at the pad. That way if there is any delay in the launch (e.g. long line at the RSO, etc.) I don't have to worry about the battery draining. I
 
external switches? sure.

14330974201_d4ceb98f31_z.jpg
 
The ones above are the most common. Cheap, but durability is a question. Mine tend to break from normal use. There are also key switches, pull-pin switches, toggle switches ....
 
I made my own mag switches, but also use Eggtimer Quantums (some disagreement about if switches are needed) and Eggtimer WiFi Switches. I did external push button switches on my first av-bay build, with external LED lighting, all the bells and whistles, and realize now it's way overbuilt (but is reliable).
 
I like the pull pin switches in conjunction with screw switches. I use the screw switches on the coupler that is covered during flight. These act as the master on/off switch. The pull pin are only used on the way to the pad, RSO, etc. With the pull pins installed and the Remove Before Flight ribbons, these keep the altimeter off. The screw switches are the master, if they are off, everything is off and it doesn't matter if you have the pins in or out. Of course, don't forget to turn on the screw switches before getting to the pad or when you pull the Remove Before Flight pins, everything will stay off.

With all of that, you need to key your av-bay caps so the threaded rods and sled align to the holes in the switch band and screw switches in the coupler. It can take some effort and design, but once you have the alignment keys on the caps in place, everything should be aligned after that.
 
A Bluetooth module, a relay and a micro controller plus a little code and you could easily arm it at a distance with a phone...

However, as both a mechanical engineer and a professional software developer, I have to strongly advise against mixing technology and black powder if the idea is to prevent unintentional explosions...





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I have used the rotary switches pictured above. They seem to work well, but are definitely delicate - I destroyed one by turning it too far with relative ease.

I recently bought a few Binder Design switches, which are much more robust. They can be mounted externally, but I don't think it would look very nice. I mounted mine on a standoff from the sled so that it is easily accessible but still recessed.

IMG_3934.jpg

IMG_3931.jpg

IMG_3922.jpg
 
I like pull-pins with RBF tags. Mostly difficult to forget to arm the electronics.

I have tried a lot of things on the way and these I find the most convenient on the launch field.

A couple of other threads have discussed them here:
https://www.rocketryforum.com/showthread.php?143967
https://www.rocketryforum.com/showthread.php?144367

Unless you have super-sized batteries the wifi options are generally too power thirsty for any decent amount of storage or pad time. This could be improved by another switch in series, but I see little point in that for most rockets I build.
 
Thanks for all the replies. I've skimmed all the linked threads. Very informational.

A perhaps silly question: for switches (e.g. screw switches, push switches) that require that you reach into the airframe through a hole in the switchband, how do you make sure the whole is aligned with the switch?
 
Thanks for all the replies. I've skimmed all the linked threads. Very informational.

A perhaps silly question: for switches (e.g. screw switches, push switches) that require that you reach into the airframe through a hole in the switchband, how do you make sure the whole is aligned with the switch?

I used CA to tack the standoff/switch assembly in place prior to gluing it in its final position.
 
Thanks for all the replies. I've skimmed all the linked threads. Very informational.

A perhaps silly question: for switches (e.g. screw switches, push switches) that require that you reach into the airframe through a hole in the switchband, how do you make sure the whole is aligned with the switch?

Once everything is aligned, make a small mark on the bulkhead and the coupler of the av bay. That way it’s easy to align the next time.

Do most people use two switches per altimeter or just one? Right now I have one switch between my altimeter and the ejection charge. This means that the only way to turn the altimeter on and off is to disassemble the bay and physically connect/disconnect the battery. It’s kind of a pain. I’m thinking I need to rebuild it with two switches, but that means if I use redundant altimeters (one of my next goals), I’ll need four switches. This is getting ridiculous!


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Do most people use two switches per altimeter or just one? Right now I have one switch between my altimeter and the ejection charge. This means that the only way to turn the altimeter on and off is to disassemble the bay and physically connect/disconnect the battery. It’s kind of a pain. I’m thinking I need to rebuild it with two switches, but that means if I use redundant altimeters (one of my next goals), I’ll need four switches. This is getting ridiculous!

One switch only to power the altimeter for me. No shunting/switching of ejections charges.

Yes, redundant electronics are ridiculous. This is why I have no plans for L3.
 
Once everything is aligned, make a small mark on the bulkhead and the coupler of the av bay. That way it’s easy to align the next time.

Do most people use two switches per altimeter or just one? Right now I have one switch between my altimeter and the ejection charge. This means that the only way to turn the altimeter on and off is to disassemble the bay and physically connect/disconnect the battery. It’s kind of a pain. I’m thinking I need to rebuild it with two switches, but that means if I use redundant altimeters (one of my next goals), I’ll need four switches. This is getting ridiculous!


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You only need one switch per altimeter. I recommend putting that one switch between the battery and the altimeter because some altimeters include a continuity check on startup which would be fooled by having a switch between the altimeter and the ejection charge.
You must disarm all charges before lowering your rocket in case you have to remove it from the pad without launching it. That’s in NFPA 1127 which is central to the Safety Codes for both Tripoli and NAR. Be sure your design allows for that. Basically you just need to be able to turn the altimeter off (or in your current design interrupt the current that might flow to the ejection charge).


Steve Shannon
 
Thanks for all the replies. I've skimmed all the linked threads. Very informational.

A perhaps silly question: how do you make sure the whole is aligned with the switch?

Simple answer: Use a ruler. Lay out your sled and ebay and plan them to line up. Dry fit everything. Measure twice, drill once.
 
You only need one switch per altimeter. I recommend putting that one switch between the battery and the altimeter because some altimeters include a continuity check on startup which would be fooled by having a switch between the altimeter and the ejection charge.
You must disarm all charges before lowering your rocket in case you have to remove it from the pad without launching it. That’s in NFPA 1127 which is central to the Safety Codes for both Tripoli and NAR. Be sure your design allows for that. Basically you just need to be able to turn the altimeter off (or in your current design interrupt the current that might flow to the ejection charge).


Steve Shannon

Procedure at the pad for arming:
  1. Rocket on the pad pointing away from flight line.
  2. Raise rocket to vertical.
  3. Arms igniters and wait for continuity confirmation.
  4. Insert igniter.
  5. Wire igniter.
  6. Walk away.
If you need to remove the rocket before launch, as Steve indicated, do those things in reverse:
  1. Remove the wires from the igniter.
  2. Remove the igniter.
  3. Turn off the altimeters.
  4. Lower the rocket to point away from the flight line.
  5. Remove the rocket.
 
how do you make sure the whole is aligned with the switch?

That's easy. Drill the hole then mount the switch where the hole is.

I'm not being funny. Without really knowing your setup..I build the electronics sled and roughly figure out the electronics layout including switch(s) locations. I then drill the hole as close to where I think it should be. I drill 'into' where the drill bit will leave a 'witness' mark on the electronics sled. I then mount the switch to match that mark.

Tony
 
That's easy. Drill the hole then mount the switch where the hole is.

I'm not being funny. Without really knowing your setup..I build the electronics sled and roughly figure out the electronics layout including switch(s) locations. I then drill the hole as close to where I think it should be. I drill 'into' where the drill bit will leave a 'witness' mark on the electronics sled. I then mount the switch to match that mark.

Tony

I really like this idea! I think I'll use it when rebuilding my 4" sled.
 
And a centering ring to mount the Fingerhut switches on, allowing for some vertical adjustment.


 
How do Fingerhut switches work? Did you mean fingertech?
 
Yes, redundant electronics are ridiculous. This is why I have no plans for L3.
Redundancy is sometimes considered optional. Bigger rockets = more energy = more risk = not ridiculous. In my opinion I am happy for you to stay not L3 :)

You only need one switch per altimeter. I recommend putting that one switch between the battery and the altimeter because some altimeters include a continuity check on startup which would be fooled by having a switch between the altimeter and the ejection charge.
I use two switches per altimeter with my pull-pin arrangement. When pulling the pin the first one powers the altimeter, the second one connects the eMatch. Rationale is that a single switch failure does not leave the pyros capable of firing unexpectedly.

Remember to consider off-nominal situations when designing and flying :wink:
 
Redundancy is sometimes considered optional. Bigger rockets = more energy = more risk = not ridiculous. In my opinion I am happy for you to stay not L3 :)


I use two switches per altimeter with my pull-pin arrangement. When pulling the pin the first one powers the altimeter, the second one connects the eMatch. Rationale is that a single switch failure does not leave the pyros capable of firing unexpectedly.

Remember to consider off-nominal situations when designing and flying :wink:

I agree 100% that redundant recovery electronics is important in large rockets due to increased potential for damage/injury.

One thing that I am not sure about is having a switch between the altimeter and ejection charges. My thinking is this:

*Having a switch between the altimeter and the ejection charge decreases the risk of ejection charges firing accidentally.
*Having a switch between the altimeter and the ejection charge increases the risk of the ejection charge failing to fire properly.
*An accidental discharge of the ejection charge has less potential to cause damage/injury than a rocket coming in ballistic/sans recovery.

I could be missing something, to be sure, but that is how I see it.
 
I agree 100% that redundant recovery electronics is important in large rockets due to increased potential for damage/injury.

One thing that I am not sure about is having a switch between the altimeter and ejection charges. My thinking is this:

*Having a switch between the altimeter and the ejection charge decreases the risk of ejection charges firing accidentally.
*Having a switch between the altimeter and the ejection charge increases the risk of the ejection charge failing to fire properly.
*An accidental discharge of the ejection charge has less potential to cause damage/injury than a rocket coming in ballistic/sans recovery.

I could be missing something, to be sure, but that is how I see it.

You’re right, with a very slight possibility of a debate about the third bullet point. An accidental discharge of the ejection charge may be more likely to happen upon arming. Except for those who use the wireless switch from Eggtimer, that usually involves someone standing right next to the rocket, sometimes up on a ladder.
 
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