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Author Topic: Arming switch DIY the easy way  (Read 1794 times)

Offline TDM

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Arming switch DIY the easy way
« on: August 13, 2019, 09:30:07 AM »
The idea of this arming switch has its roots from the battlebott designs. Basically it is a screw that when is tight it makes contact (ON) and you are good to go. When not in use open the screw a turn  or so and contact is open (OFF). The whole switch weighs about 6-8g it is bullet proof for high shock environments so it is suitable for our needs it is compact (it protrudes about 5/16in inside the fuselage) and super easy to make (it took about 15 min to do what you see in the pictures from start to finish ready to install). The installation is super easy (drill 3 holes in the fuselage side, bolt and is done).
I have used this type of arming switch with no failures at all.
The basic design is two pieces of brass flat bar that are insulated from each other with shrink tubing (this also insulates the wire ends), the plates are held together with plastic screws (these plastic screws also bolt the arming switch to the fuselage) and a steel screw in the center that acts as a switch. You can use whatever size screw with whatever size head shape you want to and fits the model.

The way to make it is easy all you need is: a hand drill a tap of whatever size screws you choose to use, a flat piece of brass, some shrink tubing, and the screws. In this case I chose 4-40 screws and a flat piece of brass 1/4x1/16 cut to the dimensions in the picture.

Pictures are self explanatory. Mark hole location, the locations used by myself are on the hand sketch. I drilled them both in assembly to ensure future alignment between screws and also added an X and a black line to make sure I maintain orientation. After that I tapped the holes on one side and created clearance on the other side ( kept the clearance on the screws somewhat tight so the plates get positioned OK).
After that I bolted the plates together to make sure I solder the wires in the right place and i do not put the wires over the assembly. You can get in trouble if you do not keep track of where to put the wires and if you keep it assembled during soldering eliminates all problems.
Put the shrink tubing on cut the holes with an Exacto knife blade make some extra cut for the arming screw to make contact and that is it.   
To assemble make the appropriate holes in the fuselage for whatever head shape screw you choose to use.
Test to make sure it work properly if not enlarge the clearance hole of the arming screw that should fix the problem. If it doesn't work it is because the plates are drilled separate and the holes do not align or you flipped the plates when you solder the wires. Either way a bigger clearance hole should fix the problem.
 
« Last Edit: August 13, 2019, 09:49:14 AM by TDM »
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Offline TDM

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Re: Arming switch DIY the easy way
« Reply #1 on: August 13, 2019, 09:31:41 AM »
The rest of the pictures
This switch weighs 7 grams After you shorten the screws you night be at 6 grams. Rough dimensions are 1.6Lx.28Wx.3H inches.
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Wolfgang Nieuwkamp

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Re: Arming switch DIY the easy way
« Reply #2 on: August 13, 2019, 02:23:17 PM »
Excellent idea!

Will install it on my next model.

Regards,

Wolfgang

Offline TDM

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Re: Arming switch DIY the easy way
« Reply #3 on: August 13, 2019, 03:04:57 PM »
You are welcome. I am glad you like it.
Just in case I hacked up a installation on a piece of light ply so you can get an idea of how it looks installed.
Stating the obvious: spot the location for the 3 holes. Drill holes for the plastic screws and clearance hole for the contact screw in the center (this all depends on your selection of type and size of screws you want to use). Bolt in and is done. Yes I could have used a sorter contact screw but I am just trying to do a tutorial.
In this case I presented an in line sample that used 4-40 screws all around (All screws that bolt something in the Revolutions project are 4-40) and an in line setup of the wires. If you wanted a return 180 turn then you can modify with a Z bend and do that which is perfectly acceptable the thing is you want some clearance so if you stack the plates after soldering there should be some clearance. The configuration is completely up to your needs, but the technique remains the same.
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Dennis Adamisin

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Re: Arming switch DIY the easy way
« Reply #4 on: August 13, 2019, 04:06:08 PM »
You described your switch during a recent Hangar Hangout, but I did not really follow your description - NOW I see it!  This is an elegant design;  simple & robust.   CLP**

Thank you for this post.
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline Tim Wescott

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Re: Arming switch DIY the easy way
« Reply #5 on: August 14, 2019, 11:00:18 AM »
I think I would use a brass screw for the contact, and for a full-sized stunter something bigger than a 4-40.  Stainless is nice in a lot of ways, but it's very resistive -- in fact, the common stainless alloys are pretty close to the alloys used for heater wire.

I'd also be concerned that the dimensions are controlled well enough that things can't slip up and make contact.

Aside from the grumping about details -- it does look good.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Howard Rush

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Re: Arming switch DIY the easy way
« Reply #6 on: August 14, 2019, 01:03:11 PM »
You might consider something than can be disarmed more quickly.  A Dzus-type device could provide a force maintaining electrical contact and disarm with a quarter turn.  A lever on the head could allow operation without a tool. 
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Offline TDM

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Re: Arming switch DIY the easy way
« Reply #7 on: August 14, 2019, 01:25:56 PM »
Tim it would be interesting to see how electrical resistance a 4-40 has. I have no way to check it. And yes I have used .015SS wire for hot wire cutting. At over 3/32 in diameter I think it will be fine. The door is opened to anything you choose to use. Aluminium screw is also practical, steel screws are also an option (but they rust).
One of the reasons for which I use this setup is because is compact and does not extend in to the fuselage where I need the space for other stuff. Another reason is that it is not unsightly with a big plug hanging out.
Howard yes anything will do. The speed at which you need to disarm the system never crossed my mind, since you can't be fast enough, by the time you get to the scene of the incident things are already burned out in an electric system, a tab on the screw will do fine as no tools are needed (nice idea), as I said whatever screws you want to use just work around those screws. Wouldn't Dzus close the circuit in both positions?
Great points gentleman.
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Howard Rush

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Re: Arming switch DIY the easy way
« Reply #8 on: August 14, 2019, 01:50:33 PM »
Maybe you could use a banana plug.  Just poke it into the hole.  It would only be ugly when armed.
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Offline Tim Wescott

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Re: Arming switch DIY the easy way
« Reply #9 on: August 14, 2019, 02:13:12 PM »
Tim it would be interesting to see how electrical resistance a 4-40 has. I have no way to check it.

If you can measure current and voltage simultaneously, you can measure the electrical resistance between any two points on your switch.  You can even approximate it with your finger.

Specifically, you can get the thing running at the design current (i.e., run it on the ground with a cut-down prop), then measure the voltage from the screw head to the copper.  You probably want to get the screw head to top layer as one measurement (there'll be some voltage drop), and a separate measurement from the screw head to the bottom layer.

Alternately, with that same cut-down prop, let it run for about 30 seconds or so with your fingertip on the screw heat.  If it gets hot, the resistance is too high.  If you're like me then you've done that test enough that you want to use the back of a finger, because after burning yourself enough times your fingers get insensitive to heat...

Aluminium screw is also practical, steel screws are also an option (but they rust).

Any dissimilar metal contact at points like these will tend to cause accelerated corrosion.  If there's any movement from vibration, you'll add fretting corrosion to the mix.  It's best to use a screw of the same alloy as the bar, and to use something reasonably conductive (like brass) and something that has corrosion properties that make it a good switch material (like brass).  Brass with a heavy gold plating would be better yet -- let me know when you find someone who will do that for cheap in small quantities.
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Online Ken Culbertson

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Re: Arming switch DIY the easy way
« Reply #10 on: August 14, 2019, 03:41:26 PM »
I really like this idea but I worry about not knowing for sure if the screw is out all of the way.    I use a much simpler bu far less eloquent method.  My biggest complaint at first was how difficult the wires were to bend around the plug and both it and the starting button stuck so far into the fuselage that it was really a pain to locate things. 
The balsa on the inside is not really necessary of you are good with shrinking covering around connections like this.  I paint my arming plugs red for a light colored fuselage and yellow for the dark ones.  Just having that plug in my hand removes all doubt as to whether or not it is armed and the off color makes it easy for the "helper" to spot it.

Ken

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Offline Tim Wescott

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Re: Arming switch DIY the easy way
« Reply #11 on: August 14, 2019, 03:53:12 PM »
I really like this idea but I worry about not knowing for sure if the screw is out all of the way.    I use a much simpler bu far less eloquent method...

If you just spin it out until there's light visible between it and the contact, you should be OK -- but yes.

I really want to make a knife switch that can be covered & contoured to match the plane, like a little hatch, and just shut to fly.  It should look like dynamite for appearance judging.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Ken Culbertson

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Re: Arming switch DIY the easy way
« Reply #12 on: August 14, 2019, 04:21:18 PM »
If you just spin it out until there's light visible between it and the contact, you should be OK -- but yes.

I really want to make a knife switch that can be covered & contoured to match the plane, like a little hatch, and just shut to fly.  It should look like dynamite for appearance judging.
I have thought about that too.  Some of the guys here just use a simple slider switch.  I sort of think that an obvious arming plug on an electric is no more a draw back than a pipe sticking out of the bottom.  I have used a pop off cowl on a profile that lets me disconnect the battery.  No complaints at contests, so far it has been in three.

I have also thought of disguising a removable plug as a small air scoop.  I plan to see what that looks like on my current build.  Nice part about a removable is that it is.....removable!

Ken
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Offline Tim Wescott

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Re: Arming switch DIY the easy way
« Reply #13 on: August 14, 2019, 05:10:49 PM »
Some of the guys here just use a simple slider switch.

Eek!  A "simple slider switch" that can do 30-40 amps is a big slider switch.  One that can't do that is trouble waiting to happen.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Crist Rigotti

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Re: Arming switch DIY the easy way
« Reply #14 on: August 14, 2019, 05:23:59 PM »
I think Ken is confused with the Igor system that uses a slide switch to turn the system on as being an "arming plug".
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Offline Tim Wescott

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Re: Arming switch DIY the easy way
« Reply #15 on: August 14, 2019, 05:59:28 PM »
I think Ken is confused with the Igor system that uses a slide switch to turn the system on as being an "arming plug".

And not an arming plug within the intent or wording of the rules, BTW.  I was here for that discussion; I think I even added my own dollop of support for it.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Ken Culbertson

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Re: Arming switch DIY the easy way
« Reply #16 on: December 19, 2019, 11:31:11 AM »
Eek!  A "simple slider switch" that can do 30-40 amps is a big slider switch.  One that can't do that is trouble waiting to happen.
Reading back through this looking for tid-bits on timers exposed an obvious brain fart on my part.  You are right, it was an Igor and there was a real arming plug on the other side.

ken
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If it is not broke you are not trying hard enough.
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