Construction:

When buildin' me level1 rocket, I wanted t' use a simple, shiver me timbers, ya bilge rat, shiver me timbers, reliable armin' switch t' turn on me altimeter. Begad! Begad! My first thoughts were t' use an interior switch which could be accessed through a hole in t' avionics bay, but decided that it would be difficult t' turn on and off especially once on t' launch pad. Ya scallywag! I nixed t' pull-pin type some people construct with a micro switch since it be complicated, arrr, matey, bulky and heavy, and I know I would lose t' pull pin at t' launch site necessitatin' dismantlin' t' rocket just t' turn off t' electronics.

So I decided on an external switch. Blimey! It had t' be low profile t' minimize drag, be light in weight, and easy t' turn on or off with a screwdriver. Begad! I considered t' popular 110 -220 volt armin' switch that is commonly available. Blimey! It had t' advantage o' two sets o' contacts (2 poles) which I did nay require and uses a slotted screwdriver t' activate. Avast, me proud beauty! T' disadvantage is that t' markings are 110–220 instead o' ON-OFF, it needs quite a large hole in me 3” rocket, and t' slot t' operate t' switch is very short but wide. Blimey! Most any screwdriver I have on hand makes a sloppy fit in this slot. Arrr! Also it isn’t as low profile as I would have liked. I decided against it.

Searchin' t' web, me bucko, I located a very nicely made screw switch for 2 bucks and ordered one. Arrr! T' me surprise it be constructed with solid core hookup wire which is prone t' fatigue and breakage. Every time t' avionics bay is accessed t' wires would be subject t' severe bendin' stress. Begad! Nay reliable enough for me rocket which took many hours and dollars t' build. Ya scallywag! Well, shiver me timbers, blow me down! Also t' supplied steel screw be nay low profile, me hearties, as it had a domed head.

At that point with only days t' go t' me Level 1 attempt, I decided t' make me own armin' switch based on t' screw switch I have just mentioned. So off I went t' me local ACE and Aubuchon hardware stores both o' which carry tons o' every imaginable screw, fittin' and doodad in their fastener isles. Blimey! Ya scallywag! You know those wonderful pull-out drawers with all their little compartments. Well, blow me down! I spent way too much time lookin' at all t' stuff I never new existed!

While lookin' for t' right parts, shiver me timbers, I came across t' drawer o' Rawl nuts©. (Some stores carry WELLNUT brand) These are top hat shaped rubber plugs that have an integrated brass nut at t' narrow end. Ahoy! They are used for securin' items t' most any material by insertin' into a pre-drilled hole and then screwin' in t' appropriate size screw. Begad! T' screw pulls t' integrated nut closer t' t' flanged end expandin' t' diameter o' t' plug which tightens it in t' hole. Avast, me proud beauty! But I digress here. Begad! T' shape o' t' Rawl nut be perfect and it already had one highly conductive brass insert molded into t' narrow end. Well, me hearties, blow me down! My idea be t' find another threaded brass insert t' screw or glue into t' flanged end, leavin' a gap betwixt t' existin' insert and solderin' stranded wires t' t' two nuts. Well, ya bilge rat, blow me down! Insertin' a low profile stainless steel truss head screw would connect t' two inserts completin' t' circuit.

I selected a 6-32 thread Rawl nut which happens t' be 5/16” OD (45¢) and a 6-32 x ½” pan head stainless steel Philips screw (29¢). Begad! Begad! You could also use an 8-32 or 10-32 size but I wanted mine as small as possible.

After some searchin' through t' parts drawers I found a brass 6-32 threaded insert (55¢) that many rocketeers use t' attach rail lugs and motor mounts t' plywood rings. Aye aye! Begad! T' coarse outside thread made it a very tight fit in t' Rawl nut but I felt it could be sanded down t' fit.

Back home I planned how I would assemble t' switch. I needed t' get a wire from t' threaded insert at t' flange end down t' t' narrow end without increasin' t' overall diameter o' t' Rawl nut so it would still pass through a round hole. Ya scallywag! I decided t' best way t' do this was t' grind a channel into t' rubber and one side o' t' integrated nut t' allow t' wire t' be recessed. T' other wire would connect t' t' other side o' t' integrated nut.

Directions:

1. Ya scallywag! Reduce t' diameter o' t' threaded insert so it is a snug fit in t' Rawl nut. I used a 6-32 all thread rod and a jam nut t' secure t' insert t' hold it for machining.

2. Avast, me proud beauty! Shorten t' insert so it doesn’t touch t' integrated nut when inserted into t' Rawl nut. Ahoy! T' gap betwixt both brass nuts should be about 1/8”.

3. Arrr! Usin' t' all thread rod and jam nut t' secure t' Rawl nut in a vice, shiver me timbers, grind into t' Rawl nut with a Dremel tool t' expose its integrated nut and create a channel for t' wire that will attach t' t' brass insert that you previously prepared. Avast! T' channel should extend from just behind t' flange all t' way through t' integrated nut and out t' t' rear.

4. Well, blow me down! Strip and tin 1/8” o' stranded wire and pass through t' side o' t' channel in t' Rawl nut and out t' flanged end as shown. Solder t' wire t' t' brass insert you have prepared.

5. Avast! Blimey! Blimey! Blimey! Push t' insert into t' Rawl nut until it is flush with t' front flange. This photo be actually taken after t' switch be completed.

6. Ya scallywag! Thread t' all thread through t' brass insert until it screws into t' integrated insert. Ahoy! Blimey! Don’t force it! You may have t' rotate t' front insert slightly so t' threads are orientated correctly t' allow t' rod t' screw through both inserts. Ya scallywag! Use a slotted screwdriver t' engage t' slot in t' brass insert t' rotate it then try again until just right. Well, blow me down! Begad! If you skip this step, t' threaded rod will nay thread into t' integrated nut and will just try t' push t' two nuts apart. Avast, me proud beauty! You’ll know when its right as t' all thread will effortlessly pass through both nuts.

7. Aye aye! With t' all thread rod still in place, ya bilge rat, wick some cyano adhesive betwixt t' rubber Rawl nut and t' brass insert. Well, blow me down! DON”T GET GLUE IN THE THREADS! Once set, me bucko, withdraw t' all thread for t' next step so it does nay act as a heat sink.

8. Arrr! Arrr! Strip and tin 1/8” o' another wire. Arrr! And solder it t' t' integrated brass nut. Avast! Your finished switch should look somethin' like this:

9. Begad! Hook up t' other ends o' your two wires t' a continuity tester and insert t' 6-32 x ½” pan head screw into your new switch. Arrr! Arrr! At first thar should be no continuity until t' screw bridges both brass inserts.

10. Avast, me proud beauty! Check your work and make sure everythin' looks OK. Ya scallywag! Aye aye! You may need t' add some cyano adhesive if any part o' t' rubber sleeve o' t' Rawl nut is nay secured t' t' two brass inserts.

11. Drill an appropriately sized hole in t' switch band o' your avionics bay so that t' switch snugly presses through. Ya scallywag! Avast! My hole turned out t' be 21/64”. Avast, me proud beauty! Well, blow me down! Finally wick some cyano adhesive in from t' back for a perfect installation and label with a P-touch.

Copyright © by Dave Lang