Construction:

When buildin' me level1 rocket, I wanted t' use a simple, reliable armin' switch t' turn on me altimeter. Well, blow me down! My first thoughts were t' use an interior switch which could be accessed through a hole in t' avionics bay, matey, but decided that it would be difficult t' turn on and off especially once on t' launch pad. Avast, me proud beauty! Begad! I nixed t' pull-pin type some people construct with a micro switch since it be complicated, matey, me hearties, bulky and heavy, matey, 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. It had t' be low profile t' minimize drag, ya bilge rat, be light in weight, and easy t' turn on or off with a screwdriver. Avast, me proud beauty! Arrr! I considered t' popular 110 -220 volt armin' switch that is commonly available. Well, blow me down! It had t' advantage o' two sets o' contacts (2 poles) which I did nay require and uses a slotted screwdriver t' activate. T' disadvantage is that t' markings are 110–220 instead o' ON-OFF, it needs quite a large hole in me 3” rocket, arrr, and t' slot t' operate t' switch is very short but wide. Avast! Most any screwdriver I have on hand makes a sloppy fit in this slot. Ahoy! Avast! Also it isn’t as low profile as I would have liked. Ya scallywag! I decided against it.

Searchin' t' web, I located a very nicely made screw switch for 2 bucks and ordered one. Begad! T' me surprise it was 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! Arrr! Nay reliable enough for me rocket which took many hours and dollars t' build. Begad! Also t' supplied steel screw was nay low profile, arrr, 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. Arrr! Arrr! 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. Arrr! Ya scallywag! You know those wonderful pull-out drawers with all their little compartments. I spent way too much time lookin' at all t' stuff I never new existed!

While lookin' for t' right parts, me bucko, I came across t' drawer o' Rawl nuts©. Arrr! (Some stores carry WELLNUT brand) These are top hat shaped rubber plugs that have an integrated brass nut at t' narrow end. Ya scallywag! 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. Avast, me proud beauty! T' screw pulls t' integrated nut closer t' t' flanged end expandin' t' diameter o' t' plug which tightens it in t' hole. Ya scallywag! Avast, me proud beauty! But I digress here. T' shape o' t' Rawl nut be perfect and it already had one highly conductive brass insert molded into t' narrow end. My idea was 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. Avast, me proud beauty! 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! 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. Well, blow me down! 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. Arrr! Blimey! 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. I decided t' best way t' do this be t' grind a channel into t' rubber and one side o' t' integrated nut t' allow t' wire t' be recessed. Ahoy! Blimey! T' other wire would connect t' t' other side o' t' integrated nut.

Directions:

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

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

3. Begad! Usin' t' all thread rod and jam nut t' secure t' Rawl nut in a vice, 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. Aye aye! T' channel should extend from just behind t' flange all t' way through t' integrated nut and out t' t' rear.

4. 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. Avast, me proud beauty! Solder t' wire t' t' brass insert you have prepared.

5. Arrr! Blimey! Push t' insert into t' Rawl nut until it is flush with t' front flange. Avast, me proud beauty! Well, me bucko, blow me down! This photo was actually taken after t' switch was completed.

6. Ya scallywag! Begad! Thread t' all thread through t' brass insert until it screws into t' integrated insert. 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. Use a slotted screwdriver t' engage t' slot in t' brass insert t' rotate it then try again until just right. Avast! If you skip this step, shiver me timbers, me hearties, t' threaded rod will nay thread into t' integrated nut and will just try t' push t' two nuts apart. Aye aye! You’ll know when its right as t' all thread will effortlessly pass through both nuts.

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

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

9. Avast! 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. Aye aye! At first thar should be no continuity until t' screw bridges both brass inserts.

10. Aye aye! Begad! Check your work and make sure everythin' looks OK. 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! My hole turned out t' be 21/64”. Ya scallywag! Finally wick some cyano adhesive in from t' back for a perfect installation and label with a P-touch.

Copyright © by Dave Lang