In this build we have a crack at a Guardians of the Galaxy movie, in particular Yondu and his Yaka arrow. A small model rocket engine seemed the logical propulsion for the arrow part, so all we needed was a whistle activated rocket launcher, seems simple enough.
Whistle activated switch
I thought of a couple of ways to do this project, the first was to hack one of those cheap whistle key fob key finder things. The trouble being there was too much work, it may be accidentally triggered and the components required bump the cost up making it less attractive. The second was to use an Arduino board, then program it, but again extra components, then code and computer link up’s.
Then I stumbled across a project called The Whistled on tindie. This tiny self contained circuit has everything built in and no programming required. For $18 it’s a no brainer for me and fits in with my keep it simple mentality.
Some additional parts were required…
Firstly I would not class myself as having any real electrical skill other than understanding very simple circuits, but I did decide to add a simple relay. When ‘The Whistled’ triggers, it powers the relay, which in turn supplies power direct from the battery. Secondly a diode is required between the outputs of the screw terminals on the whistled to stop feedback when igniting rocket igniters. A decent battery is required to power both the whistled, and the current draw of the rocket ignitor, I used a rechargeable LiPo because I already have them. I decided to place the onboard condenser microphone on the outside of the ‘Yondu box’ for long distance tests, and while I was at it, I changed the standard unit for a larger Mic. In hindsight I’m not sure that was a necessary step, I think just placing the standard mic near a pre drilled hole would have been fine.
Parts required that I should have fitted, but didn’t…
I should have definitely fitted a fuse or fuses. I rely on the rocket igniter bursting to stop the obvious short in the circuit, but if the two alligator clips where to touch for any period of time that could be the death of the whistled. [Update I did accidentally damage the unit because of the missing fuse]
Obviously when the circuit was proven to work, it was time to box it up. I decided to add some simple indicator lights and a switch for basic safety, accidentally hooking up live wires to a rocket motor would be incredibly stupid.
The above project is aimed at adults for education and entertainment purposes only, not to replicate. Anyone doing so takes full responsibility for their own actions.