Tracking and hitting a moving target (Patreon)

My projects usually start with me saying "that can't be very hard" and eventually end with me saying "wow that was really hard." This project is no exception. 

I've been trying to build a handheld automatic bow that aims and fires for you. My original goal was to aim at stationary targets but my wife told me that was lame. I've upped the ante and have been designing this to hit moving targets. Like my basketball hoops, the crux of this project is having accurate, real time data collection which I can respond to with a fast, precise mechanism.

I've been going through the all the usual motions of integration hell. As is customary I've had a major issue with most parts of the system as well a couple big facepalms of my own creation. But after all that gnashing of teeth I can see the light at the end of the tunnel and things are finally starting to gel. The video I posted above shows a typical shot from the bow with my current software + hardware. 

There are a few things that are keeping me from smashing that target repeatably. The biggest issue right now is timing. To hit the target, my prediction of when and where the target will be has to be accurate to around 40 milliseconds with perfect aiming and timing of the arrow release. If my aiming isn't perfect then that window gets smaller. 

Normally I'd tell you that to a computer 40 milliseconds is an absolute eternity, but the issue I'm dealing with is that the computer is attached to a lot of fidgety hardware that is not well characterized. In the video above the arrow is aimed well, but about 150 milliseconds too late. Things like how long the arrow takes to be released and how fast the arrow flies can easily vary by tens of milliseconds and I'm currently using guesses for pretty much everything. I suspect this is the root of most of my timing issues. 

I'll be spending my Friday night measuring an characterizing a bunch of electromechanical systems. Who needs bars with this kind of nightlife... 

Hopefully it will be working smoothly soon so I can put this video together. I've been excited about this one for several months now and it is so cool to see it coming together! As always I'm very grateful for the support so I can spend time trying to make nonsense like this work.

- Shane

P.S. I got to build yet another catapult...

[UPDATE] Things are now working beautifully. I am so pumped for this video. Here's a sneak peak: