For my birthday my kids bought me an excellent Nerf™ gun: a 25-shot chain gun. Aha, I thought, now I'll finally have the edge in our weekend Nerf battles - though the boys quickly pointed out the weakness of the new weapon. "You'll run out of bullets pretty quick Dad, then we'll get you." Having articulated their wait-Dad-out strategy, the conversation turned to what else we could do with this new bit of Nerf kit. "Wouldn't it be cool if we could set up a remote control turret?"
Wanting to build something that would deliver pretty immediate results I opted for a Lego™ Mindstorms™ based system. After a couple of false starts we came up with a simple mechanism to squeeze the Nerf gun's trigger.
The grey Lego axle is used to hold the mechanism in place and stop it from sliding up over the gun's trigger. A pair of large gears pulls two Technics beams backwards to squeeze the trigger. It's not particularly complicated, but I wanted to build something that we could get up and going before my oldest's enthusiasm waned. We were, after all, cutting into important Minecraft time.
For the software I used the NXT Remote Control app by Jacek Fedorynski. It's available for free from the Google Play store. I cannot rate it highly enough - it's simple to use, connects to the Mindstorm without any dramas and has nice set of alternative UIs for driving different styles of Mindstorm remote-control projects. I'm planning on using it for another project shortly and I'll go into the details of how to use it there - though it's really no more complicated than turning on your Mindstorms brick and syncing to the app.
The squeezing mechanism could have been a bit more robust - I would have liked to have prevented it from putting a strain on the motor once the trigger had been pulled - but it's basic and it works. The intention was to distract the kids away from Minecraft for a while and build something "real". The look on my oldest's face when we fired off the first test shot was priceless. Here we'd built something quickly that performed as expected - unlike a lot of our other projects where the payoff takes time. Hopefully it will enthuse them to get involved in some of the more complicated projects on the bench at the moment.
The Lego mechanism needed to be attached to the Nerf gun using a rubber band. OK, not strictly either Nerf or Lego kit, but again keeping with getting quick results it worked well.
Ultimately I'd like to put the whole gun on some sort of rotating base so we can swivel it around and shoot at targets around the room. But that's for another weekend.