We split the feed the fish challenge into 2 separate parts; Building and decorating the fish tank, and building the mechanisms to fire the nerf dart into the tank.
Building A Tank
As a little break from the robot, I decided to set upon the task of building the tank. We decided we wanted to make it look as realistic as possible, with a wood effect base, with an ocean theme around the outside.
Aaron however came up with a brainwave, we can use a clear Perspex front to give off the effect of glass, and decorate the internals too! We found a broken plastic display stand which we cut down to size, perfect to fit in the windows, and then ordered some small plastic aquarium plants off Amazon to put inside. We then used black insulation tape to give off the effect of a seal around the outside.
It did however become very apparent we needed something to fill the floor. With it being made solely out of cardboard, and tape we knew we wouldn’t be able to use real gravel, however eating breakfast, I had a brain wave. Rice Crispies could be used as they both look rock-ish and are very lightweight! After a quick trip to Tecos at lunch, we were very happy with the result!
Locked & Loaded
Once we had our target, it was time to come up with the mechanism for shooting. As seen in in our challenge planning post, we were planning on re-purposing a nerf style gun from home bargains. After many cross office nerf fights, we felt fairly familiar with the workings and mechanisms of the gun.
To successfully achieve the challenge, we needed to find a way of automatically cocking back the gun, pressing the trigger and reloading it.
After taking the gun apart, we realised the cocking back of the gun and trigger mechanism could be combined into one motion. we could bypass the trigger and cock it back as part of the firing mechanism. To do this, we decided to use a snail cam on a 360 degree servo. This enabled us to gradually build up tension on the string (cocking the gun back) and suddenly release it to give the forward momentum to shoot the bullet. An example of this can be seen below, with the follower being the cock of the gun.
Reloading was very simple. we could attach a servo to the pre-existing reload mechanism, which enables us to automatically twist the barrel ready to fire another shot. To do this we attached an extended post to the existing reload mechanism, and linked it up to a servo arm, using a paperclip. Luckily this worked first time!
Putting it all together
Once we had both mechanisms working, it was time to put it all together! Again, this was fairly painless, we 3d printed a base plate so that the cam could be mounted to the top of the gun.
Once this was secure, we attached everything and went for the first test shot, which surprisingly was a first time success! It’s safe to say we were over the moon!
Now the main bulk of the feed the fish challenge is complete, it’s time for us to start looking into the other 2 challenges, with the deadline fast approaching ?
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