Servo - December 2015

The optimization of the cannon was a resounding success, and it all came from an understanding of the air cannon physics that allowed us to pinpoint the biggest areas of improvement in the original design. Of course, there was even more we could do; we still want to automatically actuate the ball valve to have a proper robotic air cannon, and devising the quickest method to open the valve is another way to maximize performance. When it comes to robotics and just about any project, there is always room for improvement.

Please remember, everyone! A compressed air cannon is even more dangerous than a Red Ryder B.B. Gun, and it can do a lot worse than put your eye out. We took numerous safety precautions. Don’t try this at home without taking those proper precautions. That would be a terrible way to end up on the naughty list.

Stocking Stuffer

Since we were inspired to revisit some projects for optimization this time, we also took the opportunity to gift our 60 lb combat robot, Troublemaker with a new weapon. Or, rather an optimized version of its old weapon. When we first designed Troublemaker’s horizontal spinner, we were focused on avoiding having the force transferred back into our own bot. To that end, the spinning mechanism itself is belt driven, and on the ends of the spinner we used tethered weights. The design achieved its purpose in that we successfully avoided having Troublemaker destroy its own weapon mechanism. However, the tethered weights presented a problem that we hadn’t quite expected: The tethers were destroyed in every competition.

While it was a little tough to see what precisely happened during the fast-paced matches, we eventually deduced that the weak points were the stoppers that we used at the end of the weights. For the tethers, we used steel cables that we threaded through a hole in the center of our weights. We looped the end of the cable back around and clamped it together as a stopper.

The clamps, however, were not rated for heavy lifting. The centripetal force the stoppers needed to exert on the spinning weights — combined with some well-placed hits on other robots (or the arena) — were all that was needed to shear off the clamps.

We’ve chronicled in the pages of SERVO Magazine our efforts at an alternate weapon design: some titanium claws that wouldn’t get sheared off. The claws worked well enough, but they lacked the impact of the spinning weights. So, we devised a new design that would keep the weights on the bot.

Instead of steel cables for tethers, we opted for heavy duty chain. Since it took us a long time to cut through with a pneumatic disc cutter, we figured it would make it through three minute matches just fine. To attach the weights to the chain, we opted for shackles and eye bolts that were also rated for heavy duty lifting. The new design was now a bit more modular which would allow us to replace damaged parts easily.

It was a thrill to get Troublemaker’s spinner back to its former hard hitting glory. Now, we just had to replace the aging stiffening belt to get it to spin up quickly again.