The Arm Story

December 7, 2013
This year, we took a different approach to our arm. We decided to build a ladder lift arm using drawer slides. Originally, a modified drawer slide was being powered by a threaded rod. This method took a while to build, and we had to go to our first competition without an attached or close to done arm. That day, at the competition (which was also a work day) we decided to go another route. A mentor assisted us in beginning a drawer slide ladder lift that will be powered by a string pulley system. I could still tell this was going to take a while to build.

As our next competition approached, the arm looked like it may be complete, but was it going to work? Every meeting was mostly designated to working on the arm. It is a complicated structure. The night before our qualifier, the arm was finished and working.

The only problem: it didn’t reach high enough. That was crushing. After all the time we spent designing and building it, there was still a flaw. To help fix this, we put and extender hook on the robot to push the pendulum down. During the competition, we were able to raise the arm and score three blocks, but the arm took a while to move up and down and was not the most consistent way to score. Many improvements needed to be made before next competition. We were hoping the simple solution would be to change the gear ratio, but nothing in robotics is ever simple. We decided that the best thing to do was rework the stringing method. This way, we would get more height and speed to our arm. A month until our next competition.
During that time, work was being completed on the arm but inconsistently. The mentor, whose design it was did not show up to every meeting, and little work could be completed without him. Also, the design was complicated with lots of moving parts, so pinpointing problems was difficult. We kept working, up to the day before the competition to finish our arm. The week before, all the ball bearing fell out and needed to be found. The next meeting, our mentor was away for business so we struggled to come up with the stringing method. By this point, the hardware was done, but we were unsure of how the string went through the eye nuts to power the arm. A Saturday meeting was necessary.
On Saturday, our mentor landed in philly at 6 am and was at school to help us by 9. There were five of us there, working away to try to finish. But now we know how to string the arm! The process is as followed:

This is still confusing, but it looks so simple.

Finally, pulling on the string lifts the arm. A winch system was also made to keep the string in line where it is wound around. Finally, we have a working arm. It was not tested before the competition, but that morning, we will run the motor and see how successful our system is.
The process was a stressful learning one. I wanted to just have a completed arm at some many times, but I realize that if this works, it will be worth the wait. It is a very unique design. And a complicated one. Now, all the flaws have been worked out and we can hopefully score with blocks. The arm we have now went through a lot of changes since the original design. Many people’s collaboration helped the arm be the structure it is now. The arm will work at the competition! It was a long process, but one that will have a big payoff.
Until next time,
Grace Stridick
4390 Team Captain

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