Monday, April 16, 2007

The Home Stretch

Well, we have almost made it to the end of the semester. For better or worse it will all be over in less than 2 1/2 weeks. The robot competition, however is sooner than that. Next wednesday, April 25, is the Mechanical Engineering design day, which means thats when the robot has to be done. Let's see, today is the 16th, so that leaves only 9 days. It's time to work a miracle. The design has come across several stages since I last posted, so I'd like to showcase the current model. First, we replaced the track arm manipulation motors with servos which are easily seen in this photo:
At first the servo was directly attached to the largest gear that you see there, but it proved inadequate. This was a surprise to us since the servo is so strong that you can't really force it by hand. Anyway, we didn't want to lose the cost of the servos so we decided to hack them. Servos use a little device to tell where the arm is so that it can be controlled by the radio transmitter (which we are not using either). What we did is take out that little guy and replace it with the same type of component, just hopped up on steroids. It's the thing just behind the big gear with the wires coming out of the top. This thing tells us where the track arms are just like it would have worked in a standard radio system. The trick here is that the robot brain is what really needs to know where the servo arm is. That way we can give it a routine to perform beforehand and it can do it by itself.

Another change we made was the addition of another roller on the top of the arms. The idea behind this is reduction of the force required to lift the bot. It decreases the amount of leverage that is necessary. Here's a good picture of them:
Between these and the servos, we should be able to make the arm concept work.

Another challenge we are tackling is that of teaching the robot to navigate. Really all it has to do is follow a line or follow walls. The ones that follow walls do so by having little feelers on the sides. This method is much easier but having the track arms makes it impossible for us to use this method. Our line following array is built, but it's kind of hard to interpret the signals it is providing to the computer. Basically, the array consists of five little eyes that can tell the difference between black and white. They will be following a black line on a white background and the robot must be able to steer according to what eye is seeing the line. We should be able to at least have something by next Wednesday.

This has been a good project. If I had it to do over again I would certainly not make the project so elaborate. It has gotten several oohs and aahs for its craftsmanship, but that won't matter if it doesn't do what its supposed to. Wish us luck.


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