- 24 Jun 2017
In this video we'll discuss some new material and some theory about the workings of our rack attachment - double rack attachment for grabbing and moving two objects at a time. We've provided the building instructions for this attachment in the course and somewhere below the video and now let's discuss the idea of this attachment. Initially we had a single attachment and this single attachment was responsible for handling a single object. Then we replicated this attachment and we had two identical attachments both with motors and we tried to connect these two attachments. Or at least you should have tried to connect these two attachments together then place it on the robot and move. The problem with this approach is that you are using two motors. And the idea of this attachment is to use a single motor for powering both parts of the attachment that could grab the object. So, the goal again is to use a single motor. Why? Because we might need to use the motor for some other missions. The way we achieve this extension without the use of a single motor is with the use of a rack. And you can see the rack right here on the inside of the robot. And it's a very simple mechanism. You've probably seen it in some of the other courses at fllcasts.com and it includes a gear wheel - this one here and a chain. And when you rotate the gear wheel it pushes the chain and the whole attachment will move from here. So, you have a chain, it's with a limited length. Let me try to show it to you. You have the chain and you have the gear wheel attached to the chain like this. And then you add a motor somehow you transfer power with a motor to this axle right here on which the gear wheel is attached. And if you transfer this power from a motor, then the motor will rotate the gear wheel and this will move the whole attachment. And the next interesting thing about this attachment is the way the different parts slide to each other. When you are building such attachments where the parts slide what you should make sure is there is a strict limitation on the boundaries on which the sliding happens. Example here. I have this beam and this beam is sliding and it's supported by two other beams - this one and this one. And even if I apply some force, the beam stays in place. But if I remove this part, when I apply the force, it will bend and the two parts will not stay aligned And this will prevent them from sliding.
So, you should have all the sliding parts supported
so that you have a stable sliding. And that's very important because if you forget this, you'll have an attachment that will slide but the moment you apply some force probably from the motor or because you have a heavy object at the front it will bend and it will not slide correctly. Next, how do you attach the motor to this attachment? We left some space right here with two pins on which you can build something that holds the motor and transfer power to this axle. So, you place the motor somewhere right here probably using these two pins. But again probably - it's up to you.