In this robotics tutorial, we present a solution to extending a VEX IQ attachment to handle two hex balls at a time
- 06 Jun 2017
Make two sides grabbing mechanism
With the use of a number of gears, pulleys and belts we can control the two sides of the attachment to come together and grab a VEX hex ball or to move away from each other and release a hex ball. The system of gears, pulleys and belts is controlled by a motor.
To achieve the movement of one of the sides we need two wheels. The two wheels should move in sync. This mechanism is very interesting and important. Check out the video on how exactly it works.
The construction of one side of the VEX attachment is replicated.
Here is our solution on extending this single Hexball attachment to an attachment that could work with 2 Hexballs. And we've also use the opportunity to build the attachment in a different way - this one here so that we an show you a couple of other principles for building such attachments for grabbing. Let's get into details of this attachment. Here's how it works. You can come to the Hexballs, you rotate the motor and you grab the Hexballs.
Where do we start from? We start from the right side of this attachment right side from my point of view and this is the part of the attachment currently with the orange Hexball. We are thinking of a way to make the two sides and we are using the same constructions for the sides right here with the rubber bands to move to each other and away from each other. And we can do this with wheels. The gear wheels and the other wheels in the VEX IQ set have some holes on them and we can attach the sides of our attachment to these wheels. What will happen is that for example if we have the construction like this,
we can have the wheel moving and it will move with this side like this. The problem is that we are not fixed and this side can also move freely. It can move with the wheel but it can also move freely. That's why we need a second wheel. And we attach the side to the second wheel. Now, depending on the length of these parts it will have different effect. But if we do it like this, when we rotate these two wheels the whole side will move to the inside. And if we rotate in a reverse direction, it will move to the outside. These two wheels are large wheels and there is not enough space between them to change the rotation, to change the direction in which they are moving. So, these two wheels are moving in the same direction. And this makes the whole side move to the inside. We replicate this construction to the other side of the attachment but we just mirror it. The same principle. This means that at the end we should have both of the wheels rotate in a different direction. These two wheels right here. They should rotate in a different direction. So, recap. We have the sides, we have the wheels, we can attach the sides to the wheels because the wheels have small holes on them. From there because we attach the sides to the wheels they are loosed and they can move freely along with the wheel. That's why we need to attach the side not only to the first wheel but also to the second wheel and this makes the side move only with the wheels. Then we mirror the same image to the other side of the attachment and then we should think of a way to rotate these two wheels in the opposite direction. An important part from this whole attachment is the synchronization between the two sides and the 4 wheels here. The wheels are 2x2 connected with belts. You can see one of the belts right here. It's black and the other belt is right here. So, whenever there is some power transfered to the first wheel it will also transfer to the second wheel. The real challenge here is to synchronize the two wheels. And because of the synchronization you want to move the whole side like this. You should move it in one plain. For example, this here just moves horizontally without an angle. Currently the two sides are not synchronized and the two wheels are not synchronized correctly and you can see that the whole side moves one of its sides to the inside of our attachment. And we should avoid this because that's our goal to avoid this. What we should do is correctly synchronize these two wheels. How do we synchronize them? Now, that's the difficult part of the whole attachment. We remove the belt and we align the two wheels so that the holes on which the whole side is attached are to the right. And then when we've aligned them like this - they are horizontally and both are on the right - this hole here and this hole here. This is the correct alignment. If you have it like this, this will be a wrong alignment. Now we have it like this, we position it like this and now it's a little difficult because you should move the belt and in the same time avoid moving the other parts which is not very easy but let's try to do it.
And now we have the two
holes on which the side is connected on the same line right here. And now if I rotate this gear wheel, you see that the whole side again moves slightly to the inside but not that much because again the synchronization is not very perfect. And we could change this to make it more perfect and the side will move just horizontally.