Vex Brakes

For Sack Attack, I want to put brakes on my robot, so I cannot be pushed around if someone is stronger than me. Please post any ideas on brakes, and if you can, please post a picture or diagram of the brake.

Thank You!

The best vex has to offer in terms of what you have described is a ratchet gear, IE a one way gear. (what you see here http://upload.wikimedia.org/wikipedia/en/1/17/Ratchet_example.gif) Which is in this product: http://www.vexrobotics.com/276-1546.html. The other thing you could theoretically use is a worm gear, but that will slow down a drive too much to be effective. There is another way without necessarily “braking” per say. I find that an all steel tank drive parked parallel to the impact of the other robot is sometimes the best way to go. This is similar to the way 169 “E” played this match: (we have the wobbly tower) http://www.youtube.com/watch?v=eNc7G5p7wjk&feature=relmfu

Some teams used pnuematics that pushed something down into contact with the ground also you could try high traction tires

I’ve used encoder-based brakes in the past in FRC (a proportional loop in the code will push in the opposite direction of the encoder ticks). This could be dangerous for VEX motors though.

Another option may be pneumatic feet, where a piston pushes a brake into the foam mat. You will just have to make sure your brake doesn’t “damage” the field.

) Which is in this product: http://www.vexrobotics.com/276-1546.html. The other thing you could theoretically use is a worm gear, but that will slow down a drive too much to be effective. There is another way without necessarily “braking” per say. I find that an all steel tank drive parked parallel to the impact of the other robot is sometimes the best way to go. This is similar to the way 169 “E” played this match: (we have the wobbly tower) http://www.youtube.com/watch?v=eNc7G5p7wjk&feature=relmfu

Thanks for the advice. I don’t think we will be able to break by parking parallel because our robot will be omnidirectional.

As has been already suggested, I would use a worm gear. If the gear the worm rotates is on the output shaft and you gear it up with a 1:25 ratio (which is two 12 tooth gear-60 tooth gear combintions) your overall ratio is 24:25 or 1:1.042 (the worm gear is a 24:1 reduction). So you barely have a speed ratio.

I can make a diagram if that would be easier to follow.

The problem with a pneumatic foot is rule SG9 which states:

And definition of a field element is

So Unfortunately, although super effective, a pneumatic foot would not be allowed. I suggest going with either the racthet gear or the worm gear idea. Disciple that idea sounds interesting, could you make a diagram? I am having a hard time following it.

That would be good

I dont quite understand why a pneumatic foot would be illegal. Its not actually grabbing the tile, its just taking the weight off the wheels.

I don’t think this makes a pneumatic foot illegal, the robot isn’t really attaching to the field, it can still be lifted off or pushed, it just has more friction in the pushing direction, and if the brake is a plate of metal coated in grip cloth, there is almost no way for it to damage the tiles or sacks.

Actually I think that would work legally, I apologize. You’d have to build it with extreme caution though, but yes that is a way to do it. A picky ref could call it grasping I guess, but I agree with you now after reading it over a couple of times now.

Is there any other ways you guys would suggest without using pneumatics? These are great ways, but I’m trying to avoid using too much pneumatics.

You could do any of the above ideas with a motor :stuck_out_tongue: . The only way I can think to do it without any source of power would be to maybe have a plate geared to the tower, so when the arm lowers beneath the height required to pick up (or above the height to drop), it pushes a plate down? Or you could use the worm gear suggestion, which would work, but put a lot of friction into your drive.

Hah, too many pneumatics. There is no such thing! But seriously, if you have a spare motor or two just use them with a really high torque ratio to place feet on the ground just like the pneumatics would do.

Alright. So here we go:

https://vexforum.com/gallery/files/1/0/5/8/8/3/worm_brake.jpg

This is what I was talking about. Obviously there are no mounts and I wasn’t trying to make this compact. But this should illustrate the general concept.

Not sure I see the point of doing a drive specifically like that. Omniwheels + worm gear for a “break” That is a bad pair in my mind. Also Keep in mind Worm gears can be back driven! Its very very hard to do so, but it CAN be done. Another thing is that it takes up a ton of space!

I feel like the worm gear would break before it is back driven. If the gears were metal it would be a different story though.

I like this idea but it takes up a ton of space and there is a lot of friction.

not to mention the friction by an axle spinning 25:1

I absolutely agree with the above comments, which is why I don’t plan on putting something like this on my robot. However, if for some reason braking without the use of pneumatics was imperative, this would do it for you. You would also be able to use the new higher strength worm gear that was released with the advanced mechanics kit.

Can someone give me a specific diagram or picture of the pneumatic brake?