Brakes
 

Does your robot have brakes? If so, how well do they work? How did you design them and how did you implement them?

Re: Brakes
 

Our robot has these things that run around the field that when you smash into the robot stops. They are called walls. :D

Re: Brakes
 

I mean something that is on your robot that makes you less suceptible to pushing. I have heard that 25 has them, and i'm sure other teams do as well. So, I was just asking for some details.

Re: Brakes
 

That is correct. We have pins that go into the cheese holes in the gears. This is controlled using a servo. Feel free to ask if you have anymore questions.

Re: Brakes
 

I poked around raiderrobotix.org trying to get some more information on y'all's brakes, but I couldn't seem to find any.

Without tipping your hand completely (what's the sport in that?), can you give us some photos for inspiration? MS Paint drawings? ASCII art?

Re: Brakes
 

Are you talking about brakes to stop your wheels from turning, or a brake like a pad of brecoflex or something to come down so the robot is sitting on it make you hard to move?

Next time you are over here at AVL, let's talk. I have some ideas for you.

Re: Brakes
 

Team 229 has brakes,

They are drop down pads front and back that we lower when we get in a good shooting position, or when we are loading up. They originally started out with floor mat material on them (the stuff you put under office chairs on carpet), Then we tried them with Sorbethane (the stuff Beatty used in 2003), and now they have wedgetop on them. We found that all worked better in pushing matches than just our wheels.

I will search for pictures if you’re still interested.

Chris
Team 229

Re: Brakes
 

see our pits in Newton at Nationals and we will have a sample to show you.

As Bharat said- we use a servo to drive a pin into the gears of the drive linkage and lock up the whole gear box. The result is 130 lbs of dead weight with 6 wheel traction. You move that you deserve to win.

the idea is simple- but you need to do a little programming to go with it and the work needs to be precise. It is EASY to have the pins tear apart your whole drive train if you dont design properly. And we discovered that when they reset the FIRST fields for a blown match we need to completely reset our auto modes or they engage automatically leaving us sitting there (3 rounds at NJ!!) Servos- gotta love em!

WC :cool:

Re: Brakes
 

Team 842 has some. http://www.chiefdelphi.com/media/photos/22689

Re: Brakes
 

571 has brakes similar to these. They are about 1.5" square of the rubber belt treads attached to a piece of wood on the bottom of a pneumatic cylinder. We have them between our omni's (reverse shopping-cart drive) and they worked really well for us.

We don't have any pictures of this specifically but I'll try and take some Monday at our meeting.

Re: Brakes
 

We, Team 228 have a brake on the front of our bot. It was pretty much a requirement as we're using 4wd with AM Omni's on the front. It's a fairly straight forward design, which uses a pneumatic to push a pad down onto the carpet.

If I remember correctly, it's a 4" throw, 1.5" diameter running at a full 60psi. The pad is about 1.5" x 4" long, with Roughtop belting over the entire patch. Because of the sideloads we anticipated, the friction pad is mounted to two extra shafts running in parallel to the pneumatic shaft, which will take most of the impact loading. These shafts are fed through two mounting plates and slide on bronze bushings.

The entire assembly weights in at about 4 lbs, but we had extra weight which we wanted to put low on the robot anyways. Most of the weight comes from the shafts, which are all 1/2" steel, about a foot long a piece. If we were weight critical, we would have used a much shorter throw pneumatic. This would have greatly cut down on the side loading, and allowed us to use aluminum shafts instead, or even just the pneumatic itself.

Unfortunately, we don't have any pictures. And, since it was pretty much built on-the-fly, we don't have any sketches of it either. It worked well enough to keep us positioned, unfortunately we had more trouble with our ball delivery system.

BEN

Re: Brakes
 

Our brakes dont use any motors or pneumatics and weigh 0 pounds.

Take a guess

Re: Brakes
 

Putting the victors on brakes or the driver him/herself?

Re: Brakes
 

Nope, good guess though.

Hint, its built in to the drive.

Re: Brakes
 

Sounds like a worm drive to me

Re: Brakes
 

You are most definately correct. They work very nicely, well once we switched from 5:1 to 10:1. The only way to get us to move is by hitting us really hard.

Re: Brakes
 

All i can say is surface area and 60 tread.

Re: Brakes
 

The only problem with that is that you are going to lose 30%-40% of your power due to the massive inefficiency of the worm and worm gear (and a more efficient worm gear would be backdrivable).

Re: Brakes
 

Well, it's nice to know that some people do actually have breaks. I believe we had one last year, although I knew a lot less about the robot last year (I don't think I could have answered my own scouting sheet!) but we don't have them this year because of weight. (we came in a bit over when we first weighed in).

But people give me the weirdest looks when I ask them if they have breaks while pit scouting. :) So thanks for proving that it's not that odd of a question!

Re: Brakes
 

Team 293 is using brakes based off of 25's design:
A servo sticks a pin into a milled out gear in the gearbox.

For the ammount that they weigh, the benefit is huge. If the brakes are on, the wheels don't turn.

The only problem is that before we got the settings just right, we snapped several servo horns.

Re: Brakes
 

Our robot had brakes...
They worked really well...

Actually our robot was able to push other robots around, so we just drove into other robots and pushed them backwards. :)

Re: Brakes
 

does anyone have any pictures of the BMS brakes?? They sound very useful. I know that my team wouldnt really benefit that much because we dont have the room for more servos, plus we have a holonomic drive, but it would be nice to see what some people think is impossible for a FIRST robot.

Re: Brakes
 

It's not our robot but I think it was team 486 The Positronic Panthers (forgive me if the team/number is incorrect) has a nice bumper/brake system. They would be a "Crash Shell" around their robot that once another robot pushed into it the pushers force would be nutralized.

I know there's a video out there that shows it, and it was really nice, but since the rule changes happened this year, those bumper/brakes weren't allowed.

Re: Brakes
 

If we get into the book you will have the cad of it. but since we are not going to know any time soon see our pits at nationals.
shaun

Re: Brakes
 

179 Does :D. They use a piston with waffle tread on the bottom

Re: Brakes
 

We have used dynamic braking for the past 3 years. There is a potentiometer mounted on each of the two final drive output shafts of our 4 wheel drive skid steer. When another robot pushes against ours the wheels begin to turn. When this movement is detected, the controller applies power to those wheels in the opposite direction to oppose the movement. The more needed, the more is applied. This gives us enough braking to lock the wheels. If another robot has the power and traction to move us with our wheels skidding, then they will win the pushing match.

In 2002 we had pneumatically applied brakes that worked great. There were two flat pads about the size of a playing card covered with rubber belting. The back of the robot and the movable goal we were latched on to was lifted off the carpet when these were applied. Nobody was able to move us that year.

Jay

Re: Brakes
 

Now with the presence of, off the shelf 2 and 3 speed tranny's and 4 and 6 cim's on a drive train, it is pretty hard to not be pushed around.

Re: Brakes
 

on thurday in atlanta we (1625) put grippy tires on the back and a "foot" that rotated down in the front lifting up our omniwheels making us practically unpushable but a few team found this out and moved us by ramming :rolleyes: Our major weakness before nationals was getting pushed while shooting and made our accuracy terrible so when we added the foot thats what made us the #1 seed :cool: so basically sticky stuff rules

Re: Brakes
 

I liked 1625's breaking meathod because it was simple and effective... One of our teammates suggested something similar but it got vetoed and than his hopes jumped when he saw a robot seeded #1 all because of something he had thought of.

I wanted that on our robot after i saw its effectiveness because our robot's best defencive was its Agility.

Pavan

Re: Brakes
 

Is it like our software brake?
The code monitors the encoders and whenever the joysticks fall within a deadband, it goes to hell and high water, and current limits to maintain those specific counts, so if we get pushed, it fights as hard as it can.

Mark McLeod can illuminate more on the subject.

Re: Brakes
 

What is a Worm Drive? Can someoen Explain?

Re: Brakes
 

A drive system which utilizes worm gears.

Worm gears are nearly impossible to backdrive, so when you're not driving them with your motors, anything powered by a wormgear won't move. Therefore in a drive system, the wheels don't turn when you don't want them to. Worm gears are also terribly inneficient, and you can potentially lose 30% or more of your power in a system using them.

Re: Brakes
 

If anyone cares, 772 (Sandwich SS from LaSalle, ON) used a worm drive on each side of their drivetrain (with two small CIMs in total).

The trick with worm gears is that as their efficiency increases, the ability to backdrive them also increases—it's that inefficiency (sliding contact, mostly) that's common in so many of them that permits them to resist being backdriven. Sandwich, if I remember correctly, used custom two-start worms, which were supposed to be reasonably efficient, given the substantial reduction.

Re: Brakes
 

After our two regionals (and after Jack Jones called us out for being easily turnable) we realized that we needed to get better at holding our position. During the fix-it window after WI we added code to dynamically control the brake mode on the drive motor speed controllers. Using the encoders & code we already had on the robot for our our autonomous driving, we regularly poll our custom circuit for the number of ticks each encoder moved since the last request. If both encoder readings tell us that the wheels are "turning slow" we put all four speed controllers in brake mode. All this happens without the driver's input. When the robot is shooting, the driver puts the the robot into low gear. While this doesn't make us unmovable like 25, it does make us very difficult to move or turn if we're locked up against the ramp wall.

Re: Brakes
 

Worm gears are terribly inefficient, that's correct. We used them on our robot, and struggled getting enough power to push and climb the ramp. I don't think we'll be using them next year as they didn't work out as much of an asset this year. But at least we can say we tried! And as far as backdrive, you could still push our robot relativly easily even with the wormgears, they did have some give to them, which kind of defeated the purpose of having them on there in the first place.