Disk brakes
 

has anybody used disk brakes from a bike on their robot? if so how did they work?
and i did check the forms for this one i didnt find anything

Re: Disk brakes
 

Team 38, The Nonebots, used a disk brake on their arm in 2005. If you look in the linked photo, you'll see if just below the middle student's left wrist. IIRC, it worked pretty darn well, as they were a regional champion is Rochester (?) that year...

Team 38, 2005

BEN

Re: Disk brakes
 

We have been using disk brakes for 3 years now, and they are really good to have. We didnt use the ones from a bike though we went out and bought some from a go-kart shop.

Re: Disk brakes
 

1126 also used a brake in the 05 season. it was amazing and worked amazingly with the proper programming. i'll try to find a picture of it.

Re: Disk brakes
 

How would you actuate a disc brake on a robot?

Re: Disk brakes
 

we used a little 1/2" bore 2-3" stroke piston. it was pretty cool.

Re: Disk brakes
 

thats what we wanted to do a piston to replace the lever on a bike brake system...

Re: Disk brakes
 

I have an omni drive proof-of-concept machine i'm working on right now, uses just 2 motors to do swerve drive and am using a solenoid to actuate the disc brake on a part of the machine.

Yes, yes i know that you can't use solenoids, but if anybody ever needs to have a way to do it easily outside of first i've found it works very well.

We used got our disc brake and the caliper for it from Northern Tool at a great price. Also an awesome place to get big tires cheap too, among other things... its like harbor freight on steriods for some stuff :D

-Q

Re: Disk brakes
 

Brakes are actually a really good idea. I can think of quite a few instances where 4 locked wheels on a robot with heavy traction wheels could put up quite a defence against another robot trying to push it!

Re: Disk brakes
 

as rees ponted out to me there rather expenseve the (bike ones) and many time it is the wheels tracktion that the weak point not the drive tran, at least on are robot
but also many are fluied filled and first will not be happy with that

Re: Disk brakes
 

I can think of a pretty easy and cheap way to fab up some disc brakes.

Get some sheet aluminum, or round aluminum, cut out discs, drill them on a press, then make some sort of rubberized pad and a caliber.

Probably would cost around $50 for 4 wheels depending on how you did it.


Darn, now I want to go try it!

Re: Disk brakes
 

Here are the ones we have been using for 3 years.




http://zacm.com/gocart/brake/brakeparts.htm

Re: Disk brakes
 

Keep in mind that there are other, possibly cheaper, methods of braking, including one build into the Victor speed controllers (see what 111 and several others did last year). For a different physical method of braking, look at 25s drivetrain.

Re: Disk brakes
 

The victors use power to slow down the robot. If one were to use say a solenoid to open a precharged air loop, which in turn powered a disc, it would use virtually none.

Re: Disk brakes
 

I think a disk brake to control more than one mechanism would be interesting if used to control say...a differential like thing to separate power to two or more different mechanisms from one motor. I agree with Sean, they aren't as useful in the drivetrain as a mechanical locking mechanism in the gearbox itself like 25 had this past season.

Re: Disk brakes
 

That isn't how it works. In "brake" mode, a Victor speed controller isn't supplying any power to the motor. It's simply connecting both sides of the motor together, turning it into a dynamic brake.

Re: Disk brakes
 

another good source for brakes is here. The ones I would use are about halfway down the page. http://electricscooterparts.com/brakes.html


the 120mm is 4.72 in in diameter and with activation from a pneumatic cylinder they would be quite effective.

Re: Disk brakes
 

Hmm I wasnt aware of that, thanks for the info. However, a physical brake im sure can stop shaft movement much better than an electronic one.

Re: Disk brakes
 

Indeed it can--at the cost of extra weight and complexity. (Granted, they can be quite light if you design it right--look at 25's robot this year--but they still have mass.)

Re: Disk brakes
 

Just another one of those times when you have to take into account what you want more. :)

Re: Disk brakes
 

Disk brakes sound really inefficient for a FIRST robot. Why not just take the (+) and (-) wires and have them touch (I am not giving away any concept designs, just an ideal concept). Take a motor and spin the shaft. Now connect the two wires together and try it again. It would be a lot harder, and even harder when you have that going through a gearbox.

Re: Disk brakes
 

This is how the breaking feature on the Victors work.

Re: Disk brakes
 

However some people may want more braking power then that.

Another robot will certainly not have very much of a hard time pushing 2/4 motors on a transmission, especially if it already has the momentum going for it and it is using the same type of drivetrain.

Re: Disk brakes
 

Woah! Is it like a programmable thing? Has his been around for a long time? I never looked into detail about the Victors. :rolleyes:

Re: Disk brakes
 

I'm looking at the DeWalt transmissions. Does the anti-backdrive pin on these work well/reliably? Sounds like a good way to hold up an arm.

Re: Disk brakes
 

There's a jumper on each Victor that allows you to decide if you want to set it to brake or coast. Brake is as described, while coast is what most folks use.

Teams have, in the past, created a servo-driven mechanism that allows them to switch between the coast and brake modes in the middle of a match.

Edit: Also, apparently you can program it to switch back and forth. You learn something new every day :)

Re: Disk brakes
 

The brake/coast jumper has always been on the Victors. Just move it from one position to the other. I think it usually ships in the coast position by default so you may have never noticed it. If you connect the jumper back to the robot controller digital I/O (switches) then you can program the Victor to either brake or coast at will.

Re: Disk brakes
 

Last year IFI pointed out that the jumpers on the speed controllers could be wired to a digital IO port, allowing you to control in software the mode the speed controller was in. It made sense last year, as a team would have been able to enable brake mode, if the robot started to go in the direction opposite the one it was heading in as the match ended (WHILE DISABLED!). That is, you could have the robot coast up the ramp, and then not slide back down (if the dynamic brake was strong enough).

Re: Disk brakes
 

And you had enough traction.


The essential point that I was making is that the Victor brakes are almost always good for use in a drive-train in FIRST. I'm willing to bet that one of the robots involved in the pushing match (either yours or the robot trying to push you) will lose traction before the motors back-drive in brake mode. Especially considering a vast majority of pushing doesn't occur head on (a great deal of it is rotational in the world of FIRST, something that a braking mechanism that locks the wheels won't help with). If you want a system to prevent torqued out of position, it would have to be in contact with the playing field rather than the wheels.
Mechanical brakes (such as disk brakes) may be a valid solution for other aspects of the robot, such as arm and shoulder joints.

Re: Disk brakes
 

My post was a follow up to M. Krass's.

As for what you are saying about brake mode: it is not that strong. It does provide some resistance to motion, but not alot. Brake mode seems good for allowing the robot to stop on a dime, and also for helping to keep an arm stationary. Break mode may not help much in a pushing match.

Re: Disk brakes
 

The 2nd half of my post was a generic address to the topic as well, not specifically at you (just the initial traction comment). But the brake mode works very well from what I have heard (and determined playing against it) during pushing matches. I don't believe that 116 has ever implemented it though, so perhaps there are quirks that I didn't know.
Regardless, a vast majority of pushing in FIRST does occur rotationally though.

Re: Disk brakes
 

If you have potentiometers or a similar devices to measure the position of your wheels, you can program in a reactive braking feature that we refer to as “dynamic brakes”. When the robot is at rest and you want to stay put, the dynamic brakes are activated. The controller senses when a wheel is beginning to turn and applies just enough current to the drive motors for that wheel to keep it stationary. This can work on each side of the robot in opposing directions to keep you from being spun around.

These dynamic brakes only work when you have power, so they won’t keep you on an inclined ramp at the end of a match. They are, however, lightweight (only software) and effective in keeping the wheels from turning. The limit to the staying power is the traction between the tires and carpet.

Jay

Re: Disk brakes
 

Would these potentiometers be made for continuous rotation, or am I missing something?

Re: Disk brakes
 

Yea, I would think continuous rotation. Your gut is correct, you probably won't find many recommendations for using potentiometers where encoders are more appropriate.

You don't need to measure position (absolute) of your wheel, you can get a software based dynamic brake by using a PID-based velocity control algorithm, and setting the desired velocity to zero (this would be a side effect of the driver letting up on the joystick). Eh, I think this is what he was talking about anyway.

Re: Disk brakes
 

To elaborate on the victors dynamic breaking feature.

The key to remember is that it is 'dynamic'. The resistance is proportional to the speed that the motor shaft is turning. So, at rest, there is no resistance to movement. As the shaft begins to turn resistance to movement rises. Movement will either accelerate or decelerate until a balance between resistance and the force causing motion is reached. Then acceleration stops but motion will continue.

Because the braking power is linked to shaft speed it can never completely halt motion. If the resistance where enough to completely stop movement, then the brake can no longer function (no shaft movement means no current generated). Watching a drooping arm with a victor braking it you can sometimes see a little herkyjerky behavior- thats the arm accelerating till it is stopped and then accelerating again over and over again. Other times it just looks like it's falling in slow motion.

A Victors dynamic braking alone will not hold a robot in place and will not hold an arm horizontal. It will slow movement down, but the arm will droop and the robot will be pushed. I wouldn't depend on it to hold a robot in place, because it can't. A brake, either in the drive train or an anchor, is preferable if you absolutely have to stay in place.

-Andy A.

Re: Disk brakes
 

I really like the way 25's brakes worked.

They drilled a bunch of concentric holes in their gears, then used a servo to shove a dowel pin in. With their big knobby tires, they were almost impossible to push.

If you watch Newton Finals, you'll see 25 push Wildstang across the field, then hit the brakes. 111 tries to push them for about 15 seconds getting nothing done. 111 backs off to get some momentum and 25 breaks for the goal. Perfect driving.