How do those winch-loaded shooters work?

[Jeffy]

So I have seen some shooters from overdrive that work by winding a cord around an axle to draw back a spring or tubing. Then they lock in place via many different methods (locking pin, winch, ect.)
My question comes about the release. When you release the mecanism, does it unwind the motor? Or, is there some sort of clutch mechanism that lets it slip so that you don't lose force from winding the motor? If so, what is it?

Thanks in advance.

[,4lex S.]

As in most FRC designs, a plethora of mechanisms are used by teams. In most successful cases, the motor is not moved during a release. My team used a dog gear system to disengage from the gearbox in 08, similar to the AndyMark shifters. I would recommend taking a look at some drawings on AndyMark.biz and figuring them out.

I have also seen gate hinges and... a hood latch... used to release cables with varying success (usually good if you don't dip 'em in paint )

[Creator Mat]

There is a clutch mechanism that does release the winch without "rewinding" the motor. A good thread to see for this is this one http://www.chiefdelphi.com/forums/sh...threadid=80278. If the super shifter/ dog gear isn't your thing check out this page on mcmaster http://www.mcmaster.com/#6283k24/=5fr67j for some inspiration.

[Jeffy]

At the $350 price for the super shifters, they are pretty out of our league.
I am opting towards the rachet type things however, could someone show me an example of how to disengage the pawl?

I'm not really sure how I could setup a rachet and pawl so that it wouldn't want to unwind the motor as my cable unwinds.
Care to elaborate? I was trying to think of a realworld machine that uses something like this, but I have come up with nothing.

[Thermal]

Originally Posted by Jeffy

At the $350 price for the super shifters, they are pretty out of our league.
I am opting towards the rachet type things however, could someone show me an example of how to disengage the pawl?

I'm not really sure how I could setup a rachet and pawl so that it wouldn't want to unwind the motor as my cable unwinds.
Care to elaborate? I was trying to think of a realworld machine that uses something like this, but I have come up with nothing.

I'd think a simple servo with its output linked to the pawl could work rather well as a disengaging mechanism. Also theres always the option of a small pneumatic cylinder, but i'd figure that'd be overkill.

Heres a simple paint drawing to help illustrate (literally) my idea

[Racer26]

For the 2008 offseason we modified our robot to have a launcher mechanism based on 1114's wildly successful Simbot SS. We loaded it with a dog gear transmission (a modified AndyMark Gen 2 shifter, i believe) with one of the sets of gears removed. I forget how we stopped the spring pressure from backwinding the whole rig. I think we had a pneumatic ram that locked it in place.

[Jeffy]

I have been thinking all morning on this.
I still can't figure this out:
I can pull the cable back with a winch and it won't back drive. But when I release the winch the motor will want to spin with the springs.
What I think I need to find is some sort of clutch between the cable and the winch. Any suggestions?

[hillale]

We ran our Overdrive shooter with just one motor and no other actuation. Able to reload in approx 1.5 seconds, if I recall correctly (with a whole lot more stress on it than this year requires).

Here's a pic of it engaged and ready to fire:

http://www.chiefdelphi.com/media/photos/31538

Here's a pic of it unloaded:

http://www.chiefdelphi.com/media/photos/31539

Extremely efficient and simple, just have to grasp the concept. Feel free to ask any other questions.

[Jeffy]

Originally Posted by hillale

We ran our Overdrive shooter with just one motor and no other actuation. Able to reload in approx 1.5 seconds, if I recall correctly (with a whole lot more stress on it than this year requires).

Here's a pic of it engaged and ready to fire:

http://www.chiefdelphi.com/media/photos/31538

Here's a pic of it unloaded:

http://www.chiefdelphi.com/media/photos/31539

Extremely efficient and simple, just have to grasp the concept. Feel free to ask any other questions.

This is I think the 3rd time I have tried to figure out that linkage, and it clicked, I get it, and realize how simple it really is. It does require a non-backdriveable transmission though, correct?

Thanks alot, It is likely we will use something like this.

[Mr_I]

Originally Posted by Jeffy

This is I think the 3rd time I have tried to figure out that linkage, and it clicked, I get it, and realize how simple it really is. It does require a non-backdriveable transmission though, correct?

While a non-backdrivable transmission will do the trick, it can be done without. If you consider how the linkages work, when the main sprocket is at the "ready to fire" position, there is very little force driving the sprocket either forward or backward. If you use a position sensor that can stop the sprocket at this "ready" location, the sprocket won't move until you say "fire!" and push it just past this point.

[Aren_Hill]

Originally Posted by Jeffy

It does require a non-backdriveable transmission though, correct?

Yes it does, we acquired this trait in the form of a Dewalt XRP gearbox with a FP driving it (which also gave us a vital speed reduction).

Other options include worms gears, or a one way ratchet system (one of the easier ways, think box end ratchet wrench and a hex on the shaft)

I say it requires it for general safety, we always had the "ready to fire" position far enough away from tripped to prevent accidental firing from sharp contacts or such.

[Brandon Holley]

Originally Posted by Jeffy

I have been thinking all morning on this.
I still can't figure this out:
I can pull the cable back with a winch and it won't back drive. But when I release the winch the motor will want to spin with the springs.
What I think I need to find is some sort of clutch between the cable and the winch. Any suggestions?

In 2008 we made a "catapult" of sorts to shoot the ball. Here is a picture from the arizona regional of a ball in mid air off of one of our shots(http://www.chiefdelphi.com/media/photos/30965). From our estimates we were winching back around 300lbs of spring force.

Our initial solution was one of the andymark dog gears that everyone here has mentioned thus far. We ran into a problem however when the winch was fully cranked back. There was so much tension in the springs that the dog gear would not disengage. We were using a 1.5" bore, 1" stroke, pneumatic piston to disengage.

We went back to the drawing board and decided to use a ball lock clutch. If you do some searches here on CD for ball lock transmissions you will see that team 222 has quite a bit of experience with them. Essentially how they work is you have a hollow shaft which a gear sits on. The gear has slits cut into it so if you looked at it from the side you would see something like a + sign. The hollow shaft has spots for 4 ball bearings to sit in, so that when they are placed in the shaft, the gear spins freely around the ball bearings. You then actuate a rod inside of the hollow shaft so when the rod pushes through the shaft, it forces the ball bearings into the slots cut in the gear.

This was a very effective system for us, and will be something we use again if we ever have to winch something back and then unload it quickly.

-Brando

PS- obviously if you have any questions feel free to ask

[MrForbes]

Originally Posted by Jeffy

I can pull the cable back with a winch and it won't back drive. But when I release the winch the motor will want to spin with the springs.
What I think I need to find is some sort of clutch between the cable and the winch. Any suggestions?

We are thinking about making a winch spool that has two pins sticking out one end, and a pin going thru the motor driven shaft that will engage them. The spool will slide sideways on the motor shaft (driven by a fork in a collar, powered by a small pneumatic cylinder) to disengage the spool from the shaft.

We haven't built it yet, so don't expect it to work...but it looks like something we can make without too much trouble.

[aldaeron]

Originally Posted by ,4lex S.

As in most FRC designs, a plethora of mechanisms are used by teams. In most successful cases, the motor is not moved during a release. My team used a dog gear system to disengage from the gearbox in 08, similar to the AndyMark shifters. I would recommend taking a look at some drawings on AndyMark.biz and figuring them out.

I have also seen gate hinges and... a hood latch... used to release cables with varying success (usually good if you don't dip 'em in paint )

I don't see what a CIM motor can't be engaged and the motor controller switched to Coast while shooting. You would be rotating through a angle of less than (180 degrees * Gear Ratio). The motor will not spin faster than the ~5500 rpm it is rated for and the power generated seems negligible. What else makes these motor attached designs less successful?

Thanks!

[Daniel_LaFleur]

Originally Posted by aldaeron

I don't see what a CIM motor can't be engaged and the motor controller switched to Coast while shooting. You would be rotating through a angle of less than (180 degrees * Gear Ratio). The motor will not spin faster than the ~5500 rpm it is rated for and the power generated seems negligible. What else makes these motor attached designs less successful?

Thanks!

Drag. Especially through a gearbox.