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 )

[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.

[MrForbes]

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?

I suggest you give it a try, before you incorporate the idea into your final robot design. Shouldn't be too hard to make a prototype?

[aldaeron]

Originally Posted by squirrel

I suggest you give it a try, before you incorporate the idea into your final robot design. Shouldn't be too hard to make a prototype?

Parts on order to test this weekend!

It just seems like a lot of weight to add to use an AndyMark shifter mechanism. If it is just some amount of drag, we can get a bigger torsion spring.

[,4lex S.]

I should have mentioned earlier that our dog gear release was only based on the supershifters. For the dogs we used lovejoy connectors found in the kit a few years back. The rest was improvised from what we had around. It was messy though, and I think a pneumatically actuated rachet might be a better way to go.

[Chuck Glick]

Page 1440 on McMaster may be of interest to you.

[aldaeron]

We are trying using the ratchet from a ratchet strap and half the handle. Has a nice linear slide to disengage and can hold ~1000 lbs according to the box rating.

[RRLedford]

Team 3135, Robotic Colonels, F.W.Parker - Chicago IL

We are looking for cheaper ways to have a programmed windup with instant release of tension at any point in the wind up cycle (no gate latches, thank you). This way we can control the strength of shots in programming
We also want the winder scheme to quickly transition from release to starting next pull cycle without wasting time going through 180 degrees of rotation at a slow RPM.
Finally, we want ALL the energy stored sent to the kicker, not wasted on spinning up some freewheeling masses or linkages that remain attached to the tensioning cable after release. It should be like with a crossbow, where only the string's mass is added on to the mass of the arrow being accelerated.
We are prototyping such a scheme now & should be firing kicks off by Friday.

-RRLedford

[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?