Releasing winch system without shifters

[Ty Tremblay]

Maybe this could spark some ideas?

http://www.daytonsuperiorproducts.co...-sprocket.html

[androb4]

Originally Posted by Jon Stratis

I'm intrigued by this idea... I hope I see it somewhere to know if it works!

I think it's a pretty good idea, I don't think anyone has thought of this.

Just make sure that the windup only takes less than a revolution of that gear.

[Aren_Hill]

Originally Posted by Jon Stratis

I'm intrigued by this idea... I hope I see it somewhere to know if it works!

Ether linked out the point in Build Blitz where we explain it.

http://www.chiefdelphi.com/forums/sh...68&postcount=5

[Jon Stratis]

Originally Posted by Aren_Hill

Ether linked out the point in Build Blitz where we explain it.

http://www.chiefdelphi.com/forums/sh...68&postcount=5

I was talking about the concept of removing part of a gear to create a "slip point" for releasing the catapult, not the over-center linkage from the BuildBlitz... I've seen linkages like that before

[magnets]

Originally Posted by Ether

One nice feature of a cam is that, with a little math, you can derive the equation for the spiral so that the torque required to drive it remains constant as it is pulling back the arm. Then you can use that equation to cut out the cam.

Or, you could derive the equation so you gained mechanical advantage (and torque) as you wound back. It takes more force to stretch the surgical tubing at the end than it does at the beginning.

For another type of release mechanism, use a doorknob or gate latch.

[Ether]

Originally Posted by magnets

Or, you could derive the equation so you gained mechanical advantage (and torque) as you wound back.

What you want is for the torque required to drive the spiral cam to remain constant (think about it):

One nice feature of a cam is that, with a little math, you can derive the equation for the spiral so that the torque required to drive it remains constant as it is pulling back the arm. Then you can use that equation to cut out the cam.

It takes more force to stretch the surgical tubing at the end than it does at the beginning

True for many (most) designs but not necessarily true for all. It depends on how the mechanical advantage of the linkage changes as the kicker is being pulled back. In any event, what you want is for the torque required to drive the spiral cam to remain constant. To achieve that you would need to take into account the F=k*x spring constant of the tubing as well as any linkage geometry changes

[Ether]

Originally Posted by androb4

That's sweet!

I've made this (https://www.dropbox.com/s/vmkm7jq1km...%2012%20AM.png) the other day using Inventor's Create Spiral tool. What do you think?

I can't tell for sure but it doesn't look quite right. Can you post the generating equation?

[Lil' Lavery]

Originally Posted by magnets

It takes more force to stretch the surgical tubing at the end than it does at the beginning.

That depends on your wording and if the surgical tubing (or other spring mechanism) is strained beyond the linear elastic region. While, yes, it will take more total force to stretch the material from 0 to Y than 0 to X (assuming Y>X), the force to stretch from X to X+1 may not be more than the force required to stretch from X-1 to X.

Point 1 on that diagram represents the yield stress, where the linear elastic region stops and any further strain on the object will result in some permanent deformation.

Ideally, teams would keep their surgical turbing (or other spring) entirely within the linear elastic region so the characteristics of their launch remain consistent over time. However, the reality of the situation is often that, in order to achieve enough initial force given a limited travel distance, the tubing is stretched beyond the yield stress, and some permanent deformation occurs to the tubing each time it is stretched.

[pfreivald]

Originally Posted by androb4

I think it's a pretty good idea, I don't think anyone has thought of this.

Just make sure that the windup only takes less than a revolution of that gear.

We considered it--a rack an pinion with missing teeth on the pinion.

We were afraid that the pinion teeth near the broken teeth would end up breaking during competition.

[kevin.li.rit]

Originally Posted by Yerdan

Hi guys,are there any ways of releasing winch system without using shifters(any optional systems)?

How about scissors to cut the spring/rope?

[Cory]

Originally Posted by kevin.li.rit

How about scissors to cut the spring/rope?

I'd say it's pretty likely that they want to do this more than once a match...

[mathking]

An option we are considering is to use a bicycle disc brake like we used to 2011. We used brake cable actuated by a two inch stroke one inch bore pneumatic. The same set up is able to hold our prototype catapult. If it loses pressure, it will release its grip, so you have to be careful. Although a gradual loss of pressure tends to make it slip slowly.