Releasing winch system without shifters
 

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

Re: Releasing winch system without shifters
 

If you want a fixed shot it's very easy to use a cam to wind and release. The easiest example I can think of is 217 and 148 in 2010. I'll look for links in a bit.

Re: Releasing winch system without shifters
 

I would be really grateful if you could give me a little information about cam release mechanism.

Re: Releasing winch system without shifters
 

He's referring to the cam they used to power their kicker.

I've heard it called a da vici cam.. Like this.

http://img.rlt.com/x/12131.jpg

Re: Releasing winch system without shifters
 

Our team has talked about using a gear with some missing teeth which would be on a ratchet so that it can wind up and when its ready to shoot we can rotate the gear to the part with missing teeth and it'll slip. We haven't prototyped it yet though...

Re: Releasing winch system without shifters
 

Yerdan,

Take a look at a ratchet and pawl. Mcmaster Carr sells them

http://www.mcmaster.com/#gear-ratchets/=q8grgr

Re: Releasing winch system without shifters
 

I believe team JVN used a non shifting system which was powered by a bag motor, it had a double jointed arm on a gear which would release by simply turning it past it's point of being fully loaded. It didn't even have a gearbox, and seemed like a very good setup to me. The have their schematics on their website, much easier to see how it works using that.

Re: Releasing winch system without shifters
 

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.

Re: Releasing winch system without shifters
 

Yes it had a gearbox. A BAG motor would fry trying to do that without one. 100:1 speed reduction gearbox followed by 84:18 speed reduction external gearing.

Re: Releasing winch system without shifters
 

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?

Re: Releasing winch system without shifters
 

Would you be able to post a web link to this schematic? I have not been able to find one so far.

Re: Releasing winch system without shifters
 

Here's the CAD for Team JVN's robot.
http://www.buildblitz.com/final-cad-files/

Re: Releasing winch system without shifters
 

Ahh...yes I have the CAD. When you said schematic, I took it literally to mean you were suggesting there was a dimensioned drawing on their website of this subsystem.

Re: Releasing winch system without shifters
 

Well, discobrisco said schematic..

No they have not released a schematic with dimensions.

Have you checked out that mechanism? It's pretty cool, I was pretty impressed by that. It pretty much winds up the 2 linkages then it winds up the first linkage using an obstruction on the gear, then it releases both linkages once the second linkage passes over the obstruction, freewheeling the gear 180 degrees to allow the extension on both linkages. Kinda hard to visualize but you'll get it if you mess around with the CAD.

Re: Releasing winch system without shifters
 

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

Re: Releasing winch system without shifters
 

Maybe this could spark some ideas?

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

Re: Releasing winch system without shifters
 

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.

Re: Releasing winch system without shifters
 

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

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

Re: Releasing winch system without shifters
 

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 :)

Re: Releasing winch system without shifters
 

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.

Re: Releasing winch system without shifters
 

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.

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

Re: Releasing winch system without shifters
 

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

Re: Releasing winch system without shifters
 

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.

Re: Releasing winch system without shifters
 

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.

Re: Releasing winch system without shifters
 

How about scissors to cut the spring/rope?

Re: Releasing winch system without shifters
 

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

Re: Releasing winch system without shifters
 

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.