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View Full Version : Releasing winch system without shifters

Yerdan
13-01-2014, 08:14
Hi guys,are there any ways of releasing winch system without using shifters(any optional systems)?
Mike Schreiber
13-01-2014, 09:34
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.
Yerdan
13-01-2014, 10:39
I would be really grateful if you could give me a little information about cam release mechanism.
androb4
13-01-2014, 11:05
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
jijiglobe
13-01-2014, 11:11
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...
roystur44
13-01-2014, 12:31
Yerdan,

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

http://www.mcmaster.com/#gear-ratchets/=q8grgr
discobrisco
13-01-2014, 12:35
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.
Ether
13-01-2014, 12:36
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

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.
Ether
13-01-2014, 12:38
It didn't even have a gearbox,

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.
androb4
13-01-2014, 13:00
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.




That's sweet!

I've made this (https://www.dropbox.com/s/vmkm7jq1kmsyb5e/Photo%20Jan%2013%2C%2011%2057%2012%20AM.png) the other day using Inventor's Create Spiral tool. What do you think?
TD78
13-01-2014, 13:34
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.

Would you be able to post a web link to this schematic? I have not been able to find one so far.
androb4
13-01-2014, 14:01
Would you be able to post a web link to this schematic? I have not been able to find one so far.

Here's the CAD for Team JVN's robot.
http://www.buildblitz.com/final-cad-files/
TD78
13-01-2014, 14:22
Here's the CAD for Team JVN's robot.
http://www.buildblitz.com/final-cad-files/

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.
androb4
13-01-2014, 14:41
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.

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.
Jon Stratis
13-01-2014, 14:41
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...

I'm intrigued by this idea... I hope I see it somewhere to know if it works!
Ty Tremblay
13-01-2014, 14:46
Maybe this could spark some ideas?

http://www.daytonsuperiorproducts.com/clutches/one-way-sprocket.html
androb4
13-01-2014, 14:47
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
13-01-2014, 14:54
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/showpost.php?p=1326068&postcount=5
Jon Stratis
13-01-2014, 14:56
Ether linked out the point in Build Blitz where we explain it.

http://www.chiefdelphi.com/forums/showpost.php?p=1326068&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
13-01-2014, 15:04
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
13-01-2014, 15:20
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
13-01-2014, 15:27
That's sweet!

I've made this (https://www.dropbox.com/s/vmkm7jq1kmsyb5e/Photo%20Jan%2013%2C%2011%2057%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
13-01-2014, 16:27
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.
http://upload.wikimedia.org/wikipedia/commons/thumb/1/15/StressStrainWEB.svg/300px-StressStrainWEB.svg.png
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
13-01-2014, 16:40
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
13-01-2014, 17:04
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
13-01-2014, 17:08
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
13-01-2014, 17:10
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.