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#4337916 - 02/16/17 02:34 PM Re: Open Hardware Joystick [Re: S_Bartfast]  
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Inline advert (2nd and 3rd post)

#4355530 - 05/05/17 01:58 PM Re: Open Hardware Joystick [Re: S_Bartfast]  
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Repvez Offline
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Does anyone knows, how should desing and plan the CAM profile?
Why assimetric the profile's left and right side?
Anyone give me some infos the whole process? I have CAD softver, but I don't know how should start .

#4355598 - 05/05/17 07:34 PM Re: Open Hardware Joystick [Re: Repvez]  
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Originally Posted by Repvez
Does anyone knows, how should desing and plan the CAM profile?
Why assimetric the profile's left and right side?
Anyone give me some infos the whole process? I have CAD softver, but I don't know how should start .


The profiles are asymmetric because in one direction the mecahnism is moving towards the pivot point while the other direction is moving away from it, thus changing the length of the arm doing the work. This changes the leverage depending on which way it's traveling. To compensate for this, you need to offset the profile to maintain something close to symmetrical spring resistance.

There is a document floating around, though I'm not sure if it's supposed to be public knowledge or not so don't know if I'm supposed to share it but the offset is essentially determined by applying the involute of a circle to the profile.

Here's a translated thread that gets further into it: http://translate.google.com/translate?hl=en&sl=auto&tl=en&u=http%3A%2F%2Fwww.gavca.com%2FphpBB3%2Fviewtopic.php%3Ff%3D49%26t%3D24042

#4355603 - 05/05/17 08:11 PM Re: Open Hardware Joystick [Re: S_Bartfast]  
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You can avoid use asymmetric CAM profile (VKB style) if use double CAM ( like Baur gimbals) - no change in arm length and angles.

The document I refer in Gavca.com is this from Avia-forum - are two .doc in the topic.

http://avia-sim.ru/forum/viewtopic.php?f=28&t=646

But looks the author don't finalize his conclusions... Probable because the matter became commercial venture for them.

Anyway give you a idea of how use the Involute Curve as start point.

[Linked Image]






#4355843 - 05/07/17 10:07 AM Re: Open Hardware Joystick [Re: S_Bartfast]  
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Repvez Offline
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I think It's a little bit difficult me . The google translate doesn't help me a lot.
There isn't a easier way to know what datas have to me for the design, if I would like to draw a own CAM profile?

#4355882 - 05/07/17 03:23 PM Re: Open Hardware Joystick [Re: S_Bartfast]  
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I don't know, I follow CAM for joystick "born" since 2007/8 (RiP Sukhoi) and this discussion in Avia-forum is the more informative I see - but difficult to follow, and for me incomplete.

Looks that in sim communitty who know the matter don't reveal because think in makey money with this. No "Opensource CAM joystick". smile

Are (free) books around about CAM (more for automotive use), but the matter is complex, involve advanced math.

https://www.google.com.br/search?q=...;gws_rd=cr&ei=GTsPWdvMEoG_wASN4bWwCA

To make the matter more "fun" most of this automotive CAM is "concave", for joystick you need a "convex" CAM. biggrin


#4356781 - 05/11/17 11:29 AM Re: Open Hardware Joystick [Re: Repvez]  
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Originally Posted by Repvez
Does anyone knows, how should desing and plan the CAM profile?


Oh, I sure wish I did!

This really is what's holding me up on this project at the moment. At first I thought I'd be able to thrash out the maths without too much difficulty (after all I did manage to scrape a "PASS" in geometry while a school :P) but oh lordy!
So I ended up drafting a mega-brain at work into helping me out on this one, and tell you what, it has us both flummoxed confused —though we have made some headway smile.

In particular, after reverse engineering this photo:
[Linked Image]
It seems the relationship between "spring stretch" and "joystick deflection", rather than being linear, seems to be more quadratic.

Previously I had thought there would be a constant amount of extra spring tension produced for every additional degree of stick deflection (as in 1mm of string stretch for every 1° of stick angle), ie. a "lineal" relationship, but it in fact seems that not only is the spring tension lighter near the centre but the rate at which this tension increases is also a lot less near the centre, and I think this is even evident in the second half of this video:


It's very hard to see but to me at least it appears that the spring is indeed being stretched more in the final few degrees of movement than it is in the first few:
[Linked Image]

Edit: Oh, and by the way, here is a translated copy of the Russian text mentioned above if anyone is interested: Calculation of the loader
It's was only translated using Google's translation service but if you can manage to read between the lines some you can half guess at what it's going on about. It definitely seems that someone has done some fine work in that document but I am not yet convinced that the Involute Curve is actually related to this cam problem. The Involute Curve is most definitely related to the shape of the teeth on gears (as demonstrated romantically in this video) but I am struggling to see how it relates here. Perhaps my Russian just isn't good enough but I don't as of yet see the connection I'm afraid.

Last edited by S_Bartfast; 05/11/17 11:58 AM.
#4356893 - 05/11/17 11:50 PM Re: Open Hardware Joystick [Re: S_Bartfast]  
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Sokol1 Offline
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Quote
It seems the relationship between "spring stretch" and "joystick deflection", rather than being linear, seems to be more quadratic.


Yes, this is characteristic of VKB CAM, to add (based on simmers wishes) the "feel" that control surface (e.g. aileron) became heavy as you move the stick, the CAM profile angle change according for add this "feel". Some VKB buyers don't like this "feel", they wish for more linear "feel".

The CAM document (of avia-sim) purpose use Involute Curve as start point based on this premises:

- The force of the centering spring should be transmitted to joystick lever through the CAM.
- This force transfer should be as linear as possible.
- The mechanism should not increase the effort required to move the joystick lever more than the center spring resistance.
- The effort required for move the joystick away from the center position should increase smoothly and the return to the center position should not cause mechanical shock.
- The return of joystick to the center position should be tactile for hand.

Other characteristic of one lever CAM (VKB) is that return to physical 0 center is not possible using "soft" profile CAM: http://forum.vkb-sim.pro/viewtopic.php?f=25&t=2622






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