Chipmunk/Spacemanager constraints.

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Chipmunk/Spacemanager constraints.

(10 posts) (2 voices)

Started 1 year ago by mrTortex
Latest reply from mobilebros

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mrTortex
Member

Hello.

Me again! I'll go away soon ;)

I want to have a ball with two little legs sticking out of it. The ball should fall, land on it's legs, which rotate with the impact, then spring to a settled position.

So, I have my ball body, two leg bodies, two pin constraints and two rotation spring constraints. Should work yes? Well, it doesn't because the legs don't rotate with the body, so if the body is upside down, the legs are still pointing at the floor.

I need a way to have the child bodies inherit the rotation from the parent. Any ideas?

Thanks.

Posted 1 year ago #
mobilebros
Moderator

Use a gear constraint between the leg and body, set the gear constraint maxForce to something like 3000, maybe lower.

Posted 1 year ago #
mrTortex
Member

With a gear do you also need a pin, or pivot? The reason I ask is with a gear alone it flies off. Also, it doesn't rotate with the main body.

Posted 1 year ago #
mobilebros
Moderator

You need a pin/pivot for sure, I used a pivot. I just checked my code and I have 1 for the ratio and maxForce = 3000.

The overall effect looks pretty good I'd say, legs are somewhat "springy" like they should be.

[Edit] Reading your first post again, I'd think the rotary springs would work too, did you connect the contraint between the body and leg or between the leg and some other object?

Posted 1 year ago #
mrTortex
Member

Hello. I created a constraint between the body and leg, I'm getting very odd results. Would you mind posting a code snippet? Understand if not,

Would it possibly be anything to do with applying impulses to the body which cause it to rotate?

Posted 1 year ago #

CGPoint pt = [wherever you want it];

	_torso = [smgr addRectAt:ccpAdd(pt,ccp(0,8)) mass:12 width:12 height:24 rotation:0];
	_lleg = [smgr addRectAt:ccpAdd(pt,ccp(-6,-23)) mass:4 width:4 height:26 rotation:CC_DEGREES_TO_RADIANS(-5)];
	_rleg = [smgr addRectAt:ccpAdd(pt,ccp(6,-23)) mass:4 width:4 height:26 rotation:CC_DEGREES_TO_RADIANS(5)];

	[smgr addPivotToBody:_torso->body fromBody:_lleg->body worldAnchor:cpvadd(pt, cpv(-5, -6))];
	[smgr addPivotToBody:_torso->body fromBody:_rleg->body worldAnchor:cpvadd(pt, cpv(5, -6))];

	cpConstraint *gear = [smgr addGearToBody:_torso->body fromBody:_lleg->body ratio:1];
	gear->maxForce = 3000;
	gear = [smgr addGearToBody:_torso->body fromBody:_rleg->body ratio:1];
	gear->maxForce = 3000;

That's literally what I do to create a rectangular torso with 2 stiff straight rectangle legs.

Posted 1 year ago #

mrTortex
Member

Hello.

Thanks for the code. It turned out the way I was dealing with impulses and moving the main body around was causing odd things to occur, so I re-wrote that section and it's now working. :) However, my legs need to point out at 45 degrees, which they do to start with, but the gear brings them into alignment with the body. Is there a rotational offset available? I've tried using phase but it rotates around itself constantly, which looks kinda cool but isn't the desired effect! :)

Thanks.

Posted 1 year ago #
mobilebros
Moderator

You're on the right track its phase you want to play with; make sure it's in radians...

Posted 1 year ago #
mrTortex
Member

:) Of course. You based in the UK? I think I owe you a beer.

One odd thing I noted, the legs don't rotate outwards when they receive the weight of the body above them, they rotate inwards and push the body upwards! Some odd stuff going on again. Gotta love physics, they make everything so much more confusing. :)

Now back to figuring out my parallax issue...

Thanks again.

Posted 1 year ago #
mobilebros
Moderator

Haha no problem, and actually we're in the U.S., New Hampshire to be precise, but I appreciate the offer :) That rotation inwards still sounds like a side effect of the gear I think...

Posted 1 year ago #

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