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# Disable rotation of a body ODE

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### #1Aitorman  Members   -  Reputation: 126

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Posted 23 March 2013 - 11:06 AM

Hey there,

I want to constraint the rotation of a cube so that it can only translate. I've tried using an aMotor with the following code:

	this->aMotor=dJointCreateAMotor(this->system->getGame()->worldID,this->system->jointGroup);
dJointAttach(this->aMotor,0,this->bodyID);
dJointSetAMotorMode(this->aMotor,dAMotorUser);
dJointSetAMotorNumAxes(this->aMotor,3);
dJointSetAMotorAxis(this->aMotor,0,0,1,0,0);
dJointSetAMotorAxis(this->aMotor,1,0,0,1,0);
dJointSetAMotorAxis(this->aMotor,2,0,0,0,1);
dJointSetAMotorParam(this->aMotor, dParamVel1, 0);
dJointSetAMotorParam(this->aMotor, dParamVel2, 0);
dJointSetAMotorParam(this->aMotor, dParamVel3, 0);
dJointSetAMotorParam(this->aMotor, dParamFMax1, dInfinity);
dJointSetAMotorParam(this->aMotor, dParamFMax2, dInfinity);
dJointSetAMotorParam(this->aMotor, dParamFMax3, dInfinity);


If i'm not mistaken, that code creates an AMotor joint, attaches it to the body and the world, and sets the target velocity of each axis of the motor to be 0 and the FMax to be dInfinity. I thought that would disable the body's rotation, but it does nothing. Is there anything wrong with my code? Do you know any other way to constrain the rotation?

### #2Aitorman  Members   -  Reputation: 126

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Posted 23 March 2013 - 04:54 PM

Nevermind, I'm surprised that such a simple mistake has given me so much trouble haha. I didn't know that I could pass 0 as the joint group parameter jor dJointCreate to allocate the joint "normally" and I thought I had to pass a joint group, so I used the only one I have, the contact joint group, which is emptied each frame. That's why it did nothing.

But now I have another problem: I want the box to slide in a plane, and it does so correctly if the plane has no friction, but as soon as I put a bit of friction into it, the movement starts being a bit jerky, like it moves bit by bit at first and suddenly it gains speed and starts moving smoothly and very fast. Do you know how I can keep the smooth movement while constraining rotation?

P.S: Sorry if I make any grammar mistake, English is not my native language

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