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	<title>Real-Time Physics Simulation Forum</title>
	
	<link href="https://pybullet.org/Bullet/phpBB3/index.php" />
	<updated>2017-11-06T17:12:50+00:00</updated>

	<author><name><![CDATA[Real-Time Physics Simulation Forum]]></name></author>
	<id>https://pybullet.org/Bullet/phpBB3/app.php/feed/topic/11918</id>

		<entry>
		<author><name><![CDATA[Dirk Gregorius]]></name></author>
		<updated>2017-11-06T17:12:50+00:00</updated>

		<published>2017-11-06T17:12:50+00:00</published>
		<id>https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=40147#p40147</id>
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		<title type="html"><![CDATA[Re: featherstone ABA in Bullet]]></title>

		
		<content type="html" xml:base="https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=40147#p40147"><![CDATA[
IIRC the squared omega (angular velocity) terms lead to simulation instabilities in practice. So Bullet added damping to improve stability.<p>Statistics: Posted by <a href="https://pybullet.org/Bullet/phpBB3/memberlist.php?mode=viewprofile&amp;u=14">Dirk Gregorius</a> — Mon Nov 06, 2017 5:12 pm</p><hr />
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	</entry>
		<entry>
		<author><name><![CDATA[r_kh]]></name></author>
		<updated>2017-11-05T20:10:18+00:00</updated>

		<published>2017-11-05T20:10:18+00:00</published>
		<id>https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=40142#p40142</id>
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		<title type="html"><![CDATA[featherstone ABA in Bullet]]></title>

		
		<content type="html" xml:base="https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=40142#p40142"><![CDATA[
Hi,<br><br>i'm trying to implement Featherstone's ABA so i decided to read Bullet implementation and came across this expression<div class="codebox"><p>Code: </p><pre><code>//...//zeroAccSpatFrc[i+1].setVector(-(rot_from_world[i+1] * linkAppliedTorque), -(rot_from_world[i+1] * linkAppliedForce ))//...zeroAccSpatFrc[i+1].addVector(angDampMult * m_links[i].m_inertiaLocal * spatVel[i+1].getAngular() * (DAMPING_K1_ANGULAR + DAMPING_K2_ANGULAR * spatVel[i+1].getAngular().safeNorm()),linDampMult * m_links[i].m_mass * spatVel[i+1].getLinear() * (DAMPING_K1_LINEAR + DAMPING_K2_LINEAR * spatVel[i+1].getLinear().safeNorm()));//...//zeroAccSpatFrc[i+1].addAngular(spatVel[i+1].getAngular().cross(m_links[i].m_inertiaLocal * spatVel[i+1].getAngular()));//zeroAccSpatFrc[i+1].addLinear(m_links[i].m_mass * spatVel[i+1].getAngular().cross(spatVel[i+1].getLinear()));//...</code></pre></div>which doesn't appear in featherstone's book<br><br>i understood this is sort of damping from constant names but where does this come from?<p>Statistics: Posted by <a href="https://pybullet.org/Bullet/phpBB3/memberlist.php?mode=viewprofile&amp;u=12446">r_kh</a> — Sun Nov 05, 2017 8:10 pm</p><hr />
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