### Office Hours Related

For instance, today i have to leave right at 4 pm (end of official office hours) to pick up kids from school.

Post any questions you might have on the forum, i'll try to reply tonight.

Dan

I'll post here any topics related to office hours.

For instance, today i have to leave right at 4 pm (end of official office hours) to pick up kids from school.

Post any questions you might have on the forum, i'll try to reply tonight.

Dan

For instance, today i have to leave right at 4 pm (end of official office hours) to pick up kids from school.

Post any questions you might have on the forum, i'll try to reply tonight.

Dan

In office hours we talked about taking ground out and how Ai would be the identity matrix (assuming ground was body i in the constraint equation). However, isn't it the negative identity matrix (-I)?

also, pibar will be 6x3 if ground is one of the parts in the constraint eqn? 3 because there are three axes in which omega is described by?

For the normalization constraint of p, what is it with respect to q? I know it will be a 1x7, with the first 3 entries being zeros (not dependent on r). The equation is p'*p-1, so I was thinking it was going to be 2*p'*pdot which is a number....not a 1x4 I was hoping.

ME751Chris wrote:In office hours we talked about taking ground out and how Ai would be the identity matrix (assuming ground was body i in the constraint equation). However, isn't it the negative identity matrix (-I)?

Chris - it should always be I. Let's talk after class about why this would be -I. Body "0", the ground, doesn't have any generalized coordinates associated with it. Its A is I, and stays always constant.

I hope this helps.

dan

ME751Chris wrote:also, pibar will be 6x3 if ground is one of the parts in the constraint eqn? 3 because there are three axes in which omega is described by?

3 because the dimension of omega is 3x1. Recall that pibar is the matrix that multiplies the omega_bar in the time derivative of Phi. Since Phi is of dimension 6 (5 from revolute joint + 1 driving constraint), pibar will be 6x3.

dan

ME751Chris wrote:For the normalization constraint of p, what is it with respect to q? I know it will be a 1x7, with the first 3 entries being zeros (not dependent on r). The equation is p'*p-1, so I was thinking it was going to be 2*p'*pdot which is a number....not a 1x4 I was hoping.

think a bit about it, it's 2p', which is a 1x4. 2*p'*pdot it's the time derivative of the Euler Param normalization constraint.

dan

i don't think parsing out the data of a 7x14 matrix will work like we talked about in office today. Think about the DP1 constraint in which the Ai matrix (assuming body_i is ground) because p would be 0 0 0 0, which when making Ai, would result in a -I matrix...right?

ME751Chris wrote:i don't think parsing out the data of a 7x14 matrix will work like we talked about in office today. Think about the DP1 constraint in which the Ai matrix (assuming body_i is ground) because p would be 0 0 0 0, which when making Ai, would result in a -I matrix...right?

Chris - the p would be [1,0,0,0]. Recall that the norm of p should be 1.0 (the normalization constraint). As such, you can't have all values in p be zero.

With [1,0,0,0] the A matrix becomes the identity matrix.

dan

In computing the acceleration at time = 0, you used the following in the masspringdamperNR.m file:

accVec(crntStep,1) = (sin(2*crntTime) - c*v_old*v_old - k*x_old^1.5)/m;

How was this found?

accVec(crntStep,1) = (sin(2*crntTime) - c*v_old*v_old - k*x_old^1.5)/m;

How was this found?

Chris - see my answer from "Assignment 11" discussion thread.

dan

dan

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