I found the velocity of A. Now i'm trying to find the velocity of D so i have something to relate to O and can then find angular velocity of ODE. Can i assume that the magnitude of the velocity of A = the magnitude of velocity of D because of the slot mechanism?
8 comments:
do u use the relative equation to find velocity of a?
I used the rigid body equation deborah.
--to jonbrueck--
To answer your question, the speed of A is NOT equal to the speed of D. In order for A and D to have the same speed, they would need to be on the same rigid body and with that rigid body moving only in translation. Neither condition is true.
My suggestion is to not worry about point D. Go directly between pin O and pin A using the relative velocity equation:
v_A = v_O + (v_A/O)_rel + omega x r_A/O
where v_O = 0.
I assume that you are putting the observer on ODE with the x-axis passing through A. With that choice:
omega = omega_ODE*k
(v_A/O)_rel = v_rel*(cos(45°)*i + sin(45°)*j)
Substitute the above two equations into the above relative velocity equation. Set that equal to v_A that you have already found. You will have two scalar equations (i and j components) for two unknowns: omega_ODE and v_rel.
The same process works for the acceleration equation.
Let me know if this helps.
ive gotten it down to two equations with 3 unknowns. does omega_OCD=-omega_CD??
I'm getting my omega of ODE to equal my omega of CB. Should this have happened?
--to mschafe--
You should have two equations in terms of two unknowns: omega_ODE and the magnitude of (v_A/o)_rel. Be sure to use the known information about the rotation rate of link BC to find the velocity vector for point A (using link BC). See comment to jonbrueck above.
I am not sure what you mean by omega_CD. Typo? There is no link connecting C and D.
So i basically have no idea when we assume omega as being positive and when we put it into the equation as negative when we can figure out that it is negative. are we supposed to plug it into the acceleration equation as positive even if we solve it as clockwise in the velocity equation?
Good question.
* For unknown angular velocities, the math will take care of the signs. Assume one sign or the other: omega = omega*k or omega = -omega*k. Carry through the algebra. If the scalar omega turns out negative, it simply means that your original assumption on direction was incorrect. My suggestion is to always assume unknown angular velocities to the CCW (positive). Then a positive answer means it really was CCW; a negative answer means it was actually CW. That is easier to remember than sometimes one way and sometimes the other.
* For known angular velocities, you must give the correct sign at the beginning.
When working with the acceleration equation, use the actual numerical answer (both magnitude and direction) that you found from velocity.
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