Solution extremely sensitive to guess value

[VishnuGopalakri]

Hello All

I am doing a minimization of the torque in mathcad and the solution that i am getting is heavily influenced by the guess values and each time I change the guess value a,b etc even by a small amount,it gives me a different answer. I really am not sure why it is doing that and also how am I going to rectify it.I have enclosed my worksheet . Any help would be greatly appreciated

[Werner_E]

Vishniu Gopalakrishnan wrote:

I had checked that set of values and it gives you a very unrealistic answer for the angles when theta4 is 90 degrees.I got theta 2 and theta 3 as -34 and -28 radians.So i discarded it

I see. But you may take them modulo 2pi which should not change anything and you get 3.162 and 3.087.

Letting Mathcad make a drawing of the four-bar linkage for theta4=0 and 90° as well as at the position ogf the max torque could be helpful. Making an animation would be interesting but this could only be done with Mathcad 15 (and below) and not with Prime.

The three guesses I used give you a torque of 195 and resonable angles (theta3 seems to be 180° when theta4 is 90°, so we are at the limit).

[VishnuGopalakri]

that means that the a,b and c needs to be changed to ensure there is a solution for every angle for theta4 varying from 0-90

[VishnuGopalakri]

The only things fixed are w,d and theta1

[VishnuGopalakri]

in the worksheet mathcadtoggleprog2, as you see the maximum value of torque for a given set of a and c is at theta4=60 degrees.I would like to change a and c to minimize this maximum value of torque(T).The torque=0 is when theta4 is 0 degrees which seems to be what the minimize fuction is coming up with.

[ValeryOchkov]

See please

http://twt.mpei.ac.ru/ochkov/Carpet/carpet_eng.htm

and

http://communities.ptc.com/videos/2418