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Finding the equation of a system involving dashpots and mass on wheels 
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#1
Jun411, 01:02 PM

P: 111

1. The problem statement, all variables and given/known data
consider the mechanical system below. Find the equation depicting the system. u is the input force. sorry for the poor picture, I had to draw it on my tablet... Uploaded with ImageShack.us 2. Relevant equations F=ma 3. The attempt at a solution I'm not sure how to treat the dashpot in parallel with the mass. I came up with the following system of equations: 0=k1x+mx"+k2(xy)+b(xy) 0=b(xy)+k2(xy)+k3(yu) 


#2
Jun411, 03:54 PM

Sci Advisor
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Thanks
P: 26,160

hi lzh!
according to http://en.wikipedia.org/wiki/Dashpot, the resistance is porportional to the speed 


#3
Jun411, 10:21 PM

P: 111

hi!
oops I mistyped... 0=k1x+mx"+k2(xy)+b(x'y') 0=b(x'y')+k2(xy)+k3(yu) 


#4
Jun511, 03:15 AM

P: 128

Finding the equation of a system involving dashpots and mass on wheels
I can't tell you anything for sure since I haven't done these problems in years. The way I used to check out the mechanical "circuit" when I got overwhelmed was based on my electrical knowledge. Your dashpot is a resistor and your mass is an inductor. Always use this as a double check when you're unsure of a mechanical setup. The info for the electrical setup will always be more easy to find.
EDIT: Looking at your equations of motion now though, I think you have it or are close. There is no need to fudge with the circuit. Just find X and Y based on input u. 


#5
Jun511, 06:57 PM

P: 111

0=k1x+mx"+k2(xy)+b(x'y')
0=b(y'y')+k2(yx)+k3*y+u after some more modification, but i'm still unsure... 


#6
Jun611, 09:04 AM

P: 1,411

For starters:
Note that u would be a velocity input, not a force input. b is by'  it has no contact with the velocity at x and I think for m it is m(y"x") I haven't checked your eqautions yet, so patience please 


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