One step forward to measure the weigth of a chassis

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SIRX
Posts: 17
Joined: 17 Mar 2018, 15:22

One step forward to measure the weigth of a chassis

Post by SIRX » 10 Apr 2018, 17:39

Hi to all,
I would like measure the weight of a chassis. As the admin advices I studied the Ackermann steering car. Really, if I put a graph I see 4 curves two by two equals, right. I tried to do the same, so in to the scene:
1. add a cuboid
2. link ,with the cuboid, 4 vertical prismatic joints >motor enabled > control loop enabled > spring damper mode
3. link ,with the prismatic joints, 4 wheels
4. I respect a single planar symmetry
5. add graph > joint force e torque > 4 prismatic joints
6 I measure 4 different values of forces: wrong, I was expecting 2 by 2 equal forces.
7. It is verified the equation (M_chassis*g=F_pJ1+F_pJ2+F_pJ3+F_pJ4): right
8. The curves that I graph from Ackermann car are smouther than the others that have very much noise!
Does Someone has any suggestion?


NB Before write I tried to find a solution without success.

NB I can't know how to attach an image.

Thanks in advance
Sirx

coppelia
Site Admin
Posts: 6672
Joined: 14 Dec 2012, 00:25

Re: One step forward to measure the weigth of a chassis

Post by coppelia » 12 Apr 2018, 07:29

Hello,

can you share your scene with us? Simply add a link to your scene file (e.g. via dropbox, or similar).

Cheers

SIRX
Posts: 17
Joined: 17 Mar 2018, 15:22

Re: One step forward to measure the weigth of a chassis

Post by SIRX » 12 Apr 2018, 16:54

Hello,
meantime I carried on to work on the model that I linked by DropBox.
I get the same forces on RL and RR wheels, no more. I fear that the problem
is on the setting of the prismatic joints. I checked the symmetry, masses value, etc.
thanks for the help.
Sirx

https://www.dropbox.com/s/cb2gsk8e7kumf ... 4.ttt?dl=0

coppelia
Site Admin
Posts: 6672
Joined: 14 Dec 2012, 00:25

Re: One step forward to measure the weigth of a chassis

Post by coppelia » 16 Apr 2018, 06:48

You need to really make sure that your vehicle is built in a symmetric fashion if you want to obtain same forces left and right. For instance, at rest, all joints are at position 0, except for joint Prismatic_FL. But all wheels are at the same height. So something is wrong there.

Cheers

SIRX
Posts: 17
Joined: 17 Mar 2018, 15:22

Re: One step forward to measure the weigth of a chassis

Post by SIRX » 16 Apr 2018, 14:38

Hi Admin,
Very thanks for your help, it was very useful.
Now it works!
Cheers

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