# Revision history [back]

### Understanding contact sensor data

I am receiving contact sensor measurements that I am having a trouble making sense of. One example is the following:

Normal vector:      (-0.347998,  0.937495,  0)
Body1 wrench force: (-0.270598,  1.06599,   0.546762)
Body2 wrench force: (-0.797889, -0.838441, -0.410959)


From what I understood by going through the description of the contact sensor and per this answer by @hsu is that these forces describe the correction force applied to the CG of corresponding links to correct for the interpenetration.

In my case body 1 is a free object and body 2 is a robot hand whose base is static. I would like to understand the following:

1. Since the robot has a static base, how meaningful is this resulting force?
2. Shouldn't the contact forces for body1 and body2 be the same with a different sign?
3. In case 1. is not meaningful, would taking the negative of the force off of the second body make sense? If not, how could I obtain this contact force? What happens in case of multiple contacts from different sides of the object, e.g. during grasping?
4. Why do the directions of the forces differ so much from the normal?
5. What would be the physical interpretation of this sensor in general? If I had a glove with a haptic sensor, would it sense something similar to the body wrench force, or something similar to the contact normal, e.g. contact normal scaled with penetration depth?

Any insights on this would be much appreciated. Thank you!

### Understanding contact sensor data

I am receiving contact sensor measurements that I am having a trouble making sense of. One example is the following:

Normal vector:      (-0.347998,  0.937495,  0)
Body1 wrench force: (-0.270598,  1.06599,   0.546762)
Body2 wrench force: (-0.797889, -0.838441, -0.410959)


From what I understood by going through the description of the contact sensor and per this answer by @hsu is that these forces describe the correction force applied to the CG of corresponding links to correct for the interpenetration.

In my case body 1 is a free object and body 2 is a robot hand whose base is static. I would like to understand the following:

1. Since the robot has a static base, how meaningful is this resulting force?
2. Shouldn't the contact forces for body1 and body2 be the same with a different sign?
3. In case 1. is not meaningful, would taking the negative of the force off of the second body make sense? If not, how could I obtain this contact force? What happens in case of multiple contacts from different sides of the object, e.g. during grasping?
4. Why do the directions of the forces differ so much from the normal?
5. What would be the physical interpretation of this sensor in general? If I had a glove with a haptic sensor, would it sense something similar to the body wrench force, or something similar to the contact normal, e.g. contact normal scaled with penetration depth?

Any insights on this would be much appreciated. Thank you!

### Understanding contact sensor data

I am receiving contact sensor measurements that I am having trouble making sense of. One example is the following:

Normal vector:      (-0.347998,  0.937495,  0)
Body1 wrench force: (-0.270598,  1.06599,   0.546762)
Body2 wrench force: (-0.797889, -0.838441, -0.410959)


From what I understood by going through the description of the contact sensor and per this answer by @hsu is that these forces describe the correction force applied to the CG of corresponding links to correct for the interpenetration.

In my case body 1 is a free object and body 2 is a robot hand whose base is staticfixed to the world. I would like to understand the following:

1. Since Does the fact that the robot has is fixed to world influence the physical interpretation of the results? E.g. for a static base, how meaningful is this resulting force?object the contact forces that it feels are always 0.
2. Shouldn't the contact forces for body1 and body2 be the same with a different sign?
3. In case 1. is not meaningful, would taking the negative of the force off of the second body make sense? If not, how could I obtain this contact force? What happens in case of multiple contacts from different sides of the object, e.g. during grasping?
4. Why do the directions of the forces differ so much from the normal?
5. What would be the physical interpretation of this sensor in general? If I had a glove with a haptic sensor, would it sense something similar to the body wrench force, or something similar to the contact normal, e.g. contact normal scaled with penetration depth?

Any insights on this would be much appreciated. Thank you!