Calculating the minimum force needed to pick up an object

[karnivaurus]

Hello,

I want to use Bullet to simulate a robot gripper picking up objects using a two-fingered gripper. The gripper picks up an object by closing its fingers around the object until a certain force is applied to the object, and then the gripper moves upwards. Given the shape and mass of an object, and the shape of my robot's grippers, I want to determine the minimum force necessary applied by the fingers to pick up a particular object.

One way to solve this would be to simply try lots of different values for this force, and find the threshold which determines when the gripper "just" picks up the object without dropping it. However, even with a clever search over different forces, this would require lots of simulations per object, which is not ideal for me.

So, I am wondering whether there is a way to ask Bullet what this minimum force would be, without having to run through the simulations? I don't know whether Bullet works in this "inverse" manner, but if it does, then please let me know how I can use it.

Thank you!

[Basroil]

The minimum force required is F=Ma, where M is the mass of the object and a is the total acceleration including gravity. No need for bullet. If you are using friction only (not a good approximation if you have non-smooth small objects and a human like gripper), the normal force (gripping force) is just going to be the that force divided by the friction coefficient.

If you want to use constraints though, you can put a set of point constraints at the contact points with joint feedback and see what the resultant forces will be. Most likely it won't actually be the minimum force since you'll likely have redundancy, but it'll be a good approximation.