Universal Robots Forum

Reducing Stiffness of each joint in Free Drive

Hello,

I am trying to us UR5 robot to draw alphabets. I noticed while drawing through hand-guiding during free drive, there is high stiffness in each joint, i.e. the movement is not as free as while drawing with our hand.

Can someone give more insight into this?

Also, increasing momentum values reduces stiffness of joints in free-drive.

Is there any other way we can reduce stiffness of joints in free-drive?

One way is to make sure your payload and COG are correct.

Can you provide some more insight on this? like any link or documentation?

Basically what this does is makes sure combined weight of all the stuff attached to the end of your robot arm, including the part it’s holding, is calculated properly and the Center of Gravity is accurate. The weight of you grippers, fingers and any accessories attached to the arm has to be accurate, especially when you’re using free drive.

To test yours, move the arm into space somewhere and hold the free drive button. If the robot stays where it is you’re fairly close. If the arm floats up it is set too high, if it falls down it is set too low.

The correct settings will make free drive much easier to move and will put much less stress on the joints during execution.

Below link should get you started. It goes into more detail on setting this via script, but you can see the graphic of the page in the teach pendant to help get going. There may be better links but I didn’t spend much time searching, basically just grabbed the first one that was close enough for what you’re trying to do. Hope this helps.

https://www.universal-robots.com/articles/ur/programming/how-to-change-payload-and-center-of-gravity-settings-using-urscript/

Hey,

I have already calibrated the payload and corresponding COG.
When I put robot in free-drive, it does not fall, neither does it go up, it stands in place.

The exercise I am trying to achieve is different.

The main objective is to hand-guide the robot in free-drive.
While doing this, I noticed that there is some minimal force which I have to apply to move the robot freely.
I was hoping to ask if you can provide me some insight on how I can reduce this force, such that I can move the robot in free-drive with minimal pulling force or no force exerted.

I’m fairly new to robots so forgive my ignorance. And I’m not sure what your application is (making an actual product, teaching a child robots, getting you a beer from the fridge, etc)

Your solution will likely vary based on that answer. If you are teaching robots to someone, you’ll need to take extra precautions r.e. personal injury. Especially if it’s a child as they can be hurt more easily.

The robot needs to exert force to keep position and allow you to move it (think power assisted steering) so there will always be some resistance.

So… are the letters you are drawing random or do you know what they’re going to be before you guide the robot? If they are known ahead of time the only way I can think of that “might” work is using a force module if you know the letters before hand.

Maybe someone else has better ideas than mind. :thinking:

There is no way to natively reduce the resistance of the joints for Freedriving the robot. If the robot is slowing down and increasing its resistance because you are getting close to its safety limits, you can go into the Safety settings and reduce those assuming it is okay to do so (one easy way is to choose the factory default setting slider and move it all the way to “least restricted”). Typically the larger models will have a higher resistance.