View Full Version : extra DOF's in legs

10-13-2011, 09:11 AM
Hey again,

I was wondering if anyone can give me some examples of the reaosning behind extra DOF's in legs. I know alot of robots use 2DOF and 3DOF legs (quads and hexs). I can see why it is needed in bipeds due to the need of more leg movement for dynamic stability. I am just not sure the advantages of going higher than 3 DOF in the legs of quads and hexs. I have seen quite a few 4 DOF legs and even on rare cases 5 and 6 DOF legs. I was wondering if anyone could point out the advantage of higher than 3 DOF in the legs of quads or hexs. Thanks

10-13-2011, 11:08 AM
I've tried 2 DOF in a quad. worked pretty well for most things, except side stepping. Moved to 3 DOF to get the sidestepping I needed. 4 DOF may smooth things out, and give you better control, but also complicates the programming. More than 4 is overkill, and unnecessary I think. for my purposes, I see no need to go beyond 3.


10-13-2011, 11:10 AM
Thanks! Thats the same impression I have is beyond 3DOF there isn't much of an advantage

10-13-2011, 02:45 PM
The big advantage of 4DOF is that you can keep the foot always perpendicular to the ground -- this means that you have a constant contact patch (which leads to more predictable/reliable walking). In the case of something being remotely controlled by a human, that is probably unnecessary, but if the robot is to be autonomous it can be a big help since you'll be more likely to walk straight when you try to.

Another thing to be aware of with 2DOF is that you'll but more wear and tear on the servos, as the legs have to make an arc on the ground when moving forward (rather than pull straight back). You can minimize this by taking very short steps, but 2DOF is probably not appropriate on a heavier robot.