What are the six degrees of freedom in a robot arm?
First off: Why six?
6 degrees of freedom is the minimum needed to reach a volume of space from every angle. The longer the arm, the greater the volume that can be reached. More than 6 joints and the robot becomes kinematically redundant – it can reach the same spot at the same angle in more than one way. For example, you can pinch your nose and wiggle your elbow at the same time.
In a human arm there are at least six degrees of freedom. If your robot arm can do all of these motions then your arm can do pretty much any job a human can. So here’s a list of what the six degrees are and what they are not. Video after the break.
I just stumbled across this example that’s nearly a year old. Maybe I’m rediscovering it? It’s so short and so sweet.
Axis 1: Let your arm hang down. Raise it in front of you, turning only at the shoulder.
Axis 2: Let your arm hang down. Raise it out away from your body like you’re doing jumping jacks.
Axis 3: Bend your elbow.
Axis 4: Wave like the Queen of England by twisting at the wrist. It’s a twist between the wrist and the elbow.
Axis 5: Make a fist, then make it nod up and down. Bonus points if you draw eyes on the first knuckle of your index finger.
Axis 6: Imagine holding a big dial in your fingers. Turn the dial without moving the rest of your hand.
The robot’s tool – the claw, the gripper, the pen, the hand – is NOT a degree of freedom. Most hobby robot makers out there are incorrectly listing the number of degrees of freedom in their arms.
Intuition says each axis added is that much more complicated, so it’s probably the last axis they leave out. Oddly enough, it’s not Axis 6 that most makers omit – it’s Axis 4. Robot arms vary depending on the manufacturer, but the effect is the same. In the video I posted it’s the orange belt you see right after the elbow. In some models like this FANUC arm,
the twist is closer to the wrist. If Axis 4 is close to the elbow then motors for 5 & 6 can be closer to the wrist. If the 4/5/6 motors are behind the elbow like in the FANUC arm then the linkages between the motors and their moving parts get really interesting. Try and draw it on paper, it’s rods inside tubes inside other tubes.
Here’s another short but sweet video of the arm in the above video.
If you want to build a robot arm, I’d love to talk to you. Let’s collaborate! I’ve got the 6 axis RUMBA board which should take care of the “brain” and all the laser cutting we could ever want.
PS: I probably won’t have a post until late Sunday because I’ll be at the VHS leading 3D printer day. We meet every 2 weeks to talk, learn, and hack 3D printers.
There are 7DOF and even 8DOF robotic arms on the market:
Edit: Special thanks to Reddit user CollieMonster for pointing out a few errors and omissions.
Hello Dan,
My name is Karim. How difficult would be to make a 6 degree of freedom arm that records real time movement of the arm forced (physically made by a human) and then repeats saved series of actions.
I’ve been introduced to basic robotics as I work at the university’s Makerspace and I’m in a software program. But I really don’t know enough about either of those things to tell if what I’m talking about is very difficult to do.
Edit: sentence made no sense.
Hi dont know if this post is still active or not but I’m a total newbie to the arduino systems as well as the ins and outs to programming and electronics however I have a very surface basic understanding of the basic stuff!! I’m more of a oops learner I like modularization as well as object oriented programming or icon friendly application interfaces!! Have so many uses and visions for the application of what I like to call “the claw” would love to learn more about all subject matters in correspondence and totally down to collaborate, Indiana here, let’s nerd chat if u r willing to share more wisdom with us beginners!! Lol😉thanks again hope to talk soon!! #nerdnotes!🤗
Hi AJ. The forums would be a good place to discuss your robot project ideas.
Hi Dan,
I also built this 6 dof robotic arm (purchased only the parts from a Chinese manufacturer online) and currently I’m struggling with the how to control the 6 servos as the servo control board I bought is from a company called LoBot thru an Arduino Leonardo and there’s no online driver header code for it.
Any suggestions?
P.S: I’m still new to robotics
Dont know the software protocol to know the yesses and now of what can and can’t but from what I think I know I feel like it would b really easy to control with a 64 controller bc it has the xy and z buttons along with the joy stick motion which I believe would b extremely user friendly with this unit! I need the claw not more than almost any other possession I have and trying to process the big big world of electronics is like trying to comprehend spaces and potential multiple spaces when u haven’t left your home town lol.. Min 7 color changing LEDs and rgb led strips are a recently discovered love and obsession and again concepts mind blown!! Everyone who gets it says its second nature and super simple once it clicks but it is a whole other world of discovery and uncharted territory for me! Any hey its this simple, advice exp. Suggests, all ears plz and thank u bunches!!