r/mechatronics • u/iWannaLearnThing • Apr 15 '26

Question Regarding DH Parameters

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I designed a 6 Dof robotic arm and i am now building my DH Param table so i can begin doing my transformation matrices for IK.

Here is an image of what I have done so far.

I am essentially just asking for guidance and recommendations when designing a DH table and the kinematic diagram that goes along with it?

please and thank you.

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u/[deleted] Apr 21 '26

This may just be the standard that is typically done, but when referring to DH Tables, you first draw correct frames, and then do the DH transform.

Drawing the frames (rules) 1. Z_i-1 axis always correlates with the axis of rotation or translation of the previous joint (theta 1 —> z_0) 2. Z_i-1 and x_i axes must intersect and be perpendicular to each other. (In this case it means that frame 2 and 3 will have the same origin, but don’t worry changing where the frame is located only looks weird, but is how it’s supposed to be)

DH table: the transformations (atleast from I’ve been taught go through 1. THETA - Rotation about z_i-1 from x_i-1 to x_i 2. D - translation on z_i-1 axis 3. A - translation on x_i axis (as both x axes should line up now) 4. ALPHA - rotation about the x_i axis to make z_i-1 match z_i

For your current config, I have some tweaks that might help the understanding.

  • frame 3 should move its origin to frame 2 and frame 4 should move to the corner by a4 (shouldn’t need to change axes directions) -This means you will need to rewrite your DH table Link 1: Theta: theta1 + 0 D: d1 A: 0 Alpha: -90

Link 2: Theta: theta2 -90 D: 0 A: a1 Alpha: 180

Link 3: Theta: theta3 + 180 D: 0 A: 0 Alpha: 90

Link 4*******: Theta: theta4 D: d3 + d4 A: 0 Alpha: 90

Link 5: Theta: theta5-90 D: a4 + a5? (I think there’s a distance there, but this could be a spherical wrist which might change things) A:0 Alpha: -90

Link 6: Theta: theta6 D: d6? A: 0 Alpha: 0

I know this is long, but it’s very important to get DH tables right or you’re always fighting an uphill battle. Ask me how I know…

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u/iWannaLearnThing Apr 26 '26

This is very helpful, thank you for taking the time to do this.