# Assigning Frames and Deriving Link Parameters

The textbook I'm using doesn't have the answers to the practice questions, so I'm not sure how I'm doing. Are the following DH parameters correct given the frames I assigned?

The original question is as follows: The arm with 3DOF shown below is like the one in example 3.3, except that joint 1's axis is not parallel to the other two. Instead, there is a twist of 90 degrees in magnitude between axes 1 and 2. Derive link parameters and the kinematic equations for $^bT_w$ (where b means base frame and w means wrist frame).

$$\begin{array}{ccc} & const. & and & & \\ & angle & distance & & \\ i & \alpha_{i-1} & a_{i-1} & d_i & \bf{\theta_i} \\ \\ 1 & 0 & 0 & 0 & \theta_1 \\ 2 & -90 & L_1 & 0 & \theta_2 \\ 3 & 0 & L_2 & 0 & \theta_3 \\ \end{array}$$

Frame Assignments: • Can you convert your image to a latex-formatted table? – Ian Mar 18 '13 at 15:23
• If you want to follow Ian's suggestion (it's a good one) you might want to use Ian's edit to your other question as a template. – Mark Booth Mar 18 '13 at 18:18

Seems like you are using the Proximal convention. It's always good practice to have an extra frame called {X0,Y0,Z0} at the base. It makes visualizing so much easier. 