I'm reading "Robot Modeling and Control" by Spong. It seems to me there are mistakes in the manual solutions provided by the authors. I came across the following two questions

enter image description here

In this answer I think there is no $d_3$. It should be zero. In the following question

enter image description here

In my solution $\alpha_2=-90^\circ$ not $90^\circ$ and $\theta_3 = 0^\circ$ not $-90^\circ$. I would love to hear your feedback. Also, if you are instructor, you may need to double check this.


1 Answer 1


yes you are right in both models.

but add extending length of prismatic joint as it may be able to extend further and add theta to revolute joints

first model

add d1+a1 in the place of d1 and so on

hope it helps

  • $\begingroup$ What DH conversion you're using? What is the table you've provided? $\endgroup$
    – CroCo
    Commented Dec 7, 2021 at 15:44
  • $\begingroup$ i think it is modified dh table. for reference: [ link ](automaticaddison.com/…) $\endgroup$ Commented Dec 8, 2021 at 13:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.