Comments on: Robotic Arm Inverse Kinematics on Arduino

By: oleg

oleg — Thu, 01 Dec 2011 05:21:59 +0000

That’s transformations from joint angles to servo pulse lengths. 1500 is 1.5ms which corresponds to middle position of a servo. 11.1, 6.6, etc., are constants, like “degrees per millisecond” ratios. The rest are actual angles of various joints and direction of rotation.

By: Chris

Chris — Wed, 30 Nov 2011 16:17:35 +0000

Hi,

I am trying to use your code in my project. I really like it, you have commented everything and it’s readable. I changed the length of the “bones” and the servo limits, what I don’t understand is this part in your code:

/* Servo pulses */
float bas_servopulse = 1500.0 – (( degrees( bas_angle_r )) * 11.11 );
float shl_servopulse = 1500.0 + (( shl_angle_d – 90.0 ) * 6.6 );
float elb_servopulse = 1500.0 – (( elb_angle_d – 90.0 ) * 6.6 );
float wri_servopulse = 1500 + ( wri_angle_d * 11.1 );

Can you explain more, please ? I don’t get what are these values.
Thanks a lot,
Chris.

By: oleg

oleg — Sat, 24 Sep 2011 15:51:44 +0000

The author’s name is Oleg Mazurov.

By: Radin Mejias

Radin Mejias — Sat, 24 Sep 2011 13:08:10 +0000

Excuse me Sir, Can I ask the abstract and the authors of this project? I will used it for some purpose as a Review on Related Literature since we are also making this kind of Robotic Arm. Please? thx.

By: Lucas

Lucas — Sat, 30 Jul 2011 20:18:59 +0000

With a few modifications, the code you posted works fine with the SSC-32 servo controller. I’ll need to go through the calculations in a little more detail to see how you implemented them. The SSC-32 doesn’t come with a nice servo library like the one you used, but it isn’t that hard to write out the commands I need. It’s a blast to see your arm finally doing what you command it to do! Now if I could just have it make breakfast for me in the morning!

By: oleg

oleg — Thu, 28 Jul 2011 15:38:50 +0000

Did you notice an error in the Application Note 44 article?

I don’t remember. There are several ways to calculate angles and I was looking at many code samples to find one which can be done in the least amount of machine cycles. My calculations are based on formulas from one of the spreadsheets posted on Lynxmotion site.

One last question, why did you not use the SSC-32 servo controller that comes with the LynxMotion arm? It seems to me this would be a lot easier than making your own servo controller.

I think you can buy Lynxmotion kit without SSC-32. Servo controllers are simple circuits – I had mine lying around and just used it.

By: Lucas

Lucas — Thu, 28 Jul 2011 14:52:30 +0000

Did you notice an error in the Application Note 44 article? I believe their calculations for r’ and z’ mix up the use of cosine and sine. I assume you corrected this in your software, which I’ll be reviewing shortly. I have all of the same components and will be testing your code in a few days. Your explanation is very clear and helpful. Thanks for putting this together.

One last question, why did you not use the SSC-32 servo controller that comes with the LynxMotion arm? It seems to me this would be a lot easier than making your own servo controller.

By: Jonatas

Jonatas — Mon, 25 Jul 2011 03:12:55 +0000

IF i’m using the servo.h library, what i need to change in lines 93-96?

By: Jonatas

Jonatas — Sat, 23 Jul 2011 15:32:56 +0000

I’m using 6 servos directly to the Arduino port (2-8). To control them servo.h use the library, providing for each servant, an angle of 0-180 °.
What changes should I do in the code since I’m using this library and not servoshield.h?

By: oleg

oleg — Sun, 26 Jun 2011 17:43:11 +0000

Joints are all the same. A joint and two “bones” plus distance between far ends of two bones form a triangle. An arm is treated as a set of triangles in x,z plane, rotating base adds y plane.