Math is Hard! Let's go Shopping!

A project log for Stubby the (Teaching) Hexapod

100% open source robot platform with accessability and affordability in mind: teaching children of all ages about robots & programming

The Big OneThe Big One 06/17/2014 at 19:270 Comments

So it has taken a while to get to where I am at now... trig is hard when you have not used it for 15+ years.  It is very fun to be re-learning all the stuff which I had forgotten long ago (Law of Cosines is pure beauty!  How could I have forgotten about something like that!)

Since the last log entry, there have been a few changes:

To help myself fully understand what is happening, I drew everything up in QCad, with labeled angles and lengths, and refer to each of these figures in the source code.  (I could not imagine writing this code without such a reference: 100% required IMHO).  These diagrams are included here (see source/Leg.h for explanations and references to these figures):

Below is the output of the simulation, given the actual numbers obtained from the IK for various values.  In this example, Y and Z are both 0, and the X value varies as indicated.  (Keep in mind that the co-ordinate system has 0,0,0 on the ground directly underneath the center of the robot; this gives a 45mm offset for each leg.  So, for instance when the 140mm diagram shows a coxa joint to foot measurement of 95.3mm, the 45mm offset from center shifts it to be correct (95 + 45 = 140).

The updated frame plans (to include 50mm femurs), to be cut from 1/4" MDF, are here (and it still fits on a single 8.5x11" sheet of paper!):

Now that everything is working in simulation, the next step is to verify that it also works in real life.  Assuming I can move every leg to an arbitrary position in x,y,z co-ordinate space, I can then start the animation (gait, movements, etc).

And once that happens, I will post some more videos. :-)