Sunday, June 1, 2014

A Dog's Tail - Pitch and Yaw on the Cheap

I don't have the parts or tools to build rigs out of aluminum or steel but I need to figure out how a set of servos can control K9's tail. Wood and plastic will have to do for now until those parts break or wear out. The tail essentially is a pole that must be able to move horizontally and vertically by motor control. Here is a shot of the actual tail on the prop itself.


Fortunately, there are a few good examples already out there on how to build this motion rig. For example, here is one using only DC motors. Here is another example using Servo motors which is very impressive. This rig is built with multiple aluminum C-brackets and struts which looks very sturdy but I have no idea where to get the parts. So far I have built a test rig consisting of two RC aircraft 180 degree servo motors connected together, one to shaft of the other as seen in this example I found for sale.

Incidentally, if you are looking for the rubber fixture I am going to use, its a CV-Boot from a car. They can be found in almost any auto supply store. Here is a picture of the one I chose.


It is a close enough match to get the job done. I will end up cutting away the lower half when I mount it to the body. Now back to the test rig. Below is a video of the test rig I built just to see if my two server idea would work. The two servos are joined together with rubber bands so you will see a lot of oscillation as the arm moves around and a hanger is standing in for the antenna but other than that, it is performing the required motions.

video

Once I replace the rubber bands with firmer connections, all shaking will go away and I will have the wagging motions I need without having to construct a more complex rig. How long it will last in action will be another matter. Everything is being driven from an Arduino that is not connected to the main robot. This is just for testing purposes.  The next step will be to move everything to a permanent rig that I can attach to the CV-Boot inside the main shell. I will post pictures of that when that is completed.