Welcome back to the "DiggerBot" in process. It's nice to have a long Labor Day weekend to work on this a bit more. Above is the two-armed prototype that I made to help me figure out some more of the mechanical components. I will change this quite a bit later, design-wise...but it was very helpful to build a rough version.
I'd like to take a brief moment to give some credit to my Mom's "sketchin' buddy", APRIL, for sending me some ideas to improve the engineering of the arm movements. It's been fun collaborating with someone who has a better brain than mine for these things. Thanks, April!
Below are the bits that make up the "bike pedal" action for the top axle. The Bot-arms will attach to this part. I like to use dowel pegs and a bit of Elmer's wood glue, instead of nails and screws, to put all of this together. The tight fitting pegs will hold things in place until I'm sure things work.
I temporarily attached the arm bits, to see if the axle rotation produces the effect I want.
Next, I made the gear box, so I can figure out the drive mechanism that will be underneath. I had to add a little block of wood to the base of the axle housing, because I had cut off too much earlier. These things happen. Again...this is quick and dirty, just for figuring out if this will really function.
Now you'll see the series of "failures" before I found a workable solution. My first idea was to use one of my daughter's "ponytail holders" to attach to the drive shaft underneath. Too stretchy...not enough tension. Next I tried a bit of twine, since it was rougher. But it slipped on the wood axles. So I ground in some grooves with my dremmel tool. Still didn't work. Then I made a little "cuff" of sticky-backed foam rubber. That seemed to help. I then made a larger "gear" for the lower drive shaft, to give more tension...the string still slipped on that, too. Finally I added some foam to the gear...it worked! Sort of...the string would slide off the rubber part and snag up on the sides of the axles.
Finally, I thought of making a true "belt drive" for this. I had some "fake leather" material, cut a long strip the right length...super-glued the ends together...and added a little duct tape for good measure. Worked just right!!
I made a duplicate arm for the opposite side of the Prototype TestBot, and...VOILA!
Things will slow down a bit from here on, because I will be designing more complex shapes for the final "DiggerBot". I'm also thinking about adding some other moving parts (like the Bot's mouth opening and closing). Stay tuned!!