This is an attempt to build a two "finger" robot that will Charge spin a pen simply by rolling back and forth on the X axis.
I think I can make it spin a little more smoothly by using smaller fingers.
Am not sure if this is how a human hand accomplishes the task. I think probably the index finger needs to impart a small motion in the Z axis direction to get it spinning really fast. You can kind of see that motion in the gif below of a hand doing the charge spin.
Based on the GIF you provided and these videos, the fingers don’t simply move around a fixed axis - you’ll need to get both fingers moving which will take some interesting mechanics if you want that done using only one motor (sort of like a double windshield wiper at 180 degrees of oscillation apart from each other (if that makes sense):
Thanks for your assessment. I already built some thinner fingers and will try those first just to see if there is any change. But yes, it looks like both fingers are contributing to the movement. Not sure how to do that with one servo as I have only simple tools and materials. That would be a nice challenge for a real engineer. Two servos would be pretty easy and perhaps I will give that a shot.
Consider how one DC gear motor operates two wipers, and offset one. You can use two four-bar mechanisms with one starting at a different angle to the other, both connected to a single DC gear motor. It won’t cost much, but will take some time to think through the mechanics (even if you use simple things like popsicle sticks).
Can you draw me a picture? Sorry I’m so dense. Even handdrawn would be great. PS: I can’t order stuff from US as I am an American living in an asian country that does not receive US products.
For example in the image above, the green link could be connected to the output of a DC gear motor, and the red one is fixed. If you use two of them, notice how the yellow rods on either side will both move. In this case, since all dimensions and angles are the same, they would move in unison. If you vary the parameters, you can get them rotating at 180 degrees to each other (it’s still early in the morning, but I think just rotating one of the green rods might do it).
Thanks. I understand now.Sorry for all the work you had to do. I hope I will continue to pursue this. I just added another video using thin fingers with a tapered notch and it is better but I would like to try the idea you have proposed.
Took my time but finally finished this project. I used your idea by using a single servo to operate both fingers but it never did spin. What did work best was a single servo operating the top finger and the lower finger just mounted statically. I could get it to spin by just playing with the speed and angle parameters of the servo. I show both in my last video posted in my project.
I think a lot more could be done with this spinning project but it would take more mechanical skill than I have or am willing to put forth.
Thanks for the idea and interest. It was an interesting project but I have closed it out now and am moving on to something else.
