My progress this week has mostly been in design of my robot arm. I had some fun with this design because being for a contest there is more incentive to do interesting things and less risk in doing stuff that might not work.
To make this inexpensive and quick to build it is designed around parts that I was able to salvage or had on hand, and the rest are designed to 3D print, or atleast require minimal machining. Kinematically, all angles are tied directly to the base. There are 5 degrees of freedom, the tilt on the wrist is currently held level by a parallel bar linkage. So, as to making it fun, here's how each joint is propelled:
Turn: A slightly damaged turn table from a bench top CNC
First Link Tilt: Climbs along a giant gear sector with a motor attached near the end of the arm
Elbow: A small ballscrew drives the counter lever up and down, the line of action is almost a parallel bar, except that it will swing out of plane somewhat in the arc. I centered the pivot between the extremes of the arc to minimize this.
Wrist Roll: A tiny pinion is driven by a rod that runs all the way to the back of the elbow. A universal joint allows it to make the turn to across the wrist tilt. The wrist is supported by a large bearing which is clamped in with two 3D printed pieces, and encircled by a ring gear.
Hand movement: Cable driven, a loop of wire runs through the square aluminum tube which makes up the second link of the arm. On one end it is connected to pull the hand open and closed, on the other it wraps twice around a small drum on a motor behind the elbow, across from the wrist roll motor.
This overview shot doesn't include any of the bearings or bolts. Those big square beams aren't lazy modeling, I'm actually using some 1" square tube that I have.
The machinery on the back. Those are NEMA 17 size at the top and NEMA 23 size on the base. The turn table will also be driven by a NEMA 23.
Here's some of the parts this model was designed around along with the mostly 3D printed hand. Those are DRV8825 motor drivers. I'm working on the movement code. Luckily now that I've got these parts my 3D printer will do much of the work. I designed it so that minimal machining is required, I mainly need to cut and drill a few holes in those aluminum bars. The 3D printed gears work very well, you just have to keep the teeth fairly large, above say 0.1" tooth thickness.
Next up, building, and code
I'm working on coordinated move code. I want to make sure I make the most of the programmable digital. Of course while I do that I'll keep the 3D printer cranking out parts. I've gotten many of the sensors I've ordered for the brewing process and have been playing with them, so I should have something to show from that soon. I also scavenged up a nice miniature bar load cell that I will try integrating into the gripper if I can. It's 1x1x8 cm, so it could basically replace one of the fingers.
By the way, I thought this was interesting, there’s a PSoC 3 managed electric motorcycle on hackaday