A rendering of my Solidworks model. Belts and pulleys are not shown.
A cross section of my first axis design. The motor is coupled to the blue drive pinion with a flexible shaft coupling. The drive pinion then drives the purple sun gear, which drives the green planet gears. The planet carrier is used to transmit torque to the top platform, which rotates on the top of the body using v groove ball bearings.
The robot base, which I've been affectionately referring to as "the can". You can see the screws that hold the motor mounting plate in place here.
Top view of the motor mounting plate. Two sets of holes are included so that both NEMA 17 and NEMA 23 motors can be used. A central hole allows wiring to pass from the base of the robot up to the rest of the arm.
Bottom view of the motor mounting plate. The plate is fixed using the 4 tabs around the circumference. The tabs hold a nut in place allowing for metal threads to be used instead of plastic ones.
Interior view of the can with motor mounting plate in place. The ring gear rests on top of the shelf near the top of the plate. Four bosses along the shelf fit into cutouts on the ring gear, preventing it from rotating. This way, new ring gear parts can be printed and tested without reprinting the entire can. The motor and drive pinion are offset and the sun gear is hollow, which allows wiring to pass to the bottom of the can up to the rest of the robot with no limits on first axis rotation.
A close up of the nuts in the motor mounting plate tabs.
Bottom view of the can with motor and mounting plate in place. The four tabs around the periphery of the can allow the arm to be rigidly mounted to a surface. They also allow the can to be extended if necessary.
The planetary gearset that will drive the first axis. The gears are standard off-the-shelf sizes, but are massively oversized in terms of required pitch diameter and face width in an attempt to minimize the innacuracies of the 3D printing process. Tolerancing has been an important aspect of the gear design.
A shot of the can with all first-axis gears in place.
The top surface of the can has a ridge which serves as a guide for v-groove bearings.
Hero shot of the second axis housing.
External shot of second axis.
Arm linkages housing the third axis are printed and test fit.
Partly through machining mounting hubs to attach arm links to their axes.
Finished mounting hubs to couple arm links to axis rods.
Arm with mounting hubs in place, ready for motor testing.
A 3D printed bracket containing the four stepper motor driver chips. Banking them like this allows me to easily wire and adjust the chips, diagnose problems, and cool them actively using a fan if high current operation is desired.
I added encoders to my stepper motors to ensure accurate positioning under load. For those of you unfamiliar with encoders you can zoom in on the picture to see the gradation on the glass disc, which is pretty rad.
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Four-Axis Robotic Arm
The majority of my past embedded systems projects have given me the opportunity to enhance and apply my skills with circuitry and programming but not necessarily mechanical engineering. This is unfortunate since I am, in fact, a mechanical engineer. I'm fascinated by robotic arms so this summer I decided to design and build my own. This project allows me the opportunity to design gear sets, belt drives and structural components and also to select appropriate motors, bearings, shafts, and other components. Since I'm working on a first prototype I'm 3D printing most of the robot while also designing with the intention of eventually producing a final arm out of aluminum without massive redesigns.
