Gear actuated robot arm
Description
This is a robot arm that uses two nema17 and three 28byj-48 stepper motors to lift empty soda cans and other light objects. The robot arm uses gear trains to achieve higher lifting potential. The claw is designed to be able to open wide enough to pick up soda cans from the top or side. The claw is spring-loaded and the motor closes it by pulling on strings attached to the claw fingers. Almost all parts of this project are 3d-printed, but you will need some springs and screws for the claw as well as for mounting the motors. These screws will depend slightly on the tolerances of your printer, but 3-4mm should work well. You also do need a long bolt for mounting the main gears, but if you do not have that then you can print an additional "Gear-bolt-short" and it will suffice as a replacement. You will also need the motors as well as some 10mm (8mm inside diameter) PVC pipes for the long arms. The C arm is 220mm and the B arm is 200mm. The two PVC pipes connecting the main gears to the connectors are 210mm. These pvc pipes will fit over the adapters and can be assembled using the 3d-printable push pin bolts. For this project we used an arduino mega for controlling the stepper motors due to the high amount of digital pins required. You will also need suitable drivers for the motors. We also used two joysticks for steering, and a power supply to power all the motors. 3d-printing settings will vary between parts, for the gears and other parts that will have high amounts of force applied to them, around 30-40% infill is suitable. For parts such as the gear mount and base lower infill can be used. For the base and gear mount I used a 0.6mm nozzle to speed up printing, but this is optional. To assemble the robot arm, begin by mounting all the motors and attaching the gears that fit each motor. In the claw and the base you will need to fit the claw-gear-holder part and the base-gear-holder part respectively between the main parts and the motor. If you are unsure of any parts position please consult the Full_arm stl file or the included images to see which gears and parts go where. Assemble the claw by assembling all three fingers and mounting them to the claw-finger-base part. Each finger will have two mounting points sticking out, tie a string to the one on the inside towards the centre of the base on all three fingers, all three strings should go through the hole in the middle and stick out on the underside of the claw-finger-base. Attach a spring to the outside one on all three fingers. Mount the two additional gears that are driven by the claw motor to the claw-bottom part. You will need to use the claw-gear-holder part to keep them in place. Mount the claw-finger-base, with the fingers now attached, to the claw-bottom part. Tie all three strings together at the same length and slit the string into the slit on the claw-driven-gear part. Attach the springs to the three hooks on the claw-bottom part so that the claw fingers spring open by themselves. In my case these ended up not being strong enough, so I simply snipped off the hooks and melted three small metal hooks into the plastic in their place. Now attach the idler and driven gears to the base-gear-mount part and attach the legs to the base. Then attach all the remaining gears in their respective position in the gear-holder part. Use the gear-bolt parts to keep the gears in place by sliding them through both the gear-mount and the gears themselves so that the gears spin around them. Now cut PVC pipes to length and mount the adaptors, one end of A arm pvc pipe should be left empty since it will fit right onto the arm-A-connector part. Glue the two parts of the B-arm together. Begin mounting the gears together with the PVC pipes and connectors according to the images. Some parts will require longer push pin bolts, so use the proper bolts that close completely and give a snug fit with a couple of millimetres left. Attach the Claw-bottom-arm-connector part last to the two A and C PVC pipe connectors. Then grab the whole arm assembly and slot all three main gears into the gear-mount part. You will need to wiggle them a bit to get the gears to mesh. Once they are in, push a bolt through the hole in the gear-mount and through the holes in all three main gears, locking them in place. Now attach the Claw-bottom to the Claw-bottom-arm-connector part by sliding it on. Then attach the gear-mount-base by pushing its four pegs into the four holes on the gear-mount. Now place the whole assembly into the round hole in the base. Again you might need to wiggle a bit to get the base gear to mesh with the internal gear of the gear-mount-base part. Then screw the base holddowns down on both sides so the arm can not tip out of the base. The robot arm is now fully assembled. Wire the motors using your preferred drivers and control unit and you are ready to go! For more information on code and project see https://github.com/elliot4711/robot_arm
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