“Build a really neat, highly accurate, meter-tall, robotic arm with industrial/memory capabilities that you can make yourself for cheap!
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A Quick Preview
This is E.R.A., the 5-Axis Everything Robotic Arm with built-in position-remembering software and industrial capabilities. It also has an interchangeable end to make it useful for just about any circumstance. I’ve found it to be the perfect assistant in the shop for a variety of uses such as soldering, photography, lighting, and part gripping.
Working Concept
The main concept of how this arm works is that it uses five stepper motors and two servos to move a variety of joints that take advantage of their built in, closed-loop functionalities to remember their position in space and play them back. This can be done due to the unique functionalities shared by stepper and servo motors. This would be their ability to recognize their position in space through potentiometers (servos), and step counting (steppers).
How stepper motors work is the microcontroller (an ESP32 in this case), will send a variety of pulses to a stepper driver which translates those low voltage pulses into high voltage ones which will drive the coils in the stepper motors. In this project we are able to take advantage of that by counting the number of pulses sent to the stepper motor, effectively telling us where the motor is located in the programming.
Servo motors are similar in that they are also able to tell us what their position is, but rather through how far turned their built-in potentiometer is moved. This resistance acts as an encoder and can be communicated to the ESP32. This is also why servo motors are unable to continuously move if you’ve ever wondered. Potentiometers cannot be turned indefinitely!
The Design
When I originally started this design, I wanted it to be different from my last robotic arm in size since the longer it was the higher the value of inertia and inconsistency it had. However, when I first designed it in CAD it was so small and boring… I couldn’t bring myself to follow through with it. Instead, I doubled down and worked twice as hard to make a bigger arm that would still have the accuracy, mobility, and consistency as a smaller/less complex version. I’m glad I did, it’s super awesome now.
I designed ERA based on using GT2 Pulleys to translate the motion from the different motors to the different axes of rotation. I did this since there would be a far smaller dead zone due to the hundreds of teeth on the pulleys, as well as that I knew I would be able to get a good gear ratio from the small pulley wheels on the motors.
Having originally wanted to go for a UR3-ish design, I ended up settling on a 5-axis arm, since I found it insanely easier to manufacture and didn’t want to make it too complex. Now let’s go through the different axes and how they are driven.
The first axis is driven with a NEMA-17 stepper motor with a 15:1gear ratio using a standard 20-teeth pulley wheel and connecting it around the base.
The second is driven using dual 1.26Nm NEMA-23 stepper motors with a 10:1 planetary gearbox on each one. This is followed by a gear reduction of 3.33:1 through the special 3D-printed pulley wheels I designed for it going up onto the base of the first joint. Just be sure to get the right ones since I’ve found that some manufactures vary in size slightly. I will have the link to the ones I got in the Bill of Materials(BOM) at the bottom.
The third and fourth are quite simple. The third axis, similar to the first, is also driven just through using a NEMA-17 with a 20-teeth pulley wheel going through a slight gear ratio of 9:1 to the base of the second joint.
The fourth is just the wrist axis which requires pretty much zero special attention. It’s just a NEMA-17 with a 27:1 gearbox slapped onto it. However, I’ve honestly found that to be a bit much so feel free reduce it if you’d ever like to use the arm to screw in bolts or anything like that with quicker speed. Just note that a smaller gearbox will yield a smaller torque.”