Robotic arm design


Thread Starter

Momin Diyab

I'm working on my first robotic arm. It has 4 DOF and I don't know what type of motors to use. Stepper motors seems to be cheaper and more accurate than servos, but the models I have access to are heavier than servo motors. Servo motors also seem to have a smoother motion. Please help to decide what actuators to use and why.

William Sturm

If you have the budget, servo motors are the way to go.  They are more tolerant of overload conditions because they have high peak torque and the closed loop can help recover from a position error.  Steppers can work very well, but they must be oversized to handle peak loads, they have minimal torque reserves and are not usually closed loop.

Ken Emmons Jr.


For a robotic "Arm" type of design, most people use servo motors with
gearboxes. The more accurate ones use harmonic drive gearboxes that
don't have freeplay or backlash. In this way you can drive large torque loads with light weight, but at the cost of speed. The gearboxes still have 30-60 arc seconds error, even on the nicest ones, so a robot requiring greater accuracy would have to be very finely calibrated or use a high accuracy secondary position encoder on the output shaft of the gearbox for a "dual loop" closure.

Steppers tend to be on the low end of the scale, mostly because of top speed and accuracy, but with encoders closing the loop with steppers this line is becoming somewhat blurred.