Project files

SCARA_Parallel

A parallel SCARA robotic arm designed for a graduation project, featuring closed-loop stepper motors, harmonic reducers, carbon fiber rods, 3D-printed joints, motion control, and linear interpolation.

Future updates will include MATLAB kinematic simulations, motion control code based on STM32F407, interpolation code, and sharing of design insights.

Update Notes

2023.9.11: Updated 3D models — all parts, motors, reducers, rods, machined shafts, 3D-printed joints, and assembly files.

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1. Hardware Selection and Structural Design

1.1 Motor Selection

Due to cost and project workload considerations, servo motors or brushless motors were not chosen to drive the joints. Instead, closed-loop stepper motors were selected.

The motor model is the Jiemaikang 57J1880, purchased on Xianyu (a second-hand marketplace) for about 150 RMB per unit including the driver. The driver model is 2HSS57, also from Jiemaikang. It includes built-in motor control algorithms with current and position loops, making it as easy to control as a regular stepper motor driver — just send pulses.

In the future, if time permits, a brushless motor version with FOC control may be considered to enable dynamic control.

1.2 Reducers

Harmonic reducers were chosen. The selected model is the green LSCG series from Leaderdrive, with a 17-50 size and a 50:1 reduction ratio, purchased for 450 RMB each. Since the motor output shaft and reducer input shaft sizes differ, a custom coupling was designed to thicken the motor shaft and insert it into the reducer's hole, secured with a key pin and set screw. The motor end already has a D-shaped shaft, so it fits directly. The 3D model includes all parts and assembly methods.

1.3 Joint Rotation Axle

This was the most challenging part since I'm not a mechanical engineering major. I had no idea how to design a rotating joint. Eventually, I found flange-mounted bearings, which made the design much easier.

1.4 Rod Selection

I went through many detours. At one point, the entire structure was printed using photopolymer resin, but the stiffness was completely insufficient — the structure sagged under its own weight. Later, the design switched to carbon fiber tubes. Below are the rods used; there was a whole box of them.