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4 Degrees Of Freedom Mini Robotic Arm

Overview
Due to servo motors availability, we built a mini Robotic Arm using just 4 pieces of Futaba S3003 that make up a 4 DOF Robotic Arm.

Mini Robotic Arm Side View

The first one is used for the base. The second one is used for the elbow. The third one is used for the wrist rotation. And the last one is used for the single movement gripper. The arm base is made of plastic, while the rest of the body is being made of aluminum. The whole arm is rested on a piece of wood. The objective of the design is to learn the robotic arm concept in pick and place procedures industrially.

Mini Robotic Arm Top View

Design Concept
For the base, we use some screw heads topped with some grease for fine movement as a replacement for the weight distribution bearing. This is simply because the part is not locally available in the market. Yet even if we were to order from oversea, the simple base would cost more than RM400, which is too costly for simple project.
For elbow and wrist rotation, we share the same frame to minimize weight due to the limited torque of the standard servos.

Mini Robotic Arm elbow and wrist rotation

As for the gripper, we redesigned a simple single movement gripper to reduce the size. The same design also help to reduce the total weight for the elbow to lift.

Mini Robotic Arm gripper

The four servos are connected to the Serial Servo Controller Board through a 25pin female Centronics connector.

Serial Servo Controller

The reason to use 25 pins is simply the SSC board are designed to control up to 8 servos, where each servo is using 3 pins . Thus , the same connection can be used for later 8 DOF Robotic Arm project as well.
To give some weight for support, the base is pinned to a square wooden base. While helping the Robotic Arm (RA) to stand firmly, it allows easier handling for the arm as well.

Design Analysis
The movement of the base and elbow are not that smooth enough. Better fittings with proper alignment are needed for improvement. Yet, the torque for standard servos seems like not strong enough for the base. Perhaps to carry heavier load, a higher grade servo is required.

The wrist rotation is quite OK as it doesn't affect the whole process so much. However, for the gripper it is having some difficulty in gripping the load properly due to single grip. The best is to have more than one movement gripper, although that might burden the base and elbow .

In short, this mini RA is quite OK for a start. There are many sections that could be improved especially once all the necessary items required are available later on. Next, the actual implementation place should be clarified so that a proper design can be done.

Mini Robotic Arm Lifting a Load

Design Upgrade
Since the main objective for this project is achieved (built RA that is serially controlled by a PC), we are going into next stage ASAP. In the next stage we are going to reprogram the RA to do specific job automatically. This will require some PIC reprogramming of the job sequence for the servos to work syncronously with each other without manual control from the PC serial interface. This is to enable the RA to run independently with a preprogrammed job.
In order to do this, some manual job to record the all servos position data in each sequence are required. It will takes some time as the mechanism funny vibrations are not yet fully solved. As such a more thorough study of the the RA concept are needed so that a better quality movement can be achieved.

Mini Robotic Arm At Work

Another replacement for CS-600 (Hitec HS-5955TG)

I found another model Hitecc HS5955TG a digital servo that could be used to replace the CS-600. This one is digital type. So the previous model Futaba S3306 is now out of question since that one is analog type. This is how its looks like.One more thing is that CS-600 works on 90 degree angle, this Hitec is the same as well.The HSC-5955TG is the ultimate standard size servo period! This servo was specifically designed for use in giant scale aircraft and high performance R/C vehicles. With an amazing 333 oz-in. of torque and Titanium gears packed in a standard size case it out performs any other servo in the marketplace. We also include a heavy duty carbon brush coreless motor wrapped in a metal heatsink center case to handle the harshest environment. The new upper case incorporates hardened pins for the gears with oilite bushings to allow these series of servos to take repeated punishment. Topping it off with gold-plated connectors, heavy duty wire and 8 rubber rings in the case offering excellent water and fuel resistance, the HSC-5955TG servo is in a league by itself. We offer the HS-5955TG servo in several configurations, 90° stock rotation, 180° modified rotation, continuous rotation (potentiometer is left outside the servo case) and reverse rotation.

*Digital servos do not need to be programmed to operate. They work great right out of the box and purchasing a programmer is not neccessary.

HS-5955TG Detailed Specifications
Control System: +Pulse Width Control 1500usec Neutral
Required Pulse: 4.8-6.0 Volt Peak to Peak Square Wave
Operating Voltage Range: 4.8-6.0 Volts
Operating Temperature Range: -20 to +60°C (-68F to +140F)
Operating Speed (4.8V): 0.19 sec/60° at no load
Operating Speed (6.0V): 0.15 sec/60° at no load
Stall Torque (4.8V): 249.96 oz-in. (18 kg.cm)
Stall Torque (6.0V): 333.29 oz-in. (24 kg.cm)
Standing Torque (4.8V): 324.95 oz-in. (23.4 kg.cm) 5° deflection
Standing Torque (6.0V): 433.27 oz-in. (31.2 kg.cm) 5° deflection
Operating Angle: 60° one side pulse traveling 400usec
360 Modifiable: Yes
Direction: Clockwise/Pulse Traveling 1500 to 1900 usec
Idle Current Drain (4.8V): 3mA at stop
Idle Current Drain (6.0V): 3mA at stop
Current Drain (4.8V): 220mA/idle and 3.4 amps at lock/stall
Current Drain (6.0V): 300mA/idle and 4.2 amps at lock/stall
Dead Band Width: 2 usec
Motor Type: Coreless Metal Brush
Potentiometer Drive: 6 Slider Indirect Drive
Bearing Type: Dual Ball Bearing MR106
Gear Type: 4 Titanium Gears
Connector Wire Length: 7" (178mm)
Dimensions: 1.57" x 0.78"x 1.45" (40 x 20 x 37mm)
Weight: 2.18oz (62g)