![]() ![]() It is quite hard to find suitable gears which are easily sourced and not too large. The biggest issue I found when making the effector was the gears. This allows the design to use relatively small parts but still achieve a open aperture of about 65mm to allow the arm to pick up quite wide objects. The end-effector design is based around two counter rotating gears which use levers to make the grippers open and close laterally rather than using a pincer-action. Two C brackets bolted together Building the end-effector There are 4 bearings in all, 3 in the arm and one in the end-effector (see below). This type of bearing is quite common in remote control car models and can be purchased either from a model shop or from sites such as Ebay. ![]() ![]() The bearings are flanged meaning that they have a small metal lip on one side which prevents them from being pushed through the bracket. The bearings have an inner diameter of 4mm, and outer diameter of 8mm and are 3mm thick. If the M3 screw is a little long you can use 2-3 M3 washers on the outside of the bracket to make sure it does not dig into the back of the servo. On the other side of the bracket a flanged bearing is fitted to the 8mm hole which is then bolted through the bracket using an M3 screw and a nylon nut to prevent the rotation from unscrewing the nut (note that the flange of the bearing is on the outside of the C bracket). These are cut to size and then screwed/bolted in place. On one side the servo head is mounted using the cross shaped servo head provided with the servo. Once mounted in the servo brackets the servos are then connected to the C brackets. All of the servos (except the wrist rotate) are metal-gear and dual-metal bearing to ensure that they are physically strong since the arm will place a lot of pressure on them. The wrist-rotate servo is a Fubata S3003 standard servos which produce about 3.5kg/cm. The lower 5 servos (turntable, shoulder (x2) elbow and wrist) are SAVÖX SC-0252MG servos which produce 10.5kg/cm of torque at 6 Volts. As the arm requires a lot of torque to deal with the weight of the arm I used metal gear high-torque servos. To begin assembling the arm mechanism start by bolting all the servos in place using M3 screws and nuts. The dual-servo bracket mounted on the turntable Assembling the robot arm Once lined-up the template is then held in place by wrapping strips of sticky-tape over the template until it is completely covered: This allows you to line up the edge of the template with the aluminium without it moving around too much. To line up the template on the material I first put a small amount of paper glue on the back of the template (the paper glue common for crafts is perfect such as Pritstick). The bracket template is then printed out and cut to size using a sharp hobby knife and a metal ruler. To make the template I used a 60mm x 1000mm x 4mm aluminium bar which was cut using a mitre-saw to ensure it has a square edge. Since you will need 5 of these brackets it is a good idea to build a template and a jig to help making them easier and more consistent.Īll of the parts of the robot arm are made using very similar techniques so, for this first bracket, I will show as much detail as possible for the construction. ![]() The servo mount bracket is made from a sheet of 2mm aluminium (I sourced a 500mm x 500mm sheet from in Sweden, however you should be able to get similar sizes from your local hardware store). PNG of the libreCAD servo bracket design Constructing the robot arm Building the servo mount bracket ![]()
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