Large Hexapod build

Building swing motor limit switch assembly

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Quote Originally Posted by DiverBob View Post
I've spent the last week figuring out a limit/calibration switch setup for the swing arm motion. The issue was trying to make it fit in the available space and creating something that not only worked reliably but was reproducible and practical to built. Having it look nice is always another requirement!. I finally got the notion that I didn't have to put the switch assembly down by the gear train, instead I can use the upper pivot point and just adjust the mounting brackets. Once I got that straight then the design went forward pretty quickly.

The switch assembly consists of 2 circles of delrin. The thin circle is the switch actuator. It has a area machined out that are 120 degrees apart. The back side has a place for an adjustment to calibrate the switch actuation points. This piece is screwed into the fixed pivot point. The thicker delrin holds the micro switch with a friction fit. (The next version will have a small strap to hold the switch in place). The limit switch is positioned so that just the top of the switch is above the top of the delrin piece. The switch only needs 0.017 of movement to trigger and the trigger points only depress the switch 0.020 inches. The large hole in the middle is for the thrust bearings and a metal spacer. The limit switch holder is screwed into the movable leg pivot.

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As the leg pivots the switch is not activated until it reaches either the left or right sides or a full motion of 120 degrees. The switch is not going to be wired into the motor control circuit but will be monitored by the microcontroller during leg calibration. I can lift the leg, swing it until the limit switch actuates and use that position information to control the position encoder. There will be a couple of minor change to the next version of the switch delrin piece, I will mill out much of the flat surface shown in the first photo (delrin piece on the left) and just leave a 0.1 band around the outer perimeter. This is to reduce the friction between the two delrin pieces as they rotate against each other. I'm leaving the outer band to reduce getting dust and other contaminates inside the assembly where they could interfere with the switch.

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The next two photos are of the motor controller mount. However, I decided tonight that I'm going to change the length of the sides on the leg mount assembly so I can't mount the motor controllers in a line. Instead I'll make a new mounting bracket that can hold 4 motor controller in 2 groups of 2. This was a good test to see how easy it was to work with the expanded PVC board on the mill and find out how strong the glued connections are. That will be part of tomorrows project.

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I won't be working much on the robot for a couple of weeks as I'll be traveling but I'm getting parts and raw materials for starting the production version of the leg during my travels. I'll be checking in so let me know if you have any questions!

Bob

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Robotics , ‎ Engineering

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