Chandley Technologies - Sentry Turret Base

Sentry Turret Base

Sentry Turret Base

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Because really, who wouldn't want an automated sentry turret to do their bidding? This article will chronicle the mechanical aspects of the sentry turret: the base and the motors. This turret will be able to hit targets within 180 degrees of pan and 180 degrees of tilt, a half sphere of destruction the likes of which has never been witnessed by man.

We will initially be focusing on a small, tabletop version as a sort of testbed. We will move up to a more reasonably sized sentry turret as we move forward with the project.

This is one of the more complicated Chandley Tech projects solely because it is a combination of many different focus areas. There are Mechanical, Electrical, and Programming aspects to this project, adding to its complexity. We will be working to keep the cost and part count as low as possible so that other can recreate the work. Our goal is to be less than $50 for the full project (not including the microcontroller setup cost).

Our process as we move forward will be stairstepped, starting with this preliminary, desktop mounted version. This will be the proof of concept and will still be very cool to use and show off. The armament for this version will be a laser pointer controlled by the Propeller chip.

Project Write-Up
Pan and Tilt For the tabletop version, we opted to use two servo motors to control the pan (left to right) and tilt (up and down). These will be controlled using a Propeller microcontroller chip and a Nintendo 64 controller. Mounting them will be the biggest issue. The most likely approach will be to use a threaded metal rod and screw it directly into the servo motor. The servo mounting holes will then be attached to the parts that we wish to move. The servo motors that we will be using have 180 degrees of turning capability, meaning that this machine will be capable of hitting anything within a half-sphere in front of it. Pictures will be forthcoming.

Turret Head The turret head will be a U shaped assembly. Servos will be used to control the orientation of the head. A servo will be attached to the bottom, with a metal threaded rod connected to the servo actuator itself. This will be the connection between the servo head and the tripod. The same sort of system will be used to control the object to be pointed. The laser pointer will be attached to a threaded metal rod. This metal rod will go through the vertical parts of the turret head U, and one side will be threaded into another servo. This servo will control the tilt of the laser pointer. This will be much clearer once I have drawn a diagram......... This unit has been constructed out of wood.

Tripod The turret base itself is made of PVC pipe and pipe fittings. A wooden dowel was glued to the center of a servo mechanical connector. This dowel is glued into the top of the base so that it cannot move. The turret head , made of wood, is mounted to the servo, which is mounted to the top of the dowel.

Electronics and Programming Aspects This turret will be controlled using a Parallax Propeller chip. A Nintendo 64 controller will be interfaced with the microcontroller to control the motion of the turret. The N64 controller will allow for rate (rotation speed) control for quick movements and position (actual angle) control for fine-tuning. A relay will be wired into the microcontroller to control the firing of the laser. For control of the head, two servos will be used. This will allow for accurate control of the angle. Currently, there is no capability of angle position feedback other than tracking within the microcontroller's code.

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