The Making of V-Maid By Clint Bridges

Building an autonomous robot to perform the specific task of vacuuming a small simulated room proved to be a formidable and brain-taxing task. Each step of the process seemed to demand endless hours of problem solving and on-the-fly engineering. In this article I hope to share some of the things I learned.

Frame Construction

The first step in any robot design is choosing a motion platform. I chose to build a round base with motors and casters mounted in such a way that the robot could rotate around its vertical axis. This proved to be invaluable for maneuvering around furniture in the small arena.

The round top and bottom of the V-Maid frame are made of Delrin. The 3/8 inch thick sheets of Delrin were formed into disks by milling with a simple wooden fixture in a milling machine.

A single ¼ inch hole was drilled into the center of a rectangular piece of Delrin. A ¼ inch pin was pushed through the Delrin and into a hole in a plywood fixture so that the Delrin could spin freely. Next the proper radius from the pin to the milling bit was set and the spinning bit was progressively lowered into the Delrin as the sheet was turned. The result was a perfect circle with a ¼ inch hole in the center.

The vertical struts that connect the upper and lower Delrin disks are made of an off-the-shelf aluminum extrusion. This extrusion is made by a company called 80/20, Inc. and can be purchased by the linear foot. I chose the 1010 part number, which has a 1-inch square cross section. I bought the extrusion in 4-foot lengths and cut it to length on a Craftsman radial arm saw using a special blade.

Drive System

The motors used for V-Maid are made by Pittman in Harleysville, PA. Pittman is very easy to deal with and will sell single piece quantities of a wide selection of motors. The motors for V-Maid are Pittman GM9236S019 and have a 12 volt winding, 500 CPR quadrature encoder with index, and ¼ inch output shaft. These motors operate at about 236 max RPM and have a 19.7:1 gear reduction ratio. The wheels for the robot are mounted directly to the output shaft of the motors. Since the wheels have a ½ inch bore an adapter bushing is needed to reduce to the ¼ inch diameter required by the motors. The wheels are McMaster-Carr part number 60885K25 and are actually drive pinch rollers. The required bushing is McMaster-Carr part number 6420K12 and a 10-32 by ½ inch set-screw must be purchased separately.

Front Panel

The front panel includes switches for CPU reset, drives, vacuum, and sensors.

Vacuum System

After experimenting with several vacuum mechanisms, I chose to use brushes to push the rice into a narrow band. Then the suction from a Black & Decker Dustbuster 450 motor would pick rice up from the carpet and deposit it into a Rubbermaid food canister. The hose used to make the vacuum circuit is actually corrugated washing machine drain line hose and is available from most hardware stores. The Dustbuster motor is designed for use with a 4.8-volt rechargeable battery. I drove the motor with a 6-volt battery to increase suction. The motor draws 18 amps continuous current at 6 volts and an automotive relay rated for 30 amps was used to switch the vacuum on and off. A separate Omron timing relay shuts the vacuum relay off after the required 6 minutes and relieves some of the burden from the CPU.

The bottom of V-Maid reveals the brushes used to guide the rice toward the suction hose. The brushes are short pieces of door-bottom weather seal purchased from Home Depot.

Microcontroller

The motors that propel V-Maid have Motor Mind B variable speed controllers made by Solutions Cubed. Two outputs from the 17C756 are used to control the drive motors. These two outputs are connected to the "from master"(FM) pins of the Motor Mind Motor controllers.

Sensors

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