Servo - May 2008

Auger front end.

allowed around the rear wheel mechanism. Because the bright green plastic design is inviting, it’s a good idea to treat this as you would any of your power tools — up and away from children.

THE TEAR DOWN

Dimensions 15. 5” L x 3. 25” W x 2.2” H

Drive Rear (opposite end of auger)

Tread Rubber, one piece, 1/2” wide

Length, auger tip (total) 1.9”

Dimensions, square auger shaft 1.2” L x 0.3” square

Length, antenna 13. 5”

Weight, body (no battery) 23 oz

Weight, NiCad pack 12 oz

Charger 9 VDC wall module, 150 mA

Speed (forward/reverse) 9 in/second

Control range, outdoors 57 feet

Control range, indoors 30 feet

Battery 7.1V NiCad; capacity not listed

Drive only — 300 mA Current drain 7.1V Auger only — 500 mA Auger and drive — 800 mA

RC frequency 49. 86 MHz

Controller weight (no battery) 5 oz

TABLE 1. Looj robot specifications.

The rubber tread peels off easily, and the rear wheels are attached with Phillips head screws. After that, peering inside the Looj takes a bit of work. Unfortunately, iRobot elected to glue the cover in place. I used a sharp screwdriver to break the seal and then remove the cover. The most challenging section of the cover is over the thin bridge framing the battery compartment.

Once the cover is removed, the electronics and drive assemblies are readily accessible. The front auger motor and gearbox are easily extracted without tools. The rear compartment is more complicated. The electronics — located adjacent to the rear drive gearbox — are also easily removed with a gentle tug. Fortunately, connectors are used for power, motors, and the on-off switch. The antenna is the only wire that must be cut or unsoldered to extract the electronics unit.

The electronics assembly consists of a motherboard and two solder-on boards. The motherboard appears to be primarily for power management and input/output. One board is obviously the RF receiver, given the RF coils and the antenna connection. The other board is apparently the motor controller. One of the two 14-pin chips on the controller board is a 74HC74D flip-flop and the other is an LM339DG quad comparator. The balance of semiconductors are three-lead devices and diodes.

The rear drive motor assembly is best left inside the Looj body. The axel runs through the gearbox and out of the Looj body, making extraction problematic. I

Rear drive mechanism and antenna mount.

used modest force in an attempt to drive the axel through the gearbox, but encountered stiff resistance. Instead of possibly destroying the gearbox, I used a Dremel to saw through the body of the Looj to release the gearbox. The complete electromechanical system is