Engineers at Assembled Products Corp., Rogers, Ark. (, needed a way to propel their line of electric shopping carts both forward and reverse. So they developed the XTi Hub Motor, a dc-brush motor housed in a wheel. It is geared (21.5:1) to provide the most low-speed torque of any motor in its class. A changeable, solid-rubber tire mounts on the wheel. The complete tire and motor measures 8.5 in. diameter and 4.4 in. wide. The motor comes in three versions, including a 9.6-lb, 12-V version with a top speed of 76 rpm, and 100 W of power. There's also a 12-V version with a patented friction disc that generates 110 lb-in. of holding torque. The more powerful 24-V motor weighs 10.6 lb, has a top speed of 156 rpm, and puts out 180 W. It uses an integral mechanical brake to create 220 lb-in. of holding torque. The motors use off-the-shelf controllers and throttle systems available from many manufacturers.