The standard lightweight manual can be tricked-up with a small, powerful motor, affixed to the wheel units or attached to the base of the chair. When the assist is turned on, a forward push on the handrim gives the chair a strong boost.
These assist hubs add quite a bit of weight to the chair (from 38 to almost 50 pounds) and quite a bit of expense ($5,000 to $8,000), but the advantages are terrific, especially for lower-level quads and anyone with achy shoulders who won't have to struggle up steep hills.
A rider's range will increase dramatically using the assist, saving personal energy and wear and tear on the rotator cuffs. What's more, the chair doesn't look like a beefed-up power unit: It looks more or less “normal.”
SmartDrive is a newer power assist option for manual chairs. This is a portable drive wheel (11 pounds) that pretty easily hooks on to the base of the chair; a battery fits under the seat.
Another option, this one without batteries or motors, MagicWheels, two-gear wheelchair wheels that have a lower gear for hills when you need it, with a click of the hub, at about a third the cost of power assist units.
From the network