How can a Mindstorms robot lift something very heavy?
I'm assuming that you meant "the motor is not powerful enough".

Surely you can use a gearing ratio &amp; leverage to assist? Essentially you want the motor to turn many times for each small amount of distance traveled by the lifting arm. This means a small gear on the motor and a large gear driving the lifting. You may need to connect several gears together to get enough of a reduction, like the graphic here.

See the graphic "Reducing Gear Train" here.