[tsaksa]

You might try having one DC motor drive another one. Permanent magnet DC motors act as generators when driven like this, though you may need to add some gearing depending on what target RPM you want to control. If you vary the electrical load on the generator it will translate into a varying mechanical load on the motor. Add a few switches and some lamps and you should have a simple variable load simulator. Depending on your application you may want to add some type of flywheel to add rotational inertia as well.